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Standards must be prepared for use in the ICP-OES. In general, standards should be chosen based on the expected level of analyte in the solution. Detection limits and linear ranges vary by element, but in general, do not expect to use standards below 0.05 ppm or above 200 ppm. If the expected concentrations of analytes in solution are significantly above 200 ppm, the sample should be diluted.
All standards are prepared using the Inorganic Ventures single element 1000 ppm standards. The matrix of the standards needs to match as closely as possible the matrix of the samples. If you are analyzing Mehlich extract, your standards should be made using Mehlich extracting solution to dilute the standards.
A recently calibrated pipette with a clean tip is used to withdraw the appropriate amount of standard from the bottle and deposited into a clean 100ml volumetric flask. Multi-element standards can be used. After all standards are added to the flask, we bring to volume with the appropriate matrix.
The most highly concentrated standard can be made first, and subsequent standards made from dilutions of the original. If this is done, we make sure that the original standard is very well mixed.
We use at least five standards to perform a calibration.
Different standards may be kept for different lengths of time and under different circumstances. We are mindful of the characteristics of the analyte, matrix, vessel, and environment. For example, we don’t store boron standards in borosilicate glass, and we don’t keep standards in a Mehlich extractant matrix longer than the original shelf life of the extractant.