Identification of novel synthetic organic compounds with supersonic gas chromatography-mass spectrometry

Several novel synthetic organic compounds were successfully analyzed with a unique type of GC-MS titled Supersonic GC-MS following a failure in their analysis with standard GC-MS. Supersonic GC-MS is based on interfacing GC and MS with a supersonic molecular beam (SMB) and on electron ionization of sample compounds as vibrationally cold molecules while in the SMB, or by cluster chemical ionization. The analyses of novel synthetic organic compounds significantly benefited from the extended range of compounds amenable to analyses with the Supersonic GC-MS. The Supersonic GC-MS enabled the analysis of thermally labile compounds that usually degrade in the GC injector, column and/or ion source. Due to the high carrier gas flow rate at the injector liner and column these compounds eluted without degradation at significantly lower elution temperatures and the use of fly-through EI ion source eliminated any sample degradation at the ion source. The cold EI feature of providing trustworthy enhanced molecular ion (M+), complemented by its optional further confirmation with cluster CI was highly valued by the synthetic organic chemists that were served by the Supersonic GC-MS. Furthermore, the provision of extended mass spectral structural, isomer and isotope information combined with short (a few minutes) GC-MS analysis times also proved beneficial for the analysis of unknown synthetic organic compounds. As a result, the synthetic organic chemists were provided with both qualitative and quantitative data on the composition of their synthetic mixture, and could better follow the path of their synthetic chemistry. Ten cases of such analyses are demonstrated in figures and discussed.     

Gas chromatography-mass spectrometry with supersonic molecular beams

Gas chromatography-mass spectrometry (GC-MS) with supersonic molecular beams (SMBs) (also named Supersonic GC-MS) is based on GC and MS interface with SMBs and on the electron ionization (EI) of vibrationally cold analytes in the SMBs (cold EI) in a fly-through ion source. This ion source is inherently inert and further characterized by fast response and vacuum background filtration capability. The same ion source offers three modes of ionization including cold EI, classical EI and cluster chemical ionization (CI). Cold EI, as a main mode, provides enhanced molecular ions combined with an effective library sample identification, which is supplemented and complemented by a powerful isotope abundance analysis method and software. The range of low-volatility and thermally labile compounds amenable for analysis is significantly increased owing to the use of the contact-free, fly-through ion source and the ability to lower sample elution temperatures through the use of high column carrier gas flow rates. Effective, fast GC-MS is enabled particularly owing to the possible use of high column flow rates and improved system selectivity in view of the enhancement of the molecular ion. This fast GC-MS with SMB can be further improved via the added selectivity of MS-MS, which by itself benefits from the enhancement of the molecular ion, the most suitable parent ion for MS-MS. Supersonic GC-MS is characterized by low limits of detection (LOD), and its sensitivity is superior to that of standard GC-MS, particularly for samples that are hard for analysis. The GC separation of the Supersonic GC-MS can be improved with pulsed flow modulation (PFM) GC x GC-MS. Electron ionization LC-MS with SMB can also be combined with the Supersonic GC-MS, with fast and easy switching between these two modes of operation.     

Fast,high-sensitivity,multipesticide analysis of complex mixtures with supersonic gas chromatography-mass spectrometry

