The present invention relates to a method for verifying the authenticity of products and to authenticatable products, the use of said products in the method and a system for verifying the authenticy of products.

Forgeries and pirate copies of high-value products cause enormous economic damage year-on-year. In the case of medicaments, food and drink products and supplier and replacement parts in safety- critical fields such as aviation and the automotive industry, forgeries can also constitute a high risk to life and limb for many humans. On the first sight or due to the complexity of some products, it is frequently difficult, if not even impossible, to distinguish original products and copies from one another. For example, in the case of plastics or coatings, it is not possible or viable to introduce a serial number or another kind of information that permits product identification into the material of the product itself.

The identification systems for unambiguous product identification, e.g., fluorescence coding, DNA coding, UV coding, are limited in terms of material width and applicability. This is also valid for the unambiguous product identification using electron spin resonance coding. For the latter process, the development of stable, permanently radical substances is required, partly via chemical synthesis pathways, in order to reliably and reproducibly detect very small quantities, e.g., from ppm to ppb to ppt ranges, in products and thus to enable unambiguous product identification in harmless concentrations. The preservation of the original coloring is an important, and often even indispensable criterion for many products, e.g., especially for pharmaceuticals the whitish appearance.

Incorporating identification systems or substances into pharmaceutical products is a particular challenge since the incorporated identification systems or substances must not have any negative effect regarding the medical approval of the pharmaceutical product in question.

The medical approval of a new pharmaceutical/medical product by a competent authority, such as the European Medicines Agency or the Food and Drug Administration, requires that manufacturer of the pharmaceutical product or the person who wishes to place it on the market demonstrates that this pharmaceutical product meets the criteria required by the relevant Act on the Marketing of Medicinal Products. These criteria are quality, efficacy, and harmlessness - a tripod of evaluative terms, on which the medical approval and ongoing benefit/risk assessment of pharmaceutical products are based.

Quality primarily includes the material properties of the medicinal product, i.e., its identity, purity, quantity, etc., which are determined by its manufacturing process, and which are analytically verifiable. Quality also includes shelf life for the specified period and galenics, i.e., the specific dosage form in which the active ingredients used individually or in combination are processed with excipients in such a way that the active substances are released in the body in a defined and reliable form.

The second criterion, efficacy is, generally speaking, the sum of all desired effects with regard to the goal of treatment. It is an evaluative term that relates the individual effects that occur to the goal of the treatment and how well this goal is achieved, i.e., the extent of healing, recovery or relief of a disease, a symptom or a malaise, or the prevention of a disease or an exacerbation. Efficacy is thus defined by the individual effects considered useful according to medical experience and scientific knowledge. The statement that a particular medicinal product is effective can therefore only ever be made for a defined area of application and with regard to a certain expected or hoped-for healing success.

The third criterion, that of harmlessness, is the most complex and requires a weighing, in which several factors must be taken into account. Medical products can always have undesirable, harmful or unpleasant effects without it being possible to predict in individual cases which of the treated persons will be affected by undesirable effects and to what extent. The question is therefore: can the extent and probability of the occurrence of adverse drug reactions be accepted as a risk in view of the expected benefits in the form of efficacy, taking into account the probability of cure success and the severity of the disease.

In summary, the challenges to meet these requirements were, amongst others, to generate stable paramagnets (here: permanent radical substances), which

- do not introduce a detectable color difference into the product,

- can be detected in very low concentrations by electron spin resonance spectroscopy,

- are harmless, and

- are technically suitable and meet the criteria of homogeneity as well as reproducibility for the respective application.

US 2021/0273226 A1 discloses a secondary battery having excellent high power, discharge characteristics at a high current, and cycle characteristic, and using a radical polymer in an electrode. Specifically, this document discloses an electrode having a repeating unit having a nitroxide radical site and a repeating unit having a carboxyl group and using a copolymer having a cross-linked structure as an electrode active material for use in the organic radical battery.

WO 2008/017768 A2 disloses the cosmetic use for prevention and/or treatment of at least one cutaneous disorder at least partially induced by free radicals, of at least one polymer that can be obtained from at least one secondary polyamine containing at least one monomer containing an N- (2,2,6,6)-tetraalkyl-4-piperidinyl-2-amino-1 ,3,5-triazine substituent, according to a method comprising the following steps: solubilization of the secondary polyamine with an organic solvent non-miscible with water; the addition of water to obtain a biphasic medium; the addition to the biphasic medium, under strong stirring: (a) of an aliphatic peracid and (b) of a sufficient quantity of a basic aqueous solution, to obtain a pH in the aqueous phase of the biphasic medium ranging from 4 to 12; the recovery of the organic phase, and the removal of the organic solvent. It also covers the use of this polymer for preparing a dermatological composition, and a composition containing this polymer in combination with a photo-protecting agent.

It was found that substances comprising a repeating unit according to the formula (I) below with the definitions given there are suitable for the product verification considering the above-mentioned criteria in a variety of applications, such as pharmaceuticals, for example solid, liquid or semi-solid drug forms, blood products, food ingredients, medical devices, packaging, consumables, print products, print colors, lacquers, coatings, means of payment, and luxury goods.

One object of the present invention is therefore a computer-implemented method for verifying the authenticity of a product, comprising the steps of a) initiating a processing unit to receive and/or request an electron paramagnetic resonance (EPR) spectrum of a product, whose authenticity is to be verified, from an input/output device, b) pulling a library of EPR spectra of one, more, or a multitude of identification substances from a database, wherein each of the identification substances comprises a repeating unit according to the formula (I) wherein each of R ¹ , R ² , R ³ , and R ⁴ is independently selected from the group consisting of hydrogen, linear or branched alkyl groups with 1 to 4 carbon atoms, x is selected from the group consisting of *-CH2-C’H-CH2-**, *-C’H-CH2-**, *-CH2-C’H-**, *-C’=CH-** and *-CH=C’-**, wherein

