External Calibration Method Research Articles

Multibranch Gold Nanoparticles as Surface-Enhanced Raman Spectroscopy Substrates for Rapid and Sensitive Analysis of Fipronil in Eggs.

A sensitive strategy to rapidly detect fipronil residues in eggs using multibranch gold nanoparticles (AuNPs) as the substrate of surface-enhanced Raman spectroscopy (SERS) was investigated in this study. Under optimized conditions, fipronil molecules preferentially deposited on the multibranch gold nanoparticles with preferential (111) facet-oriented growth due to its low surface energy. This anisotropic growth promoted the increase of SERS “hot spots”, inducing a huge enhancement of Raman signals of the fipronil. An external standard calibration method was employed for quantitative analysis, and the method was validated for linearity, sensitivity, repeatability and recovery. Good linearity were found in the concentration range of 10 ng/L~10 mg/L in fipronil acetone solution (R2 = 0.9916) and 8 × 10−5 mg/m2 to 0.8 mg/m2 on eggshells (R2 = 0.9906), respectively. The recovery rate based on acetone recovered fipronil on eggshells and in egg liquids was 80.13%~87.87%, and 81.34%~88.89%, respectively. The SERS assay was successfully used to monitor fipronil in eggs.

Direct determination of Cr and Ni in oil samples by isotope dilution and external standard calibration using inductively coupled plasma mass spectrometry

In the present work, a method for the determination of Ni and Cr in crude oil samples and derivatives (petroleum asphalt cement (CAP) and malthene) through direct analysis of samples diluted in a mixture of organic solvents (xylene/butanol), by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS), was developed. An exciting advantage of the proposed method was the addition of a polar solvent (butanol) to xylene, which has allowed the dilution of the samples, making possible the use of aqueous standards for the isotope dilution, without phase separation. For comparison, external standard calibration was carried out with organic standards and dilution in the same solvent. The spectrometer was set up and the instrumental parameters were optimized for the introduction of organic samples. Oxygen was introduced into the plasma to avoid carbon build-up at the interface. For interference correction from 40Ar12C+ over 52Cr+, the dynamic reaction cell was employed with CH4 as reaction gas. Accuracy evaluation was performed by analyzing the standard reference material NIST SRM 1084a (wear-metals in lubricant oil). The agreement between the obtained results and the SRM values were within the range of 95% to 106%. The RSDs were lower than 12% for the isotope dilution, and 10% for external standard calibration. The results obtained for Ni and Cr in crude oil and derivatives have shown that both calibration methods are statistically in agreement. Although isotope dilution is not commonly used for routine analysis, it has the potential to be. The time necessary for sample preparation could be reduced with the employment of an autodiluter, and the cost of enriched isotopes is a relative issue. The ID can also be employed as a primary method to verify the accuracy of external standard calibration methods.

Simultaneous determination of 25 pesticides in Zizania latifolia by dispersive solid-phase extraction and liquid chromatography-tandem mass spectrometry

An improved quick, easy, cheap, effective, rugged, and safe (QuEChERS) method combined with ultrapressure liquid chromatography tandem mass spectrometric method (UPLC-MS/MS) was developed to simultaneously determine 25 pesticides in Zizania latifolia. The samples were extracted with methanol(MeOH) and 0.1% formic acid (80:20, v/v) and cleaned with C18 absorbent and primary-secondary amine (PSA). LC separation was performed on a BEH C18 UPLC column under the condition of gradient elution with the mobile phase consisted of 0.5% formic acid (10 mM ammonium acetate)/MeOH. External standard calibration method with matrix-matched was used for quantification, and good linearity was obtained over a concentration range of 0.5–100 μg/l, with correlation coefficients greater than 0.9901. The limit of detection (LOD) and the limit of quantitation (LOQ) of the 25 pesticides were in the range of 0.2–1.0 µg/kg and 0.5–3.3 µg/kg, respectively. The recoveries ranged from 72% to 118%, and the relative standard deviations (RSDs) were less than 20%. Thus, the proposed method is suitable for the simultaneous determination of 25 pesticides in Z. latifolia.

