การเตรียมตัวอย่างสำหรับกิจกรรมทดสอบความชำนาญห้องปฏิบัติการของรายการโลหะหนักในนํ้า

Abstract

The sample preparation for laboratory proficiency testing of heavy metals in water must be accurate, precise, and meet the requirements of ISO/IEC 17043:2010. The aim of this study is to find the suitability of sample preparation for cadmium (Cd), nickel (Ni) and lead (Pb) in water by adding known standard solutions in the deionized water, preserving with nitric acid at pH-value about 2.0, mixing, filling in bottles and labelling. The samples are randomly selected for homogeneity and stability testing. The statistical process was designed for homogeneity and stability evaluation according to the ISO 13528:2005 by comparing with the standard deviation for proficiency assessment which is the target standard deviation by perception from previous rounds, standard method and expert judgment. It was set at 7% of the assigned values which were the reference values from National Metrology Institute (Thailand). The results of homogeneity and stability assessment of three sets of samples showed that they were sufficiently homogeneous and stable. These ensured that all laboratories receive distribution units that do not differ significantly in the parameters to be analyzed.