Person-portable gas chromatography: rapid temperature program operation through resistive heating of columns with inherently low thermal mass properties

Intra-workday fluctuations of airborne contaminant concentration and the time-weighted average

Air contaminant concentrations vary between and within workdays and are often measured across a workday by passing a known air volume through a collection device. Laboratory analysis determines the contaminant mass trapped, providing a time-weighted average air concentration (C_TWA). This approach was driven by the best technologies available as exposure measurement processes developed and accuracy and measurement precision were sought. However, all integrated concentration•time (C•t) values determining C_TWA are equally weighted in assessing exposures, intra-workday concentration variability is unknown, and results are available days later. At times inappropriately, an occupational exposure limit (OEL) expressed as a C_TWA also requires equal weighting of all C•t values across an exposure period following concepts of Haber's law. Continuous monitoring (real-time detection) informs both the C_TWA and the variability of C during sampling, which are needed for stressors where a ceiling or peak OEL exists, for dangerous exposures to permanent gas-type contaminants, and for immediately dangerous to life or health (IDLH) conditions. Selective and accurate real-time detection instruments are not available for all air contaminants, but exposure magnitude information may be provided. The large amounts of data from continuous monitoring and the ability to correlate exposure maxima to specific tasks are also important. An exposure assessment role exists for selective and nonselective monitors, and in some cases, similar accuracy and precision are provided compared to laboratory analyses. Continuous monitoring may be of value when the alternative is the collection of a few C_TWA data points. Digitized personal monitor data can support the automation of some exposure control decisions or allow such decisions to be made by people in near real-time. The emerging Internet of Things (IoT) offers opportunities to integrate digital exposure data into decision-making to increase both efficiency and safety. The perceived and real uncertainty associated with real-time exposure assessments may be lessened with work to rule out the presence of know interferents and confirm the presence of target analytes.

Method development for on-site monitoring of volatile organic compounds via portable TD-GC-MS: evaluation of the analytical performances of HAPSITE® ER instrumentation and thermal desorption sampling media

Determining worker exposure to hazardous volatile organic compounds (VOCs) in air at levels exceeding the Permissible Exposure Limits and Recommended Exposure Limits established by the U.S. federal agencies of Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH), respectively, will continue to be an important part of environmental and occupational health risk assessments. The purpose of this work was to develop a reliable analytical method for rapid and on-site assessments of occupational VOC exposures using field-capable thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) instrumentation (i.e. the HAPSITE® ER). The experiments involved in this study included determining TD-GC-MS parameters suitable for efficient analyte separation and quantitation on the HAPSITE® ER, determinations of analyte mass loadings that cause mass spectrometer detector saturations, generation of calibration curves, estimations of the limits of detection (LODs) and quantification (LOQs), as well as desorption efficiency and relative response factor repeatability. The LODs using Carbopack™ B and Tenax® TA sampling media were estimated and ranged from 0.2-1.9 ng and 0.045-0.3 ng, respectively. The LOQs using Carbopack™ B and Tenax TA sampling media were estimated and ranged from 1.0-6.3 ng and 0.2-1.1 ng, respectively. We have developed a reliable analytical method for chloroform, benzene, trichloroethylene, and heptane using field-portable HAPSITE® ER instrumentation and Tenax® TA sorbent media. Reliable and accurate methods were developed for chloroform and trichloroethylene using Carbopack™ B sorbent media, however, this particular sorbent hadlow desorption efficiency and insufficient repeatability in relative response factors for many analytes. Our current and ongoing work in determining the uptake rates for analytes on Tenax® TA sorbent media will make the methods described herein applicable for on-site occupational VOC exposure assessments of chloroform, benzene, trichloroethylene, and heptane using either passive or active air sampling techniques.

Improvement of chiral separation efficiency through temperature control during one time high performance liquid chromatography analysis

This study examined how manual temperature control affects the separation of two enantiomers of five racemic mixtures using high-performance liquid chromatography (HPLC) in terms of separation factor (α), resolution (Rs), and the number of theoretical plates (N). The results showed that heating/cooling during one time HPLC analysis improved the separation factor and resolution.