We developed a new instrumental approach, termed Supersonic GC-MS, which achieves fast, sensitive, confirmatory and quantitative analysis of a broad range of pesticides in complex agricultural matrices. Our Supersonic GC-MS system is a modification of a bench-top Agilent 6890 GC+5972 MSD with a supersonic molecular beam (SMB) interface and fly-through EI ion source. One of the main advantages of Supersonic GC-MS is an enhanced molecular ion (M+) in the resulting mass spectra. For example, the M+ was observed in all 88 pesticides that we studied using the Supersonic GC-MS whereas only 36 of 63 (57%) pesticides that we investigated in standard GC-MS exhibited a M+. We also found that the degree of matrix interference is exponentially reduced with the fragment mass by about 20-fold per 100 amu increasing mass. The enhancement of the M+ combined with the reduction in matrix background noise permit rapid full scan analysis of a potentially unlimited number of pesticides, unlike selected ion monitoring or MS-MS in which specific conditions are required in segments for targeted pesticides. Furthermore, unlike the case with chemical ionization, EI-SMB-MS spectra still give accurate identification of compounds using common mass spectral libraries. In practice,we found thatlibraries favor mass spectra in which the M+ appears, thus Supersonic GC-MS produced better spectra for compound identification than standard GC-MS. To achieve even lower identification limits, the M+ plus a second major ion (still using full scan data) gives higher signal-to-chemical noise ratios than the traditional 3-ion approach. The replacement of two low-mass ions with the M+ (supersonic two-ions method) results in a significant reduction of matrix interference by a factor of up to 90. Another main advantage of Supersonic GC-MS is its exceptional suitability for fast GC-MS with high carrier gas flow-rate. Fast Supersonic GC-MS was able to analyze thermally labile pesticides, such as carbamates, that are difficult or impossible to analyze in standard GC-MS. Large volume injection using a ChromatoProbe was also demonstrated, in the 6 min analysis of pesticides at 20 ng/g in a spice matrix.     

Temperature requirements for thermal modulation in comprehensive two-dimensional gas chromatography

Temperature requirements for trapping and release of compounds in a cryogenic gas loop-type GC x GC modulator were determined. Maximum trapping temperatures on the uncoated, deactivated modulator capillary were determined for compounds from C4 (bp -0.5 degrees C) to C40 (bp 522 degrees C). The liquid-nitrogen cooled gas flow rate was reduced from a high of 15.5 to 1.5 SLPM over the range to achieve the required trapping temperature. Excessive cold jet flow rates caused irreversible trapping and peak tailing for semi-volatile compounds above C26. Alternate cold jet coolants were investigated. An ice water-cooled jet was able to trap compounds with boiling points from C18 (bp 316 degrees C) to C40 and a room temperature air-cooled jet was able to trap compounds from C20 (bp 344 degrees C) to C40. The hot jet produced launch temperatures approximately 40 degrees C hotter than the elution temperature with heating time constants of 8 to 27 ms. Modulated compound peaks were symmetrical with half-height peak widths of 43 to 56 ms for compounds with little second column retention, and 70 to 75 ms for compounds with more second column retention. The liquid nitrogen-cooled loop modulator with gas flow programming was used to produce a GC x GC chromatogram for a crude oil that contained compounds from C7 to C47.     

Flow modulation comprehensive two-dimensional gas chromatography-mass spectrometry with a supersonic molecular beam

A new approach of flow modulation comprehensive two-dimensional gas chromatography-mass spectrometry (GC x GC-MS) with supersonic molecular beam (SMB) and a quadrupole mass analyzer is presented. Flow modulation uniquely enables GC x GC-MS to be achieved even with the limited scan speed of quadrupole MS, and its 20 ml/min column flow rate is handled, splitless, by the SMB interface. Flow modulation GC x GC-SMB-MS shares all the major benefits of GC x GC and combines them with GC-MS including: (a) increased GC separation capability; (b) improved sensitivity via narrower GC peaks; (c) improved sensitivity through reduced matrix interference and chemical noise; (d) polarity and functional group sample information via the order of elution from the second polar column. In addition, GC x GC-SMB-MS is uniquely characterized by the features of GC-MS with SMB of enhanced and trustworthy molecular ion plus isotope abundance analysis (IAA) for improved sample identification and fast fly-through ion source response time. The combination of flow modulation GC x GC with GC-MS with SMB (supersonic GC-MS) was explored with complex matrices such as diesel fuel analysis and pesticide analysis in agricultural products.     

