Groups Of Isomers Research Articles

Rapid Chromatography for the Determination of Polychlorinated Biphenyls by GC-MS in Environmental Monitoring

A method for determination of polychlorinated biphenyls (PCBs) in environmental and biological materials has been developed. This method includes rapid chromatography requiring less than 10 min using an HT-8 capillary column at 30 m × 0.25 mm i.d. Rapid chromatography was performed using a column temperature gradient from 80 to 310°C at a rate of 40°C/min. Low-resolution mass spectrometry in single ion monitoring mode of simultaneous detection of 12 target ions is suggested for detection of PCBs peaks. The method not only enabled us to reduce time of analysis but also to increase the efficiency of separating PCB peaks from interferences and to reduce levels of detection of analytes resulting in a minimized sample preparation stage. The last includes extraction of the PCBs using organic solvents, preliminary alkaline hydrolysis in the case of biological objects, and cleaning up the extracts on compact cartridges. The method was tested in monitoring studies for these contaminants in soils, sediments, snow cover, fish tissues, and seal blubber. Total PCBs and isomer congener groups of the same chlorination degree and seven indicator congeners (IUPAC No.'s 28, 52, 101, 118, 138, 153, and 180) are determined with a high degree of certainty. The PCB concentrations were in the range of 1–700 ng/g dry weight for environmental samples and 500–25000 ng/g lipids for biota. The method yields measurements of total PCBs and isomer groups with a precision no greater than 10% and no greater than 15% for the indicator congeners.

Comprehensive analysis of polycyclic aromatic hydrocarbons in wastewater using stir bar sorptive extraction and gas chromatography coupled to tandem mass spectrometry

The objective of this study was the optimization and comparison of two extraction methods for the determination of polycyclic aromatic hydrocarbons (PAHs) in wastewater (WW). A distribution study of the target compounds between the aqueous phase and the suspended particulate matter (SPM) has been performed in order to establish whether the analysis of both phases is necessary. In this sense, the feasibility of stir bar sorptive extraction (SBSE) and solid-phase extraction (SPE) for the determination of 24 PAHs in WW samples has been evaluated. The results demonstrated the suitability of SBSE to perform a comprehensive analysis of liquid samples containing high amounts of SPM, such as in the determination of PAHs in WWs. A gas chromatography triple quadrupole mass spectrometry (GC–QqQ-MS/MS) method has been also optimized for the separation and detection of the target compounds, avoiding the co-elution of some groups of isomers, such as benzo[ b], [ j] and [ k] fluoranthenes and indene[1,2,3- cd]pyrene/dibenz[ a, h]anthracene. For that purpose, a specific capillary column developed for PAH determination was used. The SBSE procedure was validated and adequate parameters (such as recovery, linearity, precision, limits of detection and quantification) were obtained. Finally, the validated method was applied to the analysis of real samples collected from an experimental WW treatment plant, detecting some PAHs at concentrations in the range 0.007–0.022 μg L −1.

Detection, characterization and identification of major constituents in Zhimu‐Baihe herb‐pair extract by fast high‐performance liquid chromatography and time‐of‐flight mass spectrometry through dynamic adjustment of fragmentor voltage

This work describes a novel methodology for unequivocal identification of chemical constituents in Zhimu-Baihe herb-pair (ZMBHHP). Compounds were removed from ZMBHHP by ultrasonic extraction with 70% ethanol, and then analyzed by fast high-performance liquid chromatography (HPLC) coupled with time-of-flight mass spectrometry (TOFMS). The accurate-mass capability of the TOF analyzer allowed reliable confirmation of the identity of the detected compounds, normally with mass errors below 3 ppm in routine analysis. This mass accuracy was sufficient to verify the elemental compositions of the chemical constituents in ZMBHHP. With dynamic adjustment of fragmentor voltage in TOFMS, an efficient ion transmission was achieved to obtain the best sensitivity and abundant fragmentation. By accurate mass measurements for each molecular ion and subsequent fragment ions, a reliable identification and differentiation of 24 saponins, 3 xanthones, 1 anthraquinone and 2 alkaloids was described here, including four groups of isomers. It is concluded that this fast and sensitive HPLC/ESI-TOFMS technique is powerful in qualitative analysis of complex herbal medicines in terms of sensitivity, selectivity, resolving power, time savings and lower solvent consumption. Furthermore, the data gathered in this study may be helpful for understanding the synergistic nature of this herb pair in traditional Chinese medicine (TCM) and further pharmacokinetic studies of ZMBHHP.

