SIFT-MS SELECTED ION FLOW TUBE MASS SPECTROMETRY TECHNOLOGY OVERVIEW

Transcription

1 SIFT-MS SELECTED ION FLOW TUBE MASS SPECTROMETRY TECHNOLOGY OVERVIEW

2 NEXT GENERATION MASS SPECTROMETRY CONTENTS: 3 How SIFT-MS works 4 Soft chemical ionisation 5 Quantification in real-time 6 Utilising multiple precursor ions 7 Discriminate isobaric compounds and isomers in real-time In this guide we ve pulled together the essential concepts and principles of SIFT-MS. We have produced the guide specifically to give you an introduction to the technology behind our leading-edge SIFT-MS solutions. Of course we have a lot more information on how SIFT-MS and our products operate and deliver market-leading solutions. If you would like to know more or have any questions, we invite you to contact us or visit our website at You ll find our contact details on the back of this guide. Whether you need a turnkey solution or a leading-edge analytical instrument with proven flexibility, Syft Technologies has the technology and experience you re looking for. 2

3 HOW SIFT-MS WORKS NEXT GENERATION MASS SPECTROMETRY: IDENTIFY COMPOUNDS IN REAL-TIME QUANTIFY COMPOUNDS IN REAL-TIME SENSITIVITY AS LOW AS PPTV PUSH-BUTTON SIMPLICITY CONTINUOUS OR BATCH SAMPLING REAL RESULTS IN REAL-TIME SIFT-MS (Selected Ion Flow Tube Mass Spectrometry) uses chemical ionisation to analyse volatile compounds, either from whole-air samples or concentration media such as sorbent tubes. By combining gas-phase ion chemistry and tightly controlled reaction conditions, SIFT-MS has the unique ability to provide absolute concentrations for analytes, in real-time. Analytes can generally be detected and quantified within the 1 to 24 Da mass range, although this range is increasing with advances in the field. 5 4 THE SIFT-MS PROCESS CAN BE DIVIDED INTO FIVE MAIN STEPS. 1. Generation of ions Syft Technologies SIFT-MS instruments use either a microwave discharge or radio frequency (RF) source to generate positive ions. 2. Ion selection The ions enter an upstream chamber where a quadrupole mass filter removes all but the preferred precursor ions. Generally H 3 O +, NO + + and O 2 are selected as precursor ions. 3. Sample introduction and reaction The precursor ions pass through a venturi to a reaction chamber the flow tube where they react with sample, which enters the flow tube at a precisely controlled rate. 4. Selection of reaction products The reaction products enter a downstream chamber where they are filtered by a second quadrupole mass filter. 5. Detection A particle multiplier detects and counts the selected products. The use of thermalised ions combined with a good understanding of flow tube dynamics, well documented ion chemistry, dual quadrupoles and automated database matching systems, allows SIFT-MS to deliver real-time absolute quantification, without chromatographic separation or elaborate sample preparation

4 SOFT CHEMICAL IONISATION THE PRIMARY ADVANTAGES OF SOFT CHEMICAL IONISATION: Less analyte fragmentation, which yields simplified spectra, meaning lower interference and more accurate results No need for chromatographic columns, meaning lower running costs, real-time analysis and more analyses per hour Not all forms of ionisation are equal As with all mass spectrometry, SIFT-MS uses ionisation in the analysis process. But unlike many older forms of mass spectrometry, such as GC-MS, SIFT-MS uses relatively soft chemical ionisation. Electron Impact Ionisation SIFT-MS uses chemical ionisation because it minimises the fragmentation issues associated with harsher forms of ionisation (such as electron impact ionisation). Fragmentation occurs when harsh ionisation processes create fragment masses of the compounds that are being analysed. These fragments lead to complicated mass spectra with overlapping peaks, which make costly and time-consuming chromatographic separation necessary. SIFT-MS Soft Chemical Ionisation In contrast to harsh ionisation methods, the relatively soft chemical ionisation process used by SIFT-MS produces a significantly cleaner mass spectrum, minimising interference issues. This cleaner mass profile and reduced interference yields high accuracy and resolution without costly and timeconsuming chromatographic columns. THE RESULT The chemical ionisation used by SIFT-MS allows quick high-resolution analysis, without chromatographic columns and their associated sample preparation, costs and delays. An example The following two spectra are analyses of the common pollutant ethylbenzene. The first analysis (Figure 1) used electron impact ionisation and shows characteristic interference-generating fragmentation. The second analysis (Figure 2) used chemical ionisation with H 3 O + and shows a typically clean SIFT-MS spectrum with ethylbenzene at mass 17. Intensity/counts per second Intensity/counts per second Figure 1. Electron impact ionisation analysis of ethylbenzene Figure 2. Chemical ionisation H 3 O + analysis of ethylbenzene