* in each case denotes the bond to the carbon atom bonded to R ¹ and R ² ,

** in each case denotes the bond to carbon atom bonded to R ³ and R ⁴ , and

C’ denotes the carbon atom bonded to the Y moiety,

Y is selected from the bridging moieties (II) and (III), wherein

(II) has the structure &-(Y ¹ ) _P i-[C=X ¹ ] _P 2-(Y ² ) _P 3-B-(Y ³ ) _p6 -[C=X ² ] _P 5-(Y ⁴ ) _P 4-&& and (III) has the structure &-(Y ⁵ ) _P 9-(C=X ³ ) _P s-(Y ⁶ ) _P 7-&&, wherein p1 , p2, and p3 are each 0 or 1 , with the proviso that it is not simultaneously the case that p1 = p3 = p2 = 0, p4, p5 and p6 are each 0 or 1 , with the proviso that it is not simultaneously the case that p4= p6 = 1 and p5 = 1 , p7, p8 and 9p are each 0 or 1 , with the proviso that it is not simultaneously the case that p7 = p9 = 1 and p8 =0, each of X ¹ , X ² , and X ³ is independently selected from oxygen and sulfur, each of Y ¹ , Y ² , Y ³ , Y ⁴ , Y ⁵ , and Y ⁶ is independently selected from the group consisting of O, S, NH, and N-alkyl,

B is a divalent (hetero)aromatic moiety, or a divalent aliphatic moiety optionally substituted by at least one group selected from -NO2, -NH2, -CN, -SH, -OH, and halogen, and optionally at least one group selected from ether, thioether, amino ether, carbonyl, carboxylic ester, carboxamide, sulphonic ester and phosphoric ester,

& for Y denotes the bond via which Y is bonded to the carbon atom bonded to R ⁵ , and

&& for Y denotes the bond via which Y is bonded to X, c) comparing the EPR spectrum of step a) with the EPR spectra of the library of EPR spectra of step b) to give a conformity score, and d) initiating the processing unit to send the conformity score obtained in step c) to the input/output device of step a) and verifying the authenticity of the product of step a), when the conformity score of step c) reaches or exceeds a threshold value.

Identification substances with a repeating unit comprising a five- or six-membered ring are easily accessible both synthetically and commercially.

In an embodiment of the method according to the present invention the repeating unit of the formula

(I) is one of the repeating units according to the formula (IA) to (IC) wherein, in each of the formulae (IA) to (IC), each of R ¹ , R ² , R ³ , and R ⁴ is independently selected from the group consisting of hydrogen, linear and branched alkyl groups with 1 to 4 carbon atoms, each of R ⁵ , R ⁵ ’, and R ⁵ ” is independently hydrogen or methyl, and each of Y, Y’, and Y” is independently selected from the bridging moieties (II) and (III) with the definitions given above for the formula (I).

In one embodiment of the method according to the present invention the repeating unit of the formula

(I) is one according to the formula (IA) wherein each of R ¹ , R ² , R ³ , and R ⁴ is independently selected from the group consisting of hydrogen, linear or branched alkyl groups with 1 to 4 carbon atoms,

R ⁵ is hydrogen or methyl, and

Y is as defined above. It is believed that the stability of the nitroxyl radical of the repeating unit is increased when the substituents in close proximity to the nitroxyl radical, i.e., the residues R ¹ , R ² , R ³ , and R ⁴ , are methyl groups.

In another embodiment of the method according to the present invention R ¹ , R ² , R ³ and R ⁴ are methyl groups and R ⁵ is hydrogen or methyl.

Preferably, Y in the repeating unit according to the formula (I), (IA), (IB), or (IC) is an ester group, a thioester group, or an amide group.

The larger is the number of repeating units in the identification substance used in the method according to the present invention, the larger is the number of nitroxyl radical in said identification substances. In other words, the larger is the number of repeating units in the identification substance used in the method according to the present invention, the stronger is the paramagnet in this identification substance. This leads to a significant reduction of the detection limit for the identification substance in question. A large number of nitroxyl radical is present in the identification substance used in the method according to the present invention when the identification substance comprises or consists of a homopolymer, or a copolymer of the repeating unit according to the formula (I), (IA), (IB), or (IC).

In a further embodiment of the method according to the present invention the identification substance comprises or consists of a cross-linked or linear homopolymer, or a cross-linked or linear copolymer of the repeating unit according to the formula (I), (IA), (IB), or (IC).

Polymers of 2,2,6,6-tetramethylpiperidinyloxymethacrylate, i.e., poly(2,2,6,6-tetramethylpiperidinyl- oxymethacrylate), also known as poly-TEMPO-methacrylate or PTMA, have proved to be particularly suitable in the method according to the present invention. It is a further benefit that they are commercially easily available and synthetically easily accessible.

In a preferred embodiment of the method according to the present invention the identification substance comprises or consists of cross-linked or linear poly(2,2,6,6-tetramethylpiperidinyloxy- methacrylate) (poly-TEMPO-methacrylate, PTMA).

Preferably, the linear poly(2,2,6,6-tetramethylpiperidinyloxymethacrylate) has a number-average molecular weight (M _n ) of 83 ± 13 kDa, a weight-average molecular weight (M _w ) of 1335 ± 15 kDa, and a polydispersity index (PDI) of 16.5 ± 2.4.

Preferably, the soluble parts of the cross-linked poly(2,2,6,6-tetramethylpiperidinyloxymethacrylate) have a number-average molecular weight (M _n ) of 55 ± 2 kDa, a weight-average molecular weight (Mw) of 197 ± 2 kDa, and a polydispersity index (PDI) of 3.6 ± 1 . The identification substance used in the method according to the present invention, in particular, PTMA, does not cause a change of color when applied in a concentration of up to 5 wt.-%. When incorporated into a product, such as a tablet, the identification substance, in particular, PTMA, has a detection limit of 1 ppb, which is equal to 0.001 ppm.

In a further embodiment of the method according to the present invention the product whose authenticity is to be verified comprises at least 0.001 ppm of the identification substance.

Preferably, the product whose authenticity is to be verified comprises from 0.001 to 10,000 ppm of the identification substance.

In principle, the step c) of the method according to the present invention is not subjected to any limitations regarding the way the EPR spectrum of step a) is compared with the EPR spectra of the library of EPR spectra of step b). Nevertheless, it is preferred that the step c) is performed as a similarity analysis. In the context of the present invention the term similarity analysis is used as known to the person skilled in the art and denotes an analysis that quantifies the similarity between two objects, here the similarity between the EPR spectrum provided, received, or requested in step a) with the library of EPR spectra of step b). The result of this similarity analysis is the conformity score of step b), which indicates the degree of similarity between the EPR spectrum of step a) and the library of EPR spectra of step b).

In one embodiment of the method according to the present invention the step b) is performed as a similarity analysis.

The library of EPR spectra in step b) is not subject to any limitations regarding the number of EPR spectra. Preferably, the population of EPR spectra comprises EPR spectra recorded for a concentration series of a specific identification substance. This helps to achieve the highest possible level in precision for the method according to the present invention.

