Automated Analysis of Pollutants in Wastewater Using Atmospheric Pressure Gas Chromatography-Tandem Quadrupole Mass...

The analysis of organic pollutants using gas chromatography coupled to mass spectrometer (GC-MS) with electron impact (EI) ionization and liquid-liquid or solid-phase extraction (LLE or SPE) often suffer from a limited selectivity and arduous sample preparation. Therefore, atmospheric pressure GC-MS/MS coupled with Dual Head-Robotic Tool Change (DH-RTC) Prep and Load (PAL), and solid-phase micro extraction (SPME) arrow was investigated for its suitability. Evaluation of the SPME arrow coated with divinylbenzene-polydimethylsiloxane (DVB-PDMS) using 2-nitrotoluene and nitrobenzene showed acceptable intra-day precision (%relative standard deviation [RSD]) of less than 10% and inter-day precision (n = 35) of 10.54% and 12.45% respectively. Initial trials were conducted to assess the suitability of technique for eight multiclass compounds (from early eluting volatile organic compounds [e.g., 1,2-dichlorobenzene] to challenging late eluting polycyclic aromatic hydrocarbons [PAH] [e.g., benzo[ghi]perylene], specification markers [e.g., octafluoronaphthalene, and hexachlorobenzene], labile and toxic analytes [e.g., endosulfan, and 2,3,7,8-tetrachlorodibenzodioxin], and isobaric closely eluting PAHs [phenanthrene, and anthracene]). The precision (%RSD, n = 6) was ranged from 1.68 to 16.57, with peak asymmetry factor between 1.003 (phenanthrene) and 1.520 (anthracene). Further experiments conducted for priority pollutants (United States Environmental Protection Agency (U.S. EPA) 625.1/2016) indicated that the addition of salt significantly enhanced the responses for 28 analytes. The increase in response was ranged from 1.14-fold for Endosulfan II to 40.53-fold for pentachlorophenol. However, the %RSDs for 51 analytes were better without adding salt and for 12 analytes it improved with the addition of salt. Since the responses for 12 analytes are sufficient even without salt and standard deviations are below U.S.EPA 625.1/2016 limits, further trials were conducted without adding salt. Preliminary trials showed high RSDs up to 52.76% for high-boiling compounds, which were reduced by using internal standards (IS) and lowering the analyte load during injection. Dedicated analysis of high-boiling PAHs and selected compounds with deuterated IS achieved acceptable coefficient of determination (r²), %recoveries and %RSDs. The evaluation of method greenness (Green Analytical Procedure Index and Analytical Greenness calculator), and practicality (Blue Applicability Grade Index) indicated that this approach is environmentally sustainable and practical, providing an efficient and validated alternative method for wastewater analysis.