Chemical Ionization Mass Spectrometry Method Research Articles

Online Monitoring of the Processing of Traditional Chinese Medicine by Neutral Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry.

The pharmacological effects of traditional Chinese medicine (TCM) are closely associated with the processing procedures, which involve a multitude of intricate chemical reactions. Real-time monitoring of the dynamic changes in chemical constituents during TCM processing plays a pivotal role in ensuring quality control of TCM products. Herein, a neutral desorption atmospheric pressure chemical ionization mass spectrometry (ND-APCI-MS) method was developed for online monitoring of the TCM processing. The aerosol generated during the TCM processing was sampled in situ by neutral desorption using N2, followed by online analysis using APCI-MS. Subsequently, orthogonal partial least squares discriminant analysis (OPLS-DA) was employed to analyze the MS data to find the biomarkers associated with the processing. Compared to traditional tissue-based analytical methods, the present method employing aerosols as samples takes advantage of online analysis, nondestructive sampling, and enhanced accuracy. As a conceptual application, the processing of Rehmannia glutinosa was investigated, and several biomarkers associated with the processing were identified. These findings suggest the potential application of ND-APCI-MS for online and in situ monitoring of the processing of TCM.

Integrating density functional theory and chemical ionization mass spectrometry techniques to assess benzophenone derivatives in food packaging: implications for enhancing food quality and safety.

Benzophenone and related derivatives are widely used as photoinitiators for food packaging to cure inks or lacquers with ultraviolet (UV) light on cardboard and paper. However, there are concerns about the potential health risks of their migration into food. Knowing the physical and chemical properties of benzophenone and its derivatives could play a significant role in their quantification and analysis using chemical ionization mass spectrometry (CI-MS) methods. These parameters are evaluated using B3LYP/6-311++** density functional theory (DFT) implemented on Gaussian code. Ion-molecule chemistry through the selection of reagent ions, reaction energetics and kinetics, thermodynamic stability, and reactivity of molecules deemed to foster VOC identification and quantification via CI-MS techniques. The VOCs under study are expected to undergo exothermic reactions from H3 O+ , NH4 + , NO+ , and O2 + ions, except endothermic proton transfer from NH4 + to 2-hydroxy-4-methoxybenzophenone and 2,3,4-trihydroxy benzophenone. These compounds possess less proton affinities than NH3 and are least stable in their protonated forms. The DFT computed properties provide the basis for developing reliable and accurate methods to detect and measure the presence of benzophenone and its derivatives in packaging materials and food products.

Paternò-Büchi Reaction Mass Spectrometry Enables Positional Assignment of Polymethylene-Interrupted Double Bonds in Food-Derived Lipids.

Fatty acids (FAs) containing polymethylene-interrupted (PMI) double bonds are a component of human foods; however, they present a significant analytical challenge for de novo identification. Covalent adduct chemical ionization and ozone-induced dissociation mass spectrometry (MS) methods enable unambiguous assignment of PMI-FA double bond positions, however, no method has been reported with electrospray ionization (ESI) platform using off-the-shelf systems. In the current work, we studied the Paternò-Büchi (PB) fragmentation patterns of PMI-FA and triacylglycerol (TG) by analyzing several known food sources. PB-MS/MS and MS3 enabled complete double bond location assignments, including the isolated double bond in PMI-FA and triacylglycerols. Sea urchin ("uni"), oyster, pine nut, and ginkgo nut were characterized for their signature PMI-FA, 20:2(5Z,11Z), 22:2(7Z, 15Z), 18:3(5Z,9Z,12Z), and 20:3(5Z,11Z,14Z), respectively. Quantitative analyses of the relative abundance of these PMI-FA led to results similar to reference methods. 18:3(5Z,9Z,12Z) was enriched at the sn-1/sn-3 position in pine nut major TG.