Further, the library of EPR spectra in step b) also is not subject to any limitations regarding the variety of identification substances comprising a repeating unit according to formula (I), whose EPR spectra are part of the library of EPR spectra of step b). Preferably, the library of EPR spectra comprises EPR spectra of one, more or a multitude of identification substances comprising a repeating unit according to formula (I). It is further preferred that said library comprises EPR spectra that were recorded for a concentration series of said one, more or a multitude of identification substances comprising a repeating unit according to formula (I). Preferably, the library of EPR spectra comprises EPR spectra of one, more or a variety of identification substances comprising a repeating unit according to formula (IA) to (IC). In particular, the library of EPR spectra comprises EPR spectra of one, more or a variety of identification substances comprising a repeating unit according to formula (ID). It is further preferred that the library of EPR spectra comprises EPR spectra of an identification substance comprising or consisting of cross-linked or linear poly(2,2,6,6-tetramethylpiperidinyloxy- methacrylate).

In principle, the similarity analysis between the EPR spectrum of step a) and the EPR spectra of the library of EPR spectra of step b) is not subject to any limitation. Nevertheless, it is preferred that the similarity analysis is performed in that the similarity between a vector or matrix of the EPR spectrum of step a) with the vectors or matrices of the EPR spectra of the library of EPR spectra of step b) is analyzed.

The EPR spectra of the library of EPR spectra of step b) may be already present as vectors or matrixes. In that case the library of EPR spectra of step b) comprises not only the EPR in question but also the corresponding vectors or matrixes. Alternatively, the EPR spectra of the library of EPR spectra of step b) are transformed into the corresponding vectors or matrices.

It is therefore preferred that i) the EPR spectra of the library of EPR spectra of step b) are provided as vectors or matrices or the EPR spectra of the library of EPR spectra of step b) are transformed into vectors or matrices, and ii) the EPR spectrum of step a) is provided as vector or matrix or is transformed into a vector or matrix.

It depends on the complexity of an EPR spectrum and the amount of considered information whether it is provided as a vector or matrix. For example, when the information, which is considered, is only the intensity of one or more peaks at a specific position in the EPR spectrum, it may be sufficient that only this information is transferred into a corresponding vector, wherein in the case of more than one peak, the vector is a multi-dimensional vector. However, when further information in the EPR spectrum is considered, for example, the distance between at least two peaks, the peak area and the peak’s full width at half maximum, the information are transferred into a matrix.

It is beneficial to focus on the relevant parameters in an EPR spectrum to make the comparison in step b) as meaningful and expedient as possible. For this purpose, it is first necessary to identify the parameters which are characteristic for the spectrum in question, i.e., which are relevant in said spectrum. In principle, this step is not subject to any limitation, provided that a procedure is used which allows for the reliable and reproducible identification and quantification of relevant parameters in an EPR spectrum. Nevertheless, it is preferred that relevant parameters are identified and quantified in an EPR spectrum by means of a multivariate analysis. In the context of the present invention, the term multivariate analysis is used as known to the person skilled in the art and denotes an analysis, in which several statistical variables or random variables are examined at the same time. By comparison, in the so-called univariate analysis, each variable is analyzed individually. The relationship or dependency structures between the variables, for example a larger peak’s full width at half maximum (FWHM) requires a larger peak area, can only be detected with a multivariate analysis but not with a univariate analysis.

In an embodiment of the method according to the present invention the step b) is performed as a multivariate analysis.

While the multivariate analysis already allows the detection of relationship or dependencies between observed variables, cases may be conceivable in which only some of the variety of the observed potentially relevant variables are really relevant or meaningful. In those cases, it is beneficial to reduce the number of observed potentially relevant variables to a few underlying latent variables. It is therefore preferred that the multivariate analysis also comprises a factor analysis. In the context of the present invention the term factor analysis is used as known to the person skilled in the art and denotes a method of multivariate statistics, which is used to infer from the empirical observations of many different manifest variables, e.g., observables, statistical variables, on a few underlying latent variables, called "factors". For example, it is possible that variations in six observed variables mainly reflect the variation in two unobserved (underlying) variables.

In an alternative, it is also possible to extract the few underlying latent variables, i.e., "factors", from an EPR spectrum by means of a so-called principle component analysis. In the context of the present invention the term principle component analysis, also known as short PCA, is used as known to the person skilled in the art and denotes a method of multivariate statistics, which structures extensive data sets by using the eigenvectors of the covariance matrix. This allows data sets to be simplified and illustrated by approximating a variety of statistical variables by reducing the number of linear combinations (the main components) that are as meaningful as possible. In an alternative, it is therefore preferred that the multivariate analysis also comprises a principle component analysis.

It has been proven that the most relevant parameters in an EPR spectrum are the peak intensity, peak position (g-factor), peak area, peak’s full width at half maximum, number of peaks and the distance of peaks if more than one peak was identified in the EPR spectrum.

In an embodiment of the method according to the present invention the step b) therefore comprises the analysis of the EPR spectrum for peak intensity, peak position (g-factor), peak area, peak’s full width at half maximum, number of peaks and the distance of peaks if more than one peak was identified in the EPR spectrum.

The parameters peak intensity, peak position (g-factor), peak area, peak’s full width at half maximum, number of peaks and the distance of peaks if more than one peak was identified in the EPR spectrum thus analyzed from the EPR spectrum of step a) are then further analyzed for their similarity with the corresponding parameters in the library of EPR spectra of one or more identification substances of step b). The method according to the present invention allows for a very accurate verification of the authenticity of a product. A suitable measure for this accuracy is the coefficient of determination, often also referred to as R2 or r2 and pronounced “R squared”. In the context of the present invention this term is used as known to the person skilled in the art of statistics and denotes the proportion of the variation in the dependent variable that is predictable from the independent variable(s). The coefficient of determination can have any conceivable value ranging from O to 1 or O to 100%, wherein the higher the value for R ² is, the more accurate is the method according to the present invention.

When comparing the EPR spectrum of step a) with the library of EPR spectra of one or more identification substances of step b) in order to give a conformity score which indicates the degree of similarity, one also needs to set threshold above which the authenticity of a product is verified or not, or in other words whether a product is identified as true or false. The method according to the present invention leads to a very low error rate, specifically, the method has an R ² > 0.99.

In a further embodiment the threshold for verifying the authenticity of the product is set to a value of 99%.

