In recent times, the convention for reporting analytical results has been shifting toward the use of milligrams per liter (mg/L) as a replacement for parts per million and micrograms per liter (µg/L) as a replacement for parts per billion. This is more conveniently reported as 1.0 ppb. For example, in studies of steam purity using a specific ion electrode to measure sodium content, values as low as 0.001 ppm are not uncommon. One part per billion is equal to one-thousandth of one part per million (0.001 ppm). Therefore, it is more convenient to use parts per billion (ppb) in these cases. When elements are present in minute or trace quantities, the use of parts per million results in small decimal values. It makes no difference what units are used as long as both weights are expressed in the same units. One part per million equals one ten-thousandth of one percent (0.0001%), or one part (by weight) in a million parts-for example, 1 oz in 1,000,000 oz of water, or 1 lb in 1,000,000 lb of water.
For this reason, the results of a water analysis are usually expressed in parts per million (ppm) instead of percentage. The expression of results in percentage would require the use of cumbersome figures. Water analysis involves the detection of minute amounts of a variety of substances. Calculation of total dissolved solids by EPM.