The aim of the present work was to develop a method of measuring the concentration of serotonin in blood, which provides sufficient accuracy of measurement, and metrological characteristics of measurement and standards of control in according to modern requirements. The actual methods were developed in 80–90-s of the 20th century. The main disadvantages of these methods are: accumulated error of measurement and low data reproduction, which reduce the accuracy of measurement. The study carried out by examining the physical and chemical properties of serotonin, selection of the analytical method for determining the substance, constructing calibration curve of the analytical signal from the substance mass in solution.

The reaction of formation a fluorescing complex of serotonin with ninhydrin has been used during the development of measurement spectrofluorimetric method. To resolve an imperfection of existing methods conditions for selection and storage of blood samples were optimized, extraction phases of matter in an organic solvent and re-extraction in the aqueous phasewere improved.

The findings were processed by the least squares method and also parameters a and b of the linear calibration function were determined. At that the value of the analytical signal of null solution was subtracted from the value of analytical signal of sample. To determine blood serotonin, 2 cm3 of the whole blood test sample was placed in a test tube with 0.2 cm3 1.34 % solution of sodium oxalate and mixed. Such research should be carried out immediately after collection of biological material. Blood quantitatively transferred to the centrifuge tube, added 2 cm3 solution of hydrochloric acid with the concentration 1.0 mol/dm3 and mixed for 2–3 minutes. After 15 minutes the tubes were centrifuged for 30 minutes at 3000 rpm. The resulting supernatant fluid quantitatively was transferred to 50 cm3 glass-stoppered flask and approximately 0.3 cm3 of sodium hydroxide solution with the concentration 5.0 mol/dm3 was added (pH of sample solutions has to be in the range of 9.5 to 10.5, control – with a universal litmus paper). Further processing of the samples was carried out as in establishing the calibration dependence Fi from Ci.

The method provides a measurement of concentration of serotonin in the range from 0.06 g/cm3 to 1.0 g/cm3 of whole blood in the selection of 2 cm3 sample piece. The total relative measurement error does not exceed ± 23 % at a confidence figure of P = 0.95, convergence d is 6.4 %, reproducibility D is 7.8 %, measurement errors (error constructing the calibration chart) K is 15 %.

The method was tested in determination of serotonin levels in healthy volunteers and ranged from 0.08 mсg/cm3 to 0,35 mсg/cm3 (the norm is from 0.02 mсg/cm3 to 0.3 mсg/cm3);in children with the defects of urinary system – from 0.06 mсg/cm3 to 0.20 mcg/cm3; in children with obstructive bronchitis – from 0.17 mcg/cm3 to 0.25 mcg/ cm3; pregnant women – from 0.06 mcg/cm3 to 1.0 mcg/cm3; in individuals with drug addiction – 0.25 mcg/cm3 to 0.8 g/cm3.

The method has satisfactory metrological characteristics, accords with modern requirements for the validation of measurement methods and can be recommended to perform clinical diagnostic studies.

Keywords: serotonin, the whole blood, the method of measurement, accuracy

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