5 QUANTIFICATION IN REAL-TIME THE PRIMARY ADVANTAGES OF REAL-TIME QUANTIFICATION: See which compounds are present and their absolute concentrations (not just their relative concentrations), in real-time See processes and reactions dynamically, as they happen Run more analyses per hour, instead of waiting for results What is quantitative analysis? Quantitative analysis determines the concentrations of analytes. The concentrations can be relative (where the concentration of an analyte is presented as a percentage of all analytes present) or absolute (where the true concentration is determined). Qualitative analysis (as opposed to quantitative analysis) simply identifies the presence or absence of an analyte, perhaps with a rough estimation of concentration. SIFT-MS provides absolute quantitative analysis in real-time, unlike other methods that also use chemical ionisation. How is real-time quantitative analysis possible? Gas-phase ion chemistry allows absolute quantitative analysis of trace gases, provided the host instrument s reaction chamber conditions are precisely controlled. SIFT-MS is the only mass spectrometry technology that provides this level of control, offering an unprecedented ability to detect trace compounds and quantify them absolutely in real-time. This high degree of control is obtained by: (i) introducing thermalised precursor ions into the reaction chamber (the flow tube) (ii) understanding the physical dynamics of the flow tube, including the reaction time (iii) having a comprehensive knowledge of the ion chemistry occurring in the flow tube for each analyte. As with all analytical techniques, SIFT-MS uses a type of pattern matching database to identify analytes. This database holds information on how rapidly an analyte reacts with the precursor ion (the rate coefficient for the reaction), the products of the reaction and their relative abundances. The SIFT-MS database is unique in that it identifies analytes and provides the means by which they are quantified, in real-time. The database is accessed directly and seamlessly from the instrument s control software. THE RESULT With its instantaneous and absolute determinations of concentrations, SIFT-MS is an ideal on-line or continuous process analysis tool for gas and headspace sampling. Its rapid sampling capability also makes SIFT-MS a valuable addition to busy commercial laboratory lineups. 5

