Fast analysis of decabrominated diphenyl ether using low-pressure gas chromatography-electron-capture negative ionization mass spectrometry

This paper reports the applicability of low-pressure gas chromatography-mass spectrometry operated in electron-capture negative ionization mode (LP-GC-ECNI-MS) for the analysis of decabrominated diphenyl ether (BDE-209). Particular attention was paid to find optimal injector and oven conditions for minimal thermal degradation of BDE-209. The analytical characteristics were compared for LP-GC columns (10 m x 0.53 mm) with different film thicknesses (d(f) 0.15 microm versus 0.25microm) and for a conventional GC column (15 m x 0.25 mm, 0.10 microm d(f)). Short residence times (6.5 and 9.8 min) of BDE-209 were found for the LP-GC systems with 0.15 and 0.25microm d(f), respectively, resulting in a low elution temperature and minimal degradation. Additionally, baseline separation of 22 polybrominated diphenyl ether (PBDE) congeners (major components of PBDE technical mixtures) was possible in less than 12 min using the LP-GC-ECNI-MS system with 0.15microm d(f). The optimized method was applied for the determination of PBDEs in Belgian indoor dust samples. The obtained concentrations of BDE-209 (range 8-292 ng/g dry weight) were in the same range or lower than concentrations in dust from other European countries.     

Evaluation of low-pressure gas chromatography linked to ion-trap tandem mass spectrometry for the fast trace analysis of multiclass pesticide residues

A rapid multiresidue method for the analysis of 72 pesticides has been developed using a single injection with low-pressure gas chromatography/tandem mass spectrometry (LP-GC/MS/MS). The LP-GC/MS/MS method used a short capillary column of 10 m x 0.53 mm i.d. x 0.25 microm film thickness coupled with a 0.6 m x 0.10 mm i.d. restriction at the inlet end. Optimal LP-GC conditions were determined which achieved the fastest separation in MS/MS detection mode. Also MS/MS conditions were optimized in order to increase sensitivity and selectivity. The analytical parameters of the LP-GC/MS/MS method were compared with those obtained by GC/MS/MS using a conventional capillary column (30 m x 0.25 mm i.d. x 0.25 microm film thickness). Better precision and sensitivity values were obtained with the LP-GC/MS/MS approach. The limits of detection (LOD) of the compounds ranged from 0.1 to 14.1 microg L(-1) for LP-GC/MS/MS, lower than those obtained for conventional GC/MS/MS that ranged from 0.1 to 17.5 microg L(-1). The peak widths obtained with the short column in LP-GC are similar to those obtained using conventional capillary GC columns, and the peaks can be successfully identified by MS/MS detection with the conventional scan speed of ion-trap instruments. In addition, the analysis time was significantly reduced with LP-GC/MS/MS (32 min) versus GC/MS/MS (72 min), allowing the number of samples analyzed per day in a routine laboratory to be doubled.     

Possibilities and limitations of fast GC with narrow-bore columns

In this work, two narrow-bore capillary columns with different internal diameters (I.D.) 0.15 mm (15 m length, 0.15 microm film thickness) and 0.10 mm (10 m length, 0.10 microm film thickness) with the same stationary phase (5% diphenyl 95% dimethylsiloxane), phase ratio and separation power were compared with regard to their advantages, practical limitations and applicability in fast GC on commercially available instrumentation. The column comparison concerns fast GC method development, speed and separation efficiency, the sample transfer into the column utilizing split and splitless inlet, sample capacity, detection (analysing compounds of a wide range of polarities and volatilities--even n-alkanes C16-C28 and selected pesticides) and ruggedness (in the field of ultratrace analysis of pesticide residues in real matrix). Under conditions corresponding to speed/separation efficiency trade-off 0.10 mm I.D. versus 0.15 mm I.D. column provides a speed gain of 1.74, but all other parameters investigated were better for the 0.15 mm I.D. column concerning more efficient sample transfer from inlet to the column using splitless injection, no discrimination with split injection. Better sample capacity (three times higher for the 0.15 mm than for the 0.10 mm I.D. column) resulted in improved ruggedness and simpler fast GC-MS method development.     

