TABLE OF CONTENTS With the analytical instruments that most laboratories have, it is necessary to get the elements and other components that we want to determine into solution. The ways of making solutions from the samples are:
Acid digestions effectively dissolving the whole sample, or most of it.
Dry-ashing at 450 550 C to destroy organic matter, followed by dissolution of the residue in acid.
Extraction by hot or cold reagent solutions or solvents.
Acid digestion and ashing are usually used to determine the total contents of a component, such as a metal element, being measured. On the other hand, extractions may be targeted at the removal of a fraction of the component. Extraction may be repeated several times to remove all of the particular fraction from the sample; that would be an exhaustive extraction. In other procedures, a single extraction, under specified conditions, gives an indication of the amount of the component in the sample. The choice of the actual method used will depend on the purpose of the study. For example, it may be that the total content of a metal element in a plant indicates the requirement for that element to be added as a nutrient. Or, the total content may affect some aspect of further processing or a quality factor such as colour, taste or flavour. On the other hand an extraction may be more appropriate to determine the loss of the element in processing or cooking. In an example of practical work given in this...
