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The importance of measurements
One of the tasks facing scientists is to measure and define unknown quantities. These measurements are important because they can warn us of potential hazards from volcanoes and environmental contamination or help us develop our mineral resources to stay competitive in the worldwide economy. In Earth sciences, the measurements of geological samples are used in making policy decisions. These decisions can affect all Americans in topics ranging from pollution prevention and control to evaluation of mineral resources and wilderness areas.
Decisions are made every day based upon measurements of various substances (or areas containing them). Without quality measurements, misleading or dangerous conclusions could be drawn.
The uncertainty of measurements
There are many difficulties associated with making measurements. Quality assurance involves minimizing mistakes and correcting problems before the information is used.
When an archer releases an arrow at a target, both the distance from which the archer shoots and the size of the target define what is considered acceptable accuracy and precision. Shots from 5 yards would be expected to hit closer to the bull s-eye than shots from 50 yards. If the arrows miss the target completely, the archer is considered inaccurate. The closer together repeat shots hit the target to each other, the more precise the archer. The strength and dexterity of the archer, the acuity of the archer s eye, the adjustment of bow sights, wind conditions, and the number of shots taken also contribute to the accuracy and precision of the archer. A laboratory procedure is similar in the need to understand the variables involved and the possibilities for error.
Searching for the best
A mistake in measurements can impact decisions made on endangered animal habitat, mineral exploration, or remediation of an environmental problem. When a quality assurance program claims 99.9 percent accuracy, consider what that could mean in terms of error: 1 hour of unsafe drinking water per month, 16,000 lost pieces of mail per hour, or 176,000 checks deducted from the wrong bank accounts every day. The quest is for 100 percent accuracy and precision, even if it is not attainable. Return to this point in index.
The USGS Reference Materials Project
In the field of analytical chemistry, reference materials serve an important role in the development of new techniques and the periodic testing of established methods. Used correctly, reference materials provide investigators with a mechanism to objectively compare their results with established values and determine if any bias exists.
It was this drive to produce quality data that led the USGS and the Massachusetts Institute of Technology in the early 1950 s to jointly develop the first geochemical reference materials. This early work started a USGS tradition of preparing high-quality reference materials that are used for both domestic and international geochemical programs. To date, 29 different geochemical standards have been produced with an estimated worldwide distribution of over 20,000 units.
Samples are dried, crushed, powdered, mixed thoroughly, then bottled and analyzed. Some reference materials are distributed by the USGS in limited quantities directly to researchers and analytical laboratories. Other standards can be prepared on a contract basis for individual government agencies. Geologic analytical laboratories can compare their results to these standards.
Initially, the need for quality control led to the development of several silicate rock standards that were important in such diverse activities as the lunar program, ore-genesis studies, and volcano monitoring. When the mining and exploration industries clamored for reference materials, the USGS responded by generating six exploration standards designed to contain elevated concentrations of key elements. The USGS involvement with the mining industry continues today with the recent development of coal and gold-ore standards, which will be useful in resource appraisals.
Environmental concerns are becoming a major part of the national agenda, and the USGS Reference Material Project provides quality reference material to aid in this field of study. A major emphasis of this effort will be to conduct cooperative studies with other Federal agencies, thus helping them respond to national needs. Return to this point in index.
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