The interaction of silica–titania xerogel with triphenylmethane dyes (pyrocatechol violet, chrome azurol S, eriochrome cyanine R) has been investigated to create a new sensor material for solid phase spectrophotometric determination of food oxalates. The complex forming reaction between xerogel incorporated titanium(IV) and triphenylmethane dyes has been studied; half-reaction periods, complex composition, equilibrium constants, and xerogel sorption capacity have been calculated for each dye. Eriochrome cyanine R (ECR) is characterized by the shortest half-reaction period, the smallest equilibrium constant, and the greatest capacity; it has been chosen for the sensor material construction because titanium(IV)-ECR complex is formed faster and can be destroyed easier than other studied complexes. The interaction of this sensor material with oxalates has been described: the presence of oxalates causes sensor material discoloration and the absorbance is used as analytical signal. The analytical range is 35–900 mg/L (LOD 10.5 mg/L, n = 7). High concentrations of interfering inorganic anions, organic acids, and sucrose did not affect oxalate determination. Proposed solid phase spectrophotometric procedure has been successfully applied for the determination of oxalates in food samples (sorrel, spinach, parsley, ginger, and black pepper) and the results are in good agreement with HPLC oxalate determination.

Поступила в редакцию 27 августа 2015 г., после исправлений -22 сентября 2015 г.Для твердофазно-спектрофотометрического определения фторид-ионов в искусственной слю-не были предложены и использованы новые индикаторные материалы -модифицированные пиро-катехиновым фиолетовым кремний-титановые ксерогели. Определение основано на разрушении окрашенных комплексов иммобилизованного титана(IV) с пирокатехиновым фиолетовым фторид-ионами. Выбраны условия комплексообразования титана(IV), включенного в матрицу кремний-ти-тановых ксерогелей, с пирокатехиновым фиолетовым и условия разрушения иммобилизованных окрашенных соединений в присутствии фторид-ионов. Разработаны методики твердофазно-спек-трофотометрического определения фторид-ионов в искусственной слюне: в зависимости от объе-ма анализируемого раствора диапазоны определяемых содержаний составляют 0.05-1 мг/л (предел обнаружения 0.02 мг/л) и 5-100 мг/л (предел обнаружения 2 мг/л). Правильность методик провере-на методом «введено-найдено», относительное стандартное отклонение -0.05-0.23. Время ана-лиза 10 минут.Ключевые слова: фторид-ионы, определение, искусственная слюна, твердофазная спек-трофотометрия, кремний-титановые ксерогели. Silica-titania xerogels modified with the pyrocatechol violet have been proposed as new sensor materials for fluoride determination in the artificial saliva. The determination is based on the ability of fluoride ions to disrupt the colored titanium(IV)-pyrocatechol violet complexes. The complex reactions of matrix embedded titanium(IV) with pyrocatechol violet (resulting in blue colored xerogels) and with fluoride ions (resulting in bleaching of colored xerogels) have been investigated. The selected conditions have been used for developing the procedures of fluoride determination in the artificial saliva and water. Varying the volume of the analyzed solution two analytical ranges (0.05-1 ppm (LOD 2 ppm) and 5-100 ppm (LOD 0.02 ppm)) have been obtained. The procedures' accuracy has been evaluated using the spiked probes of the artificial saliva achieving the RSD of 5-23%. The developed sensor materials can be used for studying the efficiency of various fluor-containing products for medical diagnostics, scientific research, and also for the construction of new dental materials.