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Title:
METHOD FOR DETERMINING OXIDIZABLE SUBSTANCES
Document Type and Number:
WIPO Patent Application WO/2018/166881
Kind Code:
A1
Abstract:
Method for the preparation of a solid mixture comprising the steps: - preparing a solution comprising - oxalic acid or oxalic acid salts, - one or more inorganic salts, - lyophilizing the solution

Inventors:
GEICK, Klaus (Am Böhnerfeld 49, Grevenbroich, 41516, DE)
GUTHMANN, Helga (Am Sägewerk 34, Grevenbroich, 41516, DE)
Application Number:
EP2018/055736
Publication Date:
September 20, 2018
Filing Date:
March 08, 2018
Export Citation:
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Assignee:
HACH LANGE GMBH (Königsweg 10D, Berlin, 14163, DE)
International Classes:
C07C51/43; C07C51/50; C07C55/06; C07C55/07; G01N21/79; G01N33/18
Foreign References:
CN101475158A2009-07-08
DE19850934A12000-05-18
RU2146820C12000-03-20
DE19850934A12000-05-18
DE8703659U11987-10-22
Attorney, Agent or Firm:
PATENTANWÄLTE TER SMITTEN EBERLEIN-VAN HOOF RÜTTEN PARTNERSCHAFTSGESELLSCHAFT MBB (Burgunderstr. 29, Düsseldorf, 40549, DE)
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Claims:
Claims

1. A method for the preparation of a solid mixture comprising the

steps:

- preparing a solution comprising:

- oxalic acid or oxalic acid salts,

- one or more inorganic salts,

- lyophilizing the solution.

2. The method according to claim l, wherein the weight ratio of the inorganic salts to the oxalic acid or the oxalic acid salts is 10 to 100: 1, based on the anions.

3. The method according to claim 1 or 2, wherein the inorganic salts is selected from the group of sulfates, phosphates, chlorides and nitrates.

4. The method according to one of claims 1 to 3, wherein the salt is an ammonium salt, an alkali salt or an alkaline earth meta! salt.

5. The method according to one of claims 1 to 4, wherein the concentration of the oxalic acid or the oxalic acid salt prior to the lyophilization is 0.01 to 0.05 mol/l.

6. The method according to one of claims 1 to 5, wherein the concentration before the lyophilization of the inorganic salt is 0.1 to 5 mol/l.

7. The method according to any one of claims 1 to 6, wherein a temperature program is performed before the lyophilization.

8. A lyophilized solid mixture obtainable via the method according to any one of claims 1 to 7.

9. A method for determining oxidizabte substances In a sample solution comprising the steps:

- mixing the sample solution with sulfuric acid to obtain an acidified sample,

- adding a permanganate reagent to obtain a digestion solution,

- heating the digestion solution to carry out a digestion,

- adding a lyophilized solid mixture according to claim 8,

- adding a permanganate reagent to obtain a measurement solution,

- photometrically measuring a residual content of the permanganate reagent in the measurement solution,

- calculating the oxidizable substances in the sample solution via a measured residual content of the permanganate reagent.

10. The method according to claim 9, wherein the sample solution is a water sample.

11. The method according to claim 9 or 10, wherein the heating is performed at 100 °C for 5 to 15 minutes.

12. The method according to one of claims 9 to 11, wherein the photometric determination is performed at a wavelength of 545 nm.

13. The method according to one of claims 9 to 12, wherein the photometric determination is performed more than once.

14. A test kit comprising a lyophilized solid mixture according to claim 8, a permanganate solution and instructions for use.

Description:
Method for determining oxidizable substances

The present invention relates to a solid mixture and to a method for determining oxidizable substances in a sample.

The international ISO standard 8467 describes a method for determining organic contaminants in weakly polluted waters (drinking water, surface water, untreated water) after digestion by means of indirect titration with a defined permanganate solution and an oxalic acid solution, The performance of this method is reserved for an experienced user in a laboratory due to the many working steps and the open handling of dangerous solutions.

Before the actual titration, the water sample is mixed with sulfuric acid and with a defined amount of permanganate solution in excess and digested in a boiling water bath for 10 minutes. The still hot mixture Is subsequently mixed with a defined amount of oxalic acid solution, whereby the solution is completely decolorized, The excess of oxalic acid Is then titrated with the permanganate solution to a pale pink color. The permanganate index is calculated in mg/L based on the consumption of permanganate solution,

Several titrations must be performed to obtain a meaningful result, In addition to the titration of a blank value, a pre-titration usually takes place before the actual triple titration in order to estimate the approximate content of organic impurities in advance. AH solutions (permanganate solution, oxalic acid solution) must either be freshly prepared or tested for content prior to use. The oxalic acid solution is in particular unstable. The process also produces significant amounts of aqueous waste which must be disposed of.

The content thus determined, calculated as the permanganate index, is nonetheless a common parameter for determining water quality and is widely used In practice.

A need for alternative methods exist which should if possible overcome some of the disadvantages of the prior art.

The object is achieved in one aspect by a method for producing a lyophiiized solid mixture comprising the steps:

- preparing a solution comprising

- oxalic acid or oxalic acid salts

- one or more inorganic salts

- lyophilizing the solution.

The oxalic acid salts are preferably alkali salts, alkaline earth salts, and ammonium salts.