Pulsed flow modulation two-dimensional comprehensive gas chromatography-tandem mass spectrometry with supersonic molecular beams

Pulsed flow modulation (PFM) two-dimensional comprehensive gas chromatography (GC x GC) was combined with quadrupole-based mass spectrometry (MS) via a supersonic molecular beam (SMB) interface using a triple-quadrupole system as the base platform, which enabled tandem mass spectrometry (MS-MS). PFM is a simple GC x GC modulator that does not consume cryogenic gases while providing tunable second GC x GC column injection time for enabling the use of quadrupole-based mass spectrometry regardless its limited scanning speed. The 20-ml/min second column flow rate involved with PFM is handled, splitless, by the SMB interface without affecting the sensitivity. The combinations of PFM GC x GC-MS with SMB and PFM GC x GC-MS-MS with SMB were explored with the analysis of diazinon and permethrin in coriander. PFM GC x GC-MS with SMB is characterized by enhanced molecular ion and tailing-free fast ion source response time. It enables universal pesticide analysis with full scan and data analysis with reconstructed single ion monitoring on the enhanced molecular ion and another prominent high mass fragment ion. The elimination of the third fragment ion used in standard three ions method results in significantly reduced matrix interference. GC x GC-MS with SMB improves the GC separation, and thereby our ability for sample identification using libraries. GC-MS-MS with SMB provides better reduction (elimination) of matrix interference than GC x GC-MS. However, it is a target method, which is not always applicable. GC x GC-MS-MS does not seem to further reduce matrix interferences over GC-MS-MS and unlike GC x GC-MS, it is incompatible with library identification, but it is beneficial to have both GC x GC and MS-MS capabilities in the same system.     

A low thermal mass fast gas chromatograph and its implementation in fast gas chromatography mass spectrometry with supersonic molecular beams

A new type of low thermal mass (LTM) fast gas chromatograph (GC) was designed and operated in combination with gas chromatography mass spectrometry (GC-MS) with supersonic molecular beams (SMB), including GC-MS-MS with SMB, thereby providing a novel combination with unique capabilities. The LTM fast GC is based on a short capillary column inserted inside a stainless steel tube that is resistively heated. It is located and mounted outside the standard GC oven on its available top detector port, while the capillary column is connected as usual to the standard GC injector and supersonic molecular beam interface transfer line. This new type of fast GC-MS with SMB enables less than 1 min full range temperature programming and cooling down analysis cycle time. The operation of the fast GC-MS with SMB was explored and 1 min full analysis cycle time of a mixture of 16 hydrocarbons in the C(10)H(22) up to C(44)H(90) range was achieved. The use of 35 mL/min high column flow rate enabled the elution of C(44)H(90) in less than 45 s while the SMB interface enabled splitless acceptance of this high flow rate and the provision of dominant molecular ions. A novel compound 9-benzylazidanthracene was analyzed for its purity and a synthetic chemistry process was monitored for the optimization of the chemical reaction yield. Biodiesel was analyzed in jet fuel (by both GC-MS and GC-MS-MS) in under 1 min as 5 ppm fatty acid methyl esters. Authentic iprodion and cypermethrin pesticides were analyzed in grapes extract in both full scan mode and fast GC-MS-MS mode in under 1 min cycle time and explosive mixture including TATP, TNT and RDX was analyzed in under 1 min combined with exhibiting dominant molecular ion for TATP. Fast GC-MS with SMB is based on trading GC separation for speed of analysis while enhancing the separation power of the MS via the enhancement of the molecular ion in the electron ionization of cold molecules in the SMB. This paper further discusses several features of fast GC and fast GC-MS and the various trade-offs involved in having powerful and practical fast GC-MS.     

Fast,very fast,and ultra-fast gas chromatography-mass spectrometry of thermally labile steroids,carbamates, and drugs in supersonic molecular beams

