C6-C9. ALS historically defines the C6-C9 boundary as the midpoint between adjacent n-alkanes. This sees compounds eluti
EnviroMailTM #103
February 2016
Which Volatile Organic Compounds (VOCs) are captured in the NEPM (1999, 2013 Revision) C6-C10 TRH band? TPH/TRH BOUNDARY DEFINITIONS
INTRODUCTION TPH (C6-C9) or TRH (C6-C10) analysis is commonly used for screening samples for potential contamination of Volatile Organic Compounds (VOCs) and also to assess against specific guidelines (i.e. NEPM for C6-C10). Hydrocarbon bands are defined by the retention time of the relevant nalkane on a GC column. The key point to note is that it is the boiling point rather than the number of carbon atoms that defines which compounds will report within the band. For data interpretation and comparison of VOC results against TPH/TRH results it is also important to note that not all VOCs in the standard analytical suite fall within the C6-C9 or C6-C10 bands and that the C6-C9 and C6-C10 bands do not capture the same VOCs. This EnviroMailTM aims to clarify which VOCs are captured by each banding structure.
C6-C9 ALS historically defines the C6-C9 boundary as the midpoint between adjacent n-alkanes. This sees compounds eluting from a retention time midway between C5 & C6, up to and including midway between C9 & C10 reporting in the C6-C9 fraction. Another way of thinking of this is that ALS C6-C9 is actually C5.5 to C9.5. This approach is consistent with the TPH C10-C36 semi-volatile fraction rules and ensures that a compound with a boiling point between fractions e.g. between C9 and C10 will be captured in one fraction and will not be missed. C6-C10 Release of the NEPM guideline revision in May 2013 saw the introduction Health Screening Level TRH fractions, the volatile fraction (F1) comprising C6-C10 minus the sum of BTEX (refer to EnviroMailTM 51 for more details). The specific definition of the boundaries for the C6-C10 band (per NEPM) sees the inclusion of compounds eluting from the retention time at which C6 starts, up to and including the end of C10.
BAND DEFINITIONS - TPH (C6-C9) versus TRH (C6-C10) TPH (C6-C9) Starts at the midpoint between C5 and C6 and finishes at the midpoint between C9 and C10
TRH (C6-C10) Starts at the start of C6 and finishes at the end of C10
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IS IT SAFE FOR ME TO USE C6-C9/C6-C10 to screen for VOCs? This is really a decision for you based upon your knowledge of likely contaminants and your objectives. The key point here is that some Volatile Organic Compounds (VOCs) as reported under the USEPA 8260 VOC method will actually not report in either the C6C9 or C6-C10 fractions and therefore care is needed. The following figure shows the ALS reported VOCs under ALS method EP074 (reference method USEPA 8260) that are captured by both C6-C9 and C6-C10 as well as those VOCs not captured within these bands.
E.g. Vinyl Chloride elutes before the start of either TPH/TRH band and so is not included in either C6-C9 or C6-C10.
e.g. 1,1-Dichloroethane is included in C6-C9 but not C6-C10.
e.g. 1,3,5-Trimethylbenzene is not included in C6-C9 but is included in C6-C10.
e.g. 1,2-Dichlorobenzene elutes later than the end of both TPH/TRH bands and so is not included in either C6-C9 or C6-C10
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Brisbane, Sydney, Melbourne (Springvale), Perth, Newcastle, Roma, Darwin, Adelaide, Townsville, Mackay, Gladstone, Wollongong, Nowra, Mudgee, Chinchilla, Emerald Water Resources Group: Canberra, Bendigo, Geelong, Melbourne (Scoresby), Wangaratta, Traralgon
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