U–Pb age constraints on the Carboniferous–Permian transition in continental basins of eastern equatorial Pangaea (France): implications for the depositional history and correlations across the late Variscan Belt

Intramontane late Carboniferous–Permian basins of western Europe developed during the latest orogenic stages of the Variscan Mountain Belt in eastern Pangaea, at equatorial palaeolatitudes. Their stratigraphic framework is mainly based on continental subdivisions (e.g. Stephanian and Autunian continental stages), which can be contentious owing to biostratigraphic biases, resulting in long-distance diachronous subdivisions. To provide precise inter-basinal and global correlations to the internationally recognized chronostratigraphic marine stages, this study reports new U–Pb geochronology from the Aumance and Decize–La Machine basins, located in the northern French Massif Central. Zircon grains extracted from three volcanic ash-fall layers give weighted mean 206 Pb/ 238 U ages of 299.11 ± 0.35, 298.73 ± 0.36 and 298.59 ± 0.35 Ma (2 σ total propagated uncertainty) by the chemical abrasion isotope dilution thermal ionization mass spectrometry method, coinciding with the Carboniferous–Permian transition (Gzhelian and Asselian stages). These ages imply that the northern Massif Central basins developed synchronously in relatively short periods of time (<10 myr), reflecting substantial sedimentation rates. Finally, the new chronology of infilling of these basins confirms that they were connected during the late Carboniferous and early Permian periods, improving the knowledge on the late orogenic Variscan geodynamic setting in this area. Supplementary material: Operating conditions and complete analytical results are available at https://doi.org/10.6084/m9.figshare.c.6805228

Measuring Photodissociation Product Quantum Yields Using Chemical Ionization Mass Spectrometry: A Case Study with Ketones.

Measurements of photolysis quantum yields are challenging because of the difficulties in measuring the first-generation photodissociation products, interference from other products or contaminants, sufficient photon fluxes and/or low absorption cross sections of the photolyte to make detectable amounts of products, and quantification of the photon flux. In the case of acetone (and other atmospherically relevant ketones) the uncertainty in the photolysis quantum yield creates uncertainty in the calculated OH radical and acyl peroxy nitrate production in the atmosphere. We present a new method for determining photodissociation product quantum yields by measuring acyl peroxy radicals (RC(O)O2) produced in the photolysis of ketones in air using chemical ionization mass spectrometry (CIMS). We show good agreement of our CIMS method with previously published quantum yields of the acyl radical from photolysis of biacetyl and methyl ethyl ketone (MEK) at 254 nm. Additionally, we highlight the capabilities of this CIMS method through the measurement of photolysis branching ratios for MEK. We suggest future applications of CIMS (in the laboratory and field) to measure RC(O)O2 and associated photolysis processes.

Determination of vitamin E and its metabolites in equine urine using liquid chromatography-mass spectrometry.

Equine neuroaxonal dystrophy/degenerative myeloencephalopathy (eNAD/EDM) is a hereditary, deteriorating central nervous disease in horses. Currently, the only way to confirm eNAD/EDM is through a postmortem histological evaluation of the central nervous system. Vitamin E, specifically the isoform alpha-tocopherol (α-TP), is known to protect eNAD/EDM susceptible horses from developing the clinical phenotype. While vitamin E is an essential nutrient in the diet of horses, there are no diagnostic tests able to quantitate vitamin E and its metabolites in urine. An ultra-performance liquid chromatography-atmospheric-pressure chemical ionization mass spectrometry (UPLC-APCI-MS/MS) method was developed and validated following acidic hydrolysis and solid phase extraction to quantitate vitamin E and its metabolites in equine urine. A blank control horse urine matrix was used and spiked with different concentrations of analytes to form a standard curve using either alpha-tocopherol-d6 or chlorpropamide as the internal standard. Inter-day and intra-day statistics were performed to evaluate the method for accuracy (90% to 116%) and precision (0.75% to 14%). Matrix effects, percent recovery, and stability were also assessed. The method successfully analyzed alpha-carboxyethyl hydroxychroman (α-CEHC), alpha-carboxymethylbutyl hydroxychromans (α-CMBHC), gamma-carboxyethyl hydroxychroman γ-CEHC, and α-TP concentrations in urine to determine a baseline levels of analytes in healthy horses, and can be used to determine concentrations of vitamin E metabolites in equine urine allowing for its evaluation as a diagnostic approach in the treatment of eNAD/EDM.

Late Devonian magmatism and clastic deposition in the upper Earn Group (central Yukon, Canada) mark the transition from passive to active margin along western Laurentia

