Abstract
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 ΔEm, 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.
Highlights
Uric acid (UA) [7,9-dihydro-1H-purine-2,6,8(3H)trione] is the primary final product of purine metabolism
Experimental procedure B (DR as matrix) Under the continuously fed well stirred tank reactor (CSTR) conditions characterized by constant parameters (5.90 × 10-2 mol L-1 KIO3, 5.57 × 10-2 mol L-1 H2SO4, temperature 56.0 °C and specific flow rate, 2.95 × 10-2 min-1), the effect of concentration of UA was studied; it is found that a variation of its concentration resulted in a variation in DEm
Having in mind that the simulated results obtained by including the reaction 3 in the reaction mechanisms for both, Bray-Liebhafsky oscillatory reaction and Dushman non-oscillatory reaction, successfully reproduce the experimental results, we suggested, as a first approximation, that UA oxidation through interaction with HIO is crucial and the rate-determining step in a possible model of the mechanism of the interaction between UA and the BL matrix and Dushman reaction (DR) matrix reaction systems
Summary
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. 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] rapid methods based on a relatively simple and inexpensive equipment are desirable
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