Sampling & Analysis

• Part No.
• 0510010106
• Manuf. No.
• Standard Pack Quantity
• 1

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Description

Sampling
The importance of sampling and sample handling, prior to delivery to the laboratory, is summarized by the following statement.
The results of analysis can be no better than the sample on which it was performed.
While the taking of either aqueous or solid samples may appear easy, the collection of correct samples, both in terms of location and with respect to the analytes to be monitored, is fraught with difficulties. Any sampling must have as its aim the collection of a representative portion of the substance to be analysed. When this portion is presented for analysis, the parameters to be determined must be present in the same concentration and chemical or biological form as found in the original environment from which the portion was removed.
Samples representative of a site, or of a portion of a site, provide information that is often extrapolated to include the whole area under investigation. This is true whether the entity being sampled is a contaminated section of land, surface water, an industrial outfall, or a drum containing waste material. Therefore, samples must be representative of the specific entity being sampled, but not necessarily representative of the entire area of which it is part.
The overall objectives of a sampling program must be considered in the development of the sampling plan. Sampling may be performed for one of several purposes:
Maximum, minimum and average values for a near steady state stream with the aim of monitoring compliance versus set specifications (process control, environmental criteria). Such data can illustrate the likelihood and magnitude of occurring non-compliance provided enough data points have been analyzed from samples. Process, residue, and effluent stream analysis could have this type of objective. Even aquifer sampling (bore-holes) would fit this description. Often the relative mass-flows have to be known for proper data integration.
Maximum, minimum and average values derived from the analysis of "batch streams" such as treated backfill portions or detoxified waste batches usually require a minimum of one data point per batch to insure a representative sample. The major objective remains one of compliance and/or verification of effective management procedures for the batch streams involved.
1. Non-steady state events following a cyclic pattern are often influenced by several parameters, and these parameters in themselves may also be susceptible to cyclic changes. In other words, these confounding factors create a complex situation that requires careful analysis and planning to obtain a representative sample.
2. The cycle periods have to be known along with many other factors of influence in the "system". A typical example would be the sampling of tailings surface liquid (or solids), decant liquids or return dam bulk liquid. All of these "sample populations" undergo massive cyclic fluctuations through influence of chemical and physical changes from process management tailings surface events and seasonal climatic conditions.
3. It will be apparent that the cycle periods are not in any way synchronized and hence seemingly random data might be obtained. An objective for such sampling campaigns could be the establishment of a predictions database based on the understanding of the fundamental principles. This means that a complete, non-biased sampling effort across the longest cycle needs to be performed at least once. Alternatively, once such principles are known, selected samples taken at certain times could be analyzed for monitoring purposes. While many sampling strategies may be developed, the main, basic approaches to sampling are depicted in the following table.

Approach	Number of Samples	Potential Relative Bias	Basis of Site Selection
Judgemental	Small	Very Large	Prior history, visual assessment, and/or technical judgement
Systematic	Large	Small	Consistent grid or pattern
Random	Very Large	Very Small	Simple random selection

Sample Preservation
Once samples are removed from their natural environment, chemical or biological reactions can occur to change the composition of the sample, so it is best to analyze the sample as quickly as possible. Preservation of the sample will keep the parameter of interest in the same form as it was prior to the removal from its surroundings. No single preservation technique will preserve all parameters, so each parameter of interest must be considered and preserved specifically. While most soil samples require exclusion of light, air and warmth to preserve the integrity of the sample, aqueous samples require a more concerted effort.
Samples of aqueous cyanide species are potentially very reactive and toxic, so safety precautions such as gloves and protective clothing must be rigorously observed. Due to their reactivity, sample solutions must be tested on site prior to cyanide analysis to preserve them against the main interfering substances, oxidizing matter and sulfides.
The presence of oxidizing matter is detected by potassium iodide/starch test papers. Place a drop of the sample on a moist test paper strip. A blue coloration of the test paper indicates the presence of sufficient oxidizing matter to potentially react with the cyanide present during transport. Oxidizing agents must be reduced prior to sending the sample to the laboratory.
Procedure for Removal of Oxidizing Matter
1.Remove and retain any solids by decantation or pressure filtration.
2.Add sodium arsenite and mix. About 0.1g/L is usually sufficient.
3.Retest, and if test strip is discolored, retreat as per Step 2.
4.Return solids to sample solution and raise pH to 12 by adding 1-2 pellets of solid sodium hydroxide.
The presence of sulfides is indicated by lead acetate paper turning black. Place a drop of the sample on the test paper previously moistened with a drop of acetic acid and if the paper darkens, sulfides are indicated. Sulfides are removed by reaction with lead carbonate.
Procedure for Removal of Sulfides
1.Remove any solids by decantation or pressure filtration and hold.
2.Add lead carbonate (about 0.1 g/L) and mix.
3.Remove formed lead sulfide by pressure filtration and discard PbS precipitate.
4.Retest sample solution. If test strip is discolored, retreat as in Steps 2 and 3.
5.Return solids to sample and raise pH to 12 with solid sodium hydroxide.
Samples should be stored in a dark place at about 4 C, such as in an esky (cool box) during transport and then refrigerated at the laboratory. Soil samples for cyanide analysis (in cores or jars) must be wrapped in dark plastic and kept cool at 4 C without further treatment.
Transport and Storage
Once correctly preserved and packaged, samples should be sealed and each container (bottle or jar) individually placed in a sealed plastic bag. All samples should then be packed in an esky (cool box with some ice bricks) to keep them cool during transport. Shipment to the analytical laboratory should occur as soon as practical by overnight truck or airfreight courier. It is essential that the sampling protocol be recorded and a chain of custody included with the shipment to allow tracking prior to and during storage and analysis.