The Earn Group of central Yukon records the transition from a passive to an active margin along western Laurentia in the Late Devonian. Fine-grained clastic rocks and chert of the lower Earn Group contain late Early to Middle Devonian fossils and were deposited in an offshelf environment. The upper Earn Group comprises a mixture of sandstone and conglomerate, fine-grained siliciclastic rocks, and widespread crystal lithic tuff. Zircons from this succession are precisely dated using chemical abrasion isotope dilution thermal ionization mass spectrometry (CA–ID–TIMS) methods on igneous (ca. 363 Ma) and detrital (ca. 378–363 Ma) grains and the ages were confirmed by Frasnian to Famennian fossils. Abrupt, along-strike facies changes within the upper Earn Group of the Glenlyon–Tay River area occur across mapped faults that are inferred to have originated as syndepositional extension faults in the Late Devonian. Occurrences of ca. 363 Ma tuff horizons within all facies of the upper Earn Group provide a temporal correlation across the area. Diorite plutons intrude lower Paleozoic rocks in the area and have U–Pb zircon crystallization dates of ca. 364 Ma. The diorite has calc-alkaline composition consistent with arc magmatism or crustal contamination. The Late Devonian magmatism in the Earn Group is coincident with onset of arc magmatism in the allochthonous Yukon–Tanana terrane, and extension related to rifting and opening of the Slide Mountain ocean in a back-arc setting. Magmatic rocks in the Earn Group of central Yukon thus represent part of a remnant continental arc and back-arc stranded behind the Slide Mountain ocean in the Mississippian.

Characterization of Chinese Grape Seed Oil by Physicochemical Properties, Fatty Acid Composition, Triacylglycrol Profiles, and Sterols and Squalene Composition

Abstract This work focused on physicochemical property assaying, fatty acid composition, triacylglycerol profiles, and sterols and squalene composition of the Chinese grape seed oil. Three different methods were used to extract oil from Chinese grape seeds, solvent extraction, cold press and hot press methods. Three oils all possess very low acid value and peroxide value, suggesting their good quality as edible oil. Fatty acid composition results indicated that the total content of unsaturated fatty acids was 89.14 %, within which the majority fatty acid was linoleic acid with content of 64.11 %. Characterization of triacylglycerol profiles was achieved by a two-dimensional HPLC coupling of nonaqueous reverse-phase and silver ion HPLC with atmospheric pressure chemical ionization mass spectrometry method. There was a total of 30 TAGs including 23 regioisomers that have been determined. Unsaponifiable matters composition results revealed that the total sterols content and the squalene content were 278.49 mg/100 g and 17.81 mg/100 g, respectively.

Development of a liquid chromatography atmospheric pressure chemical ionization mass spectrometry method for determining off-flavor compounds and its application toward marine recirculating aquaculture system monitoring and evaluation of aeration as a depuration approach

The off-flavor compounds geosmin and 2-methylisoborneol (2-MIB) are well-known to impact the quality of farmed freshwater fish species, but little is known about off-flavors in marine aquaculture. To begin addressing this knowledge gap, a method for determining geosmin and 2-MIB using LC with atmospheric pressure chemical ionization (APCI) MS detection was developed. While 2-MIB was readily detected using LC-APCI/MS, geosmin exhibited on-column degradation that was independent of column chemistry and could not be eliminated. Optimized conditions were identified that balanced the separation and ionization efficiency of 2-MIB and geosmin while minimizing geosmin degradation, but the overall method sensitivity for geosmin was reduced by the on-column losses. The method was used with direct aqueous injections to determine the volatilization rates of geosmin and 2-MIB at ppb levels during aeration under laboratory conditions in both salt water and pure water to simulate marine and fresh water aquaculture, respectively. The volatilization rates of both compounds were 30% faster in salt water than in fresh water with or without aeration, but aeration was found to enhance the rate by a factor of 2.5 in both water types. The LC-APCI/MS method was combined with stir bar sorptive extraction (SBSE) to achieve greater sensitivity for determining off-flavors in recirculating aquaculture system (RAS) water. Using SBSE-LC-APCI/MS, the LODs for geosmin and 2-MIB were 70 ng/kg (part per trillion) and 6 ng/kg, respectively. The on-column losses resulted in a relatively high LOD for geosmin that renders this method unsuitable for determining geosmin at the low ng/kg levels expected in RAS. SBSE using both grab water samples and an in-situ diving unit were used to evaluate 2-MIB levels in the culture water of two separate marine RAS that were supporting the growth of European sea bass but had differing levels of water treatment. 2-MIB was readily detected using both SBSE approaches in the RAS with less sophisticated treatment when the animal stocking density was at its highest (50 kg/m3) but was not detected in the more sophisticated RAS regardless of stocking density. Geosmin was not detected in either system, but the results were inconclusive given its higher LOD. These limited results suggest that the anaerobic water treatment components, present only in the more sophisticated RAS, maintained the level of 2-MIB below the LOD.