Fragmentation study of iridoid glycosides including epimers by liquid chromatography‐diode array detection/electrospray ionization mass spectrometry and its application in metabolic fingerprint analysis of Gardenia jasminoides Ellis

A high-performance liquid chromatography-diode array detection/electrospray ionization mass spectrometry (HPLC-DAD/ESI-MS) method was applied to the characterization of ten iridoid glycosides in Gardenia jasminoides Ellis, a traditional Chinese medicine. During the process of structural elucidation, two groups of isomers including two epimers were structurally characterized and differentiated according to their distinctive fragmentation patterns which were closely related to their isomeric differentiations. Subsequently, the major compounds were purified by multi-dimensional chromatography and semi-preparative HPLC and the structure identification was confirmed with NMR techniques. The major fragmentation pathways of iridoid glycosides in Gardenia jasminoides Ellis obtained through the MS data were schemed systematically, which provided the best sensitivity and specificity for characterization of the iridoid glycosides especially the isomers so far. Based on the fragmentation patterns of iridoid glycosides concluded, seven major iridoid glycosides were characterized in rat plasma after intravenous administration of Gardenia jasminoides Ellis.

Mixed Polybrominated/chlorinated Dibenzo-p-dioxins and Dibenzofurans in Stack Gas Emissions from Industrial Thermal Processes

Very little is known about mixed polybrominated/chlorinated dibenzo-p-dioxins and dibenzofurans (PBCDD/F) in industrial thermal processes. In this study, the occurrences and characteristics of PBCDD/F from various incineration and metallurgical processes were investigated. In addition, PBCDD/F analytical protocols based on HRGC/HRMS were developed and optimized. The sum of isomer group concentrations ranged from 1.7-3740 pmol Nm(-3) for PBCDF and 0.2-582 pmol Nm(-3) for PBCDD. For some metallurgical industries, the amounts of PBDD/F and PBCDD/F emitted were similar to or even higher than the amounts of PCDD/F. The sources of bromine and brominated-precursors in these processes should be evaluated. The PBCDD/F characteristics investigated included isomer group patterns, ratio of bromine and chlorine incorporated in PBCDD/F, and ratio of halogenated furans to dioxins. Lower brominated PBCDD/F were binomially distributed. But in some cases, the concentrations of higher brominated PBCDD/F were much higher than predicted from the binomial distribution. The formation mechanisms of PBDD/F, PBCDD/F, and PCDD/F in these processes were also evaluated.

Differentiation of structural isomers in a target drug database by LC/Q‐TOFMS using fragmentation prediction

Isomers cannot be differentiated from each other solely based on accurate mass measurement of the compound. A liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/Q-TOFMS) method was used to systematically fragment a large group of different isomers. Two software programs were used to characterize in silico mass fragmentation of compounds in order to identify characteristic fragments. The software programs employed were ACD/MS Fragmenter (ACD Labs Toronto, Canada), which uses general fragmentation rules to generate fragments based on the structure of a compound, and SmartFormula3D (Bruker Daltonics), which assigns fragments from a mass spectra and calculates the molecular formulae for the ions using accurate mass data. From an in-house toxicology database of 874 drug substances, 48 isomer groups comprising 111 compounds, for which a reference standard was available, were found. The product ion spectra were processed with the two software programs and 1-3 fragments were identified for each compound. In 82% of the cases, the fragment could be identified with both software programs. Only 10 isomer pairs could not be differentiated from each other based on their fragments. These compounds were either diastereomers or position isomers undergoing identical fragmentation. Accurate mass data could be utilized with both software programs for structural elucidation of the fragments. Mean mass accuracy and isotopic pattern match values (SigmaFit; Bruker Daltonics Bremen, Germany) were 0.9 mDa and 24.6 mSigma, respectively. The study introduces a practical approach for preliminary compound identification in a large target database by LC/Q-TOFMS without necessarily possessing reference standards.

