Sampling and quantitative estimation

Samples may be taken for analysis at once, or after fractionation of the products and reactants. A set-up due to Porter and Norrish , is shown in Fig. 57. A sample 

A successful sampling valve is that due to Pratt and Purnell (Fig. 58) . A dead-space sample is first withdrawn, followed by a reacted sample. Cundall et claim a better valve is the push-pull type (Fig. 59), a variation of the valve used on some commercial glc instruments. For sample injections after fractionation, a constant volume and manometer is employed for gases, and precision microlitre syringes for liquids. 

A method which circumvents the problem of total elution is to have an absolute measure of an injected standard or of one product and use this for the quantitative estimation of the other products and undecomposed reactants. For instance, in the HCl-catalysed decomposition of di-terr.-butyl peroxide , involving the reactions 

---