Direct Analysis of Carbonyl Compounds by Mass Spectrometry with Double-Region Atmospheric Pressure Chemical Ionization.

Direct analysis of highly reactive volatile species such as the aliphatic aldehydes as vital biomarkers remains a great challenge due to difficulties in the sample pretreatment. To address such a challenge, we herein report the development of a novel double-region atmospheric pressure chemical ionization mass spectrometry (DRAPCI-MS) method. The DRAPCI source implements a separated structural design that uses a focus electrode to divide the discharge and ionization region to reduce sample fragmentation in the ionization process. Counterflow introduction (CFI) configuration was adopted in the DRAPCI source to reduce background noise, while ion transmission efficiency was optimized through simulating the voltage of the focus electrode and the ion trajectory of the ion source. The limits of detection (LODs) of four carbonyl compounds cyclohexanone, hexanal, heptanal, and octanal by DRAPCI-MS were between 0.1 and 3 μg·m-3, approximately two to eight times lower than those by atmospheric pressure chemical ionization mass spectrometry. Additionally, the DRAPCI-MS method carried out effective in situ analyses of the volatile components in expired milk and the exhaled breath of smokers, demonstrating the DRAPCI-MS as a practical tool to analyze complex mixtures. The DRAPCI-MS method provides a rapid, sensitive, and high-throughput technique in the real-time analysis of gaseous small-molecule compounds.

Characterization of the Chemical Composition of Chinese Moringa oleifera Seed Oil

AbstractThis work focused on physicochemical property assaying, fatty acid composition, triacylglycerol (TAG) profiles, and unsaponifiable matter composition of the Chinese Moringa oleifera seed oil. The results indicated that there was no significant difference in approximate nutritional components between M. oleifera seeds from China and India, while variations in the mineral element contents are significant. Both the Soxhlet extraction method and the aqueous enzymatic extraction method were adopted to extract oil from Chinese M. oleifera seeds. Oil yield obtained using the Soxhlet extraction method was higher than that obtained using the aqueous enzymatic extraction method. While both the iodine value and unsaponifiable matter content of the aqueous enzymatic extracted oil were a little higher than that of the Soxhlet extracted oil. Both oils possess a very low acid value and peroxide value, suggesting their good quality as edible oil. Fatty acid composition results indicated that this oil was especially high in oleic acid. Characterization of the TAG composition was achieved by a two‐dimensional high‐performance liquid chromatography (HPLC) coupling of nonaqueous reverse‐phase and silver ion HPLC with the atmospheric pressure chemical ionization mass spectrometry method. A total of 22 TAG including 16 regioisomers were determined. Composition results of unsaponifiable matters revealed that this oil possesses a number of phytosterols, in which β‐sitosterol and stigmasterol are most predominant.

Trace level analysis of three glycol ethers in wood stains by APCI-LC-MS/MS

A direct injection liquid chromatography tandem atmospheric pressure chemical ionization mass spectrometry method was developed for determination of diethylene glycol methyl ether, dipropylene glycol butyl ether, and dipropylene glycol methyl ether.

Artifact-controlled quantification of folpet and phthalimide in food by liquid chromatography-high resolution mass spectrometry

The European residue definition for the pesticide folpet has changed in 2016 to include its degradation product phthalimide. According to recent studies, phthalimide could also arise from other sources than folpet, including formation in the injector of gas chromatography systems from the precursor phthalic acid or phthalic anhydride. A liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry (MS) method was developed for the quantification of folpet and phthalimide. High resolution MS was deemed necessary to increase the selectivity via accurate mass, as phthalimide and folpet yielded poor fragmentation. Sample preparation by QuEChERS was optimized to ensure the stability of folpet and to prevent the contamination of phthalimide from external sources. The method was validated on four matrices from four commodity groups (i.e., high water content, high water and acid content, high starch content and dairy products). Linearity was assessed with r2 > 0.99 over the range 5–200 μg kg−1, repeatability ranged between 6.8% and 14.5%, intermediate precision between 10% and 23.8%, and trueness was within 78.6% and 124.2% with relative standard deviation from 3% to 20%. These performance parameters were all compliant with the analytical requirements stipulated in the SANTE/11813/2017 document. The method was verified on 12 additional matrices from the 4 commodity groups. The present method was suitable for the quantification of folpet and phthalimide in foods while controlling analytical artifact.