A novel pyromellitic diimide derivative: Synthesis, gelation and spontaneous colorimetric sensing of dihydroxybenzene isomers

We report on the synthesis and self-assembly of a new hydrazide derivative N′, N′-bis[4-octadecyloxybenzamido]pyromellitic diimide (compound 1) which formed gels in several apolar organic solvents such as benzene and 1, 2-dichloroethane. 1H NMR, and FT-IR spectroscopy studies confirmed that the intermolecular hydrogen bonding and van der Waals interactions were major driving forces for the formation of self-assembling gels. The gelator can form noncovalent interactions with dihydroxybenzenes, exhibiting different colors when it complexes with different positional isomers, and thus can be used to sense the positional isomers of dihydroxybenzenes by the naked eyes. This sensing property was further investigated by UV/Vis, 1H NMR, and 1H NMR NOESY spectroscopy which revealed that the charge–transfer interaction between hydroxyl groups of the dihydroxybenzene isomers (donor) and compound 1 (acceptor) accounted for this property.

Analysis of phenolic and triterpenoid compounds in licorice and rat plasma by high‐performance liquid chromatography diode‐array detection, time‐of‐flight mass spectrometry and quadrupole ion trap mass spectrometry

High-performance liquid chromatography with diode-array detection (HPLC/DAD), time-of-flight mass spectrometry (HPLC/TOFMS) and quadrupole ion trap mass spectrometry (HPLC/QITMS) were used for separation and identification of several compounds in licorice and rat plasma after oral administration of the herbal extract. Three phenolic compounds and one triterpenoid in licorice extract were unambiguously identified by comparing with the standard compounds. A formula database of known compounds in licorice was established, against which the other 42 compounds were identified effectively based on the accurate extract masses and formulae acquired by HPLC/TOFMS. In order to differentiate the isomers, tandem mass spectrometry was also used. The deduced fragmentation behaviors in QITMS were used to distinguish seven groups of isomers in licorice. By means of the three detectors, 46 compounds in licorice were identified. After oral administration of the extract, 25 compounds in rat plasma were detected and identified by comparing and contrasting the compounds measured in licorice with those in the plasma samples by HPLC/TOFMS. It is concluded that a rapid and effective method based on three analytical techniques was established, which is useful for identification of multiple compounds in licorice in vitro and in vivo. The result should be very useful for the quality control and curative mechanism study of licorice.

Determination of Polychlorinated Biphenyl Congeners in Water and Sediment in North West Persian Gulf, Iran

Polychlorinated biphenyl (PCB) was detected as isomer groups (congener numbers 28, 52, 101, 118, 138, 153 and 180) in the coastal water and sediment of four stations around Shadegan wetland protected area in the northwestern part of the Persian Gulf. Total PCB concentration range was 8-375 ng/L in water and 3.4-50.2 μg/g in sediment. Concentration of different congeners and chromatogram indicates that the source of PCB in this area can be Clophen A60; it used for long time in Iranian electronic industries. Other chlorinated hydrocarbons such as lindane, DDT and their metabolites were also present in the samples.

Simultaneous determination of dihydroxybenzene and phenylenediamine positional isomers using capillary zone electrophoresis coupled with amperometric detection

In general capillary zone electrophoresis (CZE) separation models, o-, m-, and p-phenylenediamine isomers can be separated in a weak acidic running buffer for their pK(a) values being 4.52, 5.64, 6.04, respectively, while o-, m-, and p-dihydroxybenzene isomers can be separated in a weak basic buffer for their pK(a) values being 9.40, 9.40 and 10.04, respectively. So, it is hard to find a suitable running buffer at a fixed pH in normal CZE for simultaneous separation of these two groups of positional isomers. In this paper, a novel method based on alternately running two different pH buffers in CZE coupled with amperometric detection (CZE-AD) was designed to simultaneously determine these two groups of positional isomers. It is found that when two different pH running buffers were employed alternately under appropriate order and time, the six analytes could be separated perfectly in less than 20 min and the detection limits were as low as 10(-7) mol/L. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Experimental results demonstrated that the introduced method was practical to simultaneously determine two groups of positional isomers with different pK(a) and had some advantages of high sensitivity, good repeatability and small sample requirement.

