Applications of the Photoionization Detector (PID) in Occupational Hygiene. Estimation of Air Changes per Hour in Premises with Natural Ventilation

The importance of ventilation in closed workplaces increased after the onset of the COVID-19 pandemic. New methodologies for measuring the number of air changes per hour (ACH) in a premise where natural ventilation is applied are necessary. It is demonstrated how the ionic photoionization detector (PID) can be employed for tracer gas decay methodology using a volatile organic solvent (acetone). The methodology applied to calculate ACH in a naturally ventilated room, with various combinations of door and window openings, provides ACH values of between 2 and 17 h−1. Two classrooms were studied to verify if the minimum ventilation requirements recommended by official guidelines were met. The values for ACH on different days varied, mainly between 15 and 35 h−1, with some exceptional values higher than 40 h−1 on very windy days. These results agree with the quality air data recorded by the installed CO2 sensors, ensuring adequate hygienic conditions for the users of the rooms. The fast response of the PID allows the measurement of different locations in the room during the same assay, which provides additional information regarding the air distribution inside during the ventilation process. This methodology is fast and easy, and the necessary equipment is simple to obtain and use routinely, whether it is needed to measure several rooms or to monitor one room periodically.

Atmospheric Photoionization Detector with Improved Photon Efficiency: A Proof of Concept for Application of a Nanolayer Thin-Film Electrode

Atmospheric photoionization is a widely applied soft ionization mechanism in gas sensing devices for the detection of volatile organic compounds in ambient air. Photoionization is typically induced by low-pressure Vacuum Ultraviolet (VUV) lamps with MgF2 or LiF lamp surface windows depending on the gas fill and the required wavelength transmission window. These lamps are known to exhibit gradually reduced VUV transmission due to hydrocarbon contamination. LiF surface windows are known to be especially problematic due to their hygroscopic nature, reducing VUV lamp lifetime to a mere 100 h, approximately. Here, we present a new design for the electrode of a photoionization detector based on thin-film technology. By replacing the commonplace metal grid electrode’s VUV lamp surface window with a chromium/gold thin film we obtain a doubling of photon efficiency for photoionization. Replacing the hygroscopic LiF lamp window surface with a metallic layer additionally offers the possibility to vastly increase operational lifetime of low-pressure Argon VUV lamps.

Evaluation of direct reading photoionization detector performance under various operational parameters

Background: A hand-held portable direct-reading monitor, including photoionization detector (PID) is renowned for its good sensitivity, considerable dynamic range, and nondestructive vapor detection ability in comparison to the tardy response of the PID in gas chromatography (GC), which its application has been restricted. In this study, the performance of a PID system (MultiRAE Lite) was evaluated as a replacement of GC in the measurement of toluene in a dynamic adsorption system. Methods: The test was done at different relative humidity levels (30%, 50%, and 80%), temperatures (21, 30, 40° C), and toluene concentrations (20, 100, 200, and 400 ppm). Results: The PID achieved 48% of all measurements meeting the comparison criterion. The results showed that the performance of the PID could be altered by the variables. The best performance of the PID was at temperature of 21° C, the relative humidity of 50%, and concentration of 200 ppm with the percentage of readings achieving the criterion of comparison to 58%, 54%, and 52%, respectively. The averages of the PID readings (mean ± SD at 200 ppm= 207.9 ± 8.7) were higher than the reference method measurements averages (mean ± SD at 200 ppm= 203.5 ± 5.8). The regression analysis of the toluene results from the PID and the reference method results indicated that the measurements were significantly correlated (r2 = 0.93). Conclusion: According to the results, the device response is linear. Therefore, the findings are acceptable in adsorption studies. In this way, the measurement of the sample concentration should be performed using the same instrument before and after the reactor in order to calculate the adsorption efficiency.

Characterizing the Performance of a Compact BTEX GC-PID for Near-Real Time Analysis and Field Deployment

In this study, we test the performance of a compact gas chromatograph with photoionization detector (GC-PID) and optimize the configuration to detect ambient (sub-ppb) levels of benzene, toluene, ethylbenzene, and xylene isomers (BTEX). The GC-PID system was designed to serve as a relatively inexpensive (~10 k USD) and field-deployable air toxic screening tool alternative to conventional benchtop GCs. The instrument uses ambient air as a carrier gas and consists of a Tenax-GR sorbent-based preconcentrator, a gas sample valve, two capillary columns, and a photoionization detector (PID) with a small footprint and low power requirement. The performance of the GC-PID has been evaluated in terms of system linearity and sensitivity in field conditions. The BTEX-GC system demonstrated the capacity to detect BTEX at levels as high as 500 ppb with a linear calibration range of 0–100 ppb. A detection limit lower than 1 ppb was found for all BTEX compounds with a sampling volume of 1 L. No significant drift in the instrument was observed. A time-varying calibration technique was established that requires minimal equipment for field operations and optimizes the sampling procedure for field measurements. With an analysis time of less than 15 min, the compact GC-PID is ideal for field deployment of background and polluted atmospheres for near-real time measurements of BTEX. The results highlight the application of the compact and easily deployable GC-PID for community monitoring and screening of air toxics.

Characterizing the Performance of a Compact BTEX GC-PID for Near-Real Time Analysis and Field Deployment

In this study, we test the performance of a compact gas chromatograph with photoionization detector (GC-PID) and optimize the configuration to detect ambient (sub-ppb) levels of benzene, toluene, ethylbenzene, and xylene isomers (BTEX). The GC-PID system was designed to serve as a relatively inexpensive (~$10k) and field-deployable air toxic screening tool alternative to conventional benchtop GCs. The instrument uses ambient air as a carrier gas, and consists of a Tenax-GR trap preconcentrator, a gas sample valve, two capillary columns, and a photoionization detector (PID) with a small footprint and low power requirement. The performance of the GC-PID has been evaluated in terms of system linearity and sensitivity in field conditions. The BTEX-GC system demonstrated the capacity to detect BTEX at levels as high as 500 ppb with a linear calibration range of 0-100 ppb. A detection limit lower than 1 ppb was found for all BTEX compounds with a sampling volume of 1 L. No significant drift in the instrument was observed. A time-varying calibration technique was established that requires minimal equipment for field operations and optimizes the sampling procedure for field measurements. With an analysis time of less than 15 minutes, the compact GC-PID is ideal for field deployment of background and polluted atmospheres for near-real time measurements of BTEX. The results highlight the application of the compact and portable GC-PID for community monitoring and screening of air toxics.

Comparison of Four Beddings for Ammonia Control in Individually Ventilated Mouse Cages

Ammonia control is an important characteristic of rodent bedding materials. Among natural bedding materials, corncobbedding provides excellent ammonia control but contains estrogenic compounds and is ingested by mice. By comparison,processed cellulose bedding products are biologically inert and harbor fewer bacteria but historically have shown low absorbencyor poor ammonia control. New cellulose products have been developed to address these shortcomings. Over a 2-wk period, we evaluated intracage ammonia levels in mouse IVC using 4 bedding types: shaved aspen, corncob, virgin pelleted cellulose, and refined virgin diced cellulose. Ammonia levels were measured by using 3 methods: colored reagent tubes, colorimetricpaper strips, and a photoionization detector. Corncob, pelleted cellulose, and diced cellulose showed better ammoniacontrol than aspen as early as 4 d after cage changing and throughout the 2-wk measurement period. In addition, pelletedand diced cellulose products resulted in lower ammonia levels than corncob at the end of the 14-d cage-change interval. Ourdata indicate that pelleted or refined diced cellulose are viable alternatives to natural bedding products in IVC to limit therisk of exposure of mice to high ammonia levels.