Homemade Portable Gas Chromatograph With Photoionization Detector Monitors Volatile Organic Compounds at Industrial Site

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Photoionization detectors (PIDs) are attractive for their high sensitivity and fast response time, while cost-effective equipment has been sought for online monitoring of volatile organic compounds (VOCs).

Researchers in China have conducted an experiment to detect volatile organic compounds (VOCs) at an industrial park in the Hangzhou Bay Shangyu Economic and Technological Development Zone in Zhejiang Province, a location known to emit large quantities of VOCs (1). The compounds were determined using a homemade, portable gas chromatography (pGC) system coupled to a photoionization detector (PID), with the combined method finding 17 VOCs and providing a convincing case to the researchers for broader field usage.

Hangzhou suburbs aerial view in China | Image Credit: © ABCDstock - stock.adobe.com

Hangzhou suburbs aerial view in China | Image Credit: © ABCDstock - stock.adobe.com

Published in the Journal of Chromatography A, this study reiterated the need to monitor and attempt to reduce VOC concentration in the environment, which was first reported by laboratory analysis of the manufacturing industry. A major class of ozone and particulate matter pollutants in industrialized countries, VOCs at high levels of exposure can cause damage to the human immune, nervous, and respiratory systems in the long term (1). Offline approaches to VOC analysis, including solid-phase microextraction (SPME), have been accurate but time-consuming. Fourier transform infrared spectroscopy (FTIR) and proton transfer reaction mass spectrometry (PTR-MS), or alternately proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) have been used for real-time monitoring, but these apparatuses tend to be pricey and cumbersome, according to the researchers.

To address these pitfalls, the researchers devised a “miniature,” portable gas chromatograph (pGC) with a small photoionization detector (PID), the main components of this equipment measuring only 30 cm in length × 20 cm width × 20 cm height, and weighing just 10 kg (1). The PID was also equipped with a krypton ultraviolet (UV) lamp. The PID’s two outputs, one correlating to overall chemical composition and the other providing certain information on that composition, showed high sensitivity at a low cost, the researchers said, making it hypothetically ideal for rapid analysis. Sampling time (80 s), column temperature (50 ºC), carrier gas flow rate (60 mL/min), sampling time, and filter unit were optimized to improve signal value and retention time. Specifically, polytetrafluoroethylene (PTFE) filter membranes were used to eliminate particulate matter that might interfere with the PID.

Under laboratory testing, the optimized conditions of the pGC-PID were shown to determine a total of 27 species of VOCs from among three types of standard gases. Of those, as mentioned, 17 were detected when the hardware and procedure were taken offline to the industrial site (1). The study additionally said that fast detection and high temporal resolution of 30 min demonstrated the approach’s viability.

In the group of 27 detected VOCs, detection limits were set at ≤ 10 ppb, with the lowest being 2 ppb for 1,1,2-trichloroethane. The five most abundant VOCs measured over a 7-day period at the industrial park were acetone, isoprene, methylene chloride, toluene, and paraxylene. (Toluene’s detection limit was near the low end of those set for this experiment, at 2.09 ppb.) Relative standard deviations (RSD) with respect to reproducibility and peak separation were ≤ 7%, and standard curves showed good linearity with R2 ≥ 0.99 (1).

Because of the lack of pre-processing needed for this homemade pGC-PID apparatus, as well as the fast, low-cost, and effective results determined, the researchers concluded that their method might have further uses in environmental monitoring and improved upon prior instruments deployed for such a purpose, including but not limited to PTR-TOF-MS.

Reference

(1) Pang, X.; Li, W.; Wang, S.; et al. Application of homemade portable gas chromatography coupled to photoionization detector for the detection of volatile organic compounds in an industrial park. J. Chromatogr. A 2023, 1704, 464089. DOI: 10.1016/j.chroma.2023.464089

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