Rapid separation and identification of furocoumarins in Angelica dahurica by high‐performance liquid chromatography with diode‐array detection, time‐of‐flight mass spectrometry and quadrupole ion trap mass spectrometry

High-performance liquid chromatography with diode-array detection (HPLC/DAD), time-of-flight mass spectrometry (HPLC/TOFMS) and quadrupole ion trap mass spectrometry (HPLC/QITMS) were used for separation, identification and structural analysis of furocoumarins in Angelica dahurica. Two furocoumarins (imperatorin and isoimperatorin) in Angelica dahurica extract were identified unambiguously by comparing their relative retention times, characteristic ultraviolet information and accurate mass measurement. A formula database of known furocoumarins in Angelica dahurica was established, against which the other 21 furocoumarins were identified effectively based on the accurate extract masses and formulae acquired by HPLC/TOFMS. In order to distinguish the isomers, multi-stage mass spectrometry (MSn, ion trap mass spectrometry) was used. General fragmentation behavior of the furocoumarins in the ion trap mass spectrometer was studied by the two furocoumarin standards, and their fragmentation rules in MS(n) spectra were summarized. These deduced fragmentation rules of furocoumarins were successfully implemented in distinguishing the three groups of isomers in Angelica dahurica by HPLC/QITMS. By using the three different analytical techniques, 23 furocoumarins in Angelica dahurica were tentatively identified within 30 min. Finally, HPLC/TOFMS fingerprints of Angelica dahurica were established by which it can be concluded that a rapid and effective method based on the three analytical techniques for identification of chemical components was established. This can provide help for further quality control of Angelica dahurica and pharmacology mechanism study of furocoumarins in Angelica dahurica.

Characterisation and identification of isomeric dibenzocyclooctadiene lignans from Schisandra Chinensis by high‐performance liquid chromatography combined with electrospray ionisation tandem mass spectrometry

Dibenzocyclooctadiene lignans are bioactive constituents in Schisandra chinensis (Turcz.) Baill. They are often present as isomers and this makes structural discrimination difficult. To develop a rapid approach towards the characterisation and identification of isomeric dibenzocyclooctadiene lignans from S. chinensis using HPLC-PAD-ESI-MS(n). The fragmentation behaviours of seven dibenzocyclooctadiene lignans from S. chinensis were studied using ion trap mass spectrometry with positive electrospray ionisation and loop injection. The fragmentation patterns of angeloylgomisin H, tigloylgomisin H, benzoylgomisin H and gomisin D were supported by high-resolution mass spectrometric analysis of some characteristic ions using a time-of-flight mass spectrometer. Combined with high-performance liquid chromatography and photodiode array detection, the established approach to the structural identification of dibenzocyclooctadiene lignans by ion trap mass spectrometry was applied to the analysis of extracts of S. chinensis. According to the HPLC retention behaviour, the diagnostic UV spectra and the molecular structural information provided by multistage mass spectrometry spectra and the literature, a total of 25 dibenzocyclooctadiene lignans, including seven groups of lignan isomers, were identified or tentatively characterised in S. chinensis rapidly. One of these was reported as a constituent of S. chinensis for the first time. This study has shown that HPLC-PAD-ESI-MS(n) may be used as an effective and rapid method for the characterisation and identification of isomeric dibenzocyclooctadiene lignans from S. chinensis.

