Pressure Chemical Ionization
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2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Avinash Dalmia ◽  
Erasmus Cudjoe ◽  
Jacob Jalali ◽  
Feng Qin

Abstract Background Pesticide testing for hemp has traditionally focused on techniques like QuEChERS with dSPE and SPE which demand time-consuming sample preparation, typically resulting in poor recovery rates for some pesticides, and requires the use of both LC-MS/MS and GC-MS/MS based instruments to cover the analysis for all regulated pesticides. In this study, we describe a streamlined approach for working with LC-MS/MS featuring a dual electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources using solvent extraction for faster and easier sample preparation and with 80–120% recovery for the analysis of all of 66 pesticides (regulated by California state in cannabis) with low detection limits in hemp. Methods A simple solvent extraction with acetonitrile was used to extract pesticides from hemp. A LC-MS/MS system with dual ESI and APCI source was used to determine sensitivity for the analysis of 66 pesticides in hemp matrix, 62 pesticides were analyzed using an 18-min LC-MS/MS method with an ESI source and the other 4 pesticides were measured using a 6-min LC-MS/MS method with an APCI source. Results The limit of quantitation (LOQ) of all 66 pesticides in hemp was in the range of 0.0025–0.1 μg/g which was well below the California state action limits of these analytes in cannabis products. A simple, fast, and cost-effective solvent extraction method was used for sample preparation to get good recovery in the range of 80–120% with RSD less than 20%. The unique ionization mechanism of chlorinated pesticides such as pentachloronitrobenzene using the LC-MS/MS system with an APCI source was elucidated. The proficiency test report generated with the LC-MS/MS method showed acceptable results for all of 66 pesticides in hemp with all of th z scores less than 2 with no false positives and negatives. The stability data collected over 5 days showed RSD less than 20% for 66 pesticides in hemp, and this demonstrated the robustness of the LC-MS/MS system used in this work. Conclusions A LC-MS/MS method with dual ESI and APCI sources was developed for the analysis of 66 pesticides in hemp. The recovery of all pesticides from a hemp matrix was in the acceptable range of 80–120% with RSD less than 20%.


2021 ◽  
Author(s):  
LiuDongQing Yang ◽  
Xianfeng Wang ◽  
Mikinori Kuwata Kuwata

<p>Brown carbon (BrC) is an important candidate for the direct radiative effects of aerosol particles. It has been demonstrated that positive matrix factorization (PMF) is useful in analyzing Aerosol Mass Spectrometer (AMS) data for BrC source apportionment. However, fragmentation of molecular ions in AMS has been limiting its capability to categorize BrC sources. Soft-ionization mass spectrometric techniques are known to retain molecular information of chemical species. In this study, we applied atmospheric pressure chemical ionization mass spectrometry (APCI-MS) to identify the sources of water-soluble BrC. PM2.5 filter samples were collected at a site in Singapore during March-May of 2019. The extracted water-soluble organic matter (WSOM) was analyzed using APCI-MS, time-of-flight aerosol chemical speciation monitor (ToF-ACSM) and ultraviolet-visible spectrophotometer (UV-Vis). Five factor components were obtained by PMF analysis of the APCI-MS data. The PMF output and UV-Vis data were subsequently used to estimate the absorption Ångstrom exponents (AAE) of WSOM in each component. The estimated values of AAE ranged from 3.95 to 8.71. When comparing the factor contributions with simultaneously monitored gas and aerosol data, we found that the factor with the lowest value of AAE was likely emitted from a methane-rich combustion source, located east of the observation site. </p>


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