Monolithic silica columns with various skeleton sizes and through-pore sizes for capillary liquid chromatography

Reduction of through-pore size and skeleton size of a monolithic silica column was attempted to provide high separation efficiency in a short time. Monolithic silica columns were prepared to have various sizes of skeletons (approximately 1-2 microm) and through-pores (approximately 2-8 microm) in a fused-silica capillary (50-200 microm I.D.). The columns were evaluated in HPLC after derivatization to C18 phase. It was possible to prepare monolithic silica structures in capillaries of up to 200 microm I.D. from a mixture of tetramethoxysilane and methyltrimethoxysilane. As expected, a monolithic silica column with smaller domain size showed higher column efficiency and higher pressure drop. High external porosity (> 80%) and large through-pores resulted in high permeability (K = 8 x 10(-14) -1.3 x 10(-12) m2) that was 2-30 times higher than that of a column packed with 5-mirom silica particles. The monolithic silica columns prepared in capillaries produced a plate height of about 8-12 microm with an 80% aqueous acetonitrile mobile phase at a linear velocity of 1 mm/s. Separation impedance, E, was found to be as low as 100 under optimum conditions, a value about an order of magnitude lower than reported for conventional columns packed with 5-microm particles. Although a column with smaller domain size generally resulted in higher separation impedance and the lower total performance, the monolithic silica columns showed performance beyond the limit of conventional particle-packed columns under pressure-driven conditions.     

Fast and sensitive determination of pesticide residues in vegetables using low-pressure gas chromatography with a triple quadrupole mass spectrometer

In this study, the feasibility of low-pressure gas chromatography (LP-GC) in conjunction with a triple quadrupole mass spectrometer, as a route towards fast pesticide residue analysis, was investigated. A Varian GC-MS system equipped with a mass spectrometer model 1200 was used. LP-GC-MS experiments were performed on a HP-5 10 m x 0.32 mm x 0.25 microm analytical column connected to a 2.5 m x 0.15 mm non-coated restriction precolumn at the inlet end. For comparison purposes conventional GC-MS analysis was performed on a RTX-5 30 m x 0.25 mm x 0.5 microm column. Under the optimized conditions the analysis time was reduced to 13.3 min with the LP-GC approach which corresponds to an almost threefold gain in speed versus the conventional GC (37 min). Despite the poorer separation power of the LP-GC column, the experiments conducted with tomato and onion extracts spiked with 78 pesticides proved that LP-GC-MS is of practical value to perform full scan screening analysis. Moreover, the rate of false negative results was higher in the case of conventional GC-MS while the LP-GC-MS enabled correct identification of pesticides at lower levels since the peaks were improved in both size and shape. Validation experiments were performed on a sample of 12 representative pesticides for comparison of performance characteristics of the LP-GC and GC approaches with mass spectrometer operated in scan, SIM and MS/MS mode. The LP-GC column set-up interfaced to the MS detector was found to be superior to the conventional GC with respect to obtained linearity, accuracy and precision parameters. Also, lower limits of detection in real extracts were achieved using the LP-GC approach. Finally, the LP-GC-MS/MS analysis of tomato samples with incurred pesticide residues demonstrated the applicability of the developed method for analysis of real samples.     

Ruggedness and other performance characteristics of low-pressure gas chromatography-mass spectrometry for the fast analysis of multiple pesticide residues in food crops

Low-pressure gas chromatography-mass spectrometry (LP-GC-MS) using a quadrupole MS instrument was further optimized and evaluated for the fast analysis of multiple pesticide residues in food crops. Performance of two different LP-GC-MS column configurations was compared in various experiments, including ruggedness tests with repeated injections of pesticides in matrix extracts. The tested column configurations employed the same 3 m x 0.15 mm i.d. restriction capillary at the inlet end, but different analytical columns attached to the vacuum: (A) a 10 m x 0.53 mm i.d., 1 microm film thickness RTX-5 Sil MS column; and (B) a 10 m x 0.25 mm i.d., 0.25 microm film thickness DB-5MS column. Under the optimized conditions (compromise between speed and sensitivity), the narrower analytical column with a thinner film provided slightly (<1.1-fold) faster analysis of <5.5 min separation times and somewhat greater separation efficiency. However, lower detection limits for most of the tested pesticides in real extracts were achieved using the mega-bore configuration, which also provided significantly greater ruggedness of the analysis (long-term repeatability of analyte peak intensities, shapes, and retention times). Additionally, the effect of the increasing injection volume (1-5 microl) on analyte signal-to-noise ratios was evaluated. For the majority of the tested analyte-matrix combinations, the increase in sensitivity caused by a larger injection did not translate in the same gain in analyte detectability. Considering the costs and benefits, the injection volume of 2-3 microl was optimal for detectability of the majority of 57 selected pesticides in apple, carrot, lettuce, and wheat extracts.     

