Ion Electrospray Ionization Mass Spectrometry Research Articles

Development of ultrahigh-performance liquid chromatography/mass spectrometry and ultrahigh-performance supercritical fluid chromatography/mass spectrometry assays to determine the concentration of Bitrex™ and sodium saccharin in homemade facemask fit testing solutions.

RationaleFast and easily transferable chromatography/mass spectrometry assays were required to detect and quantify the amount of Bitrex™ and sodium saccharin in homemade facemask fit testing solutions.MethodsBitrex™ solutions were analysed using reversed‐phase ultrahigh‐performance liquid chromatography coupled with positive ion electrospray ionisation mass spectrometry (UHPLC/ESI‐MS). Separation was achieved using a mobile phase gradient with an Acquity BEH C18‐packed column. Sodium saccharin solutions were analysed using ultrahigh‐performance supercritical fluid chromatography coupled with negative ion electrospray ionisation (UHPSFC/ESI‐MS). Separation was achieved using isocratic elution with an Acquity UPC2 Torus Diol packed column and a methanol (25 mM ammonium acetate) co‐solvent.ResultsThe calibration curves obtained using the ratio of the active compound to an internal standard generated linear regression values (R2) >0.99. Samples analysed prior to and after an autoclave sterilisation process and bottling gave repeatable measurements within 10% of the expected concentration.ConclusionsThe two assays afford a fast robust and quantitative analytical method for the detection of the active components used to test the efficacy of the homemade facemask testing solutions.

Analysis of Flavonoids in Dalbergia odorifera by Ultra-Performance Liquid Chromatography with Tandem Mass Spectrometry.

Dalbergia odorifera, a traditional Chinese medicine, has been used to treat cardio- and cerebrovascular diseases in China for thousands of years. Flavonoids are major active compounds in D. odorifera. In this paper, a rapid and sensitive ultra-high performance liquid chromatography-triple quadrupole mass spectrometry method was developed and validated for simultaneous determination of 17 flavonoids in D. odorifera. Quantification was performed by multiple reaction monitoring using electrospray ionization in negative ion mode. Under the optimum conditions, calibration curves for the 17 analytes displayed good linearity (r2 > 0.9980). The intra- and inter-day precisions (relative standard deviations) were lower than 5.0%. The limit of quantitation ranged from 0.256 to 18.840 ng/mL. The mean recovery range at three spiked concentrations was 94.18–101.97%. The validated approach was successfully applied to 18 samples of D. odorifera. Large variation was observed for the contents of the 17 analytes. Sativanone and 3′-O-methylviolanone were the dominant compounds. The fragmentation behaviors of six flavonoids were investigated using UPLC with quadrupole time-of-flight tandem mass spectrometry. In negative ion electrospray ionization mass spectrometry, all the flavonoids yielded prominent [M − H]− ions. Fragments for losses of CH3, CO, and CO2 were observed in the mass spectra. Formononetin, liquiritigenin, isoliquiritigenin, sativanone, and alpinetin underwent retro-Diels–Alder fragmentations. The proposed method will be helpful for quality control of D. odorifera.

Cis/Trans Isomerization of Unsaturated Fatty Acids in Polysorbate 80 During Light Exposure of a Monoclonal Antibody-Containing Formulation.

Light exposure of a monoclonal antibody formulation containing polysorbate 80 (PS80) leads to cis/trans isomerization of monounsaturated and polyunsaturated fatty acids. This cis/trans isomerization was monitored by positive electrospray ionization mass spectrometry of intact PS80 components as well as by negative ion electrospray ionization mass spectrometry analysis of free fatty acids generated via esterase-catalyzed hydrolysis. The light-induced cis/trans isomerization of unsaturated fatty acids in PS80 required the presence of the monoclonal antibody, or, at a minimum (for mechanistic studies), a combination of N-acetyltryptophan amide and glutathione disulfide, suggesting the involvement of thiyl radicals generated by photoinduced electron transfer from Trp to the disulfide. Product analysis confirmed the conversion of PS80-bound oleic acid to elaidic acid; furthermore, together with linoleic acid, we detected conjugated linoleic acids in PS80, which underwent light-induced cis/trans isomerization.

