Frequent Questions

What is the frequency of correlation samples for laboratories to remain qualified for reform testing?

There is no definition of "qualified" laboratories under the regulations. The principle requirement for correlation relates to the use of one of the alternate methods allowed until 1/1/97.

When one elects to use ASTM D1319 for measuring aromatic content in gasoline, or ASTM D4815 for the measurement of oxygenates in gasoline, correlation to the regulatory methods must be established. The principle reason for this requirement is the operator dependent nature of D1319 and D4815. This operator dependence is echoed by the relatively large reproducibility of these methods. Because of the operator dependence, each facility (or in some cases, each operator) must establish its own correlation to the appropriate regulatory methods. This correlation need not be established via an internal route, participation in an outside program or ongoing exchange group may be sufficient. The actual number of tests performed will depend on the quality of the correlation. In general, some initial group of tests will be necessary, perhaps from 15 to 30, to establish the nature of one's correlation. If both methods report identical numbers, this may be enough, and all that would be required in addition would be a few samples a month to verify that no shift has occurred.

If this initial effort describes a bias, considerably more effort may be necessary. The object would be either to describe the bias via a correlation equation, or eliminate the bias via improvement (or alteration) in the technique of the operator. The effort required will be determined by the difficulty in eliminating the bias or producing the equation. Following this, some number of samples should be run on an ongoing basis, to confirm that no shifts have occurred. Again, this number will be determined by the individual's confidence in his established correlation.

In practice, this means that each laboratory must establish this correlation if it intends to measure aromatics by ASTM D1319, or oxygenates by ASTM D4815. This correlation testing is done to define a bias, or show that none exists. It is not appropriate to include reproducibility in this discussion, since the intention is to correlate the mean of one method with the mean of a second method. In all cases, the fuel must meet its intended aromatics level as measured by GC/MS, and its intended oxygenates level as measured by OFID.(1/9/95)

This question and answer is posted at The original was posted in the Q&A posted on 1/9/95 which can found at" See Question ID 3857 for RFG (Taken from the first question on
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