Application of low-pressure gas chromatography-ion-trap mass spectrometry to the analysis of the essential oil of Turnera diffusa (Ward.) Urb

Turnera diffusa Willd. var. afrodisiaca (Ward) Urb. (syn. T. aphrodisiaca) belongs to the family of Turneraceae and is an aromatic plant growing wild in the subtropical regions of America and Africa. It is widely used in the traditional medicine as e.g. anti-cough, diuretic, and aphrodisiac agent. This work presents a 3 min chromatographic analysis using low-pressure (LP) gas chromatography (GC)-ion-trap (IT) mass spectrometry (MS). The combination of a deactivated 0.6 m x 0.10 mm i.d., restrictor with a wide-bore CP-Wax 52 capillary column (10 m x 0.53 mm i.d., 1 microm) reduces the analysis time by a factor of 3-7 in comparison to the use of a conventional narrow bore column. Chromatographic conditions have been optimized to achieve the fastest separation with the highest signal/noise ratio in MS detection. These results allow fast and reliable quality control of the essential oil to be achieved.     

Qualitative evaluation of thermal desorption-programmable temperature vaporization-comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry for the analysis of selected halogenated contaminants

The separation of 38 toxic and predominant polychlorinated biphenyl (PCB) congeners, 11 persistent halogenated pesticides, 1 brominated biphenyl (BB), and 8 polybrominated diphenyl ethers (PBDEs) has been optimized using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC-TOFMS). A thermal desorption-programmable temperature vaporization (TD-PTV) step was used for the injection. Different column sets were investigated, and a 100% dimethylpolysiloxane (15 m x 0.25 mm i.d. x 0.25 microm film thickness) narrowbore capillary column coupled to a high temperature (8% phenyl)-polycarborane-siloxane (2 m x 0.10 mm i.d. x 0.10 microm film thickness) microbore column set was selected. Of the 58 compounds investigated, only one pair of PCBs was not resolved. All other analytes were either baseline separated into the chromatographic plane or were virtually separated using the deconvolution capability of the TOFMS.     

Conventional inner diameter short capillary columns: an approach to speeding up gas chromatographic analysis of medium complexity samples.

Short capillary columns (5 m) with 0.25 mm inner diameter (I.D.) are applied to the GC analysis of medium complexity samples (up to 30 components) with the aim of shortening analysis time. This approach is complementary to fast GC with narrow-bore columns and is based on compensating the lower efficiency of short columns with conventional I.D.'s (0.25-0.32 mm) by using a stationary phase selectivity suitable to separate the components of the sample under investigation, so that the required resolution power is achieved but, at the same time, the analysis time is shortened. The qualitative and quantitative effectiveness of this approach is demonstrated through the analysis of: essential oils with different compositions (chamomile and rosemary), low-volatility triterpenes in a plant extract (Maytenus aquifolium and M. ilicfolium), thermolabile pyrethrins in a Pyrethrum extract, and a mixture of pesticides applied to protect medicinal plant crops. In all examples, GC analysis was five to ten times faster than with conventional columns.     

Effect of first-dimension column film thickness on comprehensive two-dimensional gas chromatographic separation

In comprehensive two-dimensional gas chromatography (GC x GC), samples experience two-dimensional separation implemented by a modulator which helps preserve the first-dimension separation and facilitates the second-dimension separation by periodically collecting, focusing and launching the material from the primary column onto the secondary column with a different stationary phase. Column overloading in GC x GC is a considerable problem, aggravated by the fact that two columns are involved. Broad first-dimension peaks of an analyte help produce smaller fractions of the analyte in the second-dimension, reducing the chance of secondary column overloading. One of the means to generate broad peaks in the first-dimension is to use thick film primary columns. A series of primary columns of various film thickness were tested in the study, and the results indicate that when other conditions are kept constant, 1 microm film columns often provide better resolution in both first and second-dimension but at the expense of a much longer separation time; 0.1 microm is clearly inadequate for GC x GC separation; 0.5 and 0.25 microm film columns seem to be the best compromises.     