A validated HPTLC method for the simultaneous quantifications of three phenolic acids and three withanolides from Withania somnifera plants and its herbal products

A simple, rapid and selective high-performance thin-layer chromatographic (HPTLC) method has been developed and validated for simultaneous determination of three withanolides (withaferin A, withanone and withanolide A) and three phenolic acids (caffeic acid, ferulic acid and benzoic acid) from different parts (root, stem and leaf) of Withania somnifera and its two commercially available polyherbal formulations. The extraction efficiency of withanolides and phenolic acids were tested using two solvents, chloroform and methanol, respectively. HPTLC separation was performed on silica coated aluminium plates Si 60F254; using toluene, ethyl acetate and acetic acid (60:40:4). The samples were quantitated at 231 nm. The purity and identity of peaks of all the six analytes were confirmed by matching Rf values and UV-spectrum with authentic standards. The identity of three withanolides was further confirmed by positive ion electrospray ionization mass spectrometry (ESI-MS/MS) analyses. The developed method was validated for sensitivity, linearity, reproducibility, accuracy, the limit of detection (LOD) and limit of quantification (LOQ) following the guidelines of the International Conference on Harmonization (ICH). The method was found to be linear (r > 0.99) in the range of 50–2000 ng/band for benzoic acid and 50–1000 ng/band for the other five studied metabolites. This simple and accurate HPTLC method provided enhanced resolution of studied analytes as compared to other phytoconstituents present in W. somnifera extracts. It has also been successfully applied in the analysis and quantification of two polyherbal formulations containing W. somnifera plant parts.

Understanding the Recovery of Rare-Earth Elements by Ammonium Salts

While the recovery of rare earth elements (REEs) from aqueous solution by ionic liquids (ILs) has been well documented, the metal compounds that are formed in the organic phase remain poorly characterized. Using spectroscopic, analytical, and computational techniques, we provide detailed chemical analysis of the compounds formed in the organic phase during the solvent extraction of REEs by [(n-octyl)3NMe][NO3] (IL). These experiments show that REE recovery using IL is a rapid process and that IL is highly durable. Karl-Fischer measurements signify that the mode of action is unlikely to be micellar, while ions of the general formula REE(NO3)4(IL)2− are seen by negative ion electrospray ionization mass spectrometry. Additionally, variable temperature 139La nuclear magnetic resonance spectroscopy suggests the presence of multiple, low symmetry nitrato species. Classical molecular dynamics simulations show aggregation of multiple ILs around a microhydrated La3+ cation with four nitrates completing the inner coordination sphere. This increased understanding is now being exploited to develop stronger and more selective, functionalized ILs for REE recovery.

High-molecular-weight esters in <i>α</i>-pinene ozonolysis secondary organic aerosol: structural characterization and mechanistic proposal for their formation from highly oxygenated molecules

Abstract. Stable high-molecular-weight esters are present in α-pinene ozonolysis secondary organic aerosol (SOA) with the two most abundant ones corresponding to a hydroxypinonyl ester of cis-pinic acid with a molecular weight (MW) of 368 (C19H28O7) and a diaterpenylic ester of cis-pinic acid with a MW of 358 (C17H26O8). However, their molecular structures are not completely elucidated and their relationship with highly oxygenated molecules (HOMs) in the gas phase is still unclear. In this study, liquid chromatography in combination with positive ion electrospray ionization mass spectrometry has been performed on high-molecular-weight esters present in α-pinene ozonolysis SOA with and without derivatization into methyl esters. Unambiguous evidence could be obtained for the molecular structure of the MW 368 ester in that it corresponds to an ester of cis-pinic acid where the carboxyl substituent of the dimethylcyclobutane ring and not the methylcarboxyl substituent is esterified with 7-hydroxypinonic acid. The same linkage was already proposed in previous work for the MW 358 ester (Yasmeen et al., 2010), but could be supported in the present study. Guided by the molecular structures of these stable esters, we propose a formation mechanism from gas-phase HOMs that takes into account the formation of an unstable C19H28O11 product, which is detected as a major species in α-pinene ozonolysis experiments as well as in the pristine forest atmosphere by chemical ionization–atmospheric pressure ionization–time-of-flight mass spectrometry with nitrate clustering (Ehn et al., 2012, 2014). It is suggested that an acyl peroxy radical related to cis-pinic acid (RO2⚫) and an alkoxy radical related to 7- or 5-hydroxypinonic acid (R′O⚫) serve as key gas-phase radicals and combine according to a RO2 + R′O⚫ → RO3R′ radical termination reaction. Subsequently, the unstable C19H28O11 HOM species decompose through the loss of oxygen or ketene from the inner part containing a labile trioxide function and the conversion of the unstable acyl hydroperoxide groups to carboxyl groups, resulting in stable esters with a molecular composition of C19H28O7 (MW 368) and C17H26O8 (MW 358), respectively. The proposed mechanism is supported by several observations reported in the literature. On the basis of the indirect evidence presented in this study, we hypothesize that RO2 + R′O⚫ → RO3R′ chemistry is at the underlying molecular basis of high-molecular-weight ester formation upon α-pinene ozonolysis and may thus be of importance for new particle formation and growth in pristine forested environments.