Suitable inventive inorganic salts can include those compounds which are usually purely Inorganic and free of organic impurities in order to avoid any influence on the reaction process. Examples thereof include sulfates, phosphates, chlorides, nitrates. Particularly preferred salts include sodium salts, potassium salts, lithium salts, calcium salts, magnesium salts and ammonium salts. The weight ratio of inorganic salts to oxalic acid or oxalic acid salts is 10 to 100 : 1 in the present invention. Only the anions of the inorganic salt and the oxalate are considered when calculating the weight ratios.

It has been found that the concentration of oxalic acid or oxalic acid salts in the solution prior to lyophilization is preferably in the range of 0.01 to 0,05 mol/I, The concentration of inorganic salts prior to lyophilization is accordingly in the range of 0.1 to 5 moS/S.

Lyophilization or also freeze drying is a process for the gentle drying of products which is based on the principle of sublimation, i.e., that ice crystals pass directly into the gaseous state without a liquid phase occurring.

Typical freeze-drying includes the steps of freezing, drying, and optionally a post-drying. While freezing typically occurs at atmospheric pressure, the main drying or post-drying occurs under sublimation conditions. Temperature, time and pressure can be adapted to the required quantities and drying parameters and varied over a wide range. Typical parameters can be taken from the following Table.

It is also possible to pass through a so-called temperature program while freezing.

Temperature programs serve to increase the growth of the ice crystals by changing the temperature of the frozen product, which faci!itates freeze- drying,

In a particularly preferred embodiment, the solution to be lyophilized is transferred to suitable containers and is lyophilized in these containers. The container thereby receives a precisely metered amount of oxalic acid.

In an embodiment, the permanganate index is determined by titration as it was previously, whereby, however, instead of adding a liquid oxalic acid solution or a liquid oxalic acid salt solution, the previously prepared, defined amount of oxalic acid in solid form is added. A suitable method therefor is to introduce a corresponding opened vessel with the solid mixture into the titration flask,

It is preferred that the resulting product of the lyophilization is solid, homogeneous and free from crumbs. This facilitates further processing.

In some embodiments, a small amount of an organic polymer may be added to the product to be lyophilized. Such polymers usually improve the strength of the lyophilizate. On the other hand, they are an organic component which can influence the measurement. No organic polymers are preferably used. The invention also relates to the lyophilized solid mixture obtainable by the process according to the inventive method.

It is advantageous that the production in the form of solids in the factory can produce, dose and package precisely dosed quantities. The production and dosage of the reagents to be added on site is no longer required. This also allows staff which is less well trained to be considered for implementation. The described solid mixture can in particular be used for the qualitative and quantitative determination of organic Impurities in water. According to the invention, the solid mixture is in particular suitable for the determination of organic impurities in waters analogous to ISO 8467. Only weakly contaminated samples can generally be examined for their organic impurities; these first and foremost include drinking water, surface water, untreated water, and mineral water.

It is particularly preferred that an optical determination takes place instead of a titration.

The solid mixture according to the invention is in particular suitable for detecting organic contaminants of aqueous samples by optical methods. Photometry hereby in particular comes into consideration. In this method for the qualitative and quantitative determination of organic contaminants of aqueous samples by optical methods, in particular by photometry, the aqueous sample is prepared for optical measurement by digesting the aqueous sample with sulfuric acid and with a permanganate solution in a cuvette for 10 minutes at 100 °C, for example, in a metal block thermostat.

The aqueous sample is advantageously cooled to room temperature after digestion, preferably to 20 °C via a metal block thermostat, a water bath, or in the air.

The aqueous sample is subsequently mixed with the inventive solid mixture to react with the excess of unused permanganate soiution. In the last ' reaction step, a precisely defined amount of permanganate solution is dosed into the reaction cuvette and is photometrically measured at the latest after 5 minutes, preferably after 1 minute, whereby the photometric measurement serves to calculate the organic load.

Especially when used for an optical and/or photometric measurement, the samples and reaction volumes can be significantly reduced so that fewer waste solutions arise which must be disposed of.

The inventive solid mixture has the advantage that it can be produced and distributed as a ready to use test kit in a pre-dosed form. The invention accordingly also relates to a test kit which comprises the above-described solid mixture, a permanganate solution and instructions for use.

In a particularly preferred embodiment, the test kits comprise a device for storing reagents and for introducing the reagents into reaction containers filled with the water sample to be analyzed in order to carry out qualitative and quantitative analyzes and to close the reaction containers.

The device is preferably a device with at least two spatially separated closure regions as described in DE 198 50 934 Al.

A further possibility of arranging the section which serves to close the reaction container is to provide a one-sided open container as a closure element as is described in DE 8703659 Ul.

A further possibility of arranging the container is to introduce the inventive solid mixture in a separate container as Is sold, for example, under the MicroCap brand, The device described can be used so that the reaction container Is first filled with the sample to be examined and a digestion reaction is carried out, and that the reagents present in the device are then introduced therewith.

EXAMPLES

The oxalate and permanganate concentrations were kept constant in all experiments to allow results to be compared.

The focus of the investigations was the optimization of the carrier components in terms of durability, mechanical strength and function.

The freeze-drying program used was as follows:

Freeze-Drying Program

and is shown in detail in Fig. 1.

Various mixtures of carrier components according to Tables 3 and 4 together with optional organic additives were examined for their consistency after drying. The soft lyophllizates were thereby generally less suitable than the solid lyophilizates. Table 3: Dosicap/DosiCap Zip

Table 4: MicroCap

The recovery rate for corresponding products was determined immediately after bottling and after storage for 1, 6 and 12 months. Ten respective vessels were thereby examined in parallel. Solid homogenates thereby showed less variation in the recovery rate. Compositions containing borates were less stable of the oxalic acid. No significant improvements via organic additives was achieved.