Glassware, cleaning procedure for

Early in our work we frequently obtained erratic analytical results which were subsequently traced to cross-contamination between samples. In order to eliminate this source of error we instituted use of disposable pipettes and adopted a far more rigorous cleaning procedure for that glassware which is reused. All of our glassware is also silylated by the vapor-phase procedure recently reported by Fenimore, et. al. (5). 

The proper procedures for adding model test compounds to water, frequently called spiking, have been reviewed (423). Attention to details is necessary to avoid large errors in the results. In general, spiking of the model compounds must be done from a concentrated test solution whose solvent is miscible with water the water must be free of suspended particles that can irreversibly adsorb the solutes all glassware must be clean and the spike level should not exceed the aqueous solubility. 

GT 5 Recommended operating procedure for cleaning of glassware for environmental sampling General sampling... 

Sample containers and glassware As discussed earlier, when cleaning sample containers for reuse, much care should be taken. The procedure should not be likely to introduce either contamination or the analyte into the analysis. Therefore when cleaning containers for analysis of volatile organic compound, for example, it would be foolish to use organic solvents as this could introduce the same compound that the method would be measuring. 

It is important when working with ultra-micro, amounts of material, never to use glassware or containers which have been used for macro amounts of material especially of the same element. Even Involved cleaning procedures have been found to leave prohibitive amounts of material on the container. 

Swirl the acid mixture in the container for a few minutes. If necessary, place the glassware in a warm-water bath and heat cautiously to accelerate the cleaning process. Continue heating until any sign of a reaction ceases. When the cleaning procedure is completed, decant the mixture into an appropriate waste container. 

All reagents and solvents that are used to prepare the sample for analysis should be ultrapure to prevent contamination of the sample with impurities. Plastic ware should be avoided since these materials may contain ultratrace elements that can be leached into the analyte solutions. Chemically cleaned glassware is recommended for all sample preparation procedures. Liquid samples can be analyzed directly or after dilution when the concentrations are too high. Remember, all analytical errors are multiplied by dilution factors therefore, using atomic spectroscopy to determine high concentrations of elements may be less accurate than classical gravimetric methods. 

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