LC–MS–MS and GC–MS analyses of biologically active extracts of Tunisian Fenugreek (Trigonella foenum-graecum L.) Seeds

The objective of this study is to investigate the chemical composition of biologically active extracts from Fenugreek (Trigonella foenum-graecum L.) Seeds. A variety of in vitro models such as β-carotene-linoleic acid and 1,1-diphenyl-2-picryl hydrazyl (DPPH) were used to measure the antioxidant activity. Alpha-amylase inhibitory activity was evaluated by enzyme inhibition using in vitro assay. The hexane extract with a potent inhibition ability against linoleic acid (95.4%) as well as a powerful α-amylase inhibitory activity (IC50 = 26.9 µg/mL) was analyzed by gas chromatography coupled with mass spectrometry (GC–MS). A total of 20 compounds were identified, some of them being reported for the first time in fenugreek seeds [e.g. β-thujone (10.8%), (2E, 4E)-decadienal (7.8%), heptanal (6.7%), and (2E, 4E)-heptadienal (5.3%)]. On the other hand, methanol extract exhibited a strong DPPH radical-scavenging activity (IC50 = 19.0 µg/mL) compared to that of BHT as well as the highest alpha-amylase inhibitory activity (IC50 = 52.1 μg/mL). HPLC technique coupled with negative ion electrospray ionization mass spectrometry and diode array detection (HPLC-DAD–ESI/MS) was employed to identify polyphenols in the methanol extract. The obtained results allowed the detection of 3 flavonoids glycosides and one amino acid identified on the basis of their UV and MS spectra, and comparisons with standards when available, as well as with literature data. A systematic study of the obtained MS spectra and the observed fragmentation allowed identifying for known compounds: vicenin-2, 4-hydroxyisoleucine, isoschaftoside and isoorientin. These two last compounds were identified for the first time in Fenugreek Seeds.

Quantification of three beta-lactam antibiotics in breast milk and human plasma by hydrophilic interaction liquid chromatography/positive-ion electrospray ionization mass spectrometry.

The use of cephalosporins during breast feeding raises several issues, including the risk of drug exposure through breast milk for the infant. In this paper, a hydrophilic interaction liquid chromatography/positive ion electrospray mass spectrometric assay (HILIC/ESI-MS) was developed for the quantitation of cefuroxime, cefoxitin, and cefazolin in breast milk and human plasma. The assay was based on the use of small sample size, 25 μL of biological samples, following acetonitrile precipitation of proteins and filtration that enabled injection into the HILIC/ESI-MS system. All analytes and the internal standard, alfuzosin, were separated by using a ZIC®-HILIC analytical column (150.0 × 2.1 mm i.d., particle size 3.5 µm, 200 Å) with isocratic elution. The mobile phase was composed of a 6% 12.5 mM ammonium acetate water solution in acetonitrile and pumped at a flow rate of 0.25 mL min-1 . The assay was linear over a concentration range of 0.2 to 5 µg mL-1 and 0.4 to 20 µg mL-1 for all the analytes in breast milk and in human plasma, respectively. Intermediate precision was found to be less than 4.2% over the tested concentration ranges. A run time of less than 12 min for each sample made it possible to analyze a large number of biological samples per day. The method is the first reported application of HILIC in the analysis of antibiotics in breast milk and human plasma and it can be used to support a wide range of clinical studies. Copyright © 2016 John Wiley & Sons, Ltd.

Reduced matrix effects for anionic compounds with paired ion electrospray ionization mass spectrometry

It is well-known that matrix effects in high performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS) can seriously compromise quantitative analysis and affect method reproducibility. Paired ion electrospray ionization (PIESI) mass spectrometry is an approach for analyzing ultra-low levels of anions in the positive ion mode. This approach uses a structurally optimized ion pairing reagent to post-column associate with the anionic analyte, subsequently forming positively charged complexes. These newly formed complex ions are often more surface-active as compared to either the native anion or the ion pairing reagent. No studies have examined whether or not the PIESI approach mitigates matrix effects. Consequently, a controlled study was done using five analytes in highly controlled and reproducible synthetic groundwater and urine matrices. In addition, two different mass spectrometers (linear ion trap and triple quadrupole) were used. Compared to the negative ion mode, the PIESI-MS approach was less susceptible to matrix effects when performed on two different MS platforms. Using PIESI-MS, less dilution of the sample is needed to eliminate ionization suppression which, in turn, permits lower limits of detection and quantitation.

