Flexibility in EPA
Method 1664A
This section discusses flexibility inherent in EPA Method 1664A and discusses the process of demonstrating
equivalent performance when the Method is modified. This discussion is summarized from Guidance on
Evaluation, Resolution, and Demonstration of Analytical Problems Associated with Compliance Monitoring
(EPA 821-B-93-001).
Is there flexibility in EPA Method 1664A?
Flexibility exists for making changes to EPA Method 1664A. However you must demonstrate that your
modification achieves equivalent or superior performance to the performance of Method 1664A.
What types of modifications may I make?
The types of modifications that you may make to Method 1664A are the typical changes that would make it easier
for you to practice the Method without compromising performance. For example, change of a beaker to an
Erlenmeyer flask or change of a boiling flask to a Kuderna-Danish is allowed, after a demonstration of equivalency,
because they would not be expected to adversely affect method performance. Certain changes, including change of
the extraction solvent, are not allowed as modifications, because the Freon Replacement Study data demonstrated
that significant changes in results occur when an alternate solvent is used. A change in the n-hexadecane and
stearic acid standards is not allowed because the performance data for Method 1664A were developed using these
standards. (Please refer to section 9.1.2 of EPA Method 1664A, excerpted in response to the question below).
How can I demonstrate equivalent or superior performance for a method modification?
You can demonstrate equivalent or superior performance by showing that results produced by your modification are
equal to or superior to results produced by the unmodified Method. The performance of a modified method is
measured by precision and recovery (bias), and can be extended to include detection limit as well as other measures
of method performance. You must perform the initial precision and recovery (IPR) test prior to practicing Method
1664A. This test is described in detail in Section 9 of the Method. Results of the IPR test must meet the precision
and quality control (QC) acceptance criteria in Method 1664A. After the requirements are met for the unmodified
Method, you must repeat the IPR test with the modification as an integral part of the Method. Your modification is
permitted if the QC acceptance criteria for precision and recovery of Method 1664A are met.
As stated in Section 9.1.2 of EPA Method 1664A, the purpose of allowing changes to Method 1664A is to improve
Method performance or lower the cost of measurements. Section 9.1.2 of Method 1664A states:
4-2
9.1.2 In recognition of advances that are occurring in analytical technology, the laboratory is permitted
certain options to improve separations or lower the costs of measurements, provided that all
performance specifications are met. These options include alternate extraction and concentration
devices and procedures such as solid-phase extraction, continuous liquid-liquid extraction, and
Kuderna-Danish concentration. Alternate determinative techniques, such as infrared spectroscopy
or immunoassay, and changes that degrade method performance, are not allowed. If an analytical
technique other than the techniques specified in this method is used, that technique must have a
specificity equal to or better than the specificity of the techniques in this method for HEM and/or
SGT-HEM in the sample of interest. Specificity is defined as producing results equivalent to the
results produced by this method for analytical standards (Section 9.2.2) and, where applicable,
environmental samples (Section 9.2.3), and that meet all of the QC criteria stated in this method.