Can the secondary ion be used as the quantitation ion in order to meet the minimum response factors listed in Table 4 of 8260C?
The laboratory currently cannot meet the minimum response factor for acetone using ion 58 (however, this can be achieved by using ion 43). The same situation also applies to 2-Butanone and 2-Hexanone.
The secondary ion can be used for quantitation. In the case of the compounds in question, the ions listed in Table 5 of 8260C are 43 and 58 for Acetone, 43 and 72 for 2-butanone and 43, 57, 58 and 100 for 2-hexanone. The primary ion is generally used as it is the most abundant or most characteristic, but secondary ions can be used if a compound co-elutes or there is a good reason to do so. The ketone compounds in question are known to be poor responders.
Table 4, which lists the recommended minimum response factor criteria, has this to say in the footnote: "The project-specific response factors obtained may be affected by the quantitation ion selected and when using possible alternate ions the actual response factors may be lower than those listed. In addition, lower than the recommended minimum response factors may be acceptable for those compounds that are not considered critical target analytes and the associated data may be used for screening purposes."
The method acknowledges that every laboratory may not be able to achieve the recommended minimum response factor in Table 4 and allows for the reporting of data that does not meet this criteria to be reported with qualifiers. The minimum response factors published in 8260C were provided as guidance and were not intended to be used as prescriptive quality control criteria for the laboratory. The response factors were derived from a Gas Chromatography/Mass Spectrometry (GC/MS) system at the time the method was revised in 2006. In the newer version, Method 8260D (soon to be posted on the RCRA Methods website), Table 4 is revised to list relative response factors criteria from the EPA Contract Laboratory Program. A statement is added under Table 4 noting these response factors are provided as guidance only and are not intended to be a requirement.
There are no prohibitions in the method to use a secondary ion to quantitate, but if the only motivation for doing so is to meet the minimum response factors in Table 4, that would not be needed to consider the data reportable if all other QC checks were in control.