|A Guide to the Establishment and Maintenance of Pesticide Laboratories in Developing Countries - Bulletin No.25 (NRI/Overseas Development Administration, 1990, 80 pages)|
|Laboratory equipment, glassware and reagents|
|Storage of pesticide reference materials (standards)|
The proper storage of reference materials is crucial if analytical results are to be meaningful. The store should be outside the residue laboratory and could be associated with the formulation laboratory if one exists. Most pesticide standards are best kept in a refrigerator or deep freeze although there are certain exceptions; advice from the supplier is useful in this context.
Reference standards stored in a freezer will have a shelf life of several years, although note should be taken of the 'Use by ...' information generally supplied by the manufacturer/supplier.
It is recommended that the reference materials be stored in a self de-frosting upright freezer of stainless steel construction, for ease of cleaning, and of a capacity of not less than 200 litres. The freezer should be fitted with stainless steel shelves forming discrete compartments to facilitate segregation of materials by class of compound.
A disadvantage is that freezers can be a source of moisture and whilst it is recommended that materials be kept in sealed vials this is not always possible. A useful solution is to keep the individual containers inside a larger screw-capped container to which a desiccant has been added; self-indicating silica gel is useful for this purpose. This material can be regularly changed and regenerated. The number of containers (polythene is preferred to glass) and the quantity of silica gel required depends on the quantities of reference material to be stored. Freezers function more efficiently when full and it is probably best initially to fill or nearly fill the freezer with containers holding single compounds, and to double up as the library of standards expands. With a good coding or labelling system location of individual materials can be quite rapid.
Recurrent costs for storage of reference materials are slight and unless there is a difficulty with the operation of the freezer itself, are confined to the replacement of silica gel and any damaged storage containers (assuming sufficient were purchased initially). Silica gel requirements annually will be about 1 kg.