An improved and validated p-dimethylaminobenzaldehyde procedure for the spectrophotometric determination of urea

The study introduced an optimized spectrophotometric procedure for quantifying urea using p-dimethylaminobenzaldehyde (PDAB) as a derivatizing reagent. Its main objective was to address reproducibility issues related to the aging of acidic PDAB solutions, variations in analytical factors, and detecting low urea levels. The color reagent was prepared by dissolving PDAB in a 1:1 volume ratio of glacial acetic acid to water, combined with concentrated sulfuric acid (H₂SO₄). Central Composite Design (CCD) was employed under Response Surface Methodology (RSM) to optimize the composition of the color reagent. The optimal molar ratio of PDAB to H₂SO₄ for achieving the highest absorbance of urea at a concentration of 10 mg/L was found to be 1:0.89. The analytical method was validated according to part 1040 of the standard methods for examining water and wastewater. This validation included assessments of selectivity, recovery, precision, and ruggedness. Potential interferences from ammonia, ammonium chloride, hydrazine, and thiosemicarbazide were examined. The limit of detection (LOD) and the limit of quantification (LOQ) were established at 2.2 mg/L and 10 mg/L, respectively. The method demonstrated linearity up to 100 ppm of urea, with a determination coefficient (R²) of 0.9999. For the tested matrices, mean recovery rates at three concentrations (10, 50, and 100 mg/L) ranged from 90% to 110%. Moreover, the precision, indicated by relative standard deviations during inter-laboratory comparisons, did not exceed 5%. The method showed robustness, exhibiting minimal sensitivity to changes in critical factors. This enhanced PDAB method is considered effective for determining urea levels in fertilizer laboratories.