Groundwater analysis sample preparation

Sample preparation techniques vary depending on the analyte and the matrix. An advantage of immunoassays is that less sample preparation is often needed prior to analysis. Because the ELISA is conducted in an aqueous system, aqueous samples such as groundwater may be analyzed directly in the immunoassay or following dilution in a buffer solution. For soil, plant material or complex water samples (e.g., sewage effluent), the analyte must be extracted from the matrix. The extraction method must meet performance criteria such as recovery, reproducibility and ruggedness, and ultimately the analyte must be in a solution that is aqueous or in a water-miscible solvent. For chemical analytes such as pesticides, a simple extraction with methanol may be suitable. At the other extreme, multiple extractions, column cleanup and finally solvent exchange may be necessary to extract the analyte into a solution that is free of matrix interference. 

We will take a more simplified approach to trace VOC analysis which utilizes our limited sample preparation and instrumentation capabilities. If a suitable extraction solvent can be found (i.e., one which does not interfere with the VOCs to be identified and quantitated by gas chromatography), then the analytes of interest can be isolated and concentrated from the environmental sample matrix via the pLLE technique (4, 5). A 40-mL sample which might contain extract is injected into a GC FID to determine BTEX. The extraction is performed on a sample that might contain THMs, such as chlorine-disinfected water and 2 pL of extract is injected into a GC-ECD to determine the THMs. This method is to be used for quantitative analysis of gasoline-contaminated groundwater samples. Typical levels of contamination are in the low parts per million (ppm) concentration range. A severe limitation to the pLLE method is the possible formation of emulsions when applied to wastewaters which could have an appreciable surfactant concentration level. 

For pesticide residue immunoassays, matrices may include surface or groundwater, soil, sediment and plant or animal tissue or fluids. Aqueous samples may not require preparation prior to analysis, other than concentration. For other matrices, extractions or other cleanup steps are needed and these steps require the integration of the extracting solvent with the immunoassay. When solvent extraction is required, solvent effects on the assay are determined during assay optimization. Another option is to extract in the desired solvent, then conduct a solvent exchange into a more miscible solvent. Immunoassays perform best with water-miscible solvents when solvent concentrations are below 20%. Our experience has been that nearly every matrix requires a complete validation. Various soil types and even urine samples from different animals within a species may cause enough variation that validation in only a few samples is not sufficient. 

The chemical preservation of a sample is dependent on the chemistry of the ground-water (e.g., pH) and on the chemical characteristics of the pesticide being studied. Preservatives can be added to the sample containers in the field or prepared in advance at the laboratory. To determine the need for a chemical preservative in the field (i.e., pH analyses), test the groundwater collected during the purging process and not the sample collected for analysis. 

This section discusses treatment of the water samples in preparation for instrumental analysis after they have been received, archived and stored in the laboratory. Many approaches may be taken in preparation of water samples for final analysis. The techniques employed will depend upon the type of matrix, e.g., groundwater vs surface water (containing organic materials), the instrumental method and the required detection limits. 

The optimal conditions for the preparation of groundwater candidate CRMs were tested in a feasibility study of which the results are published elsewhere [14] two materials were selected, representing typical carbonate and sandstone media. Two batches were prepared from ultrapure water by adding pro-analysis grade chemicals and their homogeneity was verified to evaluate possible effects of the preparation procedure on the sample composition [14]. The stability was also checked at +4°C and +20°C over a period of three months. 

The chemical analysis of water extracts, prepared from collected specimens of disintegrated reinforced concrete and cast-iron, and singer forms (more than 100 samples on according to all observed tunnels, running in Upper Vendian Clay beneath buried valleys), shows an anomaly high compounds of CF (up to 112.0 g/dm ) and Na+ + K+ (up to 85.6 g/dm ) that can be associated with accumulation of these ions in pores due to permanent filtration of groundwater from Kotlin artesian aquifer. 

Qualitative analysis requires that mixtures be separated into their components, which can be compounds or simple elements. Compounds, in turn, may be further separated into their constituent elements. In geology and the mining industry, for example, rocks, minerals, or soils are analyzed to find out what metals (such as copper, nickel, or titanium) or other elements (such as chlorine or phosphorus) are present. Municipal water faciUties have to identify and remove any contaminants (such as arsenic, lead, or nitrates) that might be present in surface or groundwater supplies before the water enters a city s water supply system. The food industry analyzes its products so that the labels can inform consumers of what kinds of fats, proteins, carbohydrates, vitamins, minerals, and fiber are present in canned, packaged, and prepared foods. The pharmaceutical industry analyzes samples of all of its products in the attempt to ensure against contamination. 

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