Piezoelectric Micro-dosing System for Spiking Quality Samples in Occupational Hygiene Laboratories

Quality control is crucially important in the arena of chemical analysis. Reference materials are essential for calibration and quality control processes, and for verification of the accuracy and reliability of the analytical results obtained. Owing to the complexity of their manufacture, reference materials for chemical agents occurring at workplaces are expensive and available only on a limited scale and for a small number of substances. Therefore, their cost-effective and fast production is an important aim. The Institute for Occupational Health and Safety (IFA) of the German Social Accident Insurance (DGUV) currently pursues different strategies for the production of reference materials. One strategy entails the use of a piezoelectric micro-dispensing system for non-contact spiking of extremely small quantities of substances with high reproducibility. The dispensing system is coupled to a semi-automated assembly unit for loading high numbers of samples. It is used for spiking phosphoric and sulphuric acid onto quartz fibre filters. Comparison of the results obtained on different days shows higher variability than results observed on the same day. However, after daily adjustment of the number of droplets to the current droplet volume, highly reproducible series with an adequate number of samples (>500) could be realized. The results of the internal quality control were verified in an interlaboratory comparison. Furthermore, storage stability was investigated systematically over a period of 2 years. The samples produced are suitable for use as reference materials for both inorganic acids.