Both handheld and stationary ion mobility spectrometers (IMS) were used to monitor ambient air containing dangerous concentrations of dimethyl sulfate (DMS). The Bruker Rapid Alarm and Identification Device (RAID) series of instruments achieved detection limits below the workplace exposure limits and permit the detection of DMS at concentrations down to 4 ppb (0.02 mg m-3) within a few seconds.

Introduction

DMS is the diester of methanol and sulfuric acid (Figure 1). Because of its high reactivity, DMS is widely applied as a low cost methylating agent in industrial processes. Additionally, it is also one of the most important primary products used in the personal care and pharmaceutical industries as well as agriculture industries.

Application Note #CBRNE - 1838036

Using Bruker RAID instruments to monitor Occupational Exposure Limits to Dimethyl Sulfate

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Authors

Conny Fraas, Franziska Lange, Johannes Flachowsky, Thomas ElßnerBruker Daltonik, Leipzig, Germany

Keywords Instrumentation & Software

Ion mobility spectrometry RAID-M 100

Dimethyl sulfate (DMS) RAID-AFMPlus

Occupational exposure limits TIMON

XIMS PLUS 1.0Dimethyl sulfate

Figure 1: Chemical structure of DMS.

As with other highly reactive alkylation reagents, DMS is very toxic and can cause carcinogenic and mutagenic effects [1]. Without protective equipment, exposure to DMS can result in inhalation or direct skin adsorption and its effects on the body can go unnoticed for a few hours. DMS does not irritate the eyes or skin and has no characteristic odor, so exposure to harmful concentrations might not be immediately obvious. Because this delayed, high toxicity aspect can result in fatal injuries, the handling of DMS is subject to strict guidelines, and exposure limits have been defined worldwide (Table 1).

The prescribed detection methods for the workplace, according to the Deutsche Gesetzliche Unfallversicherung (DGUV) [6] and the National Institute for Occupational Health (NIOSH) [7], are both complex and time consuming. These methods are based on the adsorption of DMS on TENAX®, the thermodesorption or elution from this adsorbent, subsequent separation by gas chromatography (GC) and finally, detection, using a mass spectrometer (MS) or an electron capture detector (ECD).

A faster, simpler, less complex technique for the direct detection of DMS, using an IMS device to measure DMS levels below the exposure limit, is presented in this application note.

Experimental

A Bruker RAID-M 100 hand-held, battery powered, ion mobility spectrometer with a 100 MBq 63Ni ionization source was used to determine the dynamic range for DMS.

RAID-AFMPlus

Figure 2: Stationary ion mobility spectrometer RAID-AFMPlus.

DMS (CAS: 77-78-1) used for calibration was purchased from Sigma Aldrich GmbH (Steinheim, Germany).

For preparation of a calibration curve, DMS was dissolved in hexane (2 mg m-3). To achieve different gas concentrations, defined volumes (1 – 100 µL) of the hexane solution were injected into a gas sampling tube, which was purged with clean air prior to the introduction of each sample. Spectra were acquired using Bruker IMS software; XIMS PLUS 1.0.

A Bruker Rapid Alarm and Identification Device Automated Facility Monitor (RAID-AFMPlusTM) (Figure 2) equipped with a photo ionization source was used to verify the results achieved with the RAID-M 100. Equally, a Bruker Toxic Industrial Monitor (TIMONTM) system could have been used.

Results

The introduction of DMS to the RAID-M 100 results in a single substance-specific signal in the negative polarity at a drift time of 9.0 ms (reduced mobility of K0 = 1.97 cm2 V-1 s-1,Figure 3A). The second peak at a drift time of 7.8 ms is the instrument specific water oxygen ion cluster (reactant ion peak in the negative mode – RIN; K0 = 2.30 cm2 V-1 s-1). In autonomous mode, the instrument software can identify DMS automatically based on this substance-specific ion peak. The resulting one peak system enables the detection of DMS in less than 10 seconds (Figure 3B).

For a quantitative output, a bar reading is integrated in the display; one to eight bars correspond to specific concen-tration areas.

Ricin detection in solid and fluid samples

Table 1: Selection of occupational exposure limits worldwide

Occupational exposure limits

Country

(organization)

Exposure limits

[ppm]

Exposure limits

[mg m-³]

Germany (BMJV1) [2] (0.022) (0.12)

USA (NIOSH3) [3] 0.1 0.5

USA (OSHA4) [3] 1 5

United Kingdom (HSE5) [4] 0.05 0.26

Japan (JSOH6) [5] 0.1 0.52

1BMJV … Federal Ministry of Justice and Consumer Protection2Former TRK value (technical guiding concentration) for production. From 2010 classified as an extremely toxic carcinogenic material and allowed to be used and produced in closed systems only.3NIOSH … National Institute for Occupational Safety and Health 4OSHA … Occupational Safety and Health Administration5HSE … Health and Safety Executive6JSOH … Japan Society for Occupational Health

IMS spectrum and spectra series of DMS

Figure 3: IMS spectrum and spectra series of DMS visualized by means of the software XIMS plus 1.0.A: 2D spectrum of a DMS measurement shows one peak for DMS and the RIN (reactant ion negative). B: 3D plot shows fast instrument response (below 10 s) and recovery (approx. 10 s).

