TABLE OF CONTENTS Weight and volume measurements form the basis for almost all analytical work we do. Eventually, for some determinations, we will have to make some other measurements too, but to turn these measurements into useful results, our calculations most frequently include weight and volume parameters. Often we want to express our result as a concentration for example as milligrams of sodium per kilogram of cheese (ppm); or grams of calcium per 100 grams of cereal (% w/w). Or the results might be more useful on a volume basis such as micrograms of benzene per litre of bottled water (ppb) and milligrams of alcohol per 100 millilitres of blood (parts per 100,000 w/v). The use of the older common names for concentration units (percent, parts per million etc.) is being discouraged because their meaning can be interpreted in different ways. Scientific units are preferred and more acceptable for laboratory work (see Table 4.1).
| Scientific units | Common name | |
|---|---|---|
| Liquids | Solids | |
| g 100 cm ?3 | g 100 g ?1 | percent (%) |
| g 1 ?1 | g kg ?1 | parts per thousand ( 0/ 00) |
| mg 1 ?1 | mg kg ?1 | parts per million (ppm) |
| ?g 1 ?1 | ?g kg ?1 | parts per billion (ppb) |
| ng 1 ?1 | ng kg ?1 | parts per trillion (ppt) |
With our usual...