In principle, the method according to the present invention is not subject to any limitations regarding the product whose authenticity is to verified. Preferably, said product is a pharmaceutical, a blood product, a nutraceutical, a food ingredient, a cosmetic, a raw material, a medical product, an implant or transplant, a packing, a consumable, a print product, a print color, a lacquer, a coating, a means of payment, a component or a construction part or material, or a luxury good.

In principle, the method according to the present invention is not subject to any limitations regarding the preparation or provision of the identification substance, provided that the identification substance is suitable for use in said method. Nevertheless, it is preferred that the identification substance in question is prepared according to the procedure disclosed in US 2019/0177455 A1 , i.e., by the steps of i) producing a dispersion D of solid particles of a compound of the formula (I) in an aqueous phase, ii) polymerizing the solid particles of the compound of the formula (I) of the dispersion D obtained in step i), giving a polymer P1 comprising repeating units of the formula (IV) with the meanings of X, Y, R ¹ , R ² , R ³ , R ⁴ and R ⁵ as defined above, (IV), wherein the polymerization in step ii) is performed at a temperature below the melting temperature of the compound of the formula (I), and iii) subjecting the polymer P obtained in step ii) to a nitroxidation to give a polymer P2 comprising repeating units of the formula (I) The procedure described above has the benefit that it gives the identification substance as finely divided polymer which can be worked up easily directly after the polymerization step. Specifically, the thus obtained product can be easily separated by filtration directly and is then present in an easy to handle particle size. It is a further benefit, that the thus obtained identification substance has a relatively narrow particle size distribution. For example, after an identification substance as described above was prepared, half of the dispersion are removed and the size of the particles remaining in the dispersion is determined, for example according to the procedure described in DIN 66156-2, and using sieve according to DIN ISO 3310, the following particle size distribution is exemplarily obtained:

The relatively narrow particle size distribution of the identification substance used in the method according to the present invention has the benefit that it allows to incorporate the identification substance in question into a product well dosed and in equal amounts. It is therefore possible to provide a product whose authenticity is to be verified with a homogeneous distribution of the identification substance in question over the entire body of the product. It is also possible to provide a product whose authenticity is to be verified with the same or essentially the same concentration of the identification substance in question over the whole batch of the product.

A further object is therefore a product, comprising an identification substance for verifying the authenticity of the product, wherein the identification substance is homogeneously distributed over the entire body of the product and wherein the identification substance comprises a repeating unit according to the formula (I) wherein each of R ¹ , R ² , R ³ , and R ⁴ is independently selected from the group consisting of hydrogen, linear or branched alkyl groups with 1 to 4 carbon atoms,

X is selected from the group consisting of *-CH2-C’H-CH2-**, *-C’H-CH2-**, *-CH2-C’H-**, *-C’=CH-** and *-CH=C’-**, wherein

* in each case denotes the bond to the carbon atom bonded to R ¹ and R ² ,

** in each case denotes the bond to carbon atom bonded to R ³ and R ⁴ , and

C’ denotes the carbon atom bonded to the Y moiety,

Y is selected from the bridging moieties (II) and (III), wherein

(II) has the structure #-(Y ¹ ) _P i-[C=X ¹ ] _P 2-(Y ² ) _p3 -B-(Y ³ ) _p6 -[C=X ² ] _P 5-(Y ⁴ ) _P 4-## and (III) has the structure #-(Y ⁵ ) _P 9-(C=X ³ ) _P s-(Y ⁶ ) _P 7-##, wherein p1 , p2, and p3 are each 0 or 1 , with the proviso that it is not simultaneously the case that p1 = p3 = p2 = 0, p4, p5 and p6 are each 0 or 1 , with the proviso that it is not simultaneously the case that p4= p6 = 1 and p5 = 1 , p7, p8 and 9p are each 0 or 1 , with the proviso that it is not simultaneously the case that p7 = p9 = 1 and p8 =0, each of X ¹ , X ² , and X ³ is independently selected from oxygen and sulfur, each of Y ¹ , Y ² , Y ³ , Y ⁴ , Y ⁵ , and Y ⁶ is independently selected from the group consisting of O, S, NH, and N-alkyl,

B is a divalent (hetero)aromatic moiety, or a divalent aliphatic moiety optionally substituted by at least one group selected from -NO2, -NH2, -CN, -SH, -OH, and halogen, and optionally at least one group selected from ether, thioether, amino ether, carbonyl, carboxylic ester, carboxamide, sulphonic ester and phosphoric ester,

# for Y denotes the bond via which Y is bonded to the carbon atom bonded to R ⁵ , and ## for Y denotes the bond via which Y is bonded to X, characterized in that said product is a pharmaceutical, a blood product, a nutraceutical, a food ingredient, a medical product, an implant or transplant, a packing, a consumable, a print product, a print color, a lacquer, a means of payment, or a luxury good.

Because of its relatively narrow particle size distribution, it is not only possible to provide a product with a homogeneous distribution of the identification substance over the entire body of the product, but it is also possible to allow for a homogeneous distribution of the identification substance over the entire batch of the product, whose authentication is to be verified. Hence, one should expect that the whole batch of the product has the same or essentially the same concentration of the identification substance.

In fact, the homogeneous distribution of the identification substance over the product batch can be proven experimentally. Specifically, six pieces of each of the tablet comprising the same identification substance according to the present invention were subjected to EPR measurements. All EPR measurements gave extremely low standard deviations. Since the intensity and also the area of the EPR measurements correlate directly with the concentration of the EPR active identification substance, it can be concluded here due to the very small deviations that the identification substance must be homogeneously distributed, otherwise these deviations would be significantly greater, especially with such a sensitive measurement methodology as EPR.

In an embodiment the product according to the present invention comprises the identification substance in the same or essentially the same concentration over the whole batch of the product. For example, when the product is a pharmaceutical, such as a tablet, all tablets comprise the identification substance in the same or essentially the same concentration.

In principle, the identification substance used in the method according to the present invention and/or the identification substance incorporated into the product according to the present invention is not subject to any limitations regarding its preparation. Nevertheless, it is preferred to prepare the identification substance by the procedure described above, in order to guarantee that the identification substance has the advantageous relatively narrow particle size distribution.

Preferably, the identification substance of the product according to the present invention is prepared by the steps i) to iii) above.

It is further preferred that the repeating unit of the formula (I) of the identification substance in the product according to the present invention is one of the repeating units according to the formula (IA) to (IC) with the definitions mentioned in connection with said formulae.

