GC-QTOF MS Research Articles

Analyses and profiling of extract and fractions of neglected weed Mimosa pudica Linn. traditionally used in Southeast Asia to treat diabetes

Mimosa pudica Linn. var. hispida Bren. (Family: Fabaceae) a neglected weed has been studied for its antidiabetic potential to propose alternative medicinal source against the global threat of diabetes mellitus. This study aimed to investigate in vitro inhibitory activity against diabetic enzymes (i.e. α-amylase & α-glucosidase) and three anti-oxidant assays were conducted to evaluate anti-diabetic potential of M. pudica’s methanol extract (MeOHi) and its sub-fractions (Hexanef, EtOAcf, Acetonef and MeOHf). In depth chemical profiling using GC Q-TOF MS was also performed for the first time for this weed, to assess the probable compounds present in the extract and sub fractions that could be linked to anti-diabetic activity. Results showed the lowest (7.18±0.0005) and highest (158.4±0.0004) IC50 for DPPH assay by MeOHi and MeOHf, respectively. Acetonef and MeOHi showed the highest TPC (60.07±1.066) and TFC (16.97±1.472), respectively. Three and two fold higher inhibitory activity than the standard acarbose at 1mg/ mL was manifested by MeOHi (95.65±0.911) & EtOAcf (51.87±3.106), respectively. Hexanef did not show inhibitory activity against both the enzymes. α-glucosidase results for the extract and sub fractions were found to be significant (p<0.05). GC Q-TOF MS analysis identified organic acids, quinolones, quinone, phenolic compounds and dodecaborane as major constituents. Presence of highly radical scavenging dodecaborane is being reported for the first time in M. pudica. High TPC and TFC values could be attributed to exert enzyme inhibitory action by M. pudica that can help in the regulation of glucose absorption and consequently glucose homeostasis. Results show that M. pudica can be proposed as an excellent alternative for future anti-diabetic implications.

Negative chemical ionization gas chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry and automated accurate mass data processing for determination of pesticides in fruit and vegetables.

Gas chromatography coupled to high resolution hybrid quadrupole time-of-flight mass spectrometry (GC-QTOF MS), operating in negative chemical ionization (NCI) mode and combining full scan with MSMS experiments using accurate mass analysis, has been explored for the automated determination of pesticide residues in fruit and vegetables. Seventy compounds were included in this approach where 50% of them are not approved by the EU legislation. A global 76% of the analytes could be identified at 1μgkg(-1). Recovery studies were developed at three concentration levels (1, 5, and 10μgkg(-1)). Seventy-seven percent of the detected pesticides at the lowest level yielded recoveries within the 70%-120% range, whereas 94% could be quantified at 5μgkg(-1), and the 100% were determined at 10μgkg(-1). Good repeatability, expressed as relative standard deviation (RSD <20%), was obtained for all compounds. The main drawback of the method was the limited dynamic range that was observed for some analytes that can be overcome either diluting the sample or lowering the injection volume. A home-made database was developed and applied to an automatic accurate mass data processing. Measured mass accuracies of the generated ions were mainly less than 5ppm for at least one diagnostic ion. When only one ion was obtained in the single-stage NCI-MS, a representative product ion from MSMS experiments was used as identification criterion. A total of 30 real samples were analyzed and 67% of the samples were positive for 12 different pesticides in the range 1.0-1321.3μgkg(-1).