FIELDABLE MASS SPECTROMETRY FOR FORENSIC SCIENCE, HOMELAND SECURITY, AND DEFENSE APPLICATIONS

Mass spectrometry is commonly used in forensic chemistry laboratories for sensitive, definitive analysis. There have been significant efforts to bring mass spectrometry analysis on-site through the development of ruggedized, fieldable instruments. Testing samples in the field is of particular interest in forensic science, homeland security, and defense applications. In forensic chemistry, testing seized drugs in the field can significantly improve efficiencies in processing of related criminal cases. The screening of passengers and luggage at transportation hubs is a critical need for homeland security for which mass spectrometry is well suited to provide definitive answers with low false positive rates. Mass spectrometry can yield reliable data for military personnel testing sites for potential chemical weapons release. To meet the needs of the forensic and security communities fieldable mass spectrometers based on membrane inlet systems and hybrid gas chromatography systems have been developed and commercialized. More recently developed ambient ionization mass spectrometry methods can eliminate the time, equipment, and expertise associated with sample preparation, and so are especially appealing for on-site analysis. We describe the development of fieldable mass spectrometry systems, with emphasis on commercially available systems that have been deployed for on-site analysis of seized drugs, chemical warfare agents, explosives, and other analytes of interest to the forensic and security communities. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Low-cost and open-source strategies for chemical separations

In recent years, a trend toward utilizing open access resources for laboratory research has begun. Open-source design strategies for scientific hardware rely upon the use of widely available parts, especially those that can be directly printed using additive manufacturing techniques and electronic components that can be connected to low-cost microcontrollers. Open-source software eliminates the need for expensive commercial licenses and provides the opportunity to design programs for specific needs. In this review, the impact of the "open-source movement" within the field of chemical separations is described, primarily through a comprehensive look at research in this area over the past five years. Topics that are covered include general laboratory equipment, sample preparation techniques, separations-based analysis, detection strategies, electronic system control, and software for data processing. Remaining hurdles and possible opportunities for further adoption of open-source approaches in the context of these separations-related topics are also discussed.

Assessing flammable storage cabinets as sources of VOC exposure in laboratories using real-time direct reading wireless detectors

Herein we present the results of measurements using wireless direct-reading photoionization detector-based gas sensors to quantify concentrations of vapors of volatile organic compounds (VOCs) in and around flammable storage cabinets containing common organic solvents, including acetone, dichloromethane, trichloroethylene, and benzene. Such cabinets are commonly employed in laboratories to contain flammable liquids. A sensor array was deployed in a series of flammable storage cabinets in working laboratories. Measurements in cabinets containing bottles of typical solvents demonstrate that vapor concentrations gradually increase upon closing the cabinet door. The results suggest that these storage units can be a source of vapors of VOCs in laboratories and the unnecessary exposure of laboratory workers to chemical vapors. Ventilation of cabinets tended to lower maximum concentrations of VOCs. However, the efficacy of this engineering control was found to depend on the quality of the cabinet door seal, as well as having debris-free flame arrestors. Opening cabinet doors resulted in release of vapors to the laboratory atmosphere, which represents an unnecessary exposure risk for workers. A countermeasure aimed at improving the seal of previously opened solvent bottles reduced measured concentrations of VOCs in cabinets below the detector's limit of detection.

A Non-invasive Monitoring of Propofol Concentration in Blood by a Virtual Surface Acoustic Wave Sensor Array

Propofol (2,6-diisopropylphenol) is widely used in total intravenous anesthesia. An unknown drug concentration in blood always leads to some side effects in patients with propofol injection. However, the drug concentration in the blood is hard to be continuously measured since invasive sampling causes a loss of blood at each measurement. Here, we introduced a virtual surface acoustic wave sensor array (VSAWSA) to non-invasively detect the propofol concentration in blood through exhaled gases. Calibration was conducted by a parallel test using gas chromatography and mass spectrometry (GC-MS) with solid-phase micro-extraction (SPME) for preconcentration. The limit of detection of VSAWSA reached 0.15 nmol/L for propofol. Six cases of clinical trials was conducted to compare the exhaled propofol concentrations to the plasma concentrations controlled by target-controlled infusion (TCI). The calibration by GC-MS ensured the feasibility, reliability, and accuracy of the VSAWSA (R = 0.9904, p <0.001). The clinical monitoring data by VSAWSA showed an excellent consistency with TCI.

