Applications of GC in quantitative analysis

HPLC has more or less supplanted GC as a method for quantifying drugs in pharmaceutical preparations. Many of the literature references to quantitative GC assays are thus old and the precision which is reported in these papers is difficult to evaluate based on the measurement of peak heights or manual integration. It is more difficult to achieve good precision in GC analysis than in HPLC analysis and the main sources of imprecision are the mode of sample introduction, which is best controlled by an autosampler, and the small volume of sample injected. However, it is possible to achieve levels of precision similar to those achieved using HPLC methods. For certain compounds that lack chromophores, which are required for detection in commonly used HPLC methods, quantitative GC may be the method of choice, for analysis of many amino acids, fatty acids, and sugars. There are a number 

A calibration solution containing ca 0.04% w/v of methyltestosterone and ca 0.04% w/v testosterone in ethanol is prepared (Solution 1). A weight of tablet powder containing ca 20 mg of methyltestosterone is extracted with 50 ml of ethanol to prepare Solution 2. Solution 3 is prepared by dissolving tablet powder containing ca 20 mg of methyltestosterone in exactly 50 ml of ethanol containing exactly the same concentration of testosterone as Solution I. In this example 0.5 pi amounts of the solutions were injected into the GC in the splitless mode. 

Solution 1 gives a response factor for the calibration solution as follows  

The amount of methyltestosterone in the tablet powder can be calculated as follows  

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