Sensitive detection of anionic metabolites of drugs by positive ion mode HPLC-PIESI-MS

The detection window for drugs of abuse, including performance-enhancing drugs, is limited by the sensitivity of analytical methodologies. Herein, paired ion electrospray ionization mass spectrometry (PIESI-MS) was employed for sensitive analysis of performance-enhancing drugs and drugs of abuse by detecting their glucuronide and sulfate conjugates. The proposed approach provides enhanced sensitivity for these drug metabolites, and overcomes the drawbacks of the less sensitive negative ion mode ESI-MS by detecting the anionic metabolites in the positive ion mode at higher m/z where the background noise is less. Absolute LODs down to sub-pg levels were obtained with the use of the optimal symmetrical or unsymmetrical ion pairing reagents. One to three orders of magnitude improvement were obtained compared to other reported methods performed in the negative ion mode. Structurally similar steroid conjugates were chromatographically separated and detected by HPLC coupled with PIESI-MS. Finally, an off-line solid phase extraction (SPE) protocol was successfully developed to eliminate any matrix effects in the analysis of human urine samples.

Microquantification of inorganic and organic phosphate by negative ion electrospray tandem mass spectrometry.

A new method for inorganic phosphate microquantification is introduced based on negative ion electrospray tandem mass spectrometry and stable isotope dilution by (18)O4-labeled phosphate. Quantification is performed using the non-labeled and (18)O3-labeled [P(18)O3](-) fragment ions at m/z 79 and 85, respectively, formed by dissociation of the [H2PO4](-) ion at m/z 97 and 105, respectively, visible in negative ion electrospray ionization mass spectrometry (ESI-MS) spectra. Tandem mass spectrometry was selected to remove an overlap with the isobaric [HSO4](-) ion at m/z 97 of sulfate and to establish an optimal sensitivity of the quantification assay. It is demonstrated that the assay can also measure the sum of inorganic and phosphoryl phosphate by prior enzymatic hydrolysis of phosphoryl phosphate. The assay works with phosphate concentrations in the micromolar range and, in combination with nano-ESI, is capable to quantitate absolute amounts of phosphate in the low nanogram range from complex samples.

Characterization of flavonoid glycosides from fenugreek (Trigonella foenum-graecum) crude seeds by HPLC-DAD-ESI/MS analysis.

Fenugreek (Trigonella foenum-graecum) is a medicinal plant which is widely used for its pharmacological properties. In this study the phenolic composition of fenugreek crude seeds originating from Morocco has been investigated. Extraction was performed from defatted seeds by a hydromethanolic solution using an Accelerated Solvent Extractor. HPLC technique coupled to negative ion electrospray ionization mass spectrometry and diode array detection was employed to identify the polyphenol in the obtained extract. The obtained results allowed the detection of 32 phenolic compounds among which various flavonoid glycosides and phenolic acids have been tentatively identified on the basis of their UV and MS spectra, and comparisons with standards when available, as well as with literature data. A systematic study of the obtained MS spectra and the observed fragmentation showed that most of the identified compounds were acylated and non-acylated flavonoids with apigenin, luteolin and kaempferol as aglycons. Hydroxycinnamic acids mostly dominated by caffeic acid derivatives were also detected. The quantitative analysis of the identified compounds showed that the phenolic composition of the studied crude fenugreek seeds was predominantly acylated and non-acylated flavone derivatives with apigenin as the main aglycon.

Proanthocyanidins in wild sea buckthorn (Hippophaë rhamnoides) berries analyzed by reversed-phase, normal-phase, and hydrophilic interaction liquid chromatography with UV and MS detection.

A rapid and sensitive method for profiling of proanthocyanidins (PAs) of sea buckthorn (Hippophaë rhamnoides) berries was established based on aqueous, acidified acetone extraction. The extract was purified by Sephadex column chromatography and analyzed using reversed-phase, normal-phase, and hydrophilic interaction liquid chromatography (HILIC). Negative ion electrospray ionization mass spectrometry (ESI-MS) in single ion recording (SIR) and full scan modes combined with UV detection were used to define the combinations and ratios of PA oligomer classes. PAs with degree of polymerization from 2 to 11 were detected by HILIC-ESI-MS. Quantification of dimeric, trimeric, and tetrameric PAs was carried out with ESI-MS-SIR, and their molar proportions were 40, 40, and 20%, respectively. Only B-type PAs were found, and (epi)gallocatechins were the main monomeric units. More than 60 combinations of (epi)catechins and (epi)gallocatechins of proanthocyanidin dimers and trimers were found. A majority of the PAs were shown to be higher polymers based on the HILIC-UV analysis.

