Overview

In general, the direct determination of additives in plastics, as opposed to carrying out a preliminary extraction technique, such as is discussed in Chapter 2, is less time consuming and more reproducible. The direct determination of all the additives in such extracts is not always possible because of spectral interferences from other additives, low relative molecular weight (MW), mass matrix oligomers and the extracting solvent. Infrared (IR), and ultraviolet (UV) spectrometric techniques have been used successfully in some cases; in others where the extract is a complex mixture, prior chromatographic separation of the additives is necessary. Methods based on a preliminary extraction of additives from the polymer, then chromatographic separation before the analytical finish are obviously much more time consuming than methods based on direct analysis of the polymer.

Much recent work on the development of direct methods has been carried out and is discussed next.

Chemometrics is the art of extracting chemically relevant information out of data produced in chemical experiments with the use of mathematical and statistical methods [2]. The main issue is to structure the chemical problem in a form that can be expressed as a mathematical problem. Chemometrics have become an integral part of spectroscopy and other areas of chemistry.

Calibration methods seek to express the dependent variable as a linear function of the independent variables. Linearisation of variables before calibration will make the calibration model less complicated. According to Beer s law, the concentration and the film thickness are proportional to the absorbance. A...