Autoxidation of terpenes, a common pathway in tropospheric and low temperature combustion conditions: the case of limonene and α-pinene

The oxidation of monoterpenes under atmospheric conditions has been the subject of numerous studies. They were motivated by the formation of oxidized organic molecules (OOM) which, due to their low vapor pressure, contribute to the formation of secondary organic aerosols (SOA). Among the different reaction mechanisms proposed for the formation of these oxidized chemical compounds, it appears that the autoxidation mechanism, involving successive events of H-migration and O2 addition, common to both low-temperature combustion and atmospheric conditions, is leading to the formation of highly oxidized molecules (HOM). In atmospheric chemistry, the importance of autoxidation compared to other oxidation pathways has been the topic of numerous studies. Conversely, in combustion, autoxidation under cool flame conditions is the main oxidation process commonly taken into account. An analysis of oxidation products detected in both conditions was performed, using the present combustion data and literature data from tropospheric oxidation studies, to investigate possible similarities in terms of observed chemical formulae of products. To carry out this study, we chose two terpenes, α-pinene and limonene (C10H16), among the most abundant biogenic components in the atmosphere, and considered in many previous studies. Also, these two isomers were selected for the diversity of their reaction sites (exo- and endo- carbon-carbon double bonds). We built an experimental database consisting of literature atmospheric oxidation data and presently obtained combustion data for the oxidation of the two selected terpenes. In order to probe the effects of the type of ionization used in mass spectrometry analyses on the detection of oxidation products, we used heated electrospray ionization (HESI) and atmospheric pressure chemical ionization (APCI), in positive and negative modes. The oxidation of limonene-oxygen-nitrogen and α-pinene-oxygen-nitrogen mixtures was performed using a jet-stirred reactor at elevated temperature (590 K), a residence time of 2 s, and atmospheric pressure. Samples of the reacting mixtures were collected in acetonitrile and analyzed by high-resolution mass spectrometry (Orbitrap Q-Exactive) after direct injection and soft ionization, i.e. (+/−) HESI and (+/−) APCI. This work shows a surprisingly similar set of chemical formulae of products, including oligomers, formed in cool flames and under simulated atmospheric conditions. Data analysis showed that a non-negligible subset of chemical formulae is common to all experiments independently of experimental parameters. Finally, this study indicates that more than 40 % of the detected chemical formulae in this full dataset can be ascribed to an autoxidation mechanism.

A LC-MS/MS method with electrospray ionization and atmospheric pressure chemical ionization source for analysis of pesticides in hemp

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%.

Ionization of Volatile Organics and Nonvolatile Biomolecules Directly from a Titanium Slab for Mass Spectrometric Analysis

Atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) and electrospray ionization (ESI)-MS can cover the analysis of analytes from low to high polarities. Thus, an ion source that possesses these two ionization functions is useful. Atmospheric surface-assisted ionization (ASAI), which can be used to ionize polar and nonpolar analytes in vapor, liquid, and solid forms, was demonstrated in this study. The ionization of analytes through APCI or ESI was induced from the surface of a metal substrate such as a titanium slab. ASAI is a contactless approach operated at atmospheric pressure. No electric contacts nor any voltages were required to be applied on the metal substrate during ionization. When placing samples with high vapor pressure in condensed phase underneath a titanium slab close to the inlet of the mass spectrometer, analytes can be readily ionized and detected by the mass spectrometer. Furthermore, a sample droplet (~2 μL) containing high-polarity analytes, including polar organics and biomolecules, was ionized using the titanium slab. One titanium slab is sufficient to induce the ionization of analytes occurring in front of a mass spectrometer applied with a high voltage. Moreover, this ionization method can be used to detect high volatile or polar analytes through APCI-like or ESI-like processes, respectively.

ANALYTICAL METHOD DEVELOPMENT AND VALIDATION FOR LIMIT OF N-NITROSODIMETHYLAMINE BY LC-MS/MS OF EMPAGLIFLOZIN, LINAGLIPTIN AND METFORMIN HCL EXTENDED-RELEASE TABLETS

As a result of the devotion of The Limit of N-Nitrosodimethylamine (NDMA), a rapid and selective LC/MS/MS technique was created and validated for Empagliflozin, Linagliptin, and Metformin Hydrochloride Extended-Release Tablets. The ionization mode of Atmospheric pressure chemical ionization (APCI) was used with high-performance liquid chromatography-tandem mass spectrophotometry (LC-MS/MS). Separation of N-Nitrosodimethylamine (NDMA) was performed on Inertsil ODS-4 (250 mm X 4.6 mm), 5μm column with a run time of 40 minutes. A mixture of Methanol and Buffer solution (630 mg of ammonium format into 1000 mL of purified water) in the ratio of (10:90, v/v) was used as the mobile phase A. A mixture of acetonitrile and methanol comprised the mobile phase B in the ratio of (50:50) % v/v. Analytes were extracted from Empagliflozin, Linagliptin, and Metformin Hydrochloride Extended-Release Tablets. According to the International council for Harmonization of technical requirement for Pharmaceuticals for Human Uses (ICH) standards, the accuracy, precision, selectivity, recovery, and stability of the method have been validated. Over a concentration range of 0.4 -3.6 ng/mL, the technique exhibited linearity. for N- Nitrosodimethylamine of Empagliflozin, Linagliptin, and Metformin Hydrochloride Extended-Release Tablets with an acceptable correlation coefficient applies (1/X2) linear regression with weights A pharmaceutical study can benefit from this method because it is simple, fast, precise, and accurate, making it ideal for pharmaceutical research.