Proficiency testing as a tool to assess the performance of visual TLC quantitation estimates

The use of rapid and inexpensive nonlaboratory-based screening tests for drug quality assessments is recommended as a component of a drug quality assurance program in poor resource settings. We have established routine Minilab test procedures to screen product quality and a proficiency testing program to determine the competency of the inspectors and reliability of results. Samples for the proficiency testing were prepared by pulverizing a standard reference tablet of the appropriate drug and making serial dilutions with starch to obtain concentrations of 0, 40, and 100%. The samples, which were labeled only with the drug name and an identifying letter, were given to inspectors for quality screening using Minilab procedures. In round 1 of the proficiency test, only 3 of 28 substandard samples were correctly identified. Round 2 of the proficiency test, which was administered after a performance qualification test for the analytical method, showed much improvement: 19 of 27 substandard drugs were correctly identified, while 5 out of 9 inspectors made the correct inference on the quality of 45 samples. However, in both rounds, 2 inspectors failed to identify substandard samples, indicating that their technical competencies need to be improved for the reliability of the results. Although the thin-layer chromatography screening methods provide a rapid means for drug quality assessment, they need to be put in the hands of competent users. The inclusion of a proficiency test in the screening program provides a measure of determining competency of the personnel and reliability of the results.