Higher mass loadability in comprehensive two-dimensional gas chromatography-mass spectrometry for improved analytical performance in metabolomics analysis

A major challenge in metabolomics analysis is the accurate quantification of metabolites in the presence of (extremely) high abundant metabolites. Quantification of metabolites at low concentrations can be complicated by co-elution and/or peak distortion when these metabolites elute close to high abundant metabolites. To increase the separation efficiency a comprehensive two-dimensional gas chromatographic-mass spectrometric method (GC x GC-MS) was set up, in which a polar first dimension column and an apolar second dimension column were used to maximize the peak capacity. The feasibility of using wider bore, thicker film columns in the second dimension to improve the mass loadability and inertness of the analytical system was investigated. Several column combinations with varying second dimension column dimensions were compared with a setup with a narrow bore column (0.1mm I.D.) in the second dimension. With a wider bore column (0.32 mm I.D.) in the second dimension the mass loadability was improved 10-fold, and the more inert column surface of the thicker film second dimension column resulted in a more accurate (automated) quantification and improved linearity in the presence of high concentrations of matrix compounds or metabolites. These benefits amply compensated the observed decrease in peak capacity of 40% compared to the narrow bore (0.1mm I.D.) thin film second dimension column. Compared to GC-MS and conventional GC x GC-MS, better performance for quantification of metabolites for typical metabolomics samples was achieved.     

Analysis of isomeric tropane alkaloids from Schizanthus grahamii by very fast gas chromatography

This study presents a very fast GC analysis applied for the baseline separation of isomeric tropane alkaloids extracted from the stem-bark of Schizanthus grahamii (Solanaceae). The work provided a challenging application where isothermal analysis in conjunction with very short narrow bore columns (3 m x 100 microm ID and 1.5 m x 50 microm ID) was particularly suited for the speeding up. Experimental parameters were used in the optimisation steps, including selection of stationary phase, temperature, internal column diameter and optimal practicable gas velocity. Some considerations about sample injection in fast isothermal analysis are also briefly presented. Finally, the investigated approach allowed a very fast baseline separation of four positional and configurational isomers in less than 9 s.     

Direct resistively heated column gas chromatography (Ultrafast module-GC) for high-speed analysis of essential oils of differing complexities

This study applies Ultrafast module-GC (UFM-GC) with direct resistively heated columns to routine analysis of a group of essential oils of differing complexities (chamomile, peppermint, rosemary and sage). Essential oils were analysed by conventional GC with conventional inner diameter (i.d.) columns (0.25 mm) of different lengths (5 and 25 m long) and by Fast GC and Ultrafast module-GC with narrow bore columns (0.1 mm i.d., 5 m long). Column performance were evaluated and compared through their Grob test, separation number and peak capacity. Ultrafast module-GC was successful in the qualitative and quantitative analysis of essential oils of different compositions with analysis times between 40 s and 2 min versus 20-60 min required by conventional GC. Critical pairs or groups of components were separated by carefully tuning selectivity of the stationary phase to compensate for loss of efficiency due to the use of short columns and high temperature rates. The Ultrafast module-GC results of peppermint e.o. analyses were also validated and compared to those obtained by conventional GC; by measuring precision over time (i.e. repeatability and intermediate precision) and accuracy. Ultrafast module-GC showed a good separation reproducibility affording reliable component identification through the relative retention times and quantitative determination through normalised peak areas. Accuracy data also showed that Ultrafast module-GC and conventional GC normalised areas and areas percentage were perfectly comparable.     

A comparison of performance of various analytical columns in pharmaceutical analysis: conventional C18 and high throughput C18 zorbax columns

New improved types of analytical columns Zorbax Eclipse XDB-C18 (75 mm x 4.6 mm i.d., 3.5 microm) and Zorbax Eclipse XDB-C18 (50 mm x 4.6 mm i.d., 1.8 microm) have been tested for determination of estradiol (active substance), methylparaben, propylparaben (preservatives) and estrone (degradation product) and compared with the conventional C18 columns (250 mm x 3.0 mm i.d., 5.0 microm). The Zorbax columns differ with their particle size, column length and ODS (octadecylsilica) type as well. Higher flow-rates (up to about 2.5 ml min(-1)) could be applied regardless to back-pressure. The analysis - previously done at 40 degrees C - could be performed even at ambient temperature. Analytical run was shortened to 3.5 min (from 12 min used for the conventional C18 column) with the same or better retention characteristics. System suitability data for all Zorbax columns show the advantages of these columns for the practical use in routine quality control of pharmaceuticals, particularly from the point of view of speed of analysis and solvent consumption.     

