Infrared analysis of plasticizers

PVC additives such as plasticizers, stabilizers and fillers can be analyzed by this method. A one gram sample of PVC is extracted in a jacketed Soxhlet apparatus with ethyl ether for 6 hours. After extraction, the solvent is evaporated and a dry plasticizer determined by gravimetry. This quantitative method of analysis is not very precise because stabilizers are other additives that may be extracted together with the plasticizer. 

To increase the precision of quantitative analysis, the plasticizer sample is diluted with carbon disulfide, its infrared absorption measured, and compared with absorptions standard of standard samples prepared also in CS2 to cover the range of concentrations from 0.5 to 3 mg/ml. For each suspected (identified) plasticizer, a series of standards has to be prepared and measured. It is also important to select a suitable wavelength for quantitative analysis. For dioctyl phthalate bands at 1725 and 1121 cm are usually used. For tricresyl phosphate band at 1191 cm is used. Similar to gravimetric method, the results are subject to various interferences when mixtirres of plasticizers or mixture of plasticizers with other additives ate used. 

Identification of a plasticizer is based on a comparison of a full spectrum of samples in the range from 4000 to 650 cm with a set of standard spectra or computerized database. This is again subjected to interferences by mixture components. Tire sample used for identification is usually used for quantitative analysis as discussed above or a special sample is extracted for the purpose of a direct quantitative analysis. 

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