Sample pre-treatment and detection

Sample preparation is an essential part of the separation process and is one of the key considerations at the start of any method development strategy. Numerous publications are available on this subject [38, 39]. In brief, the primary aim is to provide a reproducible and homogenous solution that is 

For these sample types, the choice of solvent is important because choosing a solvent system that closely matches the separation solvent minimises baseline problems and other unwanted separation effects. 

There are many sample preparation procedures published in the scientific literature, and within the scope of this chapter, only the most current and popular methods will be discussed. By far, the commonest and most popular method used for pretreatment of liquid samples is solid phase extraction (SPE) [40,41]. For solid samples, several techniques are available including supercritical fluid extraction (SFE) [42,43], microwave-assisted solvent extraction (MASE) [44,45] and accelerated solvent extraction (ASE) [46,47]. Solvent extraction methods have long been established as the standard approach to sample preparation, but the increasingly demanding needs of industries like the pharmaceutical, agrochemical and petrochemical for greater productivity, faster assays, and increased automation have led to the development of newer ways of sample preparation summarised in Fig. 2.3. 

During method development, it is critical that the derivatisation reaction is rapid, quantitative and produces minimal by-products or side reactions. These criteria are not always easy to achieve, hence, derivatisation as a sample preparation method is quite often chosen as a last resort. In pharmaceutical analysis, the use of derivatisation as a means of sample preparation is not usually the method of choice because the primary objective of any method development is to detect all major impurities and degradants in batches of the dmg substance. Quite often, many of these compounds will not have derivatisable functional groups or have inpurities that are present at such low levels that the derivatisation reaction is not optimised. 

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