Kinetic analytical method for determination of uric acid in human urine using analyte pulse perturbation technique

A J. Braz. Chem. Soc., Vol. 23, No. 8, 1450-1459, 2012. Printed in Brazil - ©2012 Sociedade Brasileira de Química 0103 - 5053 $6.00+0.00 Article Kinetic Analytical Method for Determination of Uric Acid in Human Urine using Analyte Pulse Perturbation Technique Nataša D. Pejić,*,a Jelena P. Maksimović,b Slavica M. Blagojević,a Slobodan R. Anić,c Željko D. Čupić c and Ljiljana Z. Kolar-Anić b Department of Physical Chemistry and Instrumental Methods, Faculty of Pharmacy, University of Belgrade, Vojvode Stepe 450, 11000 Belgrade, Serbia a Faculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, P.O. Box 137, 11000 Belgrade, Serbia b Department of Catalysis and Chemical Engineering, IHTM, University of Belgrade, Njegoševa 12, 11000 Belgrade, Serbia c Novos métodos simples e confiáveis para a determinação de ácido úrico (UA) são propostos e validados. Para a determinação quantitativa de UA, duas matrizes foram usadas: a reação oscilatória de Bray-Liebhafsky (BL) em um estado estacionário de não equilíbrio, estável, próximo ao ponto de bifurcação (método A), e o subsistema não oscilante (mistura de KIO3 e H2SO4), isto é, reação de Dushman (RD) em um estado estacionário (método B). Os métodos propostos são otimizados num reator tanque continuamente agitado (CSTR) e aplicados com excelentes resultados na determinação de UA em amostras de urina humana. A relação linear entre o deslocamento potencial máximo DEm e o logaritmo da concentração de UA (processo A), ou entre DEm e a concentração UA (processo B) é obtido no intervalo de concentração 2,98 × 10‑5‑2,68 × 10-4 mol L-1 e 2,98 × 10‑5‑3,58 × 10-4 mol L-1, respectivamente. Os métodos têm uma velocidade de processamento de amostra excelente de 30 amostras h-1 (método A) e 7 amostras h-1 (método B) com sensibilidade determinada para ser 1,1 × 10-5 mol L-1 (método A) e 8,9 × 10-6 mol L-1 (método B), e precisão RSD ≤ 3.4% para ambos os métodos. Alguns aspectos do possível mecanismo de ação de UA nos sistemas de reação oscilante BL e não-oscilante de Duschman, são discutidos em detalhe. Simple and reliable novel methods for the determination of uric acid (UA) are proposed and validated. For quantitative determination of UA, two matrices were used: the Bray-Liebhafsky (BL) oscillatory reaction in a stable non-equilibrium stationary state close to the bifurcation point (method A) as well as, the BL non-oscillating subsystem (mixture KIO3 and H2SO4), i.e., Dushman reaction (DR) in a steady state (method B). The proposed methods are optimized in a continuously fed well stirred tank reactor (CSTR) and applied with excellent results in the determination of UA in human urine samples. The linear relationship between maximal potential shift DEm, and both the logarithm of the UA concentration (procedure A) and UA concentration (procedure B) is obtained in the concentration range 2.98 × 10-5-2.68 × 10-4 mol L-1 and 2.98 × 10-5‑3.58 × 10‑4 mol L-1, respectively. The methods have an excellent sample throughput of 30 samples h-1 (method A) and 7 samples h-1 (method B) with the sensitivity determined to be 1.1 × 10-5 mol L-1 (method A) and 8.9 × 10-6 mol L-1 (method B) as well as the precision RSD ≤ 3.4% for both methods. Some aspects of the possible mechanism of UA action on the BL oscillating and Duschman non-oscillating reaction systems are discussed in detail. Keywords: uric acid, perturbation technique, Bray-Liebhafsky oscillatory reaction, Dushman reaction, urine *e-mail: Vol. 23, No. 8, 2012 Pejić et al. Introduction Uric acid (UA) [7,9-dihydro-1H-purine-2,6,8(3H)trione] is the primary final product of purine metabolism. As a natural antioxidant that exists in human plasma in relatively higher concentration,1 it may play a protection role, because it is involved in many pathological changes.2 Determination of this very important biological specie is very significant since abnormal levels of UA in the body fluids are symptoms of several diseases;3 continuous monitoring of UA would be often recommended in many clinical situations. For different purposes, various methods such as spectrophotometry,4 fluorimetry,5 electroanalysis,6,7 high performance liquid chromatography, 8 capillary electrophoresis, 9 chemiluminescence method 10 and other one11,12 have been commonly used to determine concentration of UA. One of the major obstacles in determination of UA is the presence of ascorbic acid as interference in the biological samples. To solve this problem, a variety of new electrochemical sensors has been developed; different modified electrodes show excellent sensitivity, good selectivity and antifouling properties.13,14 However, rapid methods based on a relatively simple and inexpensive equipment are desirable. Up to now, there have been a few papers on the determination of UA by kinetic analytical methods, including analytical techniques having the lactic acidacetone-Br--Mn2+-H2SO4 oscillatory reaction system as matrix.15 Generally, kinetic methods based on the ability of the examined substances to change kinetic parameters of chemical reactions, particularly oscillating chemical reactions, have become remarkably important in view of their comparative advantages; oscillating chemical reactions and their extreme sensitivity to external perturbations make these systems, as matrices, particularly interesting for designing kinetic methods of analysis for the determination of different biologically and pharmaceutically important compounds. 16-21 When the oscillatory reaction is the matrix, two distinct methods have been proposed. The first above-mentioned method19 is based on the relationship between the concentrations of analyte and the response of the matrix in the oscillatory state with respect to the main characters of oscillations, such as amplitude, period and others. In the second method16-18 based on perturbing the Bray-Liebhafsky (BL) oscillatory reaction as matrix in a stable stationary state in the vicinity of a bifurcation point the relationship between maximal potential displacement (DEm) in the moment of the perturbation and the analyte concentrations would be analyzed. However, using of analyte pulse perturbation (APP) technique in both oscillatory19 and stable steady state in vicinity of bifurcation 1451 point,16-18 the use of the largest Lyapunov exponent22 and the high-sensitive oscillating chemical system23 make the technique almost perfect and consequently favorable to use it in real routine analysis. New kinetic methods to the quantitative determination of UA by electrode potential measurements in the BL matrix,24,25 and Dushman reaction (DR) matrix,26 generated in continuously fed well stirred tank reactor (CSTR),27 are proposed in this paper. For this purpose, both the BL matrix in a stable steady state near a bifurcation point and DR matrix in a steady state are perturbed with variable amounts of UA, which result in substantial changes in the potentials of the matrices dynamic states that a (...truncated)