Frequent Questions

Holding time and preservation requirements for volatile organics analysis (VOA).

SW‐846 Chapter 4 recommends that for aqueous samples for 5030/8260 VOA when analysis for vinyl chloride and styrene are target compounds, an unpreserved vial be used and the holding time becomes within 7 days of collection. Our lab routinely analyzes aqueous MS/MSD samples from a large variety of sources (effluents, groundwater, surface water, etc.) that are preserved at a pH <2 with HCl with recoveries for these compounds well within 70‐130 percent.  Because we typically spike the MS/MSD samples less than 48 hours from analysis we don’t have long-term stability data of these two compounds in preserved vials.  Field samples are collected in 2 preserved vials and 2 unpreserved vials and we have analyzed samples that have detections of vinyl chloride and styrene from both preserved and unpreserved vials with statistically similar results.

 

The previous version of SW-846 Chapter 4 Table 4-1 recommended, for aqueous samples with no residual chlorine present, that "If vinyl chloride, styrene, or 2‐chloroethyl vinyl ether are analytes of interest, collect a second set of samples without acid preservatives and analyze as soon as possible." 

In Update V, Chapter 4 (July 2014 rev 5) Table 4-1, that same recommendation was revised to "If compounds that readily degrade in acidified water (e.g., 2‐chloroethyl vinyl ether) are analytes of interest, collect a second set of samples without acid preservatives and analyze as soon as possible."

The reason for this change followed discussion in the Workgroup regarding the requirement of a second set of unpreserved vials for analysis of styrene and vinyl chloride.  Stability studies were conducted and the stability data for vinyl chloride and styrene were felt to be reasonably comparable by the group.  Therefore, the Workgroup dropped the unpreserved requirement for those two compounds, but not for 2‐chloroethylvinyl ether, as the study data did not address 2‐chloroethylvinyl ether.  It is still the recommended guidance that unpreserved samples be run for 2‐chloroethylvinyl ether.

Other Category: Holding Time & Preservation

 

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