Study of the effect of matrix components of natural mineral water on the determination of dissolved forms of silicon by high-resolution electrothermal atomic absorption spectrometry with a continuous spectrum source

Abstract

The influence of the mineral composition of water on the results of silicon determination by high-resolution atomic absorption spectrometry with a continuous spectrum source (HR-CS-ETAAS) and electrothermal atomization technique using a contrAA 700 spectrometer has been studied. The study was conducted using samples of natural water from different regions of the Russian Federation and model solutions. A low degree of silicon atomization was recorded when analyzing samples with a complex matrix against the background of a strong absorption signal of matrix components. The reason for the non-selective absorption of the sample matrix by chemical compounds has been demonstrated using a water sample with the most complex composition and a total hardness of about 2000 °dH. The effect of soluble salts of Ca (II) and Mg (II) in the presence of macrocomponents — alkali metal ions K (I) and Na(I) — on the determination of silicon in water has been proved. It is shown that at the values of the total stiffness less than 15 °dH there is no dependence of the analytical signal on the content of matrix components. An assumption is made about the strong influence of calcium compounds on the determination of the analyte due to the formation of a carbide coating on the surface of a graphite furnace, the appearance of a «memory effect» and an increase in the background signal during subsequent atomization cycles. The best results of the silicon determination were obtained with tungsten, iron, magnesium, and palladium present as chemical modifiers. A method of diluting the sample solution was used to reduce the level of background absorption during electrothermal atomization of mineral water. Conditions for eliminating the influence of matrix components for real samples of mineral water and calibration solutions are proposed. A method for determination of the dissolved forms of silicon in water samples with a complex matrix has been developed. The correctness of the results of silicon determination in the samples of natural underground water in the case of a strong matrix effect was confirmed by an independent method of analysis. The results of the study reveal the entirely new prospects of using the method of high-resolution electrothermal atomic absorption spectrometry with a continuous spectrum source for the determination of silicon in natural water.