Gas chromatography-mass spectrometry (GC-MS) analyses of thermally labile compounds have been studied by using a short column fast gas chromatograph, coupled with fly-through electron ionization in supersonic molecular beams. Thirty-two compounds, which include steroids, carbamate pesticides, antibiotic drugs, and other pharmaceutical compounds, have been analyzed and the details of their GC-MS analysis are provided. The ability to analyze thermally labile compounds is discussed in relation to the speed of analysis. A new term, “speed enhancement factor” (SEF), is defined as the product of column length reduction and the carrier gas linear velocity increase, as compared with normal GC-MS conditions. Fast, very fast, and ultra-fast GC-MS are defined with a SEF in the ranges of 5–30, 30–400, and 400–4000, respectively. Trade-offs in the degree of dissociation, speed, gas chromatograph resolution, and sensitivity were studied and examined with thermally labile molecules. The experimental factors that affect the dissociation are described with emphasis on its reduction. We claim that the use of supersonic molecular beams for sampling and ionization provides the ultimate capability in the GC-MS of thermally labile compounds. The obtained 70-eV electron ionization mass spectra are shown, and an enhanced relative abundance of the molecular ion is demonstrated together with library search capability of these mass spectra, which is better than that reported with particle beam liquid chromatography-mass spectrometry. The performance of fast GC-MS in supersonic molecular beams is compared with other methods of fast GC-MS and with particle beam liquid chromatography-mass spectrometry.     

Optimization and evaluation of low-pressure gas chromatography-mass spectrometry for the fast analysis of multiple pesticide residues in a food commodity

A fast method of analysis for 20 representative pesticides was developed using low-pressure gas chromatography-mass spectrometry (LP-GC-MS). No special techniques for injection or detection with a common quadrupole GC-MS instrument were required to use this approach. The LP-GC-MS approach used an analytical column of 10 m x 0.53 mm I.D., 1 microm film thickness coupled with a 3 m x 0.15 mm I.D. restriction capillary at the inlet end. Thus, the conditions at the injector were similar to conventional GC methods, but sub-atmospheric pressure conditions occurred throughout the analytical column (MS provided the vacuum source). Optimal LP-GC-MS conditions were determined which achieved the fastest separation with the highest signal/noise ratio in MS detection (selected ion monitoring mode). Due to faster flow-rate, thicker film, and low pressure in the analytical column, this distinctive approach provided several benefits in the analysis of the representative pesticides versus a conventional GC-MS method, which included: (i) threefold gain in the speed of chromatographic analysis; (ii) substantially increased injection volume capacity in toluene; (iii) heightened peaks with 2 s peak widths for normal MS operation; (iv) reduced thermal degradation of thermally labile analytes, such as carbamates; and (v) due to larger sample loadability lower detection limits for compounds not limited by matrix interferences. The optimized LP-GC-MS conditions were evaluated in ruggedness testing experiments involving repetitive analyses of the 20 diverse pesticides fortified in a representative food extract (carrot), and the results were compared with the conventional GC-MS approach. The matrix interferences for the quantitation ions were worse for a few pesticides (acephate, methiocarb, dimethoate, and thiabendazole) in LP-GC-MS, but similar or better results were achieved for the 16 other analytes, and sample throughput was more than doubled with the approach.     

Improvement in steroid screening for doping control with special emphasis on stanozolol

The Medical Commission of the International Olympic Committee forbids the use of anabolic androgenic steroids and beta2-agonists to improve athletic performance. In this work we have selected examples of anabolic androgenic compounds and their metabolites to evaluate the GC-MS analysis of some trimethylsilyl derivatives. The aim is to set the best GC conditions to improve the detection within the whole range of analyte elution temperatures. The initial column temperature was changed to 105 or 140 degrees C followed by 40 degrees C min(-1) to 200 degrees C and then 15 degrees C min(-1) to 300 degrees C. Using 140 degrees C as the initial oven temperature it was possible to obtain narrower initial analyte distributions for the compounds that elutes at the beginning of the chromatogram as clenbuterol, mabuterol, epimethylenediol and norandrosterone, without loss of derivatized metabolites signal. Later. eluting analytes, such as the stanozolol metabolites, furazabol and oxandrolone were not affected. Temperatures below 140 degrees C. resulted in partial derivatization for some analytes mainly stanozolol related structures. Therefore evaluation of derivatization conditions as occurring in three steps, the vial, vaporization chamber and capillary column, was thoroughly assessed. The new program temperature improves the signal-to-noise ratio for some compounds and shows adequate resolution for endogenous compounds. Some of the difficult key separations necessary for doping control enforcement were also obtained with the proposed method.     