In particular, the repeating unit of the formula (I) is one according to the formula (IA) with the definitions mentioned in connection with said formulae.

It is further preferred that R ¹ , R ² , R ³ and R ⁴ 1 the formula (I) or (IA) to (IC) are methyl groups and R ⁵ is hydrogen or methyl.

Preferably, Y in the repeating unit according to the formula (I), (IA), (IB), or (IC) is an ester group, a thioester group, or an amide group.

Preferably, the identification substance comprises or consists of a cross-linked or linear homopolymer, or a cross-linked or linear copolymer of the repeating unit according to the formula (I), (IA), (IB), or (IC).

It is further preferred that the product according to the present invention comprises an identification substance comprising or consisting of cross-linked or linear poly(2,2,6,6-tetramethylpiperidinyloxy- methacrylate).

In another embodiment the product according to the present invention comprises at least 0.001 ppm of the identification substance.

In particular, the product according to the present invention comprises from 0.001 to 10,000 ppm of the identification substance. When the product is a pharmaceutical or a nutraceutical, said product can be a powder, tablet, a capsule, a soft capsule, a liquid (solution, dispersion or emulsion) or a lipid-based drug delivery system.

An identification substance, used in the method according to the present invention, such as PTMA, can be incorporated into a conventional tablet. No change of color, i.e., no discoloration of the pharmaceutical formulation as such, was determined when an identification substance, such as PTMA, was applied in a concentration of up to 5 wt.-%. The detection limit for an identification substance, such as PTMA, in tablets was 1 ppm, which is equal to 0.001 ppm.

An identification substance, used in the method according to the present invention, such as PTMA, can be incorporated into capsules, for example using EUDRACAP™, which are functional ready-to- fill and pre-locked capsules. For this purpose, an identification substance used in the method according to the present invention, such as PTMA, was dispersed in a sub-coating. This identification substance in question could be detected in the sub-coating with or without the application of an additional top-coating. An additional top-coating protects the identification substance (in the subcoating) against abrasion. The presence of the identification substance does not change the white color of EUDRACAPS™, even though it was used in a concentration of 3 wt.-%, calculated on the dry substance. Reproducible EPR measurements were conducted with coated EUDRACAPS™ (n = 6) and the identification substance, such as PTMA, could be clearly identified. The detection limit for an identification substance used in the method according to the present invention was 100 ppb, i.e., 0,1 ppm, in a solid dosage form, and 1 ppb, i.e., 0.001 ppm, for a liquid dosage form.

An identification substance, used in the method according to the present invention, such as PTMA, can be incorporated into soft capsules. The identification substance, such as PTMA, can be detected inside the soft capsules.

An identification substance, used in the method according to the present invention, can be also incorporated into a solution, dispersion or emulsion. The thus obtained solution, dispersion or emulsion comprising the identification substance can then be filled into bottles, flagons, capsules or sachets.

An identification substance, used in the method according to the present invention, can be also incorporated into a lipid-based drug delivery system (LBDDS), for example a self-emulsifying drug delivery system (SEDDS), a self-microemulsifying drug delivery system (SMEDDS), or a self- nanoemulsifying drug delivery system (SNEDDS). Forthis purpose, an identification substance, used in the method according to the present invention, such as PTMA, was solved in a specific liquid based drug delivery system. A reproducible EPR signal could be detected in the liquid based drug delivery system at a detection limit of 1 ppb as well as in the aqueous nano-emulsion after dispersion in water at a detection limit of 1 ppb. A further object of the present invention is the use of an identification substance or of a product according to the present invention for verifying the authenticity of a product by means of EPR spectrometry.

Said identification substance comprises a repeating unit according to the formula (I) wherein each of R ¹ , R ² , R ³ , and R ⁴ is independently selected from the group consisting of hydrogen, linear or branched alkyl groups with 1 to 4 carbon atoms,

X is selected from the group consisting of *-CH2-C’H-CH2-**, *-C’H-CH2-**, *-CH2-C’H-**, *-C’=CH-** and *-CH=C’-**, wherein

* in each case denotes the bond to the carbon atom bonded to R ¹ and R ² ,

** in each case denotes the bond to carbon atom bonded to R ³ and R ⁴ , and

C’ denotes the carbon atom bonded to the Y moiety,

Y is selected from the bridging moieties (II) and (III), wherein

(II) has the structure #-(Y ¹ ) _P i-[C=X ¹ ] _P 2-(Y ² ) _p3 -B-(Y ³ ) _p6 -[C=X ² ] _P 5-(Y ⁴ ) _P 4-## and (III) has the structure #-(Y ⁵ ) _P 9-(C=X ³ ) _P s-(Y ⁶ ) _P 7-##, wherein p1 , p2, and p3 are each 0 or 1 , with the proviso that it is not simultaneously the case that p1 = p3 = p2 = 0, p4, p5 and p6 are each 0 or 1 , with the proviso that it is not simultaneously the case that p4= p6 = 1 and p5 = 1 , p7, p8 and 9p are each 0 or 1 , with the proviso that it is not simultaneously the case that p7 = p9 = 1 and p8 =0, each of X ¹ , X ² , and X ³ is independently selected from oxygen and sulfur, each of Y ¹ , Y ² , Y ³ , Y ⁴ , Y ⁵ , and Y ⁶ is independently selected from the group consisting of O, S, NH, and N-alkyl, B is a divalent (hetero)aromatic moiety, or a divalent aliphatic moiety optionally substituted by at least one group selected from -NO2, -NH2, -CN, -SH, -OH, and halogen, and optionally at least one group selected from ether, thioether, amino ether, carbonyl, carboxylic ester, carboxamide, sulphonic ester and phosphoric ester,

# for Y denotes the bond via which Y is bonded to the carbon atom bonded to R ⁵ , and ## for Y denotes the bond via which Y is bonded to X.

All further definitions of the identification substance also apply to the use according to the present invention.

Another object of the present invention is a system for verifying the authenticity of a product, wherein the system i) comprises a processing unit adapted for carrying out the method according to the present invention and ii) comprises or has access to a database with a library of EPR spectra of one, more, or a multitude of identification substances.

The electron paramagnetic resonance (EPR) spectrum of a product, whose authenticity is to be verified, is provided, received and/or requested from an input/device device. This input/device can be a device for electronic data processing, which has received and/or requested the EPR spectrum in question from an EPR spectrometer. Alternatively, said device can be an EPR spectrometer as well.

