Instrumentation for Trace Organic Monitoring

Raymond E. Clement

• Publisher: CRC Press
• Year: 2018
• Print ISBN:
  9781315894621
• eBook ISBN:
  9781351090629
• Topic: Ciencias físicas
• Subtopic: Química

Instrumentation for Trace Organic Monitoring provides comprehensive coverage of instrumental analysis techniques for trace organic analytes in environmental analysis. Sampling/sample preparation is discussed, in addition to mass spectrometry techniques, including GC-MS, HRMS, LCMS, APIMS, and MS-MS. This important book also covers new chromatography techniques, supercritical fluid, solid-phase extraction, and ion mobility spectrometry, which is a new ultra-sensitive technique. Difficult problems, such as dioxin/furan analysis, organometallic speciation, atmospheric organic vapors, water analysis, and flyash toxicity testing are addressed.

chapter 1

New Applications for Ion Mobility Spectrometry Detection Techniques

A. H. Lawrence and L. Elias

The search for trace organic substances in complex organic and inorganic matrices is one of the most challenging tasks facing analytical chemists today. The presence of trace contaminants affects all aspects of our lives: the water and food we ingest, the air we breathe, the quality of the goods we produce, the environment in which we work and live—in short, our day-to-day health and security. The chemists’ ability to discern these trace contaminants, which in one form or other may signify a hazard to human welfare, has been largely due to the development of highly sensitive and selective analytical instruments.

Modem instrumental analytical chemistry can be divided into two distinct categories: the first one comprises very powerful and versatile laboratory instrumentation designed for fixed-facility use and the detailed analysis of complex mixtures, e.g., GC/MS, GC/FTIR, tandem MS, etc., and the second one involves portable or easily transportable devices which are intended for field use and the detection of specific target compounds.

The Trace Vapour Detection Section of the Applied Aerodynamics Laboratory has been involved for a number of years in a program aimed at the development of rapid on-site sampling and analysis techniques for trace organic detection. This laboratory developed a portable gas chromatograph (GC) explosives detector which was subsequently transferred to industry and is now in use at all Canadian international airports.¹ In addition, a GC-based trace narcotics detector has also been developed and field tested; expected to be in production soon, the instrument is designed to detect cocaine and heroin residues in less than 2 min.²

Recently, we have investigated the feasibility of ion mobility spectrometry (IMS) as a viable field technology for trace organic detection and monitoring. Our decision was influenced by the fact that IMS offers distinct advantages, namely, good sensitivity (subpart-per-billion levels), fast response time (0.1 to 10 sec), and operation at atmospheric pressure.

Ion Mobility Spectrometry

The operation of an IMS is analogous to the operation of a time-of-flight mass spectrometer (TOF-MS), the main difference, however, being that the TOF-MS operates under vacuum whereas the IMS operates at atmospheric pressure.

The ion mobility spectrometer is comprised of a heated inlet, an ion-molecule reaction chamber containing a radioactive source or a photoionization source, an ion drift chamber, a shutter grid interposed between the reaction and drift chambers, and an ion collector (Figure 1). The sample, in vapor form, is introduced into the ion reaction chamber by means of a carrier gas (usually nitrogen or air). Trace impurities, such as water and ammonia present in the carrier gas, are ionized by the energetic electrons released from the radioactive source and a number of positive and negative reactant ions are formed, such as (H₂O)_nH⁺ and (H₂O)_nO₂^-. These reactant ions undergo a complex series of ion-molecule reactions with the analyte, and product ions are formed. Depending on the polarity of an applied electric field, either positive or negative ions are periodically pulsed into the drift region through the gated shutter grid. In the drift region, the ions travel towards the collector through a drift gas while under the influence of the electric field. In doing so, they separate into their individual species due to their different mobilities; the transit time of a pulsed ‘packet’ of ions is generally in the order of 20 ms. A total ion mobility spectrum of ion current versus drift time can be generated in less than 5 sec. IMS results are usually reported in terms of drift time (millisecond) or the reduced mobility constant, K₀(cm²V^-1sec^-1), according to Equation 1:

Ko=d/t⋅E(273/T)(P/760)⁢(1)

where t is the drift time of the ion in seconds, d is the drift length in centimeters, E is the electric field strength in volts per centimeter, P is the drift gas pressure in torr, and T is the drift gas temperature in degrees Kelvin.³

Figure 1. Schematic of ion mobility spectrometer.

The IMS data presented in this chapter were obtained with a Phemto-Chem 100 ion mobility spectrometer (PCP Inc., West Palm Beach, FL) which contains a ⁶³Ni radioactive source, and the experimental parameters used to operate the instrument (unless indicated otherwise in the figure captions) were the same as those presented in Table 1.

Applications Research

Although IMS has received considerable attention as a laboratory technique, it has not achieved, in our opinion, its full potential as a dedicated instrument intended for field use. We have investigated a number of interesting field applications which appear suited for IMS, as outlined below.

Detection of Hidden Bombs

A study was carried out by this laboratory on the detection of ethylene glycol dinitrate (EGDN)—the most volatile effluent in dynamite formulations—using IMS.⁴ EGDN, like other organonitrates, is electronegative in character and readily forms negative ions in IMS, but undergoes dissociative electron capture reactions and does not produce a stable molecular anion. Instead, an ion peak with a reduced mobility of 2.46 to 2.48 cm²V^-1sec^-1 is produced, corresponding to the fragment ion (NO₃) (see References 5 and 6) as in Equation 2.

