This technical article covers the internal standard method of GC calibration.
The goal of any quantitative analysis is to accurately determine the concentration of target analytes in an original sample. Often, the original sample is not suitable for direct injection into a GC. Some of the reasons samples might need to undergo sample preparation prior to analysis are:
- they are solid and therefore not injectable so must first be dissolved in a suitable solvent
- they contain insoluble components that will contaminate the instrument and/or interfere with subsequent analyses, so analytes of interest must be separated from the matrix first (matrix isolation )
- they are unstable and will decompose when exposed to GC temperatures and require derivatization to form more stable products that can be analysed
- they are too complex for rapid analysis, so require a rough pre-separation
- the analytes of interest are at very low concentrations and require pre-concentration prior to analysis in order to be detected
- the analyte concentration is too high and would overload the column and/or detector, so they must be diluted
- samples are in an inappropriate solvent (e.g., water) that is incompatible or problematic with GC analysis and require a solvent exchange
By reading the full article you will learn about errors that can be introduced by sample preparation and how there can also be variability inherent in the GC system and analysis method themselves. The advantages of making a standard of high concentration are also discussed.
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