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Collection and Preservation of Water and Wastewater Samples. The objective of sampling is to collect a portion of material small enough in volume to be transported conveniently and yet large enough for analytical purposes while still accurately representing the material being sampled.
1- Meat the requirements of the sampling program.
2-Handle sample so that it does not deteriorate or become contaminated or compromised before it analyzed.
3- Ensure sampling equipments are clean and quality assured before use.
4-Use sample containers that are clean and free of contaminants.
6-Composite samples can be obtained by collecting over a period of time, depth, or at many different sampling points. 7-Make a record of every sample collected and identify every bottle.
9-Before collecting samples from distribution systems, flush lines with 3-5 pipe volumes (or until water is being drawn from the main source).
- unique sample identification number
- name of the sample collector
Grab samples are single samples collected at a specific spot at a site over a short period of time (typically seconds or minutes).
Provides a more representative sampling of heterogeneous matrices in which the concentration of the analytes of interest may vary over short periods of time and/or space.
Can be obtained by combining portions of multiple grab samples or by using specially designed automatic sampling devices .
Mixture of grab samples collected from different points simultaneously, or as nearly so as possible, using discharge-weighed methods
a-Sample labels (includingbar-code labels).
c-Field log book.
e-Sample analysis request sheet.
f-Sample delivery to the laboratory.
g-Receipt and logging of sample.
h-Assignment of sample for analysis.
Collect samples in a glass or plastic bottles that have been cleansed and rinsed carefully, given a final rinse with deionized or distilled water, and sterilized.
Volume of the sample should be 100 ml or more.
Silica , sodium, and boron may be leached from soft glass but not plastic.
Trace levels of some pesticides and metals may sorb onto the walls of glass containers.
Use glass containers for all organic analyses such as volatile organics ,semi volatile organics ,pesticides ,PCB’s ,and oil and grease.
Some analytes are light sensitive ,collect them in amber glass containers to minimize photodegradation.
Plastic caps also can be a problem.
Determine those parameters in situ.
Determine those parameters immediately after sample collection.
-volatile organic compounds
Zero head-space is important in preservation of those parameters.
Those are best collected in a separate clean bottle and acidified with nitric acid to pH below 2.0 to minimize precipitation and adsorption on container walls.
Hardness can be preserved by adding nitric acid to pH <2
Changes caused by growth of microorganisms are greatly retarded by keeping the sample at a low temperature (<4 C) but above freezing.
Dechlorinate sample , add NaOH to pH >12,
And refrigerate in dark.
1-Start microbiological examination of water samples as soon as possible after collection.
2-Ice samples preferably at <10 C during transport if they can’t be analyzed within 1h after collection.
3-Analyze samples on day of receipt whenever possible and refrigerate overnight if arrival is too late for analyzing on same day.
4-Do not exceed 30h holding time from collection to analysis for coliform bacteria. 5-Do not exceed 8h holding time for hete-
rotrophic plate counts.