O2NO−CH2−CH2ONO2→ΔN2O2−×NO3−+(M−×NO3)⁢(2)

This peak overlaps significantly with the peak associated with the reactant ions when air or nitrogen is used as the carrier gas, thus restricting its usefulness as an IMS marker for identification purposes.

It was shown that the addition of trace amounts of Cl reagent ion to the carrier stream results in increased ionization specificity and leads to the formation of a stable ion cluster (EGDN-C1)^- of m/z 187, which is well separated from the region of the reactant ions in the ion mobility spectra (Figure 2)⁴; in a separate set of experiments, the mass associated with the spectral peaks was determined by coupling the IMS to a quadrupole mass spectrometer. Using a double-dilution vapor source and a sample collection/injection technique developed in this laboratory,⁷,⁸ the minimum detectable quantity of (EGDN-CL)^-, recorded at a signal amplitude of three times the lo- noise, was determined to be 30 pg. The sensitivity obtained and speed of response observed pointed to a screening method based on IMS and chloride ion chemistry as a possible technique for detecting concealed explosives in various search scenarios, such as in aircraft and in airport terminals.

Table 1. Instrument Parameters

Figure 2. Negative ion mobility spectrum of headspace vapors from a dynamite sample. Carrier gas, purified air spiked with dichloromethane; inlet and drift temperature, 75°C; drift voltage, - 3000 V.

Forensic and Medical Applications

Forensic chemistry makes use of a variety of sophisticated analytical instrumental techniques to trace the extremely small quantities of drugs, explosives, and poisons present in various specimens. The conventional procedure adopted in forensic casework involves collecting the evidence at the scene (e.g., fire debris, empty vials, etc.) for subsequent chemical analyses to be performed in the laboratory. Laboratory results are often not available for several days.

A research project was undertaken by this laboratory to investigate the potential of IMS with regard to the on-site detection of drug residues on the hands of subjects by way of skin-surface sampling. A laboratory study was first carried out and revealed that, in simulated overdose situations, nanogram quant...

Table of contents

• Cover Page
• Half Title
• Title Page
• Copyright Page
• Preface
• Contents
• 1. New Applications for IMS Detection Techniques, A. H. Lawrence and L. Elias
• 2. Continuous Atmospheric Monitoring of Organic Vapors by Ion Mobility Spectrometry, G. A. Eiceman, A. P. Snyder, and D. A. Blyth
• 3. Ion Mobility Spectrometry (IMS) Study of Aromatic Hydrocarbons and Nitrogen- and Sulfur-Containing Compounds, Hiroyuki Hatano, Souji Rokushika, and Takashi Ohkawa
• 4. Gas, Supercritical Fluid, and Liquid Chromatographic Detection of Trace Organics by Ion Mobility Spectrometry, H. H. Hill, Jr., W. F. Siems, R. L. Eatherton, R. H. St. Louis, M. A. Morrissey, C. B. Shumate, and D. G. McMinn
• 5. Analysis of the Headspace Vapors of Marijuana and Marijuana Cigarette Smoke Using Ion Mobility Spectrometry/Mass Spectrometry (IMS/MS), S. H. Kim and G. E. Spangler
• 6. The Development and Application of a High Resolution Mass Spectrometry Method for Measuring Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans in Serum, D. G. Patterson, Jr., L. R. Alexander, W. E. Turner, S. G. Isaacs, and L. L. Needham
• 7. Comparison of Low Resolution, High Resolution Mass Spectrometry and Mass Spectrometry/Mass Spectrometry Techniques in the Analysis of Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans, Benjamin P.-Y. Lau, Dorcas Weber, and John J. Ryan
• 8. The Evaluation of Toxicity of Water Leachates from Incinerator Flyash Using Living Human Cells and Analytical Techniques, E. Jellum, A. K. Thorsrud, N. C. Herud, H. Y. Tong, and F. W. Karasek
• 9. Determination of Organometallic Species by High Performance Liquid Chromatography-Mass Spectrometry, J. W. McLaren, K. W. M. Siu, and S. S. Berman
• 10. Advantages of an API Source for Analysis by Liquid Chromatography/ Mass Spectrometry, B. A. Thomson, A. Ngo and B. I. Shushan
• 11. Parallel Column Gas Chromatography-Mass Spectrometry for the Analysis of Complex Environmental Mixtures, J. C. Marr, J. Visentini, and M. A. Quilliam
• 12. Current Status of Hyphenated Fourier Transform Infrared Techniques, Donald F. Gurka
• 13. Solvent-Free Extraction of Environmental Samples, Janusz Pawliszyn
• 14. Model Studies on the Solid-Supported Isolation, Derivation, and Purification of Chlorophenols and Chlorophenoxy Acetic Acid Herbicides, Jack M. Rosenfeld and Y. Moharir
• 15. A Surface Acoustic Wave Piezoelectric Crystal Aerosol Mass Microbalance, W. D. Bowers and R. L. Chuan
• List of Authors
• Index