Method development and validation for the determination of potassium (K2O) in fertilizer samples by flame photometry technique

Background: Fertilizer samples are tested for determining their nutrient contents; however, different methods give varying results. Therefore, the major objective of this study was to develop and validate potassium determination method by flame photometry technique. Methods: Flame photometry technique for the quantification of potassium concentration in fertilizer samples was validated in Soil and Water Testing Laboratory (ISO/IEC: 17025), Dera Ghazi Khan. The method validation was done for repeatability, reproducibility, limit of detection, limit of quantification, linearity, recovery, selectivity, and bias. Results: The limits of detection and quantification were 0.87% and 2.88% K2O, respectively. The repeatability was 0.33%, and reproducibility (T-calculated was 0.69 which was less than T-tabulated, i.e., 2.06). Linear curve was obtained for concentrations ranging from 5 to 25 ppm (K) exhibiting R2 of 0.99. The recovery for K in fertilizer sample was 98.8%. The potassium contents were identified with complete recovery without interference of other nutrients in the sample. The Z-score of all the results (Magruder USA, Fertilizer sample check program) were in acceptable range. The correlation coefficient (0.999%) depicts strong relationship between actual K value and observed values. Conclusions: By this relation, we can say that method performance was excellent. Hence, the method can be successfully used for potassium determination in fertilizer samples.