Sampling and Sample Storage

It is essential to clean the sampling bottles and all glassware used for UVF analyses in the most meticulous manner (UNEP, 1995). Briefly, laboratory glassware is soaked in detergent solution at least overnight and then scrubbed with brushes. It is rinsed with copious amounts of tapwater followed by deionized water and baked in a clean oven at 200 °C. 

Not infrequently, even research vessels are sources of petroleum which rapidly forms a plume around the ship when on station. Therefore, samples for the determination of petroleum-derived hydrocarbons in seawater should be taken immediately after the ship has come to a stop. If this is not possible, one might consider rowing a rubber dinghy some distance upwind from the ship to take the samples (do not use an outboard engine). 

After extraction and phase separation the hexane must be recovered. The use of a large separatory funnel for this purpose is discouraged, because it is difficult to keep clean. Instead, pre-extracted water is added carefully until the hexane collects in the narrow neck of the sample bottle. Portion by portion it is drawn carefully into a Pasteur pipette and transferred into a 100 mL Erlenmeyer flask. It is useful to pre-determine the level of the interface between the water and the solvent in the neck of the bottle and to use a pinch clamp on the pipette to position it just above this interface. 

Much more convenient is the following method the normal screw cap is replaced with the assembly shown in Fig. 21-2. Extracted seawater is added to the bottle through the long-stem funnel which ends near the bottom. With proper positioning of the three-way stopcock the hexane layer is thus forced into the separatory funnel, usually together with some water and sometimes as a froth. When the phases refuse to separate, a few mLof diethyl ether are added to the solvent in the separatory funnel which is then removed from the screw cap and shaken. The aqueous phase is drained and the organic phase collected in a 100 mL Erlenmeyer flask. 

Experience has shown that one extraction per sample removes 90 % of dissolved hydrocarbons from moderately contaminated water. A second extraction thus is not recommended, because the subsequent concentration of a larger solvent volume is likely to result in evaporative losses of analytes. 

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Representative Samples and Sample Storage. Sample Concentration and Clean-up Solid Phase Extraction. 

As a result of these reactions and volatilization, concentrations of nitrogen species are expected to change during sampling and sample storage. This is particularly true if precautions are not taken to limit this eventuality [29-31],... 

Aitio, A., Jarvisalo, J., Stoeppler, M. Sampling and sample storage, in Trace Metal Analysis in Biological Specimens (ed.) Stoeppler, M., Foster City, California, Biomedical Publications, in preparation... 

Waste of time and precious resources, duplication of effort and scientific and legal controversies can be minimized by carefully planning all the steps of the analytical process, from proper sampling and sample storage to the necessary laboratory pretreatment and trustworthy performance of measurements, self-consistent evaluation of the experimental data and their exploitation for subsequent action. 

M. Stoeppler, Sampling and sample storage, in M. Stoeppler (Ed.), Hazardous Metals in the Environment, 1992, Elsevier, Amsterdam, 9-18. 

All scientific studies involve some aspect of practical work. It is therefore essential to be able to observe and to record information accurately. In the context of environmental analyses, it should be borne in mind that not all practical work is carried out in the laboratory. Indeed it could be argued that the most important aspects of the whole practical programme are done outside the laboratory in the field, as this is the place where the actual sampling of environmental matrices (air, water, soil, etc.) takes place. It is still common practice, however, to transport the acquired sample back to the laboratory for analysis, so knowledge and implementation of the storage conditions and containers to be used are important. Both sampling and sample storage are covered in Chapters 3 and 4, respectively. 

In case of trace elements no contamination must be introduced in the sampling procedure this is dealt with in the chapters Sampling and Sample Storage (A. Aitio and J. Jarvisalo) and Sample Treatment (B. Sansoni and V.K. Panday). 

The urine is collected in polyethene bottles, and the specimens are refrigerated (up to 7 days) or deep frozen until use. Specimen collection must be carried out as described in Sec. Sampling and Sampling Storage (A. Aitio and J. Jarvisalo). Contamination must be strictly avoided. The sample preparation for the AAS analysis including standard addition... 

Correct sampling and sample storage are essential to obtain exact and reliable analytical re-... 

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