In an embodiment of the system according to the present invention the processing unit forms a network with an input/output device or an EPR spectrometer.

The database with the library of EPR spectra of one, more, or a multitude of identification substances of step b) is either stored in the processing unit according to the present invention or the said processing unit has access to a server or cloud, on which the library of EPR spectra of one, more, or a multitude of identification substances of step b) is stored. The alternative, that the library of EPR spectra of one or more identification substances of step b) is stored on a server or cloud, to which the processing unit has access, has the benefit that the system can be regularly up-dated with new EPR spectra of other identification substances.

In another embodiment of the system according to the present invention the library of EPR spectra of one, more, or a multitude of identification substances of step b) is stored on the processing unit or on a server or cloud, to which the processing unit has access.

A further object of the present invention is a computer-program product comprising code portions adapted for performing the method according to the present invention, when said program is loaded into a computer device. Yet a further object of the present invention is a computer-program product stored on a computer- usable medium, comprising computer readable program means for causing a computer to perform the method according to the present invention.

The present invention is further illustrated by the following examples.

Examples:

I. Materials:

(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and chromium (III) potassium sulfate dodecahydrate were obtained from Alfa Aesar GmbH & Co. KG (Karlsruhe, Germany).

Poly-TEMPO-methacrylate (PTMA) is a non-commercial product of research and development activities from Evonik Operations GmbH (Hanau, Germany) and was synthesized as a linear as well as a cross-linked polymer.

2,2,6,6-tetramethyl-4-piperidinylmethacrylate was synthesized according to methods that are state of the art.

Sodium lauryl sulfate and Disponil® SDS 15 were obtained from BASF SE (Ludwigshafen, Germany). Thioglycolic acid-2-ethylhexyl ester was purchased from Dr. Spiess Chemische Fabrik GmbH (Kleinkarlbach, Germany).

Triethylene glycol dimethacrylate and Aeroperl® 300 Pharma are products from Evonik Industries AG (Essen, Germany).

Ammonium peroxodisulfate, sodium tungstate dihydrate, phenylphosphonic acid and tungstic acid were received from Sigma Aldrich GmbH (Steinheim, Germany).

Ethylenediaminetetraacetic acid was obtained from Carl Roth GmbH (Karlsruhe, Germany).

Lactose monohydrate was purchased from DFE Pharma GmbH & Co. KG (Goch, Germany).

Talc was received from Luzenac Group Pharma (Toulouse, France).

Magnesium stearate was obtained from Merck KGaA (Darmstadt, Germany).

Corn starch was from Colorcon GmbH (Idstein, Germany).

Microcrystalline cellulose (MCC) was purchased from DuPont GmbH (Wiesbaden, Germany).

Colloidal silicon dioxide was from Carl Roth GmbH (Karlsruhe, Germany).

Ultramarine blue extra dark was purchased from Kremer Pigmente GmbH & Co. KG (Aichstetten, Germany). Copper (II) sulfate was received from VWR International GmbH (Ulm, Germany).

All other chemicals and solvents were of analytical grade and purchased commercially.

II. Methods

2.1 Synthesis of cross-linked PTMA

60.0 g of 2,2,6, 6-tetramethyl-4-piperidinylmethacrylate, 4.0 g of a 15 wt.-% aqueous sodium lauryl sulfate solution, 0.3 g of thioglycolic acid-2-ethylhexyl ester and 0.6 g of the cross-linking agent triethylene glycol dimethacrylate were mixed in a 1 -liter double jacket reactor equipped with a stirrer and return condenser containing 240 ml of water and the mixture was preheated to 65 °C. After melting of 2,2,6, 6-tetramethyl-4-piperidinylmethacrylate, vigorous stirring was applied for 15 min at 6000 rpm using an Ultra Turrax disperser. The mixture was then cooled down to 40 °C for 30 min while applying intense shearing with the Ultra Turrax disperser. At 40 °C the polymerization was initiated by adding 0.06 g ammonium peroxodisulfate and the mixture was stirred at 120 rpm for another 2 h. Stirring at 120 rpm for additional 12 h at 45 °C was conducted before increasing the temperature to 65 °C for 1 h to finalize the polymerization. Subsequently, the mixture was cooled down to 20 °C and the volume in the reactor was reduced by half using vacuum drying. The obtained polymer particles were swollen due to addition of 240 mL ethanol. 2.6 g of sodium tungstate dihydrate and 0.7 g of ethylenediaminetetraacetic acid were added for catalyzing the following oxidation step. The oxidation step was conducted using a 30 wt.-% hydrogen peroxide solution that was added in three portions of 9 g every 30 min. After 1 .5 h, an additional quantity of 26.8 g of a 30 wt.-% hydrogen peroxide solution was added. The mixture was stirred at 120 rpm at 20 °C for another 72 hours. The mixture was then heated up to 40°C for 1 h, to 45 °C for another hour while stirring the mixture. After cooling down again to 20 °C the mixture was filtered, washed with 1 L of water, and finally dried in a vacuum oven at 40 °C for 24 h.

A homogeneous powder was obtained accompanied by caking and coagulates of less than 2% in the reactor.

2.2 Synthesis of linear PTMA

196.2 g of 2,2,6, 6-tetramethyl-4-piperidinylmethacrylate, 31.8 g of Disponil® SDS 15 and 1.17 g of thioglycolic acid-2-ethylhexyl ester were mixed in a 2-liter double jacket reactor equipped with a stirrer and return condenser containing 1473 ml of water and the mixture was preheated to 67 °C. After melting of 2,2,6, 6-tetramethyl-4-piperidinylmethacrylate, vigorous stirring was applied for 15 min at 8000 rpm using an Ultra Turrax disperser. The mixture was then cooled down to 45 °C for 1 h while applying intense shearing with the Ultra Turrax disperser. At 45 °C the polymerization was initiated with adding 3.2 ml of a 10 wt.-% aqueous ammonium peroxodisulfate solution and the mixture was stirred at 120 rpm for another 2 h. A second initiation was conducted at 45 °C using a mixture of 1.6 ml of a 10 wt.-% aqueous ammonium peroxodisulfate solution combined with 1.4 ml of sodium hydrosulfide and 10 mg of iron (II) sulfate heptahydrate. Stirring at 120 rpm for additional 12 h at 45 °C was conducted to finalize the polymerization. The mixture was transferred to a 10-liter double jacket reaction vessel, 3.4 kg ethanol was added at 20 °C and temperature was afterwards reduced to -5°C while stirring the mixture at 120 rpm. When achieving the temperature of -5 °C, 151 .5 g of a 35 wt.-% hydrogenperoxide solution was added, and the mixture was swollen for 1 h. Subsequently, a venturello-ishii catalyst system consisting of 1 .7 g phenylphosphonic acid and 5.1 g tungstic acid as well as another 108 g of a 35 wt.-% hydrogenperoxide solution were added while stirring at 120 rpm and the mixture was heated up to 20 °C within 1 h. When achieving 20 °C, the temperature was maintained for 2 h before the mixture was heated up to 60 °C within the next 10 h. When reaching 60 °C, the temperature was maintained for 2 h before the mixture was cooled down to 20 °C within 1 h. During the heating-cooling procedure the mixture was continuously stirred at 120 rpm. After cooling down to 20 °C the mixture was filtered, washed with 2 L of water, and finally dried in a vacuum oven at 40 °C for 48 h.