Measurement of formic acid, acetic acid and hydroxyacetaldehyde, hydrogen peroxide, and methyl peroxide in air by chemical ionization mass spectrometry: airborne method development

Abstract. A chemical ionization mass spectrometry (CIMS) method utilizing a reagent gas mixture of O2, CO2, and CH3I in N2 is described and optimized for quantitative gas-phase measurements of hydrogen peroxide (H2O2), methyl peroxide (CH3OOH), formic acid (HCOOH), and the sum of acetic acid (CH3COOH) and hydroxyacetaldehyde (HOCH2CHO; also known as glycolaldehyde). The instrumentation and methodology were designed for airborne in situ field measurements. The CIMS quantification of formic acid, acetic acid, and hydroxyacetaldehyde used I− cluster formation to produce and detect the ion clusters I−(HCOOH), I−(CH3COOH), and I−(HOCH2CHO), respectively. The CIMS also produced and detected I− clusters with hydrogen peroxide and methyl peroxide, I−(H2O2) and I−(CH3OOH), though the sensitivity was lower than with the O2− (CO2) and O2− ion clusters, respectively. For that reason, while the I− peroxide clusters are presented, the focus is on the organic acids. Acetic acid and hydroxyacetaldehyde were found to yield equivalent CIMS responses. They are exact isobaric compounds and indistinguishable in the CIMS used. Consequently, their combined signal is referred to as the acetic acid equivalent sum. Within the resolution of the quadrupole used in the CIMS (1 m∕z), ethanol and 1- and 2-propanol were potential isobaric interferences to the measurement of formic acid and the acetic acid equivalent sum, respectively. The CIMS response to ethanol was 3.3 % that of formic acid and the response to either 1- or 2-propanol was 1 % of the acetic acid response; therefore, the alcohols were not considered to be significant interferences to formic acid or the acetic acid equivalent sum. The multi-reagent ion system was successfully deployed during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) in 2014. The combination of FRAPPÉ and laboratory calibrations allowed for the post-mission quantification of formic acid and the acetic acid equivalent sum observed during the Deep Convective Clouds and Chemistry Experiment in 2012.

UHPLC-APCI-MS Profiling of Triacylglycerols in Vegetable Oils—Application to the Analysis of Four North African Sesame Seed Varieties

Here, we describe an isocratic ultra-high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (UHPLC-APCI-MS) method for the characterization and the quantification of triacylglycerols (TAGs) in vegetable oils. The linearity and the precision of the method are validated, and the limits of detection are estimated. The APCI-MS detector shows a linear response from 1 to 1000 μg/mL, and the correlation coefficients (r2) obtained for standards TAGs exceed 0.995. As compared to previous methods, the proposed method is rapid, simpler, and more sensitive. The limits of detection estimated for several standard TAGs varies from 0.03 to 0.05 injected nanograms (6 to 10 μg/L). The application of the proposed method to the analysis of sesame oil allowed us to unambiguously identify 30 TAG species whereas previous methods have detected 19 TAGs, at the most. Among vegetable oils, sesame oil became an attractive target for adulteration due to its high commercial value. Most of the previous studies of TAG profiles of sesame oils had been devoted to the analysis of sesame oils originating from Asia and some Sub-Saharan countries. To the best of our knowledge, the TAG profiles of sesame oils from other origins are still unknown. The results we obtained for the four Tunisian sesame seed varieties clearly indicate that sesame oils can be classified according to their equivalent carbon number differences (ΔECN) with some rules similar to those required for olive oils.

Non-radioactive Chemical Ionization Mass Spectrometry Using Acetic Acid–Acetate Cluster as a Reagent Ion for the Real-time Measurement of Acids and Hydroperoxides

We have developed a non-radioactive chemical ionization mass spectrometry method using acetic acid–acetate cluster as the reagent ion. By electron impact onto an acetic anhydride–Ar gas mixture, a strong and single ion peak of the acetic acid–acetate cluster was observed. We demonstrated that the reagent ion can ionize carboxylic acids (RC(O)OH) and hydroperoxides (ROOH) produced in ethylene ozonolysis through the formation of adduct ions of these species and acetate. This technique could be used for the detection of various organic hydroperoxides as well as organic and inorganic acids in the atmosphere.