Analysis of lignans in Schisandra chinensis and rat plasma by high‐performance liquid chromatography diode‐array detection, time‐of‐flight mass spectrometry and quadrupole ion trap mass spectrometry

High-performance liquid chromatography/diode-array detection (HPLC/DAD), time-of-flight mass spectrometry (HPLC/TOFMS) and quadrupole ion trap mass spectrometry (HPLC/QIT-MS) were used for separation, identification and structural analysis of lignans in Schisandra chinensis and rat plasma after oral administration of the herbal extract. Six lignans in Schisandra chinensis extract were identified unambiguously by comparing the retention time, their characteristic ultraviolet (UV) absorption and accurate mass measurement. A formula database of known lignans in Schisandra chinensis was established, against which the other 15 lignans were identified effectively based on the accurate extract masses and formulae acquired by HPLC/TOFMS. In order to distinguish the isomers, multi-stage mass spectrometry (ion trap mass spectrometry, MSn) was also used. The fragmentation behavior of the lignans in the ion trap mass spectrometer was studied by the six lignan standards, and their fragmentation rules in MSn spectra were summarized. These deduced fragmentation rules of lignans were successfully implemented in distinguishing the three groups of isomers in Schisandra chinensis by HPLC/QIT-MS. By using the three different analytical techniques, 21 lignans in Schisandra chinensis were identified within 30 min. After oral administration of the extract, 11 lignans in rat plasma were detected and identified by comparing their retention time, characteristic UV absorption and accurate mass measurement of peaks in HPLC/TOFMS chromatograms of the herbal extract. Finally, HPLC/TOFMS fingerprints of Schisandra chinensis in vitro and rat plasma in vivo were established. It is concluded that a rapid and effective method based on three analytical techniques for identification of chemical components was established, which is useful for rapid identification of multiple components in Schisandra chinensis in vitro and in vivo. In addition, it can provide help for further pharmacology and action mechanism study of lignans in Schisandra chinensis.

Kinetic properties of dromedary pancreatic lipase: A comparative study on emulsified and monomolecular substrate

Using the classical emulsified system and the monomolecular film technique, we compared several interfacial properties of dromedary pancreatic lipase (DrPL) with those of a mammal (human) and an avian (turkey) model. Like turkey pancreatic lipase (TPL) and unlike human pancreatic lipase (HPL), in the absence of colipase and bile salts, using tributyrin emulsion or monomolecular films of dicaprin at low surface pressure, DrPL hydrolyses pure tributyrin emulsion, as well as dicaprin films maintained at low surface pressures. DrPL was also able to hydrolyse triolein emulsion in the absence of any additive and despite the accumulation of long-chain free fatty acids at the interface. The difference of behaviours between the two mammal pancreatic lipases (DrPL and HPL) can be explained by the penetration capacity of each enzyme. DrPL presents a critical surface pressure value (21 mN m −1) that is more important than this of HPL. Subsequently, the dromedary pancreatic lipase interacts efficiently with interfaces and it is not denaturated at high interfacial energy. A kinetic study on the surface pressure dependency, stereospecificity and regioselectivity of DrPL was performed using optically pure stereoisomers of either three dicaprin isomers containing a single hydrolysable decanoyl ester bond that were spread as monomolecular films at the air/water interface. Interestingly, in comparison with all the previously studied mammal pancreatic lipases, DrPL presents the highest preference for adjacent ester groups of dicaprin isomers (1,2- sn-dicaprin and 2,3- sn-dicaprin) at high surface pressure. Furthermore, DrPL forms a pancreatic lipase subgroup in which the stereopreference switches from sn-3 position to the sn-1 position when increasing the surface pressure.

Nuclear magnetic resonance and liquid chromatography–mass spectrometry combined with an incompleted separation strategy for identifying the natural products in crude extract

NMR and LC–MS combined with an incompleted separation strategy were proposed to the simultaneous structure identification of natural products in crude extracts, and a novel method termed as NMR/LC–MS parallel dynamic spectroscopy (NMR/LC–MS PDS) was developed to discover the intrinsic correlation between retention time (Rt), mass/charge ( m/ z) and chemical shift ( δ) data of the same constituent from mixture spectra by the co-analysis of parallelly visualized multispectroscopic datasets from LC–MS and 1H NMR. The extracted ion chromatogram (XIC) and 1H NMR signals deriving from the same individual constituent were correlated through fraction ranges and intensity changing profiles in NMR/LC–MS PDS spectrum due to the signal amplitude co-variation resulted from the concentration variation of constituents in a series of incompletely separated fractions. NMR/LC–MS PDS was applied to identify 12 constituents in an active herbal extract including flavonol glycosides, which was separated into a series of fractions by flash column chromatography. The complementary spectral information of the same individual constituent in the crude extract was discovered simultaneously from mixture spectra. Especially, two groups of co-eluted isomers were identified successfully. The results demonstrated that NMR/LC–MS PDS combined with the incompleted separation strategy achieved the similar function of on-line LC–NMR–MS analysis in off-line mode and had the potential for simplifying and accelerating the analytical routes for structure identification of constituents in herbs or their active extracts.