Application of gas chromatography-high resolution quadrupole time of flight mass spectrometry to the analysis of benzaldehyde, benzyl alcohol acetophenone and phenylacetaldehyde in complex aromatic samples

The study focuses on the quantitative analytical characterization of benzaldehyde, benzyl alcohol, acetophenone and phenylacetaldehyde in complex aromatic samples by gas chromatography-high resolution quadrupole time of flight mass spectrometry (GC-QTOF MS). The four compounds in real sample were accurately qualified and quantified through a comprehensive analysis of the GC retention times and the accurate masses of the ion fragments obtained by the high resolution MS. The new method therefore effectively avoids the interference of the real sample substrate, which reduces the accuracy of the analysis results. The peak area of the characteristic ion fragment for each compound was used for quantitation calculation. The MS signal responses of the four compounds showed good linear relationships with the corresponding mass concentrations and the linear regression coefficients were greater than 0. 99. The method recoveries were 87. 97% - 103.01%. The limits of detection (LODs) were 0. 01, 0. 03, 0. 02 and 0. 01 mg/L for benzaldehyde, benzyl alcohol, acetophenone and phenylacetaldehyde respectively. The contents of the four compounds in three real samples were analyzed. The study provided a new strategy for oxygenate analysis in complex aromatic samples using GC-QTOF MS. By measuring the accurate masses, the new method reduces the reliance on chromatographic separation ability and makes up the shortcomings of the traditional GC-MS methods.

Suspected-target pesticide screening using gas chromatography–quadrupole time-of-flight mass spectrometry with high resolution deconvolution and retention index/mass spectrum library

A strategy for suspected-target screening of pesticide residues in complicated matrices was exploited using gas chromatography in combination with hybrid quadrupole time-of-flight mass spectrometry (GC–QTOF MS). The screening workflow followed three key steps of, initial detection, preliminary identification, and final confirmation. The initial detection of components in a matrix was done by a high resolution mass spectrum deconvolution; the preliminary identification of suspected pesticides was based on a special retention index/mass spectrum (RI/MS) library that contained both the first-stage mass spectra (MS1 spectra) and retention indices; and the final confirmation was accomplished by accurate mass measurements of representative ions with their response ratios from the MS1 spectra or representative product ions from the second-stage mass spectra (MS2 spectra). To evaluate the applicability of the workflow in real samples, three matrices of apple, spinach, and scallion, each spiked with 165 test pesticides in a set of concentrations, were selected as the models. The results showed that the use of high-resolution TOF enabled effective extractions of spectra from noisy chromatograms, which was based on a narrow mass window (5mDa) and suspected-target compounds identified by the similarity match of deconvoluted full mass spectra and filtering of linear RIs. On average, over 74% of pesticides at 50ng/mL could be identified using deconvolution and the RI/MS library. Over 80% of pesticides at 5ng/mL or lower concentrations could be confirmed in each matrix using at least two representative ions with their response ratios from the MS1 spectra. In addition, the application of product ion spectra was capable of confirming suspected pesticides with specificity for some pesticides in complicated matrices. In conclusion, GC–QTOF MS combined with the RI/MS library seems to be one of the most efficient tools for the analysis of suspected-target pesticide residues in complicated matrices.

Analysis of Volatile Compounds from Siraitia grosvenorii by Headspace Solid-Phase Microextraction and Gas Chromatography-Quadrupole Time-of-Flight Mass Spectrometry

Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-quadrupole time-of-flight mass spectrometry (GC-QTOF MS) has been used in the present study to isolate and identify volatile components from Siraitia grosvenorii, a herbaceous perennial vine used as a natural sweetener and medicine. Compared with the static HS extraction and the different SPME fiber coatings, HS-SPME with divinylbenzene/carboxen/polydimethylsiloxane fiber was preferred to extract the target analytes including aldehyde, alcohol, acid, ester and other compounds. In the identification, a multi-dimensional qualitative analysis approach containing library searching, retention index comparison, accurate mass measurement, the second-stage mass spectrum (MS(2) spectrum) and area normalization was utilized. Finally, a total of 46 compounds were identified from S. grosvenorii. Among them, n-hexadecanoic acid, 5-hydroxymethylfurfural, 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, (Z, Z)-9,12-octadecadienoic acid and (E, E)-2,4-nonadienal were the main volatile components. The results showed that HS-SPME coupled with GC-QTOF MS is efficient for the extraction of polar volatiles from S. grosvenorii and accurate for the identification of volatile compounds in the complicated matrix.

