Chromatography focus on
Automated Analysis of Canister Air and Gas – A Cryogen-free Solution
Dr Nicola Watson, Environmental Applications Specialist, Markes International, Gwaun Elai Medi Science Campus, Llantrisant, RCT, CF72 8XL, United Kingdom. Tel: +44 (0)1443 230935; Fax: +44 (0)1443 231531; Email:
enquiries@markes.com
With growing concern over the harmful effects of long-term exposure to low levels of hazardous air pollutants, there is increasing demand for analytical laboratories to detect ever-lower levels of analyte concentrations in canister air. At the same time, canisters are increasingly used for applications other than ambient air analysis, such as soil gas and vapour intrusion studies. Traditional canister analytical technologies are challenged by the ever-wider range of analytes and concentrations of interest. For example, high-concentration samples have typically required dilution before analysis, increasing analytical uncertainty and risking introduction of contaminants. Conventionally, systems have also had to be dedicated to either high- or low-concentration analysis.
The CIA Advantage has been designed to overcome the limitations of traditional cryogen-cooled technology for canister air analysis and provide compatibility with both high- and low-concentration samples on a single analytical platform, even in a single automated sequence. Two CIA Advantage models are available. The CIA Advantage-T uses a mass-flow controller for accurate sampling of large volumes, making it ideal for analysing trace-level components. The CIA Advantage-HL model has the added capability of loop (low-volume) sampling, giving it the versatility to handle both high- and low-concentration samples (and for screening unknowns). These sampling options, together with the ability to split sample flows, mean that CIA Advantage systems can accommodate component concentrations ranging from ppt to low-percent levels. This is achieved while retaining the robust cryogen-free operation and outstanding analytical performance inherent to all Markes’ systems. In this article, we use four case studies to demonstrate the power and versatility of the CIA Advantage for canister analysis.
Case Study 1 – CIA Advantage analysis of ‘air toxics’ in accordance with US EPA Method TO-15
‘Air toxics’ comprise hazardous air pollutants ranging in volatility from freons to hexachlorobutadiene. They are usually present at sub-ppb or low ppb concentrations in air, requiring that the whole sample be transferred to the GC (a ‘splitless’ analysis), to ensure sufficient sensitivity.
Figure 1 shows the total ion chromatogram obtained from analysis of 1 L of a 1 ppb ‘air toxics’ standard using the CIA Advantage with GC and quadrupole MS in full-scan mode. The trap desorption efficiency is illustrated by the excellent peak shape of early-eluting components such as isopropanol.
A further benefit of the CIA Advantage for the analysis of these challenging samples is ‘backflush’ desorption of the focusing trap (for example, the direction of gas flow through the focusing trap during sampling is reversed during desorption). This makes it possible to use more than one sorbent in the focusing trap, allowing a wide volatility range of compounds to be quantitatively retained and efficiently desorbed/analysed.
In applications requiring analysis of both high- and low-concentration analytes in the same sample, it is important that both low-volume (loop-sampled) and high-volume (mass-flow- controlled) samples can be compared. To illustrate this, the CIA Advantage-HL was used to sample different volumes of the air toxics standard, and Figure 2 shows the response for each sample volume for eight representative compounds.
Figure 1. Total ion chromatogram for a 1 L standard containing 1 ppb air toxics, analysed splitless, cryogen-free and in full-scan mode using CIA Advantage with GC/MS (quad), according to US EPA Method TO-15. The inset shows the excellent Gaussian peak shape in an extracted-ion chromatogram of isopropanol (m/z 45)
Figure 2. Responses for loop sampling (at 0.5 and 2mL), and mass-flow-controlled sampling (at 25, 50, 100 and 200mL) for selected compounds from an air toxics standard, showing that a single curve can be fitted to both sets of points. Vertical scaling has been applied to some of the plots to allow them all to be shown on the same axes
INTERNATIONAL LABMATE - JANUARY/FEBRUARY 2012
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