Infrared spectra of S-and R-isomers of biologically active brassinosteroids

Comparative analysis of IR spectra of S-and R-isomers differing in the configuration of OH groups in the side chain of biologically active 24-epi-and 28-homocastasterones and 24-epi-and 28-homobrassinolides is carried out. Stretching vibration frequencies of H-bonded OH groups of isomers of corresponding brassinosteroids practically coincide. The optical density in maxima of these bands is higher in spectra of the R-isomers. Alteration in the configuration of the OH groups weakly influences also the band intensities of CH3, CH 2 , and CH groups. Band intensities of stretching vibrations of associated C=O groups of S-and R-isomers also neglibibly differ from each other. Their frequency characteristics do not experience substantial changes. These features differ considerably in IR spectra of castasterones and brassinolides. For castasterones, the difference in frequencies of band maxima of free and bound C=O groups amounts to ∼15 cm −1 ; for brassinolides, 23 cm −1 . Intensities of both bands are approximately equal in spectra of castasterones. The band intensity of free C=O groups of brassinolides is considerably lower than that of H-bonded ones. The above spectral differences can be used to identify these brassinosteroids. Frequencies of both symmetric and antisymmetric deformation vibrations of CH 3 and CH 2 groups are close in spectra of all brassinosteroids studied. The frequency of CH 2 in a CH 2 -OC group belongs only to brassinolides; of deformation vibrations of CH in a CH-C=O group, to castasterones. The frequency of stretching vibrations of C-O-C and C-O groups is observed only in spectra of brassinolides. In the region 1130-900 cm −1 of IR spectra of brassinosteroids, stretching vibrations of CC, CCH, and C-OH groups are predominantly observed. In the frequency range 1130-995 cm −1 , the optical density of band maxima of S-isomers is higher than that of R-isomers, which can be used to identify isomers. At the same time frequencies of corresponding bands of isomers practically coincide. Differences in the structure of the side chain of brassinosteroids do not influence essentially the frequency characteristics of the IR spectra. The exception is the band related to stretching vibrations ν(C23-OH) of the side chain which features a considerable frequency ν max ≈ 983 cm −1 only in spectra of R-isomers of homocastasterone and brassinolide.

Rapid and sensitive screening and characterization of phenolic acids, phthalides, saponins and isoflavonoids in Danggui Buxue Tang by rapid resolution liquid chromatography/diode‐array detection coupled with time‐of‐flight mass spectrometry

A novel rapid resolution liquid chromatography (RRLC) method coupled with diode-array detection (DAD) and time-of-flight mass spectrometry (TOFMS) in both positive and negative modes has been developed for quick and sensitive identification of the major compounds in Danggui Buxue Tang (DBT) preparation. Significant advantages of the use of RRLC with 1.8-microm porous particles include the much higher speed of chromatographic separation and great enhancement in sensitivity, compared with the conventional high-performance liquid chromatography (HPLC). With dynamic adjustment of the key role as fragmentor voltage in TOFMS, an efficient transmission of the ions was achieved to obtain the best sensitivity for providing the molecular formula for each analyte, and abundant fragment ions for structural information. The structural characterization of the major compounds in DBT was elucidated with authentic standards by DAD-TOF/MS, including phenolic acids, phthalides, saponins and isoflavonoids. The targets were rapidly screened from the complicated DBT matrix using a narrow mass window of 0.01 Da to restructure extracted ion chromatograms. By accurate mass measurements within 3 ppm error for each molecular ion and subsequent fragment ions, ten phenolic acids and phthalides including three groups of isomers, thirteen major saponins with a 20,24-epoxy-9,19-cyclolanostane-3,6,16,25-tetrol skeleton, sixteen isoflavonoids, corresponding glycosides, malonylglycosides, and acetylglycosides were identified in DBT preparation. The appropriate fragmentation pathways for them were also proposed based on definite elemental composition of the fragment ions.