Identification of V-type nerve agents in vapor samples using a field-portable capillary gas chromatography/membrane-interfaced electron ionization quadrupole mass spectrometry instrument with Tri-Bed concentrator and fluoridating conversion tube

A field-portable gas chromatography-mass spectrometry (GC-MS) system (Hapsite ER) was evaluated for the detection of nonvolatile V-type nerve agents (VX and Russian VX (RVX)) in the vapor phase. The Hapsite ER system consists of a Tri-Bed concentrator gas sampler, a nonpolar low thermal-mass capillary GC column and a hydrophobic membrane-interfaced electron ionization quadrupole mass spectrometer evacuated by a non-evaporative getter pump. The GC-MS system was attached to a VX-G fluoridating conversion tube containing silver nitrate and potassium fluoride. Sample vapors of VX and RVX were converted into O-ethyl methylphosphonofluoridate (EtGB) and O-isobutyl methylphosphonofluoridate (iBuGB), respectively. These fluoridated derivatives were detected within 10 min. No compounds were detected when the VX and RVX samples were analyzed without the conversion tube. A vapor sample of tabun (GA) was analyzed, in which GA and O-ethyl N,N-dimethylphosphoramidofluoridate were detected. The molar recovery percentages of EtGB and iBuGB from VX and RVX vapors varied from 0.3 to 17%, which was attributed to variations in the vaporization efficiency of the glass vapor container. The conversion efficiencies of the VX-G conversion tube for VX and RVX to their phosphonate derivatives were estimated to be 40%. VX and RVX vapors were detected at concentrations as low as 0.3 mg m^-3 . Gasoline vapor was found to interfere with the analyses of VX and RVX. In the presence of 160 mg m^-3 gasoline, the detection limits of VX and RVX vapor were increased to 20 mg m^-3 . Copyright © 2017 John Wiley & Sons, Ltd.

Review on Micro-Gas Analyzer Systems: Feasibility, Separations and Applications

Over 30 years, portable systems for fast and reliable gas analysis are at the core of both academic and industrial research. Miniaturized systems can be helpful in several domains. The way to make it possible is to miniaturize the whole gas chromatograph. Micro-system conception by etching silicon channel is well known. The main objective is to obtain similar or superior efficiencies to those obtained from laboratory chromatographs. However, stationary phase coatings on silicon surface and micro-detector conception with a low limit of detection remain a challenge. Developments are still in progress to offer a large range of stationary phases and detectors to meet the needs of analytical scientists. This review covers the recent development of micro-gas analyzers. It focuses on injectors, stationary phases, column designs and detectors reported in the literature during the last three decades. A list of commercially available micro-systems and their performances will also be presented.

Miniaturised medium pressure capillary liquid chromatography system with flexible open platform design using off-the-shelf microfluidic components

Trends towards portable analytical instrumentation of the last decades have not been equally reflected in developments of portable liquid chromatography (LC) instrumentation for rapid on-site measurements. A miniaturised medium pressure capillary LC (MPLC) system with gradient elution capability has been designed based on a flexible modular microfluidic system using primarily off-the-shelf low cost components to ensure wide accessibility to other analysts. The microfluidic platform was assembled on a breadboard and contained microsyringe pumps and switch valves, complemented with an injection valve and on-capillary detectors, all controlled by a PC. Four miniaturised microsyringe pumps, with 5, 20 and 100 μL syringe volume options, formed the basis of the pumping system. Two pairs of pumps were used for each mobile phase to create gradient elution capability. The two microsyringe pumps in each pairs were linked by two electrically operated microfluidic switching valves and both pairs of pumps were connected through a zero void volume cross-connector, thus providing a low hold-up volume for gradient formation. Sample was injected by a 20 nL nano-LC sampling valve, directly connected to a 18 cm long 100 μm i.d. Chromolith CapRod RP-18 monolithic capillary column. On-capillary LED-based UV-vis photometric detection was conducted through a piece of equal diameter fused silica capillary connected after the column. The performance of the portable LC system was evaluated theoretically and experimentally, including the maximum operating pressure, gradient mixing performance, and the performance of the detectors. The 5 μL microsyringe pump offered the best performance, with typical maximum operating pressures up to 11.4 ± 0.4 MPa (water) and gradient pumping repeatability of between 4 and 9% for gradients between 0.10% s(-1) and 0.33% s(-1). Test analytes of charged and uncharged dyes and pharmaceuticals of varying hydrophobicity showed typical RSD values of 0.7-1.4% and 3.3-4.8% in isocratic mode and 1.2-4.6% and 3.2-6.4% in gradient mode, respectively for retention time and peak area repeatability.