Capillary scale monolithic trap column for desalting and preconcentration of peptides and proteins in one- and two-dimensional separations

Monolithic columns based on poly-(styrene-divinylbenzene) (PS-DVB) were utilized both for preconcentration (in 10 mm x 0.20 mm I.D. format) and analytical separation (in 60 mm x 0.20 and 0.10 mm I.D. format) of peptides and proteins in column switching micro-scale high-performance liquid chromatography. A special holder for short monolithic preconcentration columns was designed and pressure durability tests approved long-term stability up to 400 bar. An 11-20% decrease in the average peak widths of nine peptides was obtained upon combining a preconcentration column with an analytical column as compared with a setup using an analytical column only. Trapping efficiency, especially for small and hydrophilic peptides, was optimized by using 0.10% heptafluorobutyric acid instead of 0.050% trifluoroacetic acid as solvent additive during sample loading. Using a 10 mm x 0.20 mm I.D. preconcentration column, loadabilities between 0.5 and 1.6 microg were determined by frontal analysis of proteins and bioactive peptides, respectively. A 100-fold concentration followed by direct on-line intact mass determination is demonstrated for diluted (3 micromolL(-1)) protein solutions. The applicability of the monolithic preconcentration column for multidimensional chromatography was tested by off-line two-dimensional separation, combining strong cation-exchange chromatography and ion-pair reversed-phase chromatography. Peptide identification data from digested protein mixtures demonstrated reproducibilities of 46-75% in triplicate analyses, and confident peptide identifications of low abundant peptides even in the presence of a 650-fold molar excess of high abundant peptides.     

Overloading of the second-dimension column in comprehensive two-dimensional gas chromatography

Comprehensive two-dimensional gas chromatography (GC x GC) is based on a coupling of two GC columns of different characteristics by means of a device that allows portions of the effluent from the primary column to be injected onto the second dimension column for an additional separation. The time available for the separation in the second-dimension column is very short. Thus, this separation should be very efficient. The vast majority of GC x GC practitioners use very narrow bore columns for the second dimension. While this approach is justified in principle, if peaks in the second dimension overload this column, its peak capacity is severely reduced. A series of second-dimension columns of varying internal diameters, but similar phase ratios, were used to study these effects. The results indicate that 250 microm columns often provide comparable second dimension peak widths to 100 microm columns, while at the same time being less prone to overloading, indicating that they may often be a better choice than smaller diameter columns in the second dimension of GC x GC systems.     

Elevated temperature-extended column length conventional liquid chromatography to increase peak capacity for the analysis of tryptic digests

High efficiency separations (200 000 plates) were obtained on conventional LC equipment by coupling 8 x 25 cm x 2.1 (or 4.6) mm id x 5 microm d(p) ODS columns (total length 2 m) and operation at 60 degrees C using a dedicated LC oven. The peak capacity in this 1-D set-up was 900 for the separation of human serum tryptic peptides analyzed after depletion of six highly abundant proteins. The chromatographic performance of an elevated temperature-extended column length conventional LC is highlighted.     

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.     

Electrochromatography with a 2.7 mm inner diameter monolithic column

Monolithic columns of 2.7 mm I.D. have been prepared and used in electrochromatography (EC) separation. Although capillary electrochromatography (CEC) has higher separation efficiency, it displays some shortcomings, such as limited sample loadability and restricted concentration detectability etc. In this paper, we investigate the feasibility of EC separation with millimeter diameter monolithic columns. By using a designed preparation method of monolithic column packed with about 150 microm quartz sand, the effect of Joule heating can be reduced, and the processes of frit making and column packing can be avoided. The concentration detectability of the EC is improved comparing with that of CEC. Moreover, the separation efficiency of 52,000 plates/m was achieved with a 70 mm length and 2.7 mm I.D. monolithic column.     

Crystalline degradation products of vancomycin as chiral stationary phase in microcolumn liquid chromatography

The ability of crystalline degradation products (CDPs) of vancomycin as a chiral stationary phase was reported in a previous study for enantioselective separation of drugs, amino acids and agrochemical toxins by conventional LC column (250 x 4.6 mm). In this work, the potential of CDP of vancomycin for the enantiomeric separation in micro-LC (200 x 1 mm) has been studied. The obtained separation results are better than in our previous study with conventional LC columns. The enantiomers of D,L-phenylalanine, D,L-alanine, methyldopa, atropine and propranolol were used for this evaluation. Experiments have been carried out in a stainless steel tube that was packed with chiral silica particles of 3 and 12 microm diameters. Also, three different ratios of 3 and 12 microm silica particles were used for packing material of chiral columns and the effect on aspect ratio and resolving powers was compared.