Industrial and commercial VOC quantification

Selected ion flow tube mass spectrometry (SIFT-MS) instruments represent the latest generation in the long evolutionary path of analytical instruments. Delivering analysis of volatile organic compounds (VOCs) in whole-air samples, single-digit ppb detection limits and column-free operation, SIFT-MS is complementing existing GC-based analytical services as well as opening up entirely new services.

GC-based systems have long been the workhorses of many analytical laboratories. Over the decades these systems have evolved to meet the changing and increasingly demanding needs of laboratories and their customers. Despite this evolution, some frustrating operational characteristics and limitations have proved difficult to overcome. These difficulties include column selection and column discrimination, slow analysis times, complicated sample preparation and solvent use.

SIFT-MS, with its column-free 'no wait' operation and the ability to sample raw whole air, overcomes these difficulties. While GC-based analysis systems will always be good at identifying specific VOCs, the inherent strength of SIFT-MS lies in its relatively simple operation and ability to instantly and broadly screen raw whole-air samples, identifying which VOCs are present and quantifying them (in absolute terms).

Unlike GC systems that can analyse semi-volatiles and volatiles, SIFT-MS is strongest when analysing volatiles in the 10 to 300 amu range. This means SIFT-MS generally either complements existing GC-based services or opens up entirely new services, it is not intended as a straight GC replacement.

Examples of three ways SIFT-MS adds value include:

1. SIFT-MS can augment existing GC-based services. For example, SIFT-MS can rapidly pre-screen samples, determining if further analysis is required and if so which GC configuration should be used. Significant benefit is gained in high-throughput applications where rapid pre-screening can reduce the number of samples requiring relatively slow GC analysis.
2. In some cases SIFT-MS can replace GC-based systems, eliminating the costs and delays associated with sample preparation and columns, and drastically cutting turnaround times. Examples include light hydrocarbon analysis, where SIFT-MS delivers comprehensive C1 to C8 analysis in seconds.
3. SIFT-MS opens up entirely new services, especially in time-critical applications where real-time analysis or quick turnaround is a technical or economic necessity. Examples include population-based breath testing, detection of chemical warfare agents and explosives, and inline quality control on production lines.

How SIFT-MS works

SIFT-MS scans can be divided into five fundamental steps (see Figure 1):

1. Water vapour or air passes through a mi-crowave discharge, generating a mix of ions.
2. The ions are drawn through an upstream chamber where a quadrupole mass filters the ion stream, selecting precursor ions (H3O+, O2+, or NO+).
3. The precursor ions are injected into the flow tube where they flow in a helium and argon stream. Here they react with VOCs from the sample and form product ions.
4. Product ions stream into the downstream chamber and pass through a second quadru-pole, which filters the ions according to mass.
5. The remaining ions then pass to the particle multiplier (detector) where they are counted.

Chemical ionisation is one of the keys to the efficacy of SIFT-MS. Compared to other systems using harsher electron ionisation, chemical ionisation produces less fragmentation and a much 'cleaner' fingerprint for the compound being analysed. Consequently, SIFT-MS achieves its high specificity levels without columns and chromatographic separation. SIFT-MS uses three precursor ions because this allows a multifaceted analysis of the sample (each sample analyte can be reacted with each of the three ions and the results compared). This reduces the interference issues that plague single-ion analytical systems such as PTR-MS.

Real-world applications

SIFT-MS is not new; it has long been used by research organisations such as NASA and NOAA (National Oceanic and Atmospheric Administration). Its commercialisation, however, has been limited because until recently if you wanted a SIFT-MS instrument, you had to build your own and learn how to operate it. Recent world events (such as security threats, increased world trade, the emergence of drug resistant diseases, dwindling oil and gas reserves, and cut-throat competition in the manufacturing sector) have changed this.

Growing pressure for real-time analysis and quantification of trace gases has focused the economic and technical resources needed to professionally engineer robust and commercially-viable SIFT-MS instruments. This focus has seen SIFT-MS instruments go from unwieldy multi-ton beasts operated by PhDs, to compact instruments designed to fit seamlessly into standard commercial laboratory and industrial environments. The rapid progress made by SIFT-MS instruments is illustrated by the recently released Syft Technologies Voice100, an instrument with a 730 x 1000 mm footprint and the full suite of features expected of modern analytical instruments. Such instruments mean SIFT-MS is no longer the exclusive preserve of a select group of research scientists.

While SIFT-MS still has a lot to offer research scientists, its future will increasingly be driven by commercial and industrial applications, particularly those applications where rapid VOC analysis is critical or at least beneficial. Areas where SIFT-MS is already being used or trialled include:

• Detection and quantification of air pollutants, including benzene, toluene, xylene, 1,3-butadiene, formaldehyde and acetaldehyde.
• Detection and quantification of non-methane organic compounds (NMOCs) from landfill sites.
• Analysis of human breath for the detection of disease or residues from occupational exposures.
• Detection and quantification of residual fumigants.
• Detection of hydrocarbons in soil samples, for oil and gas exploration purposes.
• Rapid analysis of microbial cultures, to aid identification and minimise diagnosis times.
• Inline monitoring of industrial production and mixing processes.
• Detection of explosives and chemical weapons.

These applications are clearly the tip of a very large iceberg. With growing market penetration this exciting technology is sure to enhance many existing applications as well as pioneer new revenue streams. SIFT-MS: it's coming to a lab near you.