Selectivity fused-silica capillary columns

Early work relied on the use of packed columns, but all modern GC analyses are accomplished using capillary columns with their higher theoretical plate counts and resolution and improved sensitivity. Although a variety of analytical columns have been employed for the GC of triazine compounds, the columns most often used are fused-silica capillary columns coated with 5% phenyl-95% methylpolysiloxane. These nonpolar columns in conjunction with the appropriate temperature and pressure programming and pressure pulse spiking techniques provide excellent separation and sensitivity for the triazine compounds. Typically, columns of 30 m x 0.25-mm i.d. and 0.25-qm film thickness are used of which numerous versions are commercially available (e.g., DB-5, HP-5, SP-5, CP-Sil 8 CB, etc.). Of course, the column selected must be considered in conjunction with the overall design and goals of the particular study. 

Hewlett-Packard 5890 gas chromatograph with capillary split/splitless inlet with HP5971 mass-selective detector equipped with a Model 7673 autosampler Fused-silica capillary column, HP-Ultra 2, 25mx0.20-mm i.d., 0.33-qm film thickness, (5% phenyl)methylpolysiloxane... 

System (4) has been reported for the simultaneous determination of cortisol and cortisone in human plasma by stable-isotope dilution-MS [178]. For the determination, capillary GC-MS with H5 -cortisol and H5 -cortisone (as internal standards) was used. The method used a SPB-1 fused-silica capillary column (7 m x 0.25 mm) and helium as the carrier gas (at 29.4 Pa), with 70 eV EIMS being used for selective-ion monitoring. The concentrations were determined from the peak height ratios of the [M-31] fragment ions of the methoxime-TMS derivatives of cortisol, cortisone, and their internal standards. The sensitivity of the method was 200 pg per injection for both cortisol and cortisone. 

The derivatized samples were analyzed on a Hewlett-Packard 5890 series IIGC (helium carrier gas) coupled to a Hewlett-Packard 5971 mass-selective detector (MSD). A 60 m, 0.32 mm i d., 0.25-im film, SE-30 fused silica capillary column (J W Scientific, Folsom, CA) was installed in the GC, and an on-column injector (SGE model OCl-3) held at ambient temperature was fitted to the colunrn inlet. Samples (0.5 p,L) were injected directly into the column held at 105°C... 

Analytical. Samples were chromatographed on a Hewlett-Packard 5880A gas chromatograph which was fitted with a 30M fused silica capillary column (DBS) and an automatic sampler. The GC was interfaced to a Hewlett-Packard 3354 Laboratory Automation System (LAS). Raw data was automatically transferred to the LAS where peaks were selected by retention time, integrated and stored in a processed file. Processed data was then transferred... 

Gas chromatographic methods have been successfully used for the determination of penicillin molecules bearing neutral side-chains in milk and tissues (95, 97), but cannot be used for amphoteric -lactams. Gas chromatography of penicillin residues is further complicated by the necessity for derivatization with diazomethane. This derivatization step is particularly important because it not only leads to formation of the volatile penicillin methyl esters but also improves their chromatographic properties (thermal stability and decreased polarity). Using a fused-silica capillary column in connection with a thermionic nitrogen-selective detector, excellent separation and sensitivity figures were obtained. 

PLAC fractions (Fr II 2, Scheme 1) were analyzed by temperature-programmed GC with fused silica capillary columns coated with SE-54 (HP5 0.2 mm inner diameter, 0.11 cm film thickness or U2 0.2 mm inner diameter, 0.33 pm film thickness). Length of the columns was 25 or 50 m. 13C-labeled PCDD/Fs added before extraction and after cleanup were used as internal standards for quantitative results and recovery, respectively. Mass selective detector (HP 5970) or magnetic sector mass spectrometer (mostly VG AutoSpec) was used for electron impact LRMS or HRMS, respectively. Mass spectral data of the analyzed substance groups are collected in Table 3. Exact quantification was achieved only in a few cases when authentic standard compound was available. In most... 