6 UTILISING MULTIPLE PRECURSOR IONS THE PRIMARY ADVANTAGES OF MULTIPLE PRECURSOR IONS: See more analytes in your samples, even those that don t react with an individual precursor or react poorly Discriminate isobaric compounds and isomers Enhanced compound resolution over single precursor techniques such as PTR-MS and ACPI-MS. What s a precursor ion? A precursor ion is an ion used to chemically ionise a sample during an analysis process. SIFT-MS uses multiple precursor ions to extend the range of compounds that can be analysed, while less sophisticated methods use a single precursor ion. Single Precursor Scans Methods that use a single precursor ion are limited to seeing those analytes that react with the precursor to form products with a unique mass. If the reaction is poor or forms isobaric compounds or isomers, accurate results for the analyte cannot be reported. Figure 1 shows a typical result for a proton transfer reaction mass spectrometry (PTR-MS) scan of industrial combustion products. PTR-MS uses the single precursor ion H 3 O +. Significant compounds identified in the H 3 O + spectrum include: methanol (m/z = 33, 51, 69), acetaldehyde (m/z = 45, 63, 81), ethanol (m/z = 47, 65, 83), acetone and propanal (m/z = 59, 77), and benzene (m/z = 79). Counts/second Multiple Precursor Scans A SIFT-MS scan, which can apply multiple precursor ions (in this example H 3 O +, NO + and O 2+ ), produces the H 3 O + spectrum plus these spectra: Counts/second NO+ m/z NO + Precursor Scan Results The NO + precursor identifies propanal (m/z = 57), formamide (m/z = 75), and acetone (m/z = 88), plus confirms benzene (m/z = 78, 18) O2+ m/z O 2 + Precursor Scan Results The O 2 + precursor identifies ethylene (m/z = 28), nitrogen dioxide (NO2) (m/z = 46), and methane (m/z = 47). These additional compounds are not reported by methods that use H 3 O + as a single precursor ion. Counts/second 5 4 H3O m/z H 3 O + Precursor Scan Results THE RESULT SIFT-MS delivers more accurate identification and quantification of analytes, including isobaric compounds and isomers, and compounds that react poorly with any one precursor ion. 6

7 DISCRIMINATE ISOBARIC COMPOUNDS AND ISOMERS IN REAL-TIME THE PRIMARY ADVANTAGES OF REAL-TIME DISCRIMINATION: See individual analytes in your samples, not just summed totals for everything that happens to share a mass See isobaric compounds and many isomers in one seamless automated scan, with no need to run multiple scans or change columns Run more scans per hour The power of multiple precursor ions Analytes that share the same mass (isobaric compounds) or compounds that share the same mass and chemical formula (isomers) simply cannot be discriminated by methods that use only one precursor ion. Relative intensity (%) For example, proton transfer reaction mass spectrometry (PTR-MS), which uses H 3 O + as its sole precursor ion, cannot discriminate the common compounds acetaldehyde and ethylene oxide. Figure 1 shows a typical PTR-MS analysis spectrum for a sample that contained acetaldehyde and ethylene oxide. Figure 1. A PTR-MS H 3 O + analysis. Acetaldehyde and ethylene oxide share mass Acetaldehyde and ethylene oxide Relative intensity (%) Relative intensity (%) SIFT-MS, with a seamless application of H 3 O +, NO + and O 2 + precursor ions, adds these two spectra to the results: + Figure 2. A SIFT-MS O 2 analysis. An improvement but still not definitive. Acetaldehyde and ethylene oxide share mass 44, with acetaldehyde products also at mass Acetaldehyde and ethylene oxide Acetaldehyde Figure 3. Clear discrimination. A SIFT-MS NO + analysis with acetaldehyde at mass 43 and ethylene oxide at mass Acetaldehyde Ethylene oxide THE RESULT From one integrated scan process, SIFT-MS provides clear, real-time discrimination of isobaric compounds and many isomers. Now you can see individual compounds even if they are isobarics or isomers. 7

8 THE VOICE SERIES ONLY VOICE SERIES SIFT-MS INSTRUMENTS OFFER THIS COMBINATION OF ADVANTAGES: Real-time results ppb and ppt sensitivity High-accuracy, laboratory-grade results Instant and seamless switching between multiple precursor ions Discrimination of isobaric compounds and isomers Whole-air sampling (no sample preparation) Does not require chromatographic separation Direct analysis of high-moisture samples (such as breath) Push-button simplicity Full training and support programmes, worldwide Copyright 27 Syft Technologies Ltd BCR Syft Technologies Head Office 3 Craft Place, Middleton PO Box Christchurch, New Zealand Phone: +64 (3) Fax: +64 (3) Syft Technologies European Office Daresbury Innovation Centre, Suite F19 Daresbury, Cheshire WA4 4FS Phone: Fax: Global Contact Info@syft.com Website: