Split Injection Mode Research Articles

High throughput chiral analysis of urinary amphetamines by GC-MS using a short narrow-bore capillary column

We report very rapid and simultaneous chiral analysis of urinary amphetamine-type stimulants (ATSs), including amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, 3,4-methylenedioxymethamphetamine, and 3,4-methylenedioxyethylamphetamine, using gas chromatography-mass spectrometry (GC-MS) with a simple procedure. A urine sample containing ATSs was subjected to extractive derivatization on a diatomaceous earth tube with trifluoroacetyl-l-prolyl chloride in a single step. The concentrated sample was analyzed by GC-MS, using a short narrow-bore capillary column (10 m × 0.1 mm i.d.) in split injection mode. All chiral isomers of the ATSs targeted in this study were chromatographically distinguishable within 5 min. By our method, ATSs in urine could be measured in the concentration range of 20–1000 ng/ml with coefficients of variation of less than 9%. Our method will be very useful for chiral analysis of ATSs in routine forensic toxicology investigations, because of its simplicity and rapidity.

Enantioselective gas chromatographic analysis of aqueous samples by on-line derivatisation: Application to enzymatic reactions

A new gas chromatography (GC) method is presented for analysing both the conversion and the enantiomeric excess ( e.e.) of samples from alcohol dehydrogenase reactions. The chiral compounds studied were a series of saturated, straight chain alcohols, ranging from 2-butanol to 2-heptanol. The alcohols were converted to the corresponding trifluoroacetylated derivatives by injecting trifluoroacetic anhydride onto the column shortly after injection of the aqueous samples in split-injection mode (1:100) onto a Chiraldex G-TA capillary GC column. Injecting seven hundred aqueous enzymatic reaction mixtures according to the above-mentioned procedure revealed no noticeable loss of column performance. Using the new GC method, conventional sample work-up procedures such as extraction and off-line derivatisation are eliminated and throughput of samples is significantly enhanced.

Rapid screening of polychlorinated biphenyls in sediments using non-equilibrium solid-phase microextraction and fast gas chromatography with electron-capture detection

A rapid method for the screening of polychlorinated biphenyls (PCBs) in sediment samples is described. Analytes are concentrated on a poly(dimethylsiloxane) (PDMS) solid-phase microextraction (SPME) fibre, separated using a narrow-bore gas chromatography column (10 m × 0.1 mm I.D.) and determined with a micro-electron-capture detector (micro-ECD). The narrow-bore column showed a similar separation efficiency to a conventional capillary one (30 m × 0.32 mm I.D.) and allowed a 3 times reduction in the analysis time. Moreover, thermal desorption of SPME fibres in the narrow-bore column did not produce any degradation in the quality of separations when compared to the split injection mode. The use of an oxidative sample treatment was mandatory to remove sulphur interferences in the chromatograms and increase the yield of PCBs during SPME for short sampling times. Under optimised conditions, a fraction of sediment (0.1–0.5 g) was mixed with 5 ml of a 0.2 M potassium permanganate solution and 0.5 ml of sulphuric acid 6 M in a 22 ml closed vessel. Sample treatment and headspace SPME of PCBs were performed simultaneously for 10 min at 100 °C. Globally, the whole analytical procedure takes about 20 min and presents quantification limits between 0.5 and 1.3 ng/g. Accuracy was evaluated by analysing a reference sediment sample with certified concentrations of several PCBs.

Fast analysis of nicotine related alkaloids in tobacco and cigarette smoke by megabore capillary gas chromatography

A novel fast megabore capillary gas chromatographic (MCGC) method for analysis of 7 nicotine related alkaloids in tobacco and cigarette smoke, including nicotine, nornicotine, myosmine, nicotyrine, anabasine, anatabine and 2,3-dipyridyl, was developed. The use of megabore capillary column GC methodology, equipped with flame ionization detector (FID), provided rapid, unambiguous nicotine related alkaloids analysis. One gram flue-cured tobacco (or Cambridge filter pad), 20 ml ether, and 5 ml 10% sodium hydroxide solution, added with n-heptadecane as the internal standard, were placed in a flask, and the flask was capped and placed in an ultrasonic bath for 15 min. A 1 μl volume was analyzed by capillary GC operating in split-injection mode on a mega bore Simplicity™-5 column. This simple procedure was compared with the previously reported packed column GC method and the Griffith still-colorimetric method. The application of the method for analysis of various flue-cured tobaccos and cigarette smoke was discussed.

Fast Temperature Programming in Gas Chromatography using Resistive Heating

The features of a resistive-heated capillary column for fast temperature-programmed gas chromatography (GC) have been evaluated. Experiments were carried out using a commercial available EZ Flash GC, an assembly which can be used to upgrade existing gas chromatographs. The capillary column is placed inside a metal tube which can be heated, and cooled, much more rapidly than any conventional GC oven. The EZ Flash assembly can generate temperature ramps up to 1200 °/min and can be cooled down from 300 to 50 °C in 30 s. Samples were injected via a conventional split/splitless injector and transferred to the GC column. The combination of a short column (5 m x 0.25 mm i.d.), a high gas flow rate (up to 10 mL/min), and fast temperature programmes typically decreased analysis times from 30 min to about 2.5 min. Both the split and splitless injection mode could be used. With n-alkanes as test analytes, the standard deviations of the retention times with respect to the peak width were less than 15% (n = 7). First results on RSDs of peak areas of less than 3% for all but one n-alkane indicate that the technique can also be used for quantification. The combined use of a short GC column and fast temperature gradients does cause some loss of separation efficiency, but the approach is ideally suited for fast screening as illustrated for polycyclic aromatic hydrocarbons, organophosphorus pesticides, and triazine herbicides as test compounds. Total analysis times - which included injection, separation, and equilibration to initial conditions - were typically less than 3 min.

Strategies for the analysis of chlorobenzenes in soils using solid-phase microextraction coupled with gas chromatography–ion trap mass spectrometry.

Solid-phase microextraction (SPME) was examined as a possible alternative to Soxhlet extraction in the analysis of chlorobenzenes at high concentrations (up to 65 μg g −1) in soils. Gas chromatography–ion trap mass spectrometry (GC–IT-MS) was used and different strategies were tested in order to obtain suitable responses for chlorobenzenes. Two headspace SPME methods, using fibres coated with polydimethylsiloxane (PDMS) as stationary phase, in splitless and split injection modes, respectively, and a direct SPME method using 100-μm PDMS fibre were studied. For headspace SPME, 7-μm and 100-μm PDMS fibres were used and good sensitivity was obtained by adding 200 μl of water to the soil, at a sampling temperature of 30°C and absorption times of 40 and 60 min, respectively. For direct SPME, which involves extraction of chlorobenzenes from stirred soil solutions using a 100-μm PDMS fibre, the effect of the addition of different organic solvents, such as methanol or acetone, on the sensitivity and the extraction time was evaluated. The shortest time to reach equilibrium (50 min) was achieved when a mixture acetone–water (30:70) was added to the sample. Repeatabilities lower than 8% were obtained for headspace and direct SPME with 100-μm PDMS fibre, whereas for 7-μm PDMS fibre, repeatabilities were slightly higher (between 7 and 11%). The SPME methods were applied to the analysis of chlorobenzenes in an industrially contaminated clay soil, CRM-530, which is a candidate reference material. Chlorobenzenes in this soil were quantified by standard addition, which led to good reproducibility (R.S.D. between 2 and 10%) for headspace and direct SPME with the 100-μm PDMS fibre and acceptable detection limits (30 to 100 pg g −1 of soil). The results were consistent with those obtained in a European intercomparison exercise.

Assay of salicylic acid and related compounds in plant cell cultures by capillary GC

A capillary gas chromatographic (GC) method for the assay of salicylic acid (1) and related compounds in plant cell cultures is described. The gas chromatograms were validated qualitatively by means of GC-mass spectrometry. The detection limits of 1 (50 ng) and 2,3-dihydroxybenzoic acid (2; 125 ng), obtained in the GC split injection mode, could be lowered 25- to 50-fold by using the splitless mode. Derivatization of these compounds with diazomethane gave the methyl esters as major derivatization products in yields of 98% and 94%, respectively. The extraction recoveries of 1 and 2 from lyophilized Catharanthus roseuscells were more than 95%, using o-anisic acid as internal standard, and tetrahydrofuran was found to be a suitable extraction solvent. © 1998 John Wiley & Sons, Ltd.

Simultaneous determination of midazolam and flumazenil concentrations in human plasma by gas chromatography.

A gas chromatographic method for the simultaneous determination of midazolam and flumazenil concentrations in human plasma has been developed, using clinazolam as the internal standard. A mixture of chloroform and ethyl acetate (80:20) was used to extract the two compounds. A 2-microliters volume of the reconstituted sample was injected using a 1:20 split injection mode. Intra-day coefficients of variation ranged from 2 to 6.9%. The assay was linear over the range 3-1000 ng/ml. This assay was subsequently used to analyze samples from a human pharmacokinetic study.

Design and use of a thermal conductivity detector at reduced pressure for temperature-programmed capillary gas chromatography

Based on a systematic study of the response characteristics of a thermal conductivity detector (TCD) at reduced pressure, a newly designed TCD was constructed and evaluated for use in temperature-programmed capillary gas chromatography. The effective cell volume is as low as 1.3 μl (physical volume 100 μl), and there is no dead corner along the sensing path. Capillary columns of I.D. ⩾0.25 mm can couple directly with the TCD without a make-up gas. The detector response time is less than 0.1 s, the linear dynamic range is about four orders of magnitude and the detection limit is about 10 ppm (v/v) for octadecane. In the split injection mode, a simple configuration of the capillary inlet system offers a constant carrier gas flow-rate through the column with temperature-programmed operation. Practical examples are given that demonstrate the applicability of this detector and the system.

Determination of parts per million levels of trifluoroacetic acid in ceronapril bulk substance by headspace capillary gas chromatography

A headspace capillary gas chromatographic method was developed to determine trifluoroacetic acid (TFA) in a bulk substance (ceronapril). The bulk sample is reacted in a sealed headspace vial with dimethyl sulfate in concentrated sulfuric acid to convert TFA to methyl trifluoroacetate (MTFA). A portion of the headspace of the vial containing the MTFA is chromatographed on a PoraPLOT Q 0.32 mm I.D. capillary column in the split injection mode with flame ionization detection. The limit of detection is less than 10 ppm (w/w).

A Collaborative Study to Evaluate Quantitation Utilizing Different Injection Modes for Capillary GC

This report by the ASTM E-19 Committee on the Practice of Chromatography presents the results from a collaborative study to evaluate the effect of various injection modes upon the precision and accuracy of hydrocarbons at the percent level and polynuclear aromatics at ppm levels. This study showed that accurate results can be obtained for hydrocarbons at the percent level using split, on-column, splitless, and direct injection modes. Accurate results can also be obtained for polynuclear aromatics at the ppm level using splitless and on-column modes. However, a greater number of participants had difficulty with the ppm analyses using splitless injections than those analyzing percent-level hydrocarbons using the split injection mode. The interlaboratory precision for both the percent hydrocarbons (split mode) and for the ppm polynuclear aromatics (splitless mode) was found to be about 6% relative standard deviation (RSD), when outlier labs were excluded. On the other hand, the on-column mode for the percent-level and ppm-level analyses were found to be about 3% RSD. Thus, the on-column injection mode resulted in a lower RSD than split and splitless modes. However, the data base for the on-column injection mode was limited. A comparison of the precision from this interlaboratory study with earlier studies using packed gas chromatographic (GC) columns in the 1960s and with a 1981 reversed-phase high performance liquid chromatographic study was made. The pooled RSD at the percent and ppm levels for the earlier ASTM E-19 studies ranged from 4 to 7%, when outliers were excluded. This was comparable to the precision found in the present capillary GC study using the split mode (percent) and the splitless mode (ppm).

Rapid method for the analysis of tobacco nicotine alkaloids

A rapid glass capillary gas chromatographic (GC) method for the analysis of the nicotine alkaloids of tobacco, including nicotine, nornicotine, myosmine, anabasine, anatabine and 2,3′-dipyridyl, was developed. The use of glass capillary GC methodology, coupled with nitrogen-specific detection, provided rapid, unambiguous alkaloid analysis. About 25 mg of cured tobacco and 1 ml of 0.05 M methanolic potassium hydroxide (containing the internal standard, 2,4′-dipyridyl) were placed in a standard 2-ml autosampler vial, and the vial was capped and placed in an ultrasonic bath for 15 min. A 1-μl volume was analyzed by glass capillary GC operating in the split-injection mode on a wall-coated Superox™-4 column. This simple procedure is compared with the previously reported Soxhlet extraction-packed column GC method and the Griffith still-colorimetric method. The application of the method for the analysis of alkaloids in various cured and green, budworm-resistant, tobaccos is discussed.