ABSTRACT
A primary standard is prepared by an absolute method with the gravimetric method being the preferred technique. The basic technique involves weighing minor and major components into a cylinder. This basic method can be modified to prepare samples at very low concentrations (parts per trillion) and containing very specific and complex mixtures such as hydrocarbons. Through the use of standards any two independent measurements may be compared provided each has a traceability pathway to the same fundamental unit of measurement. The pathway may be through the use of an absolute standard and a precise method of measurement or an absolute method of measurement alone. Standards for gas analysis may be prepared by mass, pressure or volume. The most direct and accurate method is by mass (gravimetry) in which each component is separately weighed into a gas cylinder. Preparation of standards by pressure is fast and somewhat less accurate than gravimetry.
