FAQ's

New and innovative technologies always raise questions. And at Syft we are happy to answer your questions. On this page we have posted answers for some of the questions we hear most often. Browse the short FAQs or click here to find more detailed downloadable FAQs.

Short FAQs

SIFT-MS Basics

What sensitivity and accuracy do the Syft SIFT-MS instruments have?

Our SIFT-MS instruments can currently quantitatively measure volatile organic compounds (VOCs) to better than 100 pptv (parts per trillion by volume) in dry or humid whole-air samples, with high accuracy.

How does SIFT-MS distinguish between compounds of the same mass?

By using multiple reagent ions, SIFT-MS is usually able to distinguish compounds of the same mass. Often there is at least one reagent for which the compounds have readily distinguishable products. Consider the following examples:

Propanal (or propionaldehyde) and acetone (C3H6O; mass 58) are easily distinguished by using the NO+ reagent ion, which yields product ions with different masses when reacted with these compounds

Ethanol (C2H6O; mass 46) and formic acid (CH2O2; mass 46) are also easily distinguished by using the NO+ reagent ion, as the latter does not react with NO+.
Note that neither of these pairs of compounds will be distinguishable using a technology such as proton transfer reaction mass spectrometry (PTR-MS), which uses only an H3O+ reagent ion. In the first and second examples, both compounds have a product at masses 59 and 47, respectively, when reacted with H3O+.

When referring to parts-per-million or parts-per-billion, is Syft quoting in mass units (e.g. µg L -1) or volume units (e.g. nL L-1)?

SIFT-MS provides absolute quantification in real-time in units of parts-per-billion by volume (ppbv). It is, however, a SIFT-MS convention to drop the "v" when reporting results. So SIFT-MS results are normally reported in ppb or ppm units. Users can re-instate the "v" if they wish.

This confusion often arises when comparing SIFT-MS to gas chromatography (GC). SIFT-MS, unlike GC, is a continuously sampling whole-gas analyser. SIFT-MS natively measures the instantaneous concentration of VOCs in the sample, rather than a value that corresponds to a bulk mass or volume of sample injected into the instrument.

Is SIFT-MS equally sensitive to all volatile organic compounds (VOCs)?

No, but most VOCs do react with at least one reagent ion at rates fast enough to enable quantitation at pptv levels.

Methane is the most significant analyte to which SIFT-MS shows low sensitivity. Methane has a small rate coefficient with O2+ and does not react at all with H3O+ and NO+. Its detection limit is about 2 ppmv.

Do acidic compounds such as NOx and SO2 cause problems for SIFT-MS?

Acidic gases such as NOx and SO2 should not pose problems to Syft Technologies' SIFT-MS instruments, unless the gases are concentrated.

Is it possible to sequentially scan a range of masses on the quadrupole mass filter so that product ions of unknown compounds can be detected even if they are not yet ‘calibrated’ for SIFT-MS?

Yes. Our software allows product masses of unknown analytes to be monitored in selected ion mode (SIM). Once the compound has been identified and "calibrated" (either with a standard concentration or by determination of its reaction rate coefficient and product ion distribution), it can easily be quantified. Moreover, semi-quantitative estimates of concentration can be made from earlier full mass scans or SIM scans.

Can Syft Technologies' SIFT-MS instruments use negative reagent ions to analyse for compounds with high electron afinity?

Yes. For example, Voice200 series instruments can include a negative-ion source, and utilises reactions of O2- for the quantitative measurement of sulfuryl fluoride. A number of other negative-ion applications are under development.

What are the general application areas where SIFT-MS can be used?

SIFT-MS is an analytical technique that has a diverse range of applications due to:

Its real-time quantitative analysis capability
Limits of quantitation down to 50 pptv
The absence of discrimination against compounds of different types (e.g. alkanes and aldehydes can be analysed simultaneously with no configuration changes)
Its ability to analyse most compounds in the presence of water vapour.
Examples of applications include:

Fumigant detection
Food, flavour and fragrance analysis
Breath research and population breath screening
Microbial detection and profiling
Detection of hydrocarbons in surface prospecting , mudlogging and other well drilling applications
Environmental air monitoring
Industrial stack emission analysis
Emission testing of motor vehicles
Occupational safety and health / Industrial Hygiene compliance
Homeland security.

Furthermore, Syft Technologies' SIFT-MS instruments can analyse whole-air samples (e.g. from breath or ambient air, sample bags, SUMMA canisters and headspace vials) and from preconcentrated samples (e.g. thermal desorption tubes and SPME fibres).

Sample formats for SIFT-MS

What forms of sample can conveniently be analysed by SIFT-MS?

Direct sampling of ambient air and breath is straightforward for SIFT-MS, as is sampling from containers such as sample bags, headspace vials and SUMMA-type canisters. Instruments can also be incorporated into automated sampling systems and industrial production systems.

Analysis performed on our instruments is generally independent of the sample humidity. Therefore no sample preconditioning whatsoever is required.

Is SIFT-MS compatible with thermal desorption?

Yes. Our SIFT-MS instruments can provide quantitative analysis from thermal desorption tubes.

What sensitivity does thermal-desorption SIFT-MS have?

The sensitivity increases based on:

1. A larger volume of air being sampled
2. Detection of only a few compounds.

The reason for the latter is that the pulse of sample passed from a thermal desorber to an analytical instrument is short. For SIFT-MS, the pulse of VOCs must be analysed for all compounds very rapidly, whereas for GC-MS the chromatographic separation allows analytes to be detected sequentially as they are separated without overloading the mass spectrometer.