Gas and liquid chromatography of metal chelates of pentamethylene dithiocarbamate

Capillary GC and HPLC of metal chelates of pentamethylene dithiocarbamate were examined. Copper(II), nickel(II), cobalt(III), iron(III), manganese(II) and chromium(III) chelates formed in slightly acidic media (pH 5) were extracted in methyl isobutyl ketone or chloroform. Capillary GC elution and separation was carried out on methylsilicone DB-1 column (25 m x 0.2 mm I.D.) with film thickness 0.25 microm. Electron-capture detection was used. Elution was carried at initial column temperature 200 degrees C with an increment at a rate of 5 degrees C/min up to 250 degrees C and maximum temperature was maintained for 10 min. Symmetrical peaks with baseline separation were obtained with the metal chelates investigated with linear calibration range between 5 and 25 microg/ml for each metal ion and detection limits in the range of 0.5-6.0 microg/ml corresponding to 27-333 pg of metal ion reaching to the detector. HPLC separation was carried out from LiChrosorb ODS, 5 microm column and complexes eluted with methanol-water-1 mM sodium acetate (70:28:2, v/v) with a flow-rate of 1.2 ml/ml. UV detection was at 260 nm. The detection limits obtained were in the range 2-6 microg/ml. The methods were applied to the determination of metal ions in canal water and coal samples with RSD values within 4.15%. The results when compared with a standard flame atomic absorption spectrophotometric method and revealed no significant difference.     

Evaluation of solid-phase microextraction desorption parameters for fast GC analysis of cocaine in coca leaves

By its simplicity and rapidity, solid-phase microextraction (SPME) appears as an interesting alternative for sample introduction in fast gas chromatography (fast GC). This combination depends on numerous parameters affecting the desorption step (i.e., the release of compounds from the SPME fiber coating to the GC column). In this study, different liner diameters, injection temperatures, and gas flow rates are evaluated to accelerate the thermal desorption process in the injection port. This process is followed with real-time direct coupling a split/splitless injector to a mass spectrometer by means of a short capillary. It is shown that an effective, quantitative, and rapid transfer of cocaine (COC) and cocaethylene (CE) is performed with a 0.75-mm i.d. liner, at 280 degrees C and 4 mL/min gas flow rate. The 7-microm polydimethylsiloxane (PDMS) coating is selected for combination with fast GC because the 100-microm PDMS fiber presents some limitations caused by fiber bleeding. Finally, the developed SPME-fast GC method is applied to perform in less than 5 min, the quantitation of COC extracted from coca leaves by focused microwave-assisted extraction. An amount of 7.6 +/- 0.5 mg of COC per gram of dry mass is found, which is in good agreement with previously published results.     

Sensitivity comparison of gas chromatography–mass spectrometry with Cold EI and standard EI

Gas chromatography–mass spectrometry (GC–MS) with Cold EI is based on interfacing GC and MS with supersonic molecular beams (SMBs) along with electron ionization of vibrationally cold sample compounds in SMB in a fly-through ion source (hence the name Cold EI). Cold EI improves all the central performance aspects of GC–MS, and in this paper, we focus on its improvement of signal-to-noise ratio (S/N) and limits of detection (LODs). We found that the harder the compound for analysis with standard EI, the greater the Cold EI gain in S/N and LOD. The lower LOD and higher S/N of Cold EI emerge from a few reasons: (a) similar ionization yield as standard EI, (b) enhanced abundance of molecular ions, (c) elimination of vacuum background noise, (d) elimination of ion source-related peak tailing and degradation, (e) ability to lower the elution temperatures via the use of high column flow rates, and (f) greater range of thermally labile and low-volatility compounds that can be analyzed. We demonstrate the superior S/N and lower LOD of Cold EI versus standard EI in a range of compounds, from the simple-to-analyze octafluoronaphthalene all the way to reserpine and an organo-metallic compound that cannot be analyzed by standard EI. These compounds include methyl stearate, cholesterol, n-C₃₂H₆₆, large polycyclic aromatic hydrocarbons, dioctyl phthalates, diundecyl phthalate, pentachlorophenol, benzidine, lambda-cyhalothrin, and methidathion. The significantly lower Cold EI LODs that can be over 1000 times better than in standard EI further result in far superior response linearity and greater measurement dynamic range.     