The use of dried matrix spot for determination of Pb and Ni in automotive gasoline by solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry

In this work a simple and practical method for the determination of Pb and Ni in automotive gasoline by solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry was investigated. In the proposed method, disks of filter paper were used to pre-concentrate and store Pb, Ni and other trace elements from automotive gasoline samples. For this, a volume of sample was deposited and dried out on a filter paper disk previously adapted into a polytetrafluoroethylene mold, and then the gasoline-embedded filter paper was either cut into small pieces or pulverised and introduced directly into the graphite furnace for trace element determination. Temperature program, use of chemical modifier, chromatographic effect and volume of sample were investigated. Calibration curves using organic and inorganic standards of the analytes as well as external and internal calibration methods were evaluated. Using optimised conditions, characteristic masses and limits of detection of 6 and 11 pg, and 0.5 and 2.1 μg L-1 were found for Pb and Ni, respectively. The accuracy of the method was evaluated with spike-recovery tests and a certified reference material of wear lubricant oil. The spike-recovery tests were accomplished for 9 samples and the best results were obtained with the pulverised filter paper. A second method that employs a transversely heated filter atomiser was applied as a comparative one. The filter paper was shown to be a simple and inexpensive tool for storage and transportation of gasoline samples, and it allowed the pre-concentration of the analytes, since a larger volume of sample can be dried out on it.

Non-targeted analysis of the particulate phase of heated tobacco product aerosol and cigarette mainstream tobacco smoke by thermal desorption comprehensive two-dimensional gas chromatography with dual flame ionisation and mass spectrometric detection

An analytical methodology based on thermal desorption and comprehensive two-dimensional gas chromatography with dual time-of-flight mass spectrometry and flame ionization detection (TD-GC × GC-TOFMS/FID) has been developed for non-target analysis of volatile organic compounds (VOCs). The technique was optimised for the measurement of the VOC content of the particulate phase (PP) fraction of aerosols produced by a tobacco heating product (THP1.0) and 3R4F mainstream tobacco smoke (MTS). The method involves sampling the PP fraction on quartz wool packed in a sorbent tube directly connected to machine-puffing, followed by a dilution through a TD recollection procedure over Tenax/Sulficarb sorbent before TD-GC × GC-TOFMS/FID analysis. The comparison of the VOC content of the PP fraction of aerosols produced by THP1.0 and MTS highlighted the compositional difference between tobacco combustion (592 peaks) and tobacco heating process (160 peaks). Mass spectrometric signals were used for qualitative analyses based on linear retention indices, mass spectral matches, and GC × GC structured chromatograms, which collectively identified up to 90% of analytes detected in PP samples. FID signals were used for semi-quantitative analyses based on a chemical class external calibration method. The global chemical composition of PP samples showed that hydrocarbons, oxygenated, and nitrogen-containing compounds were fewer in number and much less abundant in THP1.0 PP. Overall, 93 compounds were common to the two sample types. Excepted for a few highly volatile compounds (mainly furan family) as well as glycerine and its acetate, analyte concentrations were higher in MTS PP.

A Procedure for the Control of the Residual Chloramphenicol (Laevomycetin) in Food Products of Animal Origin

A standardized procedure is developed for the determination of chloramphenicol in food products of animal origin of different groups using HPLC with tandem mass spectrometric detection with a limit of detection of 0.2 µg/kg. The extraction of chloramphenicol from aqueous solutions with organic solvents was studied. Optimized procedures for the extraction of chloramphenicol, purification of the extracts, and preconcentration of the analyte and the use of the deuterated form of chloramphenicol ensure quantitative determination using an external calibration method with an internal standard with the maximum expanded uncertainty of the results 18.4%.

