Proficiency Testing Performance in Chemistry Department; a 10-year study of trends in benzoic acid in food

Abstract Proficiency testing (PT) is considered an indicator to improve competency for laboratory quality management systems. The laboratories participating in PT maintain personnel competency, monitor lab performance, and ensure the validity of the results. The chemistry department started with 20 parameters with participation by its branch laboratories in 1995 and declared it an interlaboratory comparison, then upgraded to PT after applying the procedure following ISO/IEC 17043. Over ten years of results from 2012 to 2021, the chemistry department, which covers the headquarters and 10 branches, achieved satisfactory performance. Only the year 2012 faced an outlier result from the Malacca branch, and two questionable results from the Bintulu and Sibu branches in 2016. Investigation of the outlier and questionable results was based on 4M (Manpower, Method, Machine, and Material). The relationship between the 4M is always mutually beneficial; lacking one will not guarantee high quality. Exploring these 4M provides the lab with a structured framework for root cause analysis by helping the lab understand how each one may have contributed to a particular issue. The trends of PT performance can also be analyzed to increase the quality system. For example, for the Sarawak branch, the Z-score data tends to be over 0, with all the points falling on the upper side, showing that a systematic error occurred. To improve the accuracy of the lab, an investigation is needed. Thus, PT acts as a valuable tool for the laboratory to improve and carry out necessary investigations and corrective actions if any outlier results were obtained in the analysis.