Analytical method validation for cobalt determination on organic fertilizer

Cobalt determination has been carried out as one of the micro elements in organic fertilizer. The analytical method for the determination of cobalt used SNI 19-7030-2004 about compost from organic domestic waste that has been modified. Sample preparation was carried out by the wet ashing method using 65% nitric acid and perchloric acid. The wet ashing was using the Kjedhal tube for 12 hours. Cobalt determination was carried out using the AAS instrument at λ = 240.7 nm. Validation parameters used were linearity, Limit of Detection (LOD), Limit of Quantitation (LOQ), precision and accuracy. Cobalt content in solid organic fertilizer was 10.32±4.06 mg/kg. Linearity used cobalt standard solution of 0 – 5 mg/L and it produced regression equation with R2 = 0.9971. The Limit of Detection (LOD) and the Limit of Quantitation (LOQ) in this study were 0.015 and 0.029 mg/L. The precision was calculated by the repeatability method with the result of% RSD = 1.21% (≤2%). Accuracy used recovery of spiked matrix. The average% recovery result from 6 repetitions is 90.7% (85-115%). All the validation parameters of the method are in the acceptability range so that this modification method can be used as a routine method in determining cobalt levels in solid organic fertilizer.