Analytical performance for determination of synthetic pyrethroids residue in Indonesian fermented cocoa using GC-ECD

Pyrethroid insecticides are causing problems for the environment because they are toxic at such small concentrations and very difficult to determine. Characteristics of pyrethroids insecticides include high efficiency, wide spectrum, low biodegradability, and low mammalian and avian toxicity. They also demonstrate strong selectivity for insects and invertebrates. This study presents the results of the analysis conducted on four synthetic pyrethroids in fermented cocoa samples from Indonesia. The pesticides were extracted using acetonitrile and the analysis was carried out by Gas Chromatography with Electron Capture Detector (GC-ECD). Column programming temperature was conducted to get a complete separation. The total operation took less than 10 minutes to separate four standards of synthetic pyrethroids. The synthetic pyrethroids were identified by their retention times and quantified using an external calibration method. The linearity test was carried out for four standard synthetic pyrethroids, namely: lambda-cyhalothrin, permethrin, cypermethrin, and fenvalerate, from 1 μg/kg to 10 μg/kg. The coefficient of correlation (r) was found to be 0.9999; 0.9998; 0.9944; and 0.9999 for lambda-cyhalothrin, permethrin, cypermethrin, and fenvalerate, respectively. The detection limit for synthetic pyrethroids residue was found to be below the EU and Japan regulations, and the method can be applied for the determination of synthetic pyrethroids residues in fermented cocoa.

Identification and Quantification of (t)RNA Modifications in Pseudomonas aeruginosa by Liquid Chromatography-Tandem Mass Spectrometry.

Transfer RNA (tRNA) modifications impact the structure and function of tRNAs, thus affecting the efficiency and fidelity of translation. In the opportunistic pathogen Pseudomonas aeruginosa translational regulation plays an important but less defined role in adaptation to changing environments. In this study, we have explored tRNA modifications in P. aeruginosa through LC-MS/MS approaches. Neutral loss scanning (NLS) demonstrated the potential to identify previously unknown modifications, whereas multiple reaction monitoring (MRM) was able to detect modifications with high specificity and sensitivity. In this study, the MRM-based external calibration method allowed for quantification of the four canonical and 32 modified ribonucleosides, out of which 21 tRNA modifications were quantified in the total tRNA pool of P. aeruginosa PA14. We also purified the single tRNA isoacceptors tRNA-ArgUCU, tRNA-LeuCAA, and tRNA-TrpCCA and determined their specific modification patterns, both qualitatively and quantitatively. Deeper insights into the nature and dynamics of tRNA modifications in P. aeruginosa should pave the way for further studies on post-transcriptional gene regulation as a relatively unexplored molecular mechanism of controlling bacterial pathogenicity and mode of growth.

Reduction of Interferences Using Fe-Containing Metal-Organic Frameworks for Matrix Separation and Enhanced Photochemical Vapor Generation of Trace Bismuth.

Photochemical vapor generation (PVG) has emerged as a promising sample introduction method for atomic spectrometry in recent years. Despite its great success, a major impediment for the wide application of PVG is the interferences from the coexisting ions, especially transition-metal ions. In this work, iron and 1,3,5-benzenetricarboxylic (Fe-BTC), a Fe-containing metal-organic framework (MOF) material, was synthesized and first used as a platform integrating the sample matrix separation, preconcentration, and photocatalysis for the highly selective determination of elements by PVG. Bismuth was selected as a model analyte. Fe-BTC served not only as the photocatalyst for the PVG of Bi3+ but also as an efficient absorbent for the separation of analytes from the sample matrix. Compared with the previous PVG system, the performance of tolerating interferences toward coexisting ions of the proposed method has been greatly improved after using Fe-BTC-based matrix separation. Thus the excess of 10 mg L-1 of Co2+ and 100 mg L-1 of Cu2+, Ni2+, and Fe3+ caused no obvious interferences for 1 μg L-1 of Bi determination. Under the optimal conditions, the limit of detection (LOD, 3σ) of the developed method was 0.3 ng L-1 with the inductively coupled plasma-mass spectrometry (ICPMS) measurement, which could be lowered down to 0.04 ng L-1 after ten times of preconcentration with Fe-BTC prior to analysis. This method was successfully applied for the analysis of Bi in complicated sample matrices of soil (GBW07401), sediment (GBW07310), nickel-iron alloy (GBW01622), and nickel alloys (GBW01641) by the external calibration method.

