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Requests to analytical laboratories need to be clear and concise for the results to achieve the desired goal whether the sample is for crystalline silica determination or some other analysis. The
following points are a guideline for most efficient submission of analytical samples.
Make sure your sample is representative of the material or process being evaluated. Use proper sampling procedures.
Provide adequate quantities of the sample. Although less than one gram of material is sufficient for most techniques used for crystalline silica, a larger quantity allows for other procedures
(such as preconcentration of analyte phase) and multiple tests.
Use an identification label on the sample that allows proper tracking to the source. Retain adequate records to allow interpretation of the results when received. The analytical laboratory will probably add their own number for record correlation.
Be specific in the request for analytical work. If you need phase identification or confirmation and/or quantification, indicate all requests with the initial sample submission. Specimen preparation and data collection depend on the analysis to be performed.
Provide as much information on the sample as possible. Indicate how the sample was collected and what phases it may contain, both the silica phases and possible interference. Withholding
information for fear of biasing the result is not justified.
If you suspect that the sample may contain silica phases other than or in addition to quartz, indicate this information at the time of initial submission. This information may be based on
previous analyses or a knowledge of the sample and process involved. If the sample contains natural, unreacted raw materials or if the sample has been processed (chemically, thermally or otherwise), this information is important to suggest the phases that might be present.
If you have questions on the results, do not hesitate to contact your analytical laboratory. The analytical laboratories are serious in their efforts to provide you the most accurate results at the most reasonable price, and they will be happy to review the results with the requester.
Reports from different laboratories will appear different, but the basic data reported will be the same. Analyses for bulk crystalline silica will usually be reported as weight percent or weight fraction.
Determine the method of analysis. There are several methods used by analytical laboratories for silica. These techniques include X-ray diffraction, infrared, chemical, or optical. Each technique has advantages and disadvantages with respect to the other methods.
Determine units of reporting. Results may be reported as
1. total weight or weight fraction of crystalline silica or
2. weight fraction of each silica phase.
Phases typically reported are quartz and/or cristobalite and rarely tridymite or opal.
X-ray diffraction and infrared are based on recorded spectra. A full report containing these spectra is rarely supplied unless the requester so indicates with the initial order. Spectra are recorded digitally but displayed graphically. The trace may only cover the range of analytical significance. Infrared is generally sensitive to total crystalline silica only whereas X-ray
diffraction can distinguish the specific phase present.
Check report to determine procedure for instrument calibration and sample standardization and for the standards used. Instrument calibration and procedure standardization are not the same. There are many instrument standards. There are a few silica standards available for quartz and cristobalite; the same is not true for tridymite and opal.
Report should discuss the limits on the accuracy of the analysis. Many factors contribute to the potential accuracy of any analysis: availability of adequate sample, concentration of analyte,
technique employed, interference problems, etc.
Look for statements on corroborating tests. Some sample situations require special treatment and additional tests. Examples which require departures from routine methods include distinguishing opal and cristobalite and quantifying quartz in the presence of mica.