ESTABLISHMENT AND VALIDATION OF A RELIABLE GRAVIMETRIC METHOD FOR HUMIC ACID ESTIMATION
Keywords:
Gravimetric analysis, Method validation, Humic acid, Fertilizer analysis, Analytical developmentAbstract
Fertilizer samples are routinely analyzed to determine their nutrient composition; however, discrepancies in analytical results may occur due to variations in testing procedures and methodologies. Therefore, this study aimed to develop and validate a gravimetric method for the quantitative determination of humic acid in fertilizer samples. Method validation was performed at the Soil and Water Testing Laboratories (SWTL), Dera Ghazi Khan, an ISO 17025-accredited laboratory. The validation parameters included repeatability, reproducibility, limit of detection (LOD), limit of quantification (LOQ), recovery, and bias assessment.
Descriptive statistical analyses, including mean, standard deviation, and relative standard deviation (RSD), were used to evaluate method performance, while reproducibility was assessed through a t-test. The calculated LOD and LOQ values were 0.145% and 0.484% humic acid, respectively. The method demonstrated high precision, with a repeatability RSD of 0.4725%, and the calculated t-value at the 5% significance level was lower than the tabulated value (2.262), confirming reproducibility within a 95% confidence interval. The recovery percentage for humic acid was 102.34%. Furthermore, Z-scores obtained through QUATEST3 (Vietnam) proficiency testing were within acceptable limits, and a strong correlation (r = 0.999) between actual and measured values confirmed the reliability and accuracy of the method.
Overall, the developed gravimetric procedure satisfied all validation criteria, demonstrating that it is accurate, precise, and suitable for routine determination of humic acid content in fertilizer samples.