Web interface of the RAID-AFMPlus

Figure 5: Web interface of the RAID-AFMPlus showing detected DMS with a concentration of approx. 16 to 20 ppb (4 of 8 bars).

Figure 4: Display output of the RAID-M 100 showing detected DMS of a concentration of approx. 16 to 20 ppb (4 of 8 bars).

Figure 4 and 5 show examples of display outputs for a handheld (instrument display) and a stationary instrument (web interface at connected personal computer) at a concentration of 16 to 20 ppb of DMS, respectively.

The lowest detectable DMS concentration in ambient air is 4 ppb (0.02 mg m-3) [8]. This high sensitivity is significantly better than the lowest required occupational exposure limits (cf. Table 1). Further test measurements showed a fast instrument recovery (about 10 s) after substance detection (cf. Figure 3B). To protect this very sensitive instrument against an overload, back flush mode starts automatically at high gas phase concentrations. The gas flow direction

is changed and cleaned air, derived from a specially con- structed cleaning filter, flushes the sample introduction area to remove all chemical residues. The response time in seconds and a very high sensitivity makes Bruker RAID instruments

Display output of the RAID-M 100

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Bruker DetectionDivision of Bruker Daltonik GmbH

Leipzig · GermanyPhone +49 (341) 2431-30 Fax +49 (341) 2431-404 detection@bruker.comwww.brukerdetection.com

Bruker DetectionDivision of Bruker Daltonics Ltd.

Coventry · United KingdomPhone +44 (2476) 855-200Fax +44 (2476) 465-317detection@bruker.comwww.brukerdetection.com

Bruker Detection Corp.

Billerica, MA · USAPhone +1 (978) 663-3660Fax +1 (978) 667-5993 detection@bruker.comwww.brukerdetection.com

References

[1] Carsten Schmuck, Bernd Engels, Tanja Schirmeister, Reinhold Fink: Chemie für Mediziner, Pearson Studium - Medizin, p. 457[2] The MAK-Collection for Occupational Health and Safety, Part I: MAK Value Documentations, Vol. 27, 2012[3] NIOSH pocket guide to chemical hazards, 2007, p. 116[4] EH40/2005 Workplace exposure limits, Health and Safety Exe-cutive, UK, second edition, 2011, p. 17[5] Recommendation of Occupational Exposure Limits, J Occup Health, Vol. 53, 2011, p. 398

[6] DGUV Information 213-507 - Verfahren zur Bestimmung von Dimethylsulfat. http://www.arbeitssicherheit.de/de/html/library/law/5004647%2C1%2C20061001 (accessed June 17, 2015)[7] NIOSH Manual of Analytical Methods. http://www.cdc.gov/niosh/docs/2003-154/pdfs/2524.pdf (accessed June 17, 2015) [8] Johannes Flachowsky, Joachim Stach, Michaela Brodacki: A fast detection method of dimethyl sulfate in chemical plants using hand held ion mobility spectrometers (RAID-M), Intern. J. of Ion Mobility Spectrometry, Vol 6, 2003, p. 2

ideally suited as detection devices for the monitoring of DMS exposure limits. All data collected by the RAID-M 100 can also be transferred, without any correction, to the RAID-AFMPlus (cf. Figure 2) or TIMON instrument.

The RAID-M 100 or the RAID-AFMPlus can be used as DMS monitors in different fields of the chemical industry. Major applications for the handheld instrument are the monitoring of leakages and hence the exposure limit during production processes. Additionally, this instrument can be used routinely to test the security of DMS storage containers, portable tanks or pipelines. Figure 6 shows the inspection of a tank for a DMS contamination using a RAID-M 100.

In the case of a positive result (alarm) the container is decontaminated by an ammoniacal solution and the measurement procedure repeated.

For permanent 24/7 detection in a fixed area (e.g. workplace monitoring) the stationary instruments, RAID-AFMPlus or TIMON, are the better choice. Both of these installed instruments can be protected by either explosion proof housings or by pressurized enclosures intended for use in potentially explosives atmospheres according to the directive 94/9/EC (EC-Type Examination Certificate: BVS 14 ATEX E 050).

Conclusion

The RAID-M 100, RAID-AFMPlus , and the TIMON are ideally suited for the ambient air monitoring of a DMS exposure, and DMS can be detected at low ppb levels within a few seconds. The minimum detectable DMS concentration (4 ppb, 0.02 mg m-3) is lower than the required international occupational exposure limits.

The battery operated, lightweight, handheld RAID-M 100 is ideal for mobile leak detection applications, whereas the stationary RAID-AFMPlus or TIMON are best suited for a 24/7 workplace monitoring because of their low maintenance requirements; service intervals in the order of 18 months are the norm.

Tank inspection using RAID-M 100

Figure 6: A portable pressure tank UN T14 (CCR) is inspected by the RAID-M 100. The alarm LEDs indicate a DMS contamination.

Tank inspection using RAID-M 100