Novel formation of [2M-H](+) species in positive electrospray mass spectra of indoles.

When subjected to positive ion electrospray ionisation (ESI+) mass spectrometry (MS), indoles with a 3-alkyl substituent show a propensity to form novel [2M-H](+) 'covalently bound dimers'. This process, which appears to be initiated in the nebuliser of the instrument, is mechanistically interesting, analytically useful and potentially significant in organic synthesis. A selection of 2- and 3-substituted indoles have been synthesised and analysed by ESI-MS. The formation of the 'homo' and 'hetero' dimers of these compounds has been investigated using ESI+ mode. The mechanism of formation of the observed 'dimeric' species has been probed by synthesising authentic samples of the dimeric compounds. 'Dimeric' species corresponding to [2M-H](+) have been observed for all 3-substituted indoles studied, but not for indoles substituted in just the 2-position. By infusing equimolar mixtures of labelled and unlabelled indoles through the instrument, the expected approximately statistical mixture of homo- and heterodimeric species has been observed. Further experiments have established that this novel dimerisation occurs in the droplets formed in the nebuliser of the instrument. It has been shown that 3-substituted indoles form [2M-H](+) dimers in high abundance in the spray obtained from the nebiliser of an ESI+ instrument. The mechanism for the dimerisation does not involve the known 2M dimeric species that is readily formed in the solution-phase chemistry of indoles.

Identification and quantification of flavonoid glycosides from fenugreek (Trigonella foenum-graecum) germinated seeds by LC–DAD–ESI/MS analysis

The phenolic composition of fenugreek (Trigonella foenum-graecum) germinated seeds originating from Morocco has been investigated. After germination, extraction was performed from defatted germinated seeds by a hydromethanolic solution using an accelerated solvent extractor. HPLC coupled to negative ion electrospray ionization mass spectrometry and diode array detection was employed to identify the polyphenol in the obtained fenugreek germinated seeds extract. A total of 28 identified phenolic compounds were grouped into flavone di C-glycosides, flavonol O-diglycosides, flavone tri- and tetra O-, C-glycosides and acylated flavone O-, C-glycosides. Most of the identified flavones were apigenin and luteolin adducts, while only two kaempferol glycosides were detected as flavonols. Quantitative analysis of the identified compounds showed that the phenolic composition of the studied germinated fenugreek seeds was predominated by acylated and non-acylated flavone derivatives with apigenin as main aglycone. Germinated fenugreek seeds could be considered as a rich source of bioactive phenolic compounds.

Ion chromatography electrospray ionization mass spectrometry method development and investigation of lithium hexafluorophosphate-based organic electrolytes and their thermal decomposition products

A method based on the coupling of ion chromatography (IC) and electrospray ionization mass spectrometry (ESI-MS) for the separation and determination of thermal decomposition products of LiPF6-based organic electrolytes is presented. The utilized electrolytes, LP30 and LP50, are commercially available and consist of 1mol/l LiPF6 dissolved in ethylene carbonate/dimethyl carbonate and ethylene carbonate/ethyl methyl carbonate, respectively. For the separation method development three ion chromatographic columns with different capacity and stationary phase were used and compared. Besides the known hydrolysis products of lithium hexafluorophosphate, several new organophosphates were separated and identified with the developed IC-ESI-MS method during aging investigations of the electrolytes. The chemical structures were elucidated with IC-ESI-MS/MS

Mechanism and Sensitivity of Anion Detection Using Rationally Designed Unsymmetrical Dications in Paired Ion Electrospray Ionization Mass Spectrometry

Paired ion electrospray ionization (PIESI) mass spectrometry was developed as a useful technique that provides sensitive detection for anions in the positive ion mode. The ion-pairing reagent (IPR) utilized plays an essential role affecting the detection limits. This work describes the design and synthesis of two novel dications with unsymmetrical structures and their utilization for anion detection and mechanistic insights. The performance of dications was evaluated for seven selected anions in both single ion monitoring (SIM) mode and selected reaction monitoring (SRM) mode. The unsymmetrical dications allowed sensitive detection for these anions with down to subpicogram limits of detection (LOD) and an improved sensitivity from 1.5 to 12 times compared to the corresponding symmetrical dications. The enhanced sensitivity could be attributed to the surface activity of the unsymmetrical dications, which results in a concurrent strong partitioning of the anion to the aerosol droplet surface. Surface activity measurements of the anion/IPR complex were conducted, and a correlation between the observed ESI responses and the surface activity of the complex was found. The mechanism was further explored and explained based on the concepts of the equilibrium partitioning model (EPM).

