TECHNICAL FIELD - The radiodiagnostic mainly used in Positron Emission Tomography (PET) is the ¹⁸ F- fluorodeoxyglucose; the synthesis of this molecule is usually performed in nuclear medicine departments, using automatic synthesis apparatus, by nucleophilic substitution on a substrate of hydroxyl acetylated mannopyranose of the

F, prepared in a cyclotron by proton irradiation of O enriched H ₂ O. In the synthesis the reagent 4,7,13,16,21,24 hexaoxa 1,10 diaazabicyclo 8,8,8 hexacosane, also known as Kryptofix 2.2.2., is used as a phase transfer catalyst, in the anhydrous conditions required for the nucleophilic substitution.

BACKGROUND ART -- It is well known that every chemical substance is potentially toxic, and that the chemical reagents concentration in each injectable solution should be kept as low as possible, at the end of any pharmaceutical or radiopharmaceutical synthesis. According to the USA Pharmacopeia (USP), and to the FDA Chemistry, Manufacturing, and Controls Committee prescriptions, the maximum allowed Kryptofix concentration in the injectable solution of 18F- fluorodeoxyglucose in the USA is 50 microg/ml. According to the European Pharmacopeia, the maximum allowed Kryptofix concentration in Europe is 2.2 mg/V, where V is the volume of the injectable solution. The analytical methods currently used in the characterization of the Kryptofix 2.2.2 in aqueous solutions are variations of the technique known as Thin Layer Chromatography, in which a mixture methanol - 30% ammonium hydroxide, with ratio 9:1, or pure 30% ammonium hydroxide, are used as eluent; the presence of Kryptofix 2.2.2 is revealed by chloroplatinate or iodine fumes staining. The toxicity of chemical substances is usually defined from its Lethal Dose 50 (LD ₅₀ ), i.e. the concentration of the substance that is able to kill 50% of the injected animals. For Kryptofix 2.2.2 the LD ₅₀ of i.v. injection in rats is 35 mg/kg; among the reagents used in ¹⁸ F-fluorodeoxyglucose synthesis this is the most toxic substance. As a comparison, the solvent used in the synthesis of F-fluorodeoxyglucose (acetonitrile), commonly considered a toxic substance, has a LD ₅₀ for i.v. injection in rats of 1680 mg/kg. Keeping these values in mind, it is easy to understand that, apart from maximum allowed limits, it is highly desirable to keep the concentration of Kryptofix 2.2.2 as low as possible in all injectable products. The current scientific literature reports some colorimetric methods for the qualitative and semi- quantitative determination of Kryptofix 2.2.2 (Chaly T, Dahl JR. Thin layer chromatographic detection of Kryptofix 2.2.2. in the routine synthesis of [ ¹⁸ F]2-fluoro-2-deoxy-D- glucose. Nucl Med Biol. 1989;16:385-387), (Mock BH, Winkle W, Vavrek MT. A colour-spot test of the detection of Kryptofix 2.2.2. in the routine synthesis of [ ¹⁸ F]FDG preparation. Nucl Med Biol. 1997;24: 193-195). These methods, basically based on the technique of Thin Layer Chromatography, with iodine fumes or chloroplatinate staining as revelation step, are affected by a low, erratic sensitivity, and do not allow a quantitative and reproducible determination of the Kryptofix. Alternative methods (Ferrieri RA, Schlyer DJ, Alexoff DL, Fowler JS, Wolf AP. Direct analysis of Kryptofix 2.2.2. in ¹⁸ FDG by gas chromatography using a nitrogen-selective detector. Nucl Med Biol. 1993;20:367-369) allow a quantitative determination of Kryptofix 2.2.2 only by using complex analytical instrumentation and long execution times. DESCRIPTION OF INVENTION ~ In the present invention an analytical method, a product and a kit are proposed, that allow a quantitative determination in short times of the Kryptofix 2.2.2 in aqueous solutions, particularly in injectable solutions of radiopharmaceuticals, more particularly in solutions of ¹⁸ F-fluorodeoxyglucose. The method offers a high sensitivity and reproducibility, doesn't requires complex analytical instrumentation, and the obtained results are independent from the manual ability of the operator. The principle of the method is based on the fact that the Kryptofix, like all the tertiary amines, react with the ion PtI ₆ ^" , forming a blue coloured coordination complex. By considering that in the solution of injectable solutions of positron emitters radiopharmaceuticals, and particularly in solutions of F-fluorodeoxyglucose, are not present other tertiary amines, the reaction is only indicative of the presence of the Kryptofix. In the method and kit described in the present invention, a very regular revelation spot of the iodoplatinate reagent is obtained; this fact strongly increases the reproducibility of the measurements, and allows a reliable quantitative determination. Besides, a wash-out step of the un-reacted iodoplatinate is disclosed in the present invention, which makes the coloured coordination complex