Determining Collision Cross‐Sections of Aromatic Compounds in Crude Oil by Using Aromatic Compound Mixture as Calibration Standard

Collisional cross section (CCS) values of a set of aromatic compounds were determined and the compounds were evaluated as standards for calibration and standardization. External calibration with poly‐DL‐alanine and internal and external calibration with the aromatic compounds were performed using the ion mobility mass spectra obtained from crude oils. The results showed that the external calibration method using the set of aromatic compounds is both accurate and easy to implement. The improved accuracy obtained using these aromatic standards can be explained by their greater structural similarity with the analytes in the crude oils. We anticipate that the adoption of these standards will increase the utility of IM‐MS in petroleum analysis and make it easier to directly compare results from different studies.

Hexafluoroisopropanol-alkyl carboxylic acid high-density supramolecular solvent based dispersive liquid-liquid microextraction of steroid sex hormones in human urine

A hexafluroisopropanol (HFIP)-alkyl carboxylic acid high-density supramolecular solvent (SUPRAS) was proposed and combined with dispersive liquid-liquid microextraction (DLLME) for extraction and preconcentration of steroid sex hormones in human urine prior to analysis by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Octanoic acid was used as extraction agent and HFIP, with the properties of high density, strong hydrogen bond donor and high hydrophobicity, was used as dispersing agent of DLLME as well as coacervation-inducing agent and density-regulating agent of octanoic acid. HFIP-octanoic acid SUPRAS was spontaneously formed in the process of DLLME and located in the bottom of a urine solution due to its density higher than water. Thus, the SUPRAS phase at trace volume was easy to be collected after centrifugation using normal centrifuge tubes. Five hormones (four estrogens and progesterone) were chosen as analytes. Urine hydrolysis time, extraction conditions and derivatization conditions for estrogens were optimized. Under the optimal conditions, only 0.07 mL of organic solvent (HFIP) was consumed. An external standard calibration method was used for quantification, and a linear relationship was obtained with correlation coefficients higher than 0.9957 and p values for linear trend less than 0.0001. Limits of detection of the method based on a signal-to-noise ratio of 3 were 0.01-0.10 μg L−1. The recoveries ranged from 82.7% to 120.2%, and intra-day and inter-day relative standard deviations of the method were less than 15%. The matrix effects of 84.0%–105.7% showed no urine matrix interferences with MS detection, which was mainly due to the restricted access property of HFIP-octanoic acid SUPRAS with reverse micelle aggregates. The absence of matrix effects contributed to the reliable quantitation by external calibration, avoiding the use of expensive isotopically labeled internal standards. The novel SUPRAS-based DLLME method, coupled with HPLC-MS/MS, was applied for determination of target hormones in real urine.

Comprehensive comparative compositional study of the vapour phase of cigarette mainstream tobacco smoke and tobacco heating product aerosol

A simple direct sample collection/dilution and introduction method was developed using quartz wool and Tenax/sulficarb sorbents for thermal desorption and comprehensive two-dimensional gas chromatography (TD-GC × GC) analyses of volatile organic compounds from vapour phase (VP) fractions of aerosol produced by tobacco heating products (THP1.0) and 3R4F mainstream tobacco smoke (MTS). Analyses were carried out using flame ionisation detection (FID) for semi-quantification and both low and high resolution time-of-flight mass spectrometry (LR/HR-TOFMS) for qualitative comparison and peak assignment. Qualitative analysis was carried out by combining identification data based on linear retention indices (LRIs) with a match window of ±10 index units, mass spectral forward and reverse library searches (from LR and HRTOFMS spectra) with a match factor threshold of >700 (both forward and reverse), and accurate mass values of ± 3 ppm for increased confidence in peak identification. Using this comprehensive approach of data mining, a total of 79 out of 85 compounds and a total of 198 out of 202 compounds were identified in THP1.0 aerosol and in 3R4F MTS, respectively. Among the identified analytes, a set of 35 compounds was found in both VP sample types. Semi-quantitative analyses were carried out using a chemical class-based external calibration method. Acyclic, alicyclic, aromatic hydrocarbons and ketones appeared to be prominent in 3R4F MTS VP, whereas larger amounts of aldehydes, ketones, heterocyclic hydrocarbons and esters were present in THP1.0 aerosol VP. The results demontsrate the capability and versatility of the method for the characterization and comparison of complex aerosol samples and highlighted the relative chemical simplicity of THP1.0 aerosol in comparison to MTS.

