AOAC RI ERP EBOOK FOR FERTILIZERS

AOAC RESEARCH INSTITUTE AOAC OFFICIAL METHODS OF ANALYSIS (OMA)

OMAMAN-28/AOAC 2006.03 Study Director: Sharon Webb, University of Kentucky, Division of Regulatory Services, 103 Regulatory Services Bldg, Lexington , Kentucky 40546-0275 2006.03 results. Two examples can be made with concern to cobalt and nickel (Group A). a) Cobalt. Material ‘P’, result: 0.52 vs 0.57 (collaborative study), RSD = 20.46 vs 66.74 (collaborative study) b) Nickel. Material ‘P’, result: 38.90 vs 33.39 (collaborative study), RSD = 3.89 vs 13.42 (collaborative study). In general, RSD for Group B metals remain low enough. Comparability Comparability to AOAC 2006.03 for Group A elements has been calculated by testing 15 of the original collaborative study materials with both digestion methods. Data are expressed as a percentage recovery of the original grand average result. Many results show higher recovery values. Probably, these results demonstrate the enhanced recovery “power” of the proposed method, on the basis of RDS values. Working Range The working range of the method is determined by the working calibration standards. Each laboratory should determine the range best suited to their instrument’s capability. In general, 10 % extrapolation from the highest calibration standard often produces acceptable results for Group A and B elements. LOD and LOQ With reference to Group A, the paper shows the instrument LOD (estimated with standard solutions) and the method LOQ and LOD (estimated with validation materials). Interestingly, the LOQ for Group B elements are completely dependent upon the calibration range since the method is not working close to the instrument limits. Ruggedness trial Generally, results have not shown appreciable effects from the deviations of the method. Obtained results (differences) are all within normal variation and indicate that the method is sufficiently rugged with respect to the conditions studied. Significant work was done and data generated; information presented well. Method presents a step forward in speed, safety and scope. Digestion is relatively simple and straightforward, with few chances for human error beyond sample weight. Updating the instrumentation to ICP-OES is very important. Scope and ranges are well covered by the materials used. Digestion options are well researched. Some of the optimization steps are dated and based on studies from 30 years ago. System hardware and performance has changed and this needs to be considered. I.E. Meremt's robustness test is a guideline for plasma conditions BUT NOT for analytical optimization of the method/ICP. Also, Cs is a buffer for consideration on Axial/DV/TI systems, it is not typically used Page 7 of 14

ER 9

ER 10 Robust Method Cons/Weaknesses of the Manuscript: ER 1