Kinetic-spectrophotometric approach to the modified Berthelot procedure for serum urea determination
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ORIGINAL PAPER
Kinetic‑spectrophotometric approach to the modified Berthelot procedure for serum urea determination Ivana D. Rašić Mišić1 · Snežana S. Mitić1 · Danijela A. Kostić1 · Snežana B. Tošić1 · Emilija T. Pecev‑Marinković1 · Ana S. Miletić1 Received: 18 January 2020 / Accepted: 11 August 2020 © Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract The results of developed kinetic-spectrophotometric method for serum urea determination by modified colorimetric Berthelot procedure were presented in this paper. To obtain high sensitivity, all reaction rates were monitored spectrophotometrically by measuring the change of absorbance with time at 700 nm. A differential variant of the tangent method was used for the processing of the kinetic data based on linear dependence of absorbance on time. The method is valid over the 0.25–2.50 µg cm−3 urea concentration interval with RSD range 8.33–2.02%. The limit of detection was calculated as 0.09 µg c m−3. The interference effects of some metal ions, anions, antibiotics, and other molecules were investigated to access the method selectivity. The method was successfully applied for the determination of urea in human quality control blood serum. Keywords Kinetics · Urea · Modified Berthelot procedure · UV/Vis spectrophotometry · Human blood serum
Introduction Urea (carbamide, carbonyl diamide) is the predominant final product of amino acids and protein catabolism in human body. Namely, ammonium is produced during amino acids catabolism. This compound is very toxic for human health, because it damages almost all vital organs. Nature created the way body fights against ammonia using liver enzymes and converting it into urea. Formed in the liver, urea is mostly transported by the bloodstream to the kidneys where it is filtered through the glomeruli and excreted into the urine (McKee and McKee 1996). Urea in blood serum and urine fluctuates in healthy subjects as its concentration depends on the renal function, the nitrogen intake from food, the endogenous protein catabolism, and the state of hydration and diuresis. Normal serum urea values (mmol d m−3) are: 0.5–1.0 (newborns), 1.5–3.0 (infants), and 2.5–7.5 (adults). A fall in serum urea levels in adults under 2 mmol d m−3 and decrease in urine urea can be observed in terminal stages of severe hepatic * Ivana D. Rašić Mišić [email protected] 1
Department of Chemistry, Faculty of Sciences and Mathematics, University of Niš, Višegradska 33, 18000 Niš, Serbia
insufficiency together with hyperammonemia as well as in cases of decreased protein intake and in increased protein synthesis (late pregnancy or early childhood). In acute and chronic renal insufficiencies, high increase in serum urea concentration appears and it is always associated with the high levels of creatinine (Majkić-Singh et al. 1995). Urea was one of the first substances to be determined in biological fluids. All methods for the clinical urea determination can be divided into two groups: direct and indirect. Direct methods
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