Separation and sensitive determination of sphingolipids at low femtomole level by using HPLC-PIESI-MS/MS

A highly sensitive paired ion electrospray ionization mass spectrometry (PIESI-MS) approach was developed for the trace determination of sphingolipids. Apart from their structure role, specific sphingolipids can play a role in cell signaling and as disease markers. With the optimal pairing reagents, detection limits ranged from low femtomole to picomole levels for 14 selected sphingolipids. This improved the detection sensitivity of ESI-MS for many of these analytes up to ~4000 times.

Hydrophilic interaction liquid chromatography/positive ion electrospray ionization mass spectrometry method for the quantification of alprazolam and α-hydroxy-alprazolam in human plasma

A hydrophilic interaction liquid chromatography/positive ion electrospray-mass spectrometry (HILIC-ESI/MS) has been developed and fully validated for the quantification of alprazolam and its main metabolite, α-hydroxy-alprazolam, in human plasma. The assay is based on 50μL plasma samples, following liquid-liquid extraction. All analytes and the internal standard (tiamulin) were separated by hydrophilic interaction liquid chromatography using an X-Bridge-HILIC analytical column (150.0mm×2.1mm i.d., particle size 3.5μm) under isoscratic elution. The mobile phase was composed of a 7% 10mM ammonium formate water solution in acetonitrile and pumped at a flow rate of 0.20mLmin(-1). Running in positive electrospray ionization and selected ion monitoring (SIM) the mass spectrometer was set to analyze the protonated molecules [M+H](+) at m/z 309, 325 and 494 for alprazolam, α-hydroxy-alprazolam and tiamulin (ISTD) respectively. The assay was linear over the concentration range of 2.5-250ngmL(-1) for alprazolam and 2.5-50ngmL(-1) for α-hydroxy alprazolam. Intermediate precision was less than 4.1% over the tested concentration ranges. The method is the first reported application of HILIC in the analysis benzodiazepines in human plasma. With a small sample size (50μL human plasma) and a run time less than 10.0min for each sample the method can be used to support a wide range of clinical studies concerning alprazolam quantification.

One-year study of nitro-organic compounds and their relation to wood burning in PM10 aerosol from a rural site in Belgium

Nitro-organic compounds were determined in a one-year set of atmospheric PM10 filter samples that were collected at a rural background site in Hamme, Belgium. In an earlier study, it was found that the site was substantially impacted by wood burning, making the filter samples appropriate for further investigations on wood burning indicators. In total, four groups of nitro-aromatic compounds (with molecular weights (MWs) of 139, 155, 169, and 183), α-pinene-related nitrooxy-organosulfates (MW 295), and the resin acid dehydroabietic acid (DHAA, MW 300) were quantified using liquid chromatography combined with negative ion electrospray ionization mass spectrometry. The annual mean concentrations were 0.94, 6.0, 7.7, 4.8, 7.8, and 1.76 ng m−3 for the sum of the nitrophenols (MW 139), 4-nitrocatechol (MW 155), the sums of the methyl-nitrocatechols (MW 169), of the dimethyl-nitrocatechols (MW 183), and of the α-pinene-related nitrooxy-organosulfates (MW 295), and DHAA (MW 300), respectively. 4-nitrocatechol, the sum of the methyl-nitrocatechols, and the sum of the dimethyl-nitrocatechols were substantially correlated with levoglucosan (r-values of 0.71, 0.66, and 0.65, respectively), consistent with their proposed origin from biomass burning. The nitro-aromatic compounds were also observed during the summer months, indicating a non-negligible usage of wood burning for domestic purposes at the site. The α-pinene-related nitrooxy-organosulfates (MW 295) were detected in high concentrations during the winter period, but they were poorly correlated with the biomass burning tracers. All of the targeted species showed a clear seasonal variation with highest concentrations in winter, followed by autumn, spring, and summer. Based on the DHAA measurements, it is suggested that burning of softwood is likely an important source for the formation of all the nitro-organic compounds measured.