Hence the sensitivity of the thermal-desorption SIFT-MS analysis is reduced as the number of analytes increases.

Care must also be taken in thermal-desorption SIFT-MS that a safe level of preconcentration is used. This level is often lower than the safe-sample-volumes (SSVs) quoted in the thermal desorption literature. Too much sample (including reactive species that are not being analysed) can easily take the reagent ion signal outside of the linear regime (i.e. more than 10% of the reagent ion is reacted away). Hence a SSV has to be determined in a given application.

Thermal-desorption SIFT-MS sensitivity is very much application specific.

How easy is it to switch between whole-gas and thermal desorption sample introduction when using Syft Technologies' SIFT-MS instruments?

It is very easy to switch sample introduction modes. If using one of our instruments with thermal desorption, we recommend the instrument be configured with two inlets: a thermal desorber inlet (which will often be a GC-type injector) and the standard whole-gas sampling inlet. This hardware configuration allows direct sampling of breath, headspace, ambient air and bagged samples, as well as thermal desorption analysis.

Switching between sample introduction modes is a simple point and click software process. Hardware reconfiguration is not necessary.

Can SIFT-MS analyse liquid samples?

At the present time SIFT-MS cannot analyse liquids by direct injection into the inlet.
SIFT-MS instruments can, however, analysis the headspace above liquids. This is due to the ability of SIFT-MS to analyse most VOCs in the presence of high water vapour concentrations. The concentration of each VOC in the aqueous solution is determined by using the Henry's Law coefficient, which describes how the VOC is partitioned between the headspace and the aqueous phase.

Can solvent extraction sorbent methods be used with SIFT-MS?

No. Extractions almost invariably involve organic solvents, to which the instrument is highly sensitive. The solvent saturates the instrument so that the analytes cannot be detected.

See also the answer to the preceding question regarding the analysis of liquids by SIFT-MS.

Is Solid-Phase Microextraction (SPME) compatible with Syft Technologies' SIFT-MS instruments?

Yes. Certain forms of SPME can be used with SIFT-MS. Fibre coatings containing adsorbent particles (such as Carboxen/PDMS), work well with our instruments.
Sufficient sensitivity is not obtained using single fibres made of purely absorbent coatings, such as poly(dimethylsiloxane) (PDMS). However, by using a larger volume of absorbent material (e.g., multiple fibres) the sensitivity can be improved significantly.

Injector ports are supplied as optional extras for SIFT-MS instruments to be used with SPME.

Can Syft Technologies' SIFT-MS instruments perform stack emission analyses for VOCs in a manner similar to that described in US EPA Method 18 for GC?

Yes. Our instruments are ideally suited to real-time whole-air analysis of VOCs (and some inorganic gases, such as water, ammonia, nitrogen dioxide and ammonia) from low ppb to about 1%. As such, our instruments can be used (via a suitable heated transfer line) to directly sample and analyse in real time from an emission source. Alternatively, remote samples can be taken in sample bags and returned to the laboratory for analysis.

Is SIFT-MS able to analyse for organic pesticides?

Many organic pesticides are semi-volatile organic compounds (SVOCs). Only some have a volatility that makes them appropriate for SIFT-MS analysis.

Can SIFT-MS detect and quantify polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and dioxins?

These compounds are all semi-volatile organic compounds (SVOCs) and as such their volatility is often too low for analysis by SIFT-MS.

What odorous and flavour compounds can Syft Technologies' SIFT-MS instruments detect?

Any flavour compounds that are sufficiently volatile. Some examples of odorous compounds our instruments can detect are:

Hydrogen sulfide, methyl sulfide, dimethyl sulfide, dimethyl disulfide and other thiols and thioethers
Aldehydes, ketones, alcohols, volatile carboxylic acids (saturated and unsaturated) and esters
Ammonia and amines (primary, secondary and tertiary)
Terpenes and terpeneols.

Human and Animal Health Applications

How are breath samples measured directly with Syft Technologies' SIFT-MS instruments?

Measurements from breath are usually made from a slowly exhaled breath (about 10 seconds in duration), and then averaged over several breaths.

Ethane is regarded as an important marker of oxidative stress. Can it be detected using SIFT-MS instruments?

SIFT-MS can detect and quantify ethane readily in dry air at low ppbv levels and at ppm levels in moist samples. However, at present, when it occurs at sub-ppbv levels it is not reliably detectable, due to complex chemistry.

Can Syft Technologies' SIFT-MS instruments detect NO in breath?

Yes. Although this requires careful subtraction of background levels of NO to get the subject's true NO reading.

Can Syft Technologies' SIFT-MS instruments profile organic compounds in breath?

Yes. The best way to do this is to collect the breath in an inert sampling bag (e.g. Tedlar, Flexfilm or Teflon) and analyse it immediately using full mass scans with all three SIFT-MS reagent ions. Any delay in analysis means that the reactive compounds begin to decay.

Direct breath measurements are ideally suited to selected ion mode (SIM) analysis, as temporal variations are monitored with ease.

Competitors

What are the benefits of SIFT-MS over PTR-MS?

SIFT-MS and PTR-MS are relatively similar techniques in that they are both direct MS VOC analysis techniques, but there are some important differences. These are discussed in the White Paper A Comparison of SIFT-MS and PTR-MS. See below for a pdf version of the document.
 

DOWNLOADABLE FAQ's
 

(79 KB PDF) Which Compound Classes can be analysed with SIFT-MS?

(85 KB PDF) How does PTR-MS differ from SIFT-MS