S.O.P. No. MLD 066 - Determination of Oxygenates and Nitriles in Ambient Air by Capillary Column Gas Chromatography/Mass Spectrometry
This document describes the procedures followed by Monitoring and Laboratory Division (MLD) staff to analyze oxygenated and nitrile hydrocarbons by Gas Chromatography with Mass Spectrometry detection, (GC/MS), in ambient air samples collected from the California Toxic Monitoring Network. Staff of the Northern Laboratory Branch (NLB), Organic Laboratory Section (OLS), developed the method. This Standard Operating Procedure (SOP) is based on the U.S. Environmental Protection Agency (EPA) Toxic Organic Compounds in Ambient Air Method TO-15, “Determination of Volatile Organic Compounds (VOCs) In Air Collected In Specially-Prepared Canisters And Analyzed by Gas Chromatography/Mass Spectrometry (GC/MS)”, EPA/625/R-96/010b, January 1999. Table 1, page 21, lists the Target Compounds and their Chemical Abstract Service (CAS) numbers.
SUMMARY OF METHOD
Ambient air is collected in a SUMMA polished stainless steel canister using a Xontech 910A sampler. The sampling procedure for Toxic samples is detailed in the Air Resources Board Quality Assurance Manual, Volume II, Appendix Q. All the operational procedures and sampling conditions for each sample are documented in the field. A record of this information is sent back to the OLS along with the sample. Upon receipt, the sample canister pressure is measured with a calibrated external pressure gauge. This information and particulars of the collection are documented in the laboratory. The sample is then analyzed according to the SOP in the laboratory.
An ambient air sample is introduced into the analytical system from a pressurized canister through stainless steel or Teflon tubing with the aid of a mass flow controller (MFC) and a vacuum system. A digital readout attached to the MFC provides a visual indication of the proper sample flow during sampling. Automated sampling of up to 16 canisters can be accomplished using the system’s multi-position stream selector valve.
The sample is trapped on a sorbent trap at 50°C. The sorbent trap consists of carbopack B, carbopack C and carboxen 1000. Moisture in the sample is removed from the sorbent trap by dry purging it with an inert gas. After purging, the sorbent trap is rapidly heated to 300°C to transfer or desorb the contents onto a cryofocuser which is cooled to -130°. The cryofocuser is rapidly heated to 300oC to inject the sample onto a DB-624 capillary column.
The sample mixture is separated into individual components by their interaction with the capillary column's stationary phase, using temperature programmed gas chromatography. A Mass Selective Detector (MSD) detects the components eluting from the column. The target analytes, as shown in Table 1, page 21, are subsequently identified and quantified. Identification of a component in a sample is based upon both the retention time and mass spectral matching. The response of one mass fragment, the Primary Quantitation Ion, is used for quantitation.