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The sample volume refers to the sample volume in the headspace vial and sometimes the amount of sample entering the gas chromatograph (GC). In fact, the latter should be called injection volume. In headspace-gas chromatography, the injection volume is controlled by injection time (pressure equalization system) or quantitative tube (pressure control loop system), which is also affected by factors such as temperature and pressure.
In fact, the absolute injection volume in the headspace GC analysis does not make much sense hplc vials manufacturer in china. What is important is the reproducibility of the injection volume. As long as the injection conditions are fully reproduced, the reproducible injection volume is guaranteed. Even in quantitative analysis, it is generally not necessary to know the value of the absolute injection amount. The sample volume in the headspace vial has a large impact on the analytical results because it directly determines the beta.
For a given gas-liquid equilibrium system, K and Co are constant and β is proportional to the concentration in the headspace gas. It is also said that when the sample volume Vs is increased, β is decreased, and Cg is increased, so sensitivity is increased. But for the specific sample system, it depends on the size of K. In other words, when K>>β, the change in sample volume has little effect on the sensitivity of the analysis. When K<<β, the effect is great. For example, dioxane and cyclohexane in an aqueous solution were analyzed and equilibrated at 60 ° C with a 20 ml sample vial. At this time, the K of the dioxane was 642, and the cyclohexane was 0.04. When the sample amount was changed from 1 ml to 5 ml, the analytical sensitivity (peak area) of dioxane was increased by only 1.3%, while cyclohexane was increased by 452%. Therefore, the amount of sample is determined by the nature of the sample system.
Another problem associated with the amount of sample is its reproducibility. Because static headspace GC often only samples once from one vial, when parallel experiments are performed, several samples need to be prepared and placed in separate hplc vials manufacturer in china. At this time, whether the volume of each sample reproduces also affects the analysis result. The smaller the partition coefficient of the component to be tested (the greater the solubility in the condensed phase), the greater the error of the result caused by the fluctuation of the sample volume; conversely, the larger the partition coefficient, the smaller the effect. However, in practice, the partition coefficient of the sample system is often unknown, so we recommend that the volume of each sample be consistent with each other at all times. For specific analysis, the sample volume is also related to the volume of the vial. The upper limit of the sample volume is 80% of the volume of the vial so that there is sufficient headspace for sampling. A sample volume of 50% of the vial volume is often used. Sometimes only a few microliters of sample are used. The nature of the sample, the purpose and method of analysis are the main factors determining the volume of the sample hplc vials manufacturer in china.
This is the end of the introduction of Effect of sample volume on headspace-gas chromatograph. I hope it can help you.
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