A new multivariate standard addition strategy for stripping voltammetric electronic tongues: Application to the determination of Tl(I) and In(III) in samples with complex matrices

A new multivariate standard addition strategy applicable to stripping methods was proposed as an extention of the classical univariate standard addition method for the resolution of complex samples involving overlapped peaks and complex matrices. The proposed strategy consists in alternate additions of the considered analytes and the further extrapolation to a simulated blank solution measured by skipping the preconcentration step (deposition time = 0). This calibration approach was successfully tested in tonic water samples spiked with Tl(I) and In(III) using a sensor array based on a SeCyst-SPCNFE and an ex-situ-BiSPCE, providing good concordance between replicates and much better accuracy than the usual multivariate external calibration method.

Quantification of THC in Cannabis plants by fast-HPLC-DAD: A promising method for routine analyses

Nowadays, Gas Chromatography Mass Spectrometry (GC-MS) is mainly used in forensic sciences but suffers from limitations when the analysed compounds are thermally instable as it is the case for THC-A (Tetrahydrocannabinolic Acid) which is converted into Δ9-THC (Δ9-Tetrahydrocannabinol) that subsequently partially degrades. We propose herein a Fast High Pressure Liquid Chromatography (Fast-HPLC-DAD) method which allows the efficient separation of CBN (Cannabinol), CBD (Cannabidiol), THC-A and Δ9-THC, the major cannabinoids compounds found in cannabis plants in less than 5 min. Our method allows also the proper quantification of Δ9-THC in plant extracts using an external calibration method with a very good accuracy as pointed out by a recovery of 100.53 ± 3.12%. It is also an interesting low cost alternative to Ultra High Pressure Liquid Chromatography (UPLC) for routine analyses in forensic sciences.

Quantitative determination of the veterinary drug monensin in horse feed samples by square wave voltammetry (SWV) and direct infusion electrospray ionization tandem mass spectrometry (DI–ESI–MS/MS)

This paper presents for the first time the determination of monensin monosodium salt (MnzNa) by means of square wave voltammetry (SWV), cyclic voltammetry (CV), and, in parallel, direct infusion electrospray ionization tandem mass spectrometry (DI–ESI–MS/MS). The influence of various factors, such as pH, buffer composition, and SWV parameters on current response was studied. The best SWV signal was obtained at about −1.50 V versus an Ag/AgCl/KCl reference electrode in Britton–Robinson (B–R) buffer. Under optimal conditions, the SWV response of the renewable silver amalgam film electrode Hg(Ag)FE was linear over two MnzNa concentration ranges, from 7.5 × 10−8 to 5.0 × 10−7 mol L−1 and from 5.0 × 10−7 to 1.0 × 10−5 mol L−1. The limits of detection and quantification were 1.27 × 10−8 mol L−1 and 4.23 × 10−8 mol L−1, respectively. The applicability of the developed SWV method was investigated in the determination of MnzNa in horse feed by the standard addition method. CV was applied to understand the electrode mechanism of MnzNa. Finally, direct infusion electrospray ionization tandem mass spectrometry (DI–ESI–MS/MS) was used to determine MnzNa in horse feed samples by the external calibration method. The detector response was linear in the concentration range of 1.1 × 10−7 to 1.4 × 10−6 mol L−1. The obtained limits of detection and quantification were 3.4 × 10−8 mol L−1 and 1.1 × 10−7 mol L−1, respectively. Statistical analysis of MnzNa determination results from SWV and DI–ESI–MS/MS did not reveal any significant differences between them.

Sample Pretreatment Method for Determination of Indicator Polychlorinated Biphenyls in Seafood using Ultrasonic Extraction Followed by Dispersive Solid-Phase Extraction and Gas Chromatography - Electron Capture Detection.

A simple, rapid and novel method has been developed and validated for the determination of seven indicator polychlorinated biphenyls (PCBs) in seafood samples by gas chromatography coupled to electron capture detector. Freeze-dried samples were done first ultrasonic extraction by n-hexane:methylene chloride:acetone (3:1:1, v/v), and then one-step clean-up (dispersive solid-phase extraction clean-up) or two-step clean-up (concentrated sulfuric acid purification and dispersive solid-phase extraction clean-up) was selected according to the lipid contents of the samples, if the lipid content was no more than 1%, one-step clean-up was used, otherwise, two-step clean-up was chose. The linearity of this method ranged from 1.25 to 100 μg/L, with regression coefficients ranging between 0.9991 and 0.9998. The limits of detection were in low ng/g level, ranging between 0.005 and 0.0076 ng/g (wet weight). The recoveries of spiked seven PCBs with external calibration method at different concentration levels in Pseudosciaena polyactis, Penaeus vannamei and Sinonovacula constricta were in the range of 78-105%, 73-110% and 75-107%, respectively, and with relative standard deviations of 3.3-5.1%, 3.5-6.3% and 3.4-5.1% (n = 5), respectively. The performance of the proposed method was also compared with traditional soxhlet extraction and column chromatography clean-up on the same real seafood samples and comparable efficiencies were obtained. It is concluded that this method can be successfully applied for the determination of PCBs in different seafood samples.

Water quantification in silicate glasses by Raman spectroscopy: Correcting for the effects of confocality, density and ferric iron

New series of alumino-silicate glasses spanning a wide range of chemical compositions (basanites, tholeiitic basalts, calcalkaline andesites, peraluminous and peralkaline rhyolites) and with water contents from 0.02 to 6.70 wt% were used for improving the method of quantification of dissolved water with a highly confocal Raman micro-spectrometer. After reconsideration of previously proposed methods for spectra acquisition and postanalysis data treatment, we define the main critical steps that allow minimizing glass matrix effects. First, we carefully assess the variation of Raman band intensities, in both water (~3000–3800 cm−1) and alumino-silicate vibration (~200–1250 cm−1) regions with focus depth of the laser beam inside the sample. Our results indicate that in the first 2–10 μm depth, the intensity increase in the alumino-silicate region is twice as high as that in the water region. Optimal focus depths, where the signal of the water band is maximum and the intensity ratio of the water band to alumino-silicate band is minimum, vary with glass composition and confocal performance of the Raman spectrometer. This influences both external and internal calibration slopes. Second, this study recognizes critical parameters related with glass density, presence of ferric iron and dissolved carbonates as mainly responsible for matrix effects on the internal calibration method. (a) We provide a procedure for correcting the effect of glass density on water internal calibration based on the observation that the integrated intensity (i.e. the area) of the alumino-silicate envelope generally drops with the increase of water content and decrease of glass density. (b) In CO2-bearing glasses, the intensity of the ν1 Raman vibration of dissolved carbonate at ~1087 cm−1 has to be subtracted from the intensity of the alumino-silicate envelope before applying the density correction. (c) Using peak-fitting, the intensity of the 850–1250 cm−1 envelope of peralkaline rhyolitic glasses is corrected for the effect of the presence of four-fold coordinated Fe3+, as revealed by the strong Raman scattering of the vibrational mode at ~980 cm−1. Following this procedure, all the studied glasses define a single calibration line in spite of their compositional variability, when using either of the two classical approaches referred to as external and internal calibration methods. The linear fits of the external and internal calibrations reproduce the whole dataset within 0.13–0.11 wt% (high and standard confocality) and 0.17 wt%, respectively. The accuracy of the external calibration is evaluated based upon comparison with ion-probe measurements of water dissolved in natural glass inclusions: the relative standard deviation is ~4% (1σ) on average, and reaches ~12% (1σ) for water contents of ~0.1 wt%.

New Calibration Model: Combining Integrated Calibration Method and H-point Standard Addition Method to Detect and Avoid Interference Effects

ABSTRACTA new calibration methodology based on the combination of integrated calibration method (ICM) and the H-point standard addition method (HPSAM) is presented. It allows the diagnosis and correction of errors caused in an analytical system by different kinds of interference effects. Six calibration solutions consisting of mixtures of sample, diluent, and one standard are prepared in accordance with the ICM principle to integrate the external calibration method with the standard addition method and thereby to detect and eliminate proportional interferences. Absorbance increments chosen according to the HPSAM principle are proposed to correct the errors caused by additive interferences. A set of as many as six apparent estimations of analyte concentration in a single calibration procedure is calculated for validating accuracy. As a consequence, doing calibration by the ICM-HPSAM method, it is possible to obtain the final analytical results with considerably improved accuracy. The determination of calcium in several different water samples (containing amounts between 4.9 and 127 mg L−1) with Arsenazo III has been chosen as an example because it is biased if the errors are not diagnosed and corrected. The results are characterized by small (not higher than 8%) relative error (RE), and good precision (RSD values smaller than 6%).

Characterization and quantification of flavonoids and saponins in adzuki bean (Vigna angularis L.) by HPLC\u2013DAD\u2013ESI\u2013MSn analysis

BackgroundBioactive activities of adzuki bean have been widely reported, however, the phytochemical information of adzuki bean is incomplete. The aim of this study was to characterize and quantify flavonoids and saponins in adzuki bean. High performance liquid chromatography with diode array detection and electro spray ionization-tandem multi-stage mass spectrometry (HPLC–DAD–ESI–MSn) were applied to do qualitative and quantitative analyses.ResultsA total of 15 compounds from adzuki bean were identified by HPLC–DAD–ESI–MSn. Among 15 compounds identified, four flavonoids (catechin, vitexin-4″-O-glucoside, quercetin-3-O-glucoside, and quercetin-3-O-rutinoside) and six saponins (azukisaponin I, II, III, IV, V, and VI) in adzuki bean were further quantified by external calibration method using HPLC–MS with the program of time segment and extract ion chromatogram (EIC) analysis.ConclusionsCurrent qualitative and quantitative method based on HPLC and MS technique provides a scientific basis for in vitro and in vivo pharmacological study in the future.Graphical abstractIsolation and characterization of flavonoids and saponins from adzuki bean.

Catalytic fast pyrolysis of biomass with noble metal-like catalysts to produce high-grade bio-oil: Analytical Py-GC/MS study

Four kinds of noble metal-like catalysts W2C/AC, W2N/AC, Mo2C/AC and Mo2N/AC were prepared and used for catalytic fast pyrolysis of biomass to upgrade the fuel properties of biomass pyrolysis vapors. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments were performed to analyze the volatile pyrolytic products in pyrolysis vapors. Effects of catalyst, pyrolysis temperature and catalyst-to-biomass ratio on the pyrolytic product distribution were examined thoroughly. Actual yields of major pyrolytic products were determined by an external calibration method. Results showed that tungsten-based catalysts performed better than molybdenum-based catalysts, and W2C/AC possessed comparable performance to Pd/AC catalyst. From the pyrolysis of biomass and its single component, W2C/AC and W2N/AC catalysts exhibited promising capability to promote the decomposition of lignin to generate monomeric phenolic compounds, especially stable phenolics. Meanwhile, they would also affect the holocellulose pyrolysis by decreasing anhydrosugars and linear aldehydes, while increasing furans, cyclopentanones and linear ketones. As for an overall effect, catalysis by W2C/AC and W2N/AC catalysts was capable to convert those undesirable pyrolytic products (containing aldehyde group, CC bond or carboxyl group) through decarbonylation, hydrogenation, decarboxylation and other reactions, and thus decrease the instability, acidity and oxygen content of pyrolytic products for obtaining high-grade bio-oil.