Evaluation of the uncertainty statement in the case of mercury speciation analysis

Nowadays, the evaluation of the uncertainty statement is more and more incorporated into quality assurance procedures. In this paper, the uncertainty statement of a mercury speciation analytical method is presented using the relationships fixed by GUM (Guide to the Expression of Uncertainty in Measurement). According to the developed analytical method, the sample is digested using an alkaline phase, then phenylation is applied to derivatize the organomercury compounds found in the digested solution. Finally, following solid phase microextraction (SPME) of the phenylated species, detection with GC-AFS is carried out. The main purpose of this work is to identify the analytical steps that have the strongest influence on the reproducibility of the measurements. The presented approach is based on an investigation executed in more steps and so it provides an opportunity to determine the uncertainty of each applied analytical step. Based on the completed experiments, the alkaline digestion and the calibration were the most critical steps regarding reproducibility. Phenylation derivatization, SPME and volume and weight measurements during sample preparation were less dominant processes in this respect.