Qualitative and quantitative analysis of Radix Astragali products by fast high-performance liquid chromatography-diode array detection coupled with time-of-flight mass spectrometry through dynamic adjustment of fragmentor voltage

A novel fast high-performance liquid chromatography (HPLC) method coupled with diode array detection (DAD) and time-of-flight mass spectrometry (TOF/MS) was developed for qualitative and quantitative analysis of Radix Astragali products. The potential of fast HPLC on 1.8-μm particles was compared with the performance of HPLC on conventional 5-μm particles columns. Significant advantages of fast HPLC include high-speed chromatographic separation, four times faster than HPLC with conventional columns, and great enhancement in sensitivity with limits of detection low to 0.001 ng. With dynamic adjustment of fragmentor voltage in TOF/MS, an efficient transmission of the ions was achieved to obtain the best sensitivity and abundant fragmentation. By accurate mass measurements within 5 ppm error for each molecular ion and subsequent fragment ions, a reliable identification and differentiation of six major saponins including two groups of isomers and twelve main isoflavonoids was described here for the first time. For quantitative analysis by fast HPLC–TOF/MS, linearity of response over two orders of magnitude was demonstrated ( r 2 > 0.99) for all analytes. Intra-day reproducibility was below 3% RSD and inter-day values were below 5% RSD. A good correlation (slope = 1.1108, r 2 = 0.9853) was observed for accuracy test. It is concluded that the fast and sensitive HPLC-DAD–TOF/MS is powerful in qualitative and quantitative analysis of complex herbal medicines in terms of time savings, sensitivity, selectivity, precision, accuracy as well as increasing sample throughout and lowering solvent consumption.

Structure and energetics of InN and GaN dimers

Large-scale mapping of various dimers of indium nitride and gallium nitride in singlet and triplet electronic states is reported. Second-order perturbation theory with Møller–Plesset partitioning of the Hamiltonian (MP2) and coupled-cluster with single and double excitations corrected for the triple excitations (CCSD(T)) are used for the geometry determinations and evaluation of excitation and dissociation energies. For gallium and nitrogen we have used the singly augmented correlation-consistent triple-zeta basis set (aug-cc-pVTZ), for indium we have used the aug-cc-pVTZ-pseudopotential basis set. The dissociation energies are corrected for basis set superposition error (BBSE) including geometrical relaxation of the monomers. We compare and discuss the similarities and dissimilarities in the structural patterns and energetics of both groups of isomers, including the effect of the BSSE. Our computations show that there are not only different ground states for In 2N 2 and Ga 2N 2 but also different numbers of stable stationary points on their potential energy surface. We compare our results with the molecular data published so far for these systems.

The primary aerobic biodegradation of biodiesel B20

We describe the primary aerobic biodegradation of a B20 fuel (20% soybean fatty acid methyl esters, 80% petroleum diesel) by unacclimated inocula from a rainwater detention pond. Biodegradation was rapid and essentially complete, with an overall median ‘half-life’, at ∼100 ppm B20, of 6.8 days ( n = 34). Using purge-and-trap and extraction methodologies, both coupled to GC/MS, and hexachloroethane and hexachlorobenzene as conserved internal markers in the B20, we followed the biodegradation of total detectable material, 76 individual analytes and eight undifferentiated groups of isomers, and calculated their half-lives under these conditions. The fatty acid methyl esters, n-alkanes and iso-alkanes, and simple and alkylated aromatic compounds were the most readily degraded compounds, followed by the naphthenes. The last (identified) compounds to be degraded were ethylalkanes, trisubstituted cyclohexanes and decalins, but even these disappeared with an apparent ‘half-life’ of <30 days.