The reactor was fed with 1.6 Nl/min of 1000, 2000 and 4000 ppm of methane in air. The mixtures were obtained by mixing N-50 synthetic air and 2.5 % (vol.) CH4 in N-50 synthetic air (Air Products). 40 ppm of SO2 (from a cylinder of 370 ppmV SO2 in N-50 synthetic air. Air Products) were added when the effect of sulphur on the catalysts activity was studied. Flow rates were controlled by calibrated mass flow controllers (Brooks 5850 TR). Exhaust gas was analysed by gas chromatography (Hewlett Packard HP 5890 Series II). Methane in the inlet and outlet streams was analysed using a 30 m fused silica capillary column with apolar stationary phase SE-30, and a FID detector. CO and CO2 were analysed using a HayeSep N 80/100 and a molecular sieve 45/60 columns connected in series, and a TCD detector. Neither CO, nor partial oxidation were detected in any experiment, the carbon mass balance fitting in all the cases within 2%. Methane conversions were calculated both from outlet methane and CO2 concentrations, being both values very close in all the cases. Methane (2000 ppmV) and SO2 (40 ppmV) concentrations have been selected because they are representative of industrial emissions, such as coke oven emissions. 

Relative retentions..the a values..usually vary Inversely with column temperature, but are most strongly affected by the choice of liquid phase. In packed column chromatography, the choice of liquid phase Is usually the most effective route by which separation efficiency Is Influenced. In capillary GC, however, there Is normally such an abundance of theoretical plates that the choice of liquid phase Is a relatively unimportant parameter for many analyses. In some cases however. It does become desirable (or even necessary) to select a liquid phase in which the relative retentions of certain solutes Is larger. Until quite recently, this posed a real problem with the fused silica capillary column, because the more polar liquid phases, l.e. those In which relative retentions are usually greater, coated fused silica only reluctantly, and produced columns whose useful lives were quite limited. The development of stable bonded phase columns ( ) eventually overcame this difficulty (vide Infra). 

HPLC analysis of calystegines is somewhat difficult due to their solubility and high polarity, which limit the selection of column packings and solvent mixtures. Moreover, their lack of chromophore excludes spectroscopic methods of detection without pre- or post derivatization of the samples. Gas chromatography on fused silica capillary column coupled with mass spectrometry is the most suitable analytical technique used for the determination of calystegines. However, the high polarity and the nonvolatility of the compounds preclude their analysis without derivatization and numerous derivatization reagents have been tested [9]. 

A 30 to 50 m fused silica capillary column with a 5% phenyl-95% methyl-polysiloxane chemically bonded stationary phase (DB-5, CP Sil-8, HP Ultra 2, PTE-5) is very often used, while several oven temperature programs have been applied for PCB analysis. Table 18.7 shows a selection of combinations of column lengths, stationary phases, oven temperature programs, and detectors. Table 18.8 shows the stationary phase composition of the capillary columns listed in Table 18.7. Cochran et al. " have reviewed the most recent developments for the capillary GC of PCBs with detailed lists of PCB retention times on common capillary columns. 

The chemical composition of S. desoleana oil was determined by GC and GC/MS analyses by different authors [6, 71-72, 74], Generally, GC analyses were performed using fused silica capillary columns with different polarity like 5% diphenyl 94% dimethyl 1% vinylpolysiloxane bonded phase and Carbowax 20M bonded phase columns. Moretti et al. [72, 74] reported the relative retention indices of the oil constituents, calculated as described in the literature [75], and quantitative data obtained using ethylene glycol monobutyl ether as an internal standard. These authors also reported GC/MS data obtained from a GC apparatus directly coupled to a mass selective detector (MSD, 70 eV). 

The Gasbadge and OVM 3500 samplers were applied in a study of 230 homes in western Germany (Krause et al., 1987). The exposure period for both types of badge was 2 weeks, and 57 VOCs were determined. GC analyses were conducted with two fused silica capillary columns of different polarity, and detection was by simultaneous FID/ECD. During the course of the study the commercial manufacture of the Gasbadge monitor was discontinued. Table 1.5-2 shows results of a selection of the compounds monitored that includes compounds with both significant outdoor sources such as benzene from motor vehicle exhausts and indoor sources such as solvents containing undecane. 

Volatile and aromatic components Separation of volatile components is achieved on either fused silica capillary columns or packed columns. Individual volatile components are detected with a FID and identified by the use of reference standards. Methods using specific detectors, such as the NