Basic approaches and methods for quality assurance and quality control in sample collection and storage for environmental monitoring

Abstract Quality assurance systems for environmental field investigations, including the sampling of environmental specimens for chemical analysis, are still at the beginning of their development and acceptance. Sampling is therefore often the weakest link in the chain of environmental analysis. The main problems for quality control in environmental sampling are that sampling normally cannot be repeated and that independent control measures in the form of reference methods are not applicable. This is an attempt to analyse the whole analytical procedure from sampling to data evaluation, to estimate and compare the main sources, characteristics, quality (e.g. random or systematic) and quantity of possible errors appertaining to each of the more or less elementary steps (Table 1), and to give recommendations, how to avoid, reduce or control errors especially due to sampling. Quality assurance in sampling as in other fields consists of three major elements: planning, documentation and control (Masing, 1988). Planning requires a clear definition of the task and the objectives, exact definition and, if necessary, subdivision of the sampling area, the choice of adequate specimens, tools, materials, timing, statistical sampling designs, standardized sampling methods written as standard operating procedures (SOP), and finally, the agreement on a written sampling plan. Detailed, formalized and, as far as possible, on-line documentation is the basis for an effective control of errors in the whole process. It is necessary to document completely and unambiguously the timing and the results of the sampling, the actual weather conditions, the location, extent and essential properties of the sampling area, the composition and constitution of the samples, possible deviations from the SOP and the sampling plan and special events during the process, as well as all the steps of treatment, transportation and storage of the samples.