Application of a thermal desorption cold trap injector to multidimensional GC and GC-MS

The Thermal desorption Cold Trap injector (TCT) was used as a part of modified multidimensional GC (MDGC) or MDGC mass spectroscopy (MS) systems. These systems were based on a preparative GC (GC1), an analytical GC (GC2), or GC-MS and the TCT. The TCT was mounted on the GC2 or GC-MS. Analysis was carried out as follows: first, the volatile compounds heart-cut after separation on the GC1 column were adsorbed onto the Porapak Q column out of the GC1 oven. This Porapak Q column was then coupled to the TCT, and the volatile compounds adsorbed on the Porapak Q were thermally desorbed, cold trapped, and injected onto an analytical column in the GC2 or GC-MS. Repeatability of the retention time (RT) and area % of model samples consisting of citronellol, decanol, and geranyl acetate was examined. Also, the volatile compounds present at very low concentrations in ethanol solution were concentrated on the Porapak Q column. These were injected onto the analytical column by the same method as described above, and the repeatability of the RT and area % on the chromatogram was examined. In the two experiments, the standard deviation of the RT and area % for each compound was about 0.02 and less than 2.85, respectively. A commercial geranium oil was successfully analyzed by this technique. The results indicate that this modified MDGC and MDGC-MS system are very useful for detection and determination of compounds in complex mixtures.     

Analysis of 35 priority semivolatile compounds in water by stir bar sorptive extraction-thermal desorption-gas chromatography-mass spectrometry. I. Method optimisation

A multiresidue method for the determination of 35 organic micropollutants (pesticides and polycyclic aromatic hydrocarbons) in water has been optimised using stir bar sorptive extraction (SBSE) and thermal desorption coupled to capillary gas chromatography-mass spectrometry (GC-MS). In the present work, the different parameters affecting the extraction of the analytes from the water samples to the PDMS-coated stir bars and optimisation of conditions affecting thermal desorption are investigated. The optimised conditions consist of a 100-ml water sample with 20% NaCl addition extracted with 20 mm length x 0.5 mm film thickness stir bars at 900 rpm during 14 h at ambient temperature. Desorption is carried out at 280 degrees C during 6 min under a helium flow of 75 ml/min in the splitless mode while maintaining a cryofocusing temperature of 20 degrees C in the programmed-temperature vaporisation (PTV) injector of the GC-MS system. Finally, the PTV injector is ramped to a temperature of 280 degrees C and the analytes are separated in the GC and detected by MS using full scan mode (m/z 60-400). Under the described conditions, the good repeatability, high analyte recoveries and robustness, make SBSE a powerful tool for routine quality control analysis of the selected semivolatile compounds in water samples.     

Capillary gas chromatographic determination of methylglyoxal from serum of diabetic patients by precolumn derivatization using meso-stilbenediamine as derivatizing reagent

Stilbenediamine is used as derivatizing reagent for methylglyoxal (MGo) and dimethylglyoxal for the gas chromatographic (GC) determination of MGo from the serum of diabetic patients and healthy volunteers. The derivatization is obtained at pH 3. GC elution and separation are carried out on an HP5 column (30 m x 0.32 mm i.d.) at column temperature 150 degrees C with a programmed heating rate of 50 degrees C/min up to 250 degrees C, and a total run time of 7 min. The nitrogen flow rate is 5 mL/min and detection is carried out by flame ionization detection. The linear calibration curves are obtained with a range of 0.076-0.760 microg/mL and the detection limit is 25 ng/mL MGo. The amounts of MGo found in the serum of healthy volunteers and diabetic patients are 0.025-0.065 microg/mL and 0.115-0.228 microg/mL, with coefficient of variation 1.3-3.1% and 1.4-3.3%.     