more clearly visible, so lowering the detection limit of the analytical determinations, and increasing the reproducibility of the quantitative measurements. A commercial kit or a method for the quantitative determination of the Kryptofix 2.2.2 is actually lacking in the market, and only analytical techniques that require the use of complex and expensive analytical chemistry equipments have been described in the current scientific literature. BEST WAY FOR CARRYING OUT THE INVENTION - Example of use of the method for the determination of Kryptofix in the concentration range 0-200 micrograms/ ml: A solution containing both sodium chloroplatinate in H ₂ O (0.5% weight) and potassium iodide in H ₂ O (10% weight) is prepared (Solution A); 1 ml of solution A is diluted with 1-1.5 ml of acetone (Solution B). A solution in acetone- ethanol (9:1 vol) of TWEEN 80 (3% weight) is prepared (Solution C). A circular plate with diameter of about 1 cm (revelation plate) is obtained, by cutting it from a silica gel high performance thin layer chromatography sheet. A volume of 5-10 microlitres of Solution B is deposited in the centre of the revelation plate, obtaining a circular pink- brown spot with a diameter of about 7-10 millimetres (revelation spot). The addition of a volatile solvent (acetone, in the present case) to the aqueous solution is fundamental in the obtainment of a regular deposition and migration of the drop, finally resulting in a homogeneous and highly reproducible revelation spot. The revelation plate, prepared as described above, is glued on a plastic plug, and the plug is inserted on the lower part of a glass or clear plastic tube, with length of about 5 cm; on the upper part of the tube is inserted a second plastic plug, provided with a central hole with diameter of some mm. Through the hole of the plug, a pipette plastic tip, of the type commonly used with precision pipettes in the field of analytical chemistry for the delivery of accurately known amount of liquids, is introduced. The height of the glass, or plastic, tube is chosen in such a way that, when a pipette tip is inserted through the hole of the upper plug, the lower extremity of the tip grazes the revelation plate on the lower plug. The operator fills the precision pipette tip with 5 microlitres of the injectable solution to analyze, and completely inserts the tip in the glass or plastic tube, through the upper plug hole. By pressing the expulsion button of the pipette, the 5 microlitres of the solution to be analyzed are deposited in the centre of the revelation spot of the plate, and the Kryptofix reacts with the PtI ₆ ^~~ ion (iodoplatinate) present on the plate, originating a central blue-violet stain, which superimpose to the pink-brown iodoplatinate spot. Successively, a volume of 10 microlitres of solution C is deposited in the centre of the obtained blue-violet stain, by using a second pipette tip; the solution C washes away the un-reacted iodoplatinate, but has no effect on the reaction stain. As final result, a clearly visible blue-violet stain on a white background is obtained, whose intensity is proportional to the amount of Kryptofix in the solution to be analyzed. The use of solution C is fundamental in the obtainment of a clean revelation spot. The revelation plate can also be obtained by direct preparation on a support, mixing opportune amounts of adsorbents, like typically, but not exclusively, silica, or alumina, and variable amounts of binders, like typically, but not exclusively, calcium sulphate, polyvinylpirrolidone, polyvinyl alcohols, polystyreneacrylates, polyvynilacrylates polyacrilates,, polyacrylamides, carboxymethylcellulose, hydroxypropylmethylcellulose, alkaline silicates, and/or their combinations. For a semi-quantitative determination of the Kryptoflx concentration, the lower plug that contains the revelation plate is detached from the glass or plastic tube, and the colour intensity of the obtained stain is evaluated by simple visual comparison with a series of calibrated stains, obtained in a similar way by using known amounts of Kryptofix. To obtain a quantitative determination of the Kryptoflx, the stain is scanned by a scanner, or is photographed by a photographic camera or a digital micro-camera. The image is then analyzed by an image analysis software, the optical density of the stain is measured, and compared with a scale of calibrated optical densities obtained in a similar way, by using known amounts of Kryptofix. The method, in the hands of different operators, has always furnished reliable, reproducible and precise analytical determinations. For instrumental determination the maximum error is about 10%. The determination is performed in about five minutes, and avoids any accidental contamination, due to the reduced solution volumes, and to the geometry of the proposed device.