© copyright FACULTY of ENGINEERING ‐ HUNEDOARA, ROMANIA 159 1. Simion JITIAN THE SPECTROPHOTOMETRIC DETERMINATION OF PYRENE DYES IN PHARMACEUTICALS AND COSMETICS 1. UNIVERSITY “POLITEHNICA” OF TIMIŞOARA, FACULTY OF ENGINEERING HUNEDOARA, ROMANIA ABSTRACT: The paper introduces a method used for the determination of the component concentrations of a ternary mixture of pyrene dyes. The method uses the zero-order spectra of these dyes in the spectral range 190÷500 nm. It is based on a combination of the determinant method (Cramer's method) with information on the absorption bands of the dyes in the mixture. The method is applied using the slope and intercept values from the linear calibration curves of the pyrene dyes standard solutions: HP3S, P3S and P4S, at three different wavelengths: The three wavelengths: 290nm, 367nm and 375nm, were selected by means of the Kaiser method. When there is a spectral region in which only one of the components has absorption, the concentration can be determined independently of the presence of the other two dyes in the ternary mixture. The method used to determine the concentrations of the other two dyes was the Cramer method or the bivariate spectral calibration method (BSC) that solves a system of two equations with two unknowns. KEYWORDS: Cramer method, spectrophotometry, pyrene dyes, HP3S, P3S, P4S INTRODUCTION The paper describes a method used for the determination of the pyrene dye concentrations in a ternary mixture when there is a spectral region in which only one of the components shows absorption [1]. The method is based on combining the Cramer determinant method or the bivariate spectral calibration method (BSC) with information on the absorption bands of the dyes in mixture. The dyes used in this paper are: trisodium salt of 8-hydroxi-1,3,6-pyrene trisulphonic acid (Pyranine, HP3S), trisodium pyrene-1,3,6-trisulphonate (P3S) and 1,3,6,8-pyrenetetrasulphonic acid tetrasodium salt (P4S). They are used in a mixture (D&C Green No.8) as additives in pharmaceuticals and cosmetics. The pyrene dyes contain aromatic ring structures so that they are harmful to human health when they are in high concentrations. The controlled use and the accurate analysis of their contents are of great importance. The structures of these dyes are shown in Figure 1. HP3S P3S P4S Figure 1. The structures of the pyrene dyes: HP3S, P3S and P4S The absorbance corresponding to a substance depends on its concentration, the depth of the material and the wavelength. Within a limited range of concentrations, the absorbance depends linearly on the concentration. The slope (sensitivity) m and the intercept n of the straight line calibration, depends on the wavelength. n c m n c d A + ⋅ = + ⋅ ⋅ ε = (1) The absorbance of a mixture of the three components, that have concentrations in the domain in which the absorbance of each depends linearly on the concentration, is additive. Measuring the absorbance at three different wavelengths: λ 1 , λ 2 , λ 3 allows the determination of the concentration: c 1 , c 2 , c 3 of the three components in the mixture. ⎪ ⎩ ⎪ ⎨ ⎧ + ⋅ + + ⋅ + + ⋅ = + + = + ⋅ + + ⋅ + + ⋅ = + + = + ⋅ + + ⋅ + + ⋅ = + + = 3 3 3 3 3 3 2 2 3 2 3 1 1 3 1 3 3 3 2 3 1 3 X 2 3 3 2 3 2 2 2 2 2 2 1 1 2 1 2 3 2 2 2 1 2 X 1 3 3 1 3 1 2 2 1 2 1 1 1 1 1 1 3 1 2 1 1 1 X n c m n c m n c m A A A A n c m n c m n c m A A A A n c m n c m n c m A A A A (2)