To ensure accuracy of results, environmental samples submitted for laboratory analysis needs to be representative of the environmental characteristics at the time of sampling.
Water quality is susceptible to change as a result of the physical, chemical and biological reactions occurring in the container between the time of the sample collection to the time the analysis is conducted in the laboratory. This can be minimised by applying appropriate sample preservation procedures at the time of sample collection.
Different samples require different preservation techniques. Therefore appropriate chemicals are added to the sampling containers to avoid water quality changes. Sample containers can vary in material and design (glass, plastic bottles or zero-head space vials).
It is also important to note that sample holding time refers to the time frame around when a sample is collected in a container to the time it is analysed at the laboratory. Microbiological samples are susceptible to holding times and should be transported to the laboratory within 24 hours of sample collection.
For some chemical analyses, a suitable preservative is not always available so tests should be conducted as soon as possible.
Preservation techniques are specific to each analysis so a number of containers containing different preservatives are required for each sample.
Dissolved analytes such as metals should be filtered through a 0.45micron filter in the field prior to the placement in the acid preserved container. The ‘Filtered’ box on the container label should also be ticked.
Samples requiring total metals can be placed directly into an acid preserved container and the ‘Unfiltered’ box should be ticked on the label. Note it is not possible to filter acidified samples in the laboratory for dissolved metals. The acid in the sample bottle will start to dissolve the metals during transport causing an over estimated result. Samples requiring total and dissolved metals will require two (2) bottles.
Microbes are particularly susceptible to changes during transport. Bacteria can grow during the period between sample collection and analysis which would ultimately provide an over estimated result.
Potable water typically contains chlorine therefore sodium thiosulphate preservative should be added to the sampling container to neutralise the effects of the chlorine. This ensures that the chlorine does not kill off bacteria during transport. Exceedance of holding times may result in under estimated results.
Microbiological samples need to be collected in a laboratory prepared (sterilised) container to avoid environmental cross-contamination.
Symbio Laboratories can provide laboratory prepared sampling containers to meet NATA requirements and to ensure that the quality of the sample received is representative of the environmental characteristics at the time of sampling.