Identification of pesticide residues in common fruits and vegetables by gas chromatography-quadrupole time-of-flight mass spectrometry

A new screening method was developed for the determination of 152 pesticide multi-residues in different chemical species with a Carbon NH2 column using solid-phase extraction (SPE) coupled with gas chromatography-quadrupole time-of-flight mass spectrometry (GC-QTOF MS). In the first stage (MS1) accurate mass database, up to three-five ions of the pesticides were monitored. The presence of at least three ions and the accomplishment of the intensity ratio (Q/q(i)) within the established tolerances were used as the confirmation of intensity criteria. The pesticides which have less characteristic ions or the peaks of the characteristic ions detected were up the tolerance were determined in the second stage (MS2) and the spectral difference was evaluated using MS2 library for the identified. Cabbage, tomato, pear were selected as typical fruits and vegetables to spike and detected all the 152 pesticides at two concentration levels of 5.0 and 10.0 microg/kg. The recoveries in the range of 70%-120% at two concentration levels were 91.45% and 94.08% for cabbage, 88.20% and 88.80% for tomato, 86.84% and 92.10% for pear respectively. Using the established 152 pesticide MS2 library some suspected pesticides were identified, and at the same time the analysis scope was expanded.

Reliable screening of pesticide residues in maternal and umbilical cord sera by gas chromatography-quadrupole time of flight mass spectrometry

The widespread use of pesticides induces heavy adverse effects on human health, especially for the pregnant women and the newborns. In this study, a screening method has been developed for the determination of multi-pesticides in maternal and umbilical cord sera. All pesticides in sera were collected using solid phase extraction (SPE), and analyzed by gas chromatography-quadrupole time of flight mass spectrometry (GC-QTOF MS). To set up the quality criteria, a database of 50 pesticides was created and the accurate masses of 3 up to 5 representative ions with their intensity ratios were included for each pesticide. In addition, a novel "identification points" (IPs) system relying on the accurate MS1 and MS2 spectra was used to interpret the data for each suspected pesticide. The methodology was then applied to a pair of maternal and umbilical cord sera. A total of six pesticide residues were screened out successfully. In conclusion, GC-QTOF MS combined with an accurate mass database seemed to be one of the most efficient tools for systematic pesticide analysis.

Rapid simultaneous screening and identification of multiple pesticide residues in vegetables

A method for the rapid simultaneous screening and identification of multiple pesticide residues in vegetables was established using a novel database and gas chromatography in combination with hybrid quadrupole time-of-flight mass spectrometry (GC–QTOF MS). A total of 187 pesticides with different chemical species were measured by GC–QTOF MS to create the database, which collected the retention time and exact masses of ions from the first-stage mass spectrum (MS1 spectrum) and second-stage mass spectrum (MS2 spectrum) for each pesticide. The workflow of the created database consisted of “MS1 screening” for possible pesticides by chemical formula match and “MS2 identification” for structural confirmation of product ion by accurate mass measurement. To evaluate the applicability of the database, a spinach matrix was prepared by solid phase extraction, spiked with a mixture of 50 pesticides at seven concentrations between 0.1 and 10ppb, and analyzed by GC–QTOF MS. It was found that all of the 50 pesticides with concentrations as low as 5ppb were detected in the “MS1 screening” step and accurate masses were identified with errors less than 2.5mDa in the “MS2 identification” step, indicating high sensitivity, accuracy, selectivity and specificity. Finally, to validate the applicability, the new method was applied to four fresh celery, rape, scallion and spinach vegetables from a local market. As a result, a total of 13 pesticides were found, with 11 in celery, 9 in rape, 3 in scallion and 2 in spinach. In conclusion, GC–QTOF MS combined with an exact mass database is one of the most efficient tools for the analysis of pesticide residues in vegetables.