A homogeneous powder was obtained accompanied by caking and coagulates of less than 2% in the reactor.

2.3 Molecular weight analysis using gel permeation chromatography (GPC)

The molecular weight distribution of PTMA was determined using an Agilent 1 100 Series GPC-SEC Analysis System comprising a pump (G1310A), autosampler (G1313A), column oven (G1316A), Rl- detector (G1362A) and a control module (G1323B), all from Agilent Technologies (Frankfurt am Main, Germany). Separation was achieved using a GRAM precolumn (8 x 50 mm, 10 pm) and another three GRAM columns (8 x 300 mm, 10 pm) in series all maintained at 60 °C. The eluent consisted of N,N-dimethylacetamide, lithium bromide, tris(hydroxymethyl)aminomethane (TRIS), and water (1000:2:2:10 w/w), the flow rate was set to 1 mL/min and an injection volume of 100 pL was applied. The Rl-detector was maintained at 40 °C and a polymethylmethacrylate solution (1 g/L eluent) was used as a standard. A solution of PTMA (1 g/L eluent) was used for analysis and the number-average molecular weight (M _n ), the weight-average molecular weight (M _w ) and the polydispersity index (PDI) of PTMA was determined in triplicate.

2.4 Manufacture of powders and powder mixtures

Solid substances that presented with a particle size > 500 pm were ground to a powder using a mortar and a pestle made of ceramic. Powder mixtures were prepared as follows: All substances for manufacture of powder mixtures were ground using a mortar and a pestle to guarantee similar particle sizes in orderto receive homogenous powder mixtures. Powders were all accurately weighed into a jar of proper size, closed with a screw cap afterwards and mixed for 10 min using a Turbular mixer from WAB Group (Nidderau-Heldenbergen, Germany). In case of the substance TEMPO, preliminary steps of dissolving TEMPO in aceton (mixture ratio 1 :1 w/w) and adding it to Aeroperl® 300 Pharma (mixture ratio TEMPO: Aeroperl® 300 Pharma 1 :1) were conducted to obtain a homogenous powder mixture. Aceton was then removed at 30 °C in a drying cabinet for 2 h.

2.5 Tablet manufacturing (compression)

Powder mixtures were further processed into tablets using an eccentric press EP-1 from ERWEKA GmbH (Langen, Germany). A pair of round stamps made of steel having a diameter of 5 mm were used for compression. The eccentric press was used in the automatic mode applying compression forces of 5 kN. After filling the template of the eccentric press with a certain quantity of a powder mixture, the compression was conducted and tablets of 75 mg with a thickness of 3 mm each were targeted.

2.6 Sample preparation / processing of different substances / dosage forms for electron paramagnetic resonance (EPR) measurement

Substances and dosage forms of a solid state were prepared for EPR measurement using a quartz glass EPR tube from Bruker GmbH (Mannheim, Germany) with an inner diameter of 3.5 mm and a length of 165 mm.

Powder: For the analysis of powders or solid particulate substances, EPR tubes were filled with powders/solid particulate substances to a minimum filling level of 2 cm.

Tablet: The analysis of tablets required the usage of a cylindrical, self-made (3D-printed) sample holder that was made of polylactide acid (PLA) and connected to the EPR tube. The self-made sample holder had a round-shaped cavity with a diameter of 5 mm for tablet (diameter of 5 mm) loading.

2.7 Electron paramagnetic resonance (EPR) measurement

EPR measurements were conducted using a MS-5000 EPR device from Freiberg Instruments GmbH (Freiberg, Germany). Before running any measurements, a 15 min warm-up run to equilibrate the temperature of the EPR device to a temperature range of 30 - 33 °C was performed for better comparison of collected EPR data at similar measurement temperatures. Samples for EPR measurement were prepared and then inserted into the vertical sample cavity using special quartz glass EPR tubes for solids or glass capillary tubes for liquids respectively as described. EPR tubes were connected to a specific sample holder to reproducibly maintain the sample at the same position in the cavity of the EPR device. Ideally, for EPR analysis using the MS-5000 device, the distance from the bottom of the sampler holder to the medium filling level of the sample inside the EPR tube was 62 ± 1 mm. The EPR tube was then fixed inside the cavity using a screw cap. Subsequently, the EPR measurement was started at a fixed frequency (9.45 GHz) after, depending on the sample properties, the adjustment parameters of the EPR device such as magnetic field range, microwave power, sweep time and modulation factor have been selected individually. A substance/sample was regarded as EPR-active if a peak signal could be detected that revealed a signal to noise ratio (S:N ratio) higher than 3:1 . EPR spectrograms were finally characterized by analyzing the peak intensity, the peak position (g-factor), the peak area, the peak’s full width at half maximum (FWHM) as well as the distance of peaks, if a number of peaks > 1 has been identified.

2.8 Stability studies

6 tablets containing PTMA (cross-linked) were kept in a 30 ml amber glass, closed with a screw cap, and stored at constant and controlled conditions (30 °C/65% RH) in a climatic chamber from Binder GmbH (Tuttlingen, Germany) for three months. After three months, they were again analyzed via EPR technology. The EPR measurement results of these tablets were compared with those obtained immediately after manufacture.

2.9 Principal component analysis (PCA) for verification of PTMA tablets

A special PCA software tool, developed, customized, and provided by HS Analysis GmbH (Karlsruhe, Germany) was used for unique sample identification based on specific EPR signaling (EPR fingerprint) of PTMA using a training as well as an evaluation mode. This software tool was trained using the EPR data of PTMA using a calibration curve. The PCA describing the data set with a very high R ² > 0.999 and a therefore necessary score level was selected for the evaluation mode. Different operators (preprocessing) such as integrate, differentiate, selecting magnetic field range(s) could be added in this software. The evaluation of unknown EPR data sets was conducted based on the selected PCA in the training mode. The threshold whether a sample was identified as true or false was set to a conformity level of 99.0% (R ² > 0.990).

