Quantitative Analysis

To be able to carry out quantitative work, the gas chromatograph must be calibrated with accurately prepared mixtures of known composition. Dynamic methods for calibration such as gas stream

Figure 8 Mixing time for halothane prepared in helium. Squares, 1.1 % halothane at 8.5 bar; diamonds, 1.2% halothane at 5.0 bar; triangles, 1.4% halothane at 3.1 bar.

mixing, permeation, diffusion and evaporation generate continuous flows of mixtures of known composition and are generally employed in studies where large volumes of standards at low concentrations are needed. Static methods for producing standard gas mixtures are appropriate when relatively small volumes of mixtures are required at moderately high concentration levels and have been widely used in calibrating gas chromatographic instruments. The preparation of calibration mixtures in gas cylinders involves either volumetric or gravimetric mixing. Gravimetric methods in which the the concentrations are determined from the mass of each component present in the cylinders irrespective of the temperature and pressure of the mixture represent the nearest approach to an absolute method, provided the mixture is homogenous. The mixing rate is inversely proportional to the total pressure and is rapid if thermal or mechanical agitation of some kind is introduced to cause turbulence in the gas (usually the cylinder is rolled in a horizontal position). Without mechanical mixing, equilibration is likely to take several days (Figure 8). Syringe dilution methods (even with all-glass syringes) are not suitable for calibration purposes, particularly at lower concentrations, due to the adsorption of the liquid anaesthetics (see Figure 2).

Quantitative evaluation may be performed either by peak height or by peak area. The most commonly used method is based on direct calibration with standard samples which bracket the anticipated values in the unknown sample. The correlation peak value versus concentration generally exhibits a linear plot. The basic condition for successful quantitative analysis is a high degree of constancy of operating conditions and the accuracy of the analysis is significantly affected by apparatus parameters, characteristics of the detector and the skill of the analyst.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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