On-flow gas chromatographic method for the determination of the enantiomer interconversion energy barrier

A novel on-flow gas chromatographic (GC) method is developed for the determination of the kinetic rate constants and interconversion energy barrier of thermally labile enantiomers. The validity of the developed method is approved by the study of interconversion of 1-chloro-2,2-dimethylaziridine enantiomers on an achiral column. The overall experiments are performed in a series of three columns placed in two independently heated GC ovens. The racemate of the 1-chloro-2,2-dimethylaziridine is injected and separated in the first chiral column at 60 degrees C in which the interconversion of enantiomers is suppressed. Separated enantiomers are then transferred into the achiral column, where the enantiomers are interconverted at a selected temperature under the current carrier gas flow. Effluent from this column is transferred into the second chiral column, where the native enantiomers and those originated by the on-flow interconversion on an achiral column are again separated at 60 degrees C. Chromatograms obtained by monitoring the effluents from the second chiral column are used to determine the peak areas of the original and the newly interconverted enantiomers. The corresponding peak areas and the interconversion times are used to calculate the interconversion rate constants and energy barriers of the 1-chloro-2,2-dimethylaziridine enantiomers. The apparent energy barriers of the enantiomers of 1-chloro-2,2-dimethylaziridine are equal for both enantiomers within a 95% confidence interval and independent of the polarity of the stationary phase of the column in which the interconversion of enantiomers occur.     

树兰花挥发性成分的提取及鉴定

采用超临界CO2流体从树兰花中提取挥发油,得油率为2.64%。利用气相色谱-质谱联用仪(GC-MS)对树兰花油中的化学成分进行分离和鉴定,共分离出54种组分,确认了其中的48种成分,其中有18种萜烯类化合物和12种酯类物质等成分,如α-蛇麻烯、亚麻酸乙酯、大根香叶烯-D、β-榄香烯、古巴烯、石竹烯、茉莉酮酸甲酯、β-蛇麻烯-7-醇和棕榈酸乙酯等。     

Comparison of two-stage retention index monitoring capillary gas chromatography and selected ion monitoring capillary gas chromatography – mass spectrometry as analytical tools

Two-stage capillary GC with two-stage retention index monitoring is an efficient analytical technique which can be used for detection and determination of small amounts of volatile compounds in complex mixtures of hundreds or thousands of other compounds. The system employs two capillary columns, coated with different stationary phases, connected on-line with the aid of a micro valve; the first column acts as a pre-separating unit from which unresolved fractions of interest are cut (transferred) into another column for final, interference-free separation of the compounds to be determined. This technique has been compared with selected ion monitoring capillary GC-MS using a hydrocarbon mixture as a test sample for comparing resolution, repeatability, and the practical usefulness of the techniques. Results indicate that two-stage capillary GC is very useful for mixtures containing compounds which produce mostly non-specific ions in the MS ion source whereas compounds producing specific ions can be easily analyzed by capillary GC – single ion monitoring MS even if they are not perfectly separated by a single capillary column.     

Rapid column heating method for subcritical water chromatography

A novel resistive heating method is presented for subcritical water chromatography (SWC) that provides higher column heating rates than those conventionally obtained from temperature-programmed gas chromatography (GC) convection ovens. Since the polarity of water reduces dramatically with increasing temperature, SWC employs column heating to achieve gradient elution. As such, the rate at which the mobile phase is heated directly impacts the magnitude of such gradients applied in SWC. Data from the current study demonstrate that the maximum column heating rate attainable in a typical SWC apparatus (i.e. using a GC convection oven) is around 10 degrees C/min, even at instrument oven settings of over three times this value. Conversely, by wrapping the separation column with ceramic insulation and a resistively heated wire, the column heating rates are increased five-fold. As a result, elution times can be greatly decreased in SWC employing gradients. Separations of standard alcohol test mixtures demonstrate that the retention time of the latest eluting component decreases by 35 to 50% using the prototype method. Additionally, solute retention times in this mode deviate by less than 1% RSD over several trials, which compares very well to those obtained using a conventional GC convection oven. Results suggest that the developed method can be a useful alternative heating technique in SWC.