EVALUATION OF THE SUITABILITY OF VACUTAINERS FOR STORAGE OF NUTRIENT AND DISSOLVED ORGANIC CARBON ANALYTES IN WATER SAMPLES

Vacutainers are widely used for water-sample collection. Possible interferences due to the adsorption/release of analytes at the internal surface of vacutainers could affect the solute concentrations in filtrates. To gauge their suitability for storage of conventional analytes, the stability of NO3-, NH4+, soluble reactive phosphorus (SRP) and dissolved organic carbon (DOC) concentrations, preserved in vacutainers, was monitored. Borosilicate glass vials were employed for reference purposes. Results revealed that vacutainers are suitable for NO3- in all types of filtrates and are also an appropriate storage container for water samples containing NH4+ (especially for seawater) if samples are analysed soon after collection. However, if collected samples are to be analysed for SRP and DOC, conditions apply, since both solutes interact with the inner surface, and this introduces inaccuracy. The magnitude of the artefact depends on the solute concentration, temperature and type of water sample. Based on quantification of adulteration of the original analyte concentrations and water-source typology used in this study, the safe operational time frame between collection and analysis for NH4+, SRP and DOC, where storage artefacts do not significantly affect (5%) the final results, is limited to a time period of up to ten days. Furthermore, employing operational process blanks is recommended.