Basics of Canister-GC/MS analysis

This is an EANET training presentation (Session 2: Methodology) by Yujiro Ichikawa of the Atmospheric Environment Division, focused on the basics of canister sampling and GC/MS analysis for VOCs. It outlines two blocks: (1) VOCs sampling (canisters and flow controllers), and (2) Canister–GC/MS measurement (chromatography fundamentals; mobile/stationary phases; preconcentration/sample injection; GC columns; MS detector).

Sampling with canisters—hardware and handling.
The slides introduce canister sampling for atmospheric VOCs: air is drawn into an evacuated, inert-coated stainless-steel canister via a flow controller (orifice/restrictor). Canisters come in multiple sizes; the deck shows common volumes with ~6–15 L most used for ambient work. Critically, uncoated interiors cannot stably store many VOCs; inert coating is required to reduce wall losses and reactions. Flow controllers (example: Entech CE1200E) and restrictors govern fill rates for grab or time-integrated samples.

Chromatography fundamentals—why and how separation works.
A short history credits Tswett (1906) and defines core terms: mobile phase, stationary phase, sample, detector, and column. The deck contrasts gas chromatography (GC) and liquid chromatography (LC), then walks through a GC system for VOCs, emphasizing sample injection via an autosampler and a preconcentrator (cryogenic or sorbent trapping) that focuses trace VOCs before they enter the column.

Preconcentration and carriers.
For canister-based VOC measurements, helium is used in the preconcentrator to inject samples into the GC/MS; thus He is effectively the only carrier option in this configuration (as presented here).

GC columns—choosing for separation.
An overview of capillary columns covers stationary-phase chemistry (polarity), length, internal diameter (I.D.), and film thickness, and how each affects retention, efficiency, sample loading, and resolution. The deck explains phase ratio (β) and gives a reference table for commonly used β values in ambient VOC monitoring. Practical levers include adjusting oven temperature programs and matching stationary-phase polarity to compound classes to resolve co-eluting species.

Chromatographic trade-offs, at a glance.

Length: longer → higher theoretical plates but longer run time; helpful when separating dozens of VOCs.

I.D.: narrower → better efficiency but lower loading and higher backpressure.

Film thickness: thicker → stronger retention and higher loading but broader peaks.
These variables interact through β (phase ratio); selecting a column is about balancing resolution vs time/sensitivity for target analytes.

Detector choice and mass spectrometry basics.
The deck inventories GC detectors, then dives into MS as the workhorse for speciated VOCs at trace levels. It shows the MS vacuum system, ion sources (notably EI and CI), and mass analyzers (with a schematic of a quadrupole). EI (electron ionization) provides rich fragmentation patterns for library matching; CI (chemical ionization) is softer, often improving molecular-ion visibility. The electron multiplier serves as the MS detector.

Putting the system together—end-to-end workflow.
A typical ambient VOC workflow runs: (1) canister sampling with appropriate flow control and inert-coated vessels; (2) autosampler + preconcentrator to capture/cryofocus low-ppbv VOCs; (3) column selection and temperature program tuned to the VOC list; and (4) GC/MS with EI (and/or CI) and quadrupole scanning or SIM modes, with QA/QC anchored in blanks, standards, check mixes, and leak checks. The deck closes by flagging an on-site practical to be given at CESS in October.

Keywords

Canister sampling; inert-coated stainless canisters; flow controller; restrictor; time-integrated vs grab sampling; autosampler; preconcentrator (cryotrap/sorbent); helium carrier; chromatography basics; mobile vs stationary phase; GC vs LC; GC column (polarity, length, I.D., film thickness); phase ratio (β); oven temperature program; resolution vs runtime trade-offs; mass spectrometry; high vacuum; EI/CI ion sources; quadrupole analyzer; electron multiplier detector; ambient VOC speciation.