III. Results

Substances that demonstrated an EPR signaling are also referred to as “tag” or “tag substance” in the following.

3.1 Synthesis of PTMA

PTMA either cross-linked or linear were obtained as fine, white to pale pink powders.

3.2 Molecular weight analysis PTMA (linear) was analyzed for its molecular weight and its polydispersity index (PDI) (Table 1). No filtering was conducted for the linear type of PTMA.

Table 1 : M _n , M _w and PDI of PTMA; PTMA (linear) determined via GPC analysis. Each value designates the mean ± S.D. (n = 3).

3.3 EPR measurements of powder mixtures

The substance TEMPO was used for EPR measurements of powder mixtures. TEMPO-Aeroperl® 300 Pharma was mixed with the placebo powder mixture (Table 2) in varying concentrations and subsequently a quantity of 300 ± 3 mg of the obtained powder mixtures containing TEMPO was analyzed via EPR technology. The filling level of 5 ± 0.1 cm in height inside the EPR tube with TEMPO powder mixtures was similar for all replicates. The EPR measurement parameters for analyzing the tag substance TEMPO are depicted in table 3 and the results of the EPR analysis of the powder mixtures incorporating TEMPO are shown in table 4.

Table 2: Composition of placebo powder mixture. Table 3: EPR measurement parameters for TEMPO incorporated in a powder mixture.

Table 4: Tag concentration and EPR measurement data of powder mixtures incorporating TEMPO in different concentrations. Each value designates the mean ± S.D. of n = 3.

3.4 EPR measurements of tablets

The placebo powder mixture (Table 2) was used for tablet manufacturing (compression) experiments in the following. This powder mixture (Table 2) was mixed with PTMA in varying concentrations and compressed to obtain tablets for EPR analysis. The obtained, round-shaped tablets presented with a weight of 75 ± 2 mg and a thickness of 3 ± 0.1 mm. Each individual powder mixture composition, with or without (placebo) the tag substance PTMA was compressed 6 times as well as subsequent EPR analysis was conducted with all 6 tablets obtained. The EPR measurement parameters for analyzing the tag substance PTMA are depicted in table 5 and the results of the EPR analysis of the manufactured tablets incorporating PTMA are shown in table 6.

Table 5: EPR measurement parameters for PTMA (cross-linked) or PTMA (linear) incorporated in tablets.

Table 6: Tag concentrations and EPR measurement data of tablets incorporating PTMA (crosslinked) or PTMA (linear). Each value designates the mean ± S.D. of n = 6.

The linear type of PTMA revealed a slightly lower signal intensity when comparing tablets of a similar PTMA concentration either containing PTMA (cross-linked) or PTMA (linear). All tablets in the PTMA concentration range of 1 ppb - 10,000 ppm presented with a white appearance.

Considering the M _w of PTMA, the molar detection limit of the linear type of PTMA in tablets was calculated using the following equation:

Equation (1) included the following parameters: n was the calculated molar amount of PTMA in the tablet in mol, m was the quantity of PTMA in the tablets in gram and M _w was the determined numberaverage molecular weight of PTMA in gram/mol. The molar detection limit of PTMA (cross-linked) in tablets using equation (1) was calculated based on a tag concentration of 1 ppb (PTMA) in a 75 mg tablet with a hypothetical, Active M _w of 100 kDa. A molar amount (detection limit) of 7.5 x 10 ^-16 mol of PTMA (cross-linked) incorporated in tablets was determined. A similar signal intensity of PTMA (linear) compared to PTMA (cross-linked) as shown in table 6 resulted in a detection limit of 5.62 x 10- ¹⁷ mol of PTMA (linear) in tablets. PTMA incorporated in tablets could be detected in a femtomolar concentration range.

3.5 Stability studies Tablets incorporating PTMA (cross-linked) in its highest concentration (10,000 ppm) were subjected to storage stability studies at 30 °C/65% RH. The EPR measurement parameters are shown in table 7 and were similar to those EPR parameters (Table 5) adjusted for PTMA tablets analyzed immediately after manufacture. The EPR results of the storage stability studies with PTMA tablets are depicted in table 8.

Table 7: EPR measurement parameters for PTMA (cross-linked) incorporated in tablets after three months of storage at 30 °C/65% RH.

Table 8: Tag concentrations and EPR measurement data of tablets incorporating PTMA (crosslinked) after three months of storage at 30 °C/65% RH. Each value designates the mean ± S.D. of n = 6.

PTMA (cross-linked) tablets demonstrated to be storage stable over three months at the selected storage conditions with regard to their EPR signaling. Compared to the corresponding EPR measurement data collected at the time of manufacture (PTMA (cross-linked) 10,000 ppm), signal intensity and area did slightly increase whereas g-factor and FWHM remained unchanged.

3.6 Principal component analysis (PCA) for verification of PTMA tablets

PCA was applied to verify PTMA tablets based on the unique EPR signaling of PTMA. Therefore, a training mode using tablets incorporating PTMA of varying concentrations was passed to identify the parameters for the most-promising PCA before an evaluation step to finally verify PTMA tablets against placebo or other potential tag substances was conducted. A training with PTMA (crosslinked) tablets was performed (Table 9) and the evaluation via PCA against placebo tablets (Table 10) and tablets containing other potential tag substances (Table 1 1) was successfully conducted.

Table 9: Training with PTMA (cross-linked) tablets and selection of PCA parameters. Table 10: Evaluation via PCA of PTMA tablets and placebo tablets after training with PTMA tablets (Table 9). Table 11 : Evaluation via PCA of tablets incorporating different potential tag substances (ultramarine blue extra dark, chromium (III) potassium sulfate dodecahydrate, copper (II) sulfate) after training with PTMA tablets (Table 9). PTMA (cross-linked) tablets were evaluated again via PCA after the tablets were stored at 30°C/65% RH for three months and the results (Table 12) demonstrated an accurate identification of PTMA tablets as the determined R ² values were comparable with those collected of PTMA tablets immediately after manufacture.

Table 12: Evaluation via PCA of PTMA (cross-linked) tablets (after three months of storage) after training with PTMA tablets (Table 9).