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

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. 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. 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. By this relation, we can say that method performance was excellent. Hence, the method can be successfully used for potassium determination in fertilizer samples.