Direct high-precision U–Pb geochronology of the end-Cretaceous extinction and calibration of Paleocene astronomical timescales

The Cretaceous–Paleogene (K–Pg) boundary is the best known and most widely recognized global time horizon in Earth history and coincides with one of the two largest known mass extinctions. We present a series of new high-precision uranium–lead (U–Pb) age determinations by the chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) method from volcanic ash deposits within a tightly constrained magnetobiostratigraphic framework across the K–Pg boundary in the Denver Basin, Colorado, USA. This new timeline provides a precise interpolated absolute age for the K–Pg boundary of 66.021±0.024/0.039/0.081 Ma, constrains the ages of magnetic polarity Chrons C28 to C30, and offers a direct and independent test of early Paleogene astronomical and 40Ar/39Ar based timescales. Temporal calibration of paleontological and palynological data from the same deposits shows that the interval between the extinction of the dinosaurs and the appearance of earliest Cenozoic mammals in the Denver Basin lasted ∼185 ky (and no more than 570 ky) and the ‘fern spike’ lasted ∼1 ky (and no more than 71 ky) after the K–Pg boundary layer was deposited, indicating rapid rates of biotic extinction and initial recovery in the Denver Basin during this event.

Structure determination of organic aging products in lithium-ion battery electrolytes with gas chromatography chemical ionization mass spectrometry (GC-CI-MS)

For Gas Chromatography Chemical Ionization Mass Spectrometry (GC-CI-MS) method development, a standard lithium-ion battery (LIB) electrolyte was thermally aged at 95 °C for a faster generation of decomposition products.

Determination of Trialkyl Phosphates in Wastewater by Solid Phase Extraction–Flow Injection–Atmospheric Pressure Chemical Ionization–Mass Spectrometry

ABSTRACTA solid phase extraction–flow injection–atmospheric pressure chemical ionization–mass spectrometry method was developed for the determination of tris[2-chloroethyl]phosphate, tris[2-chloroisopropyl]phosphate, tris[1,3-dichloroisopropyl]phosphate, triethyl phosphate, tributyl-n-phosphate, and tris[2-butoxyethyl]phosphate in wastewater for degradation studies. The mass spectrometry conditions were optimized for each compound and collision-induced dissociation mass spectra were obtained. Lower limits of quantitation from 3.0 to 25.2 ng ml−1 for distilled water were obtained using a 30 mg solid phase extraction cartridge for a 25-fold sample concentration. The lower limits of quantitation were from 15.3 to 70.2 ng ml−1 for wastewater. A 100-fold sample concentration was achieved using a 500 mg cartridge, leading to lower limits of quantitation for trialkyl phosphates in wastewater between 6.3 ng ml−1 for tris[2-butoxyethyl]phosphate and 83 ng ml−1 for tris[1,3-dichloroisopropyl]phosphate. Recoveries for 50.0 ng ml−1 concentrations were from 69% for tris[2-chloroisopropyl]phosphate) to 92% for tris[1,3-dichloroisopropyl]phosphate. Wastewater blanks had peak areas comparable in size to a few ng ml−1 of trialkyl phosphates, presumably from matrix interferences and procedurally generated sample contamination. Evaporative concentration was employed to further increase the sensitivity for the trialkyl phosphates.

Novel Approach to Stable Chlorine Isotope Analysis using Gas Chromatography-Negative Chemical Ionization Mass Spectrometry

A novel approach to compound-specific stable chlorine isotope analysis is presented to overcome many of the major drawbacks of existing methods. Contemporary methods often require either several laborious off-line procedures prior to isotope analysis or complicated mathematical data calculations and evaluation schemes to derive the chlorine isotope ratios from the mass spectra. In contrast to previous methods, our on-line setup was based on the use of gas chromatography-negative chemical ionization mass spectrometry. The ion traces of 35Cl−(m/z 35) and 37Cl−(m/z 37) were recorded to directly determine the isotopic ratios of chlorine. The chlorine fragments were obtained from each specific chlorinated compound using the appropriate energy and an optimized acquisition mode, and the method completely avoided isobaric interferences. The principle and the mechanism of this approach were presented and explained using trichloroethene. Optimization of the gas chromatography-negative chemical ionization mass spectrometry parameters and method validation were achieved using chlorinated alkenes, chlorinated benzenes, and organochlorine pesticides. The sensitivity of the method over previous methods was significantly improved, and the ultra-trace injection amounts of 0.4–473.5 pmol resulted in standard deviations (1σ) ranging from 0.55‰–2.15‰. The present study suggested that the gas chromatography-negative chemical ionization mass spectrometry method offered an innovative approach to compound-specific chlorine isotope analysis, and it could facilitate the application of compound-specific stable chlorine isotope analysis in environmental fields.