5 MATERIALS: APPARATUS, REAGENTS, SAMPLES

5.1 Introduction

Quality analytical work can only be performed if all materials used are suitable for the job, properly organized and well cared for. This means that the tools are adequate and in good condition, and that sample material receives attention with respect to proper handling, storing and disposal.

The tools used for analysis may be subdivided into four categories:

1 Primary measuring equipment (pipettes, diluters, burettes, balances, thermometers, flow meters, etc.)

2. Analytical apparatus or instruments.

3. Miscellaneous equipment and materials (ovens, furnaces, fridges, stills, glassware, etc.)

4. Reagents.

The saying that a chain is as strong as its weakest link applies particularly to these items. An analyst may have gone out of his/her way (as he/she should) to prepare extracts, if the cuvette of the spectrophotometer is dirty, or if the wavelength dial does not indicate the correct wavelength, the measurements are in jeopardy. Both the blank and the control sample (and a possible "blind" sample or spike) most likely will reveal that something is wrong, but the harm is already done: the problem has to be found and resolved, and the batch might have to be repeated. This is a costly affair and has to be minimized (it is an illusion to think that it can be totally prevented) by proper handling and maintenance of the equipment.

Also the quality and condition of a number of other working materials have to be watched closely. The calibration of thermometers, burettes and pipettes, particularly the adjustable types, may exceed the acceptable tolerance (and be put out of use). New glassware may look clean but always needs to be washed. Glassware may give off unwanted elements (boron, silicon, sodium). The same goes for milling and grinding equipment (pestles and mortars, tungsten carbide grinders, brass or steel sieves). For virtually all analyses glassware needs to be rinsed with deionized water after washing. Therefore, if glassware, such as volumetric flasks, is shared by analysts, they should be able to rely on the loyalty and good laboratory practice of their colleagues.

A similar reasoning applies to reagents. One of the most prominent sources of the errors made in a laboratory is the use of wrongly prepared or old reagents. Therefore, reagents have to be prepared very carefully and exactly following the prescriptions, they have to be well labelled and expiry dates have to be observed closely. Filtering a pH buffer solution in which fungi are flourishing may save time and reagent but is penny-wise and pound-foolish.

Of equal importance for the quality of the work is the proper handling of the sample material. Not only the technical aspects such as sample preparation, but particularly the safeguarding of identity and integrity of the samples as well as the final storage or disposal (chain of custody).

As part of the overall quality assurance, in this chapter a number of instructions and suggestions are presented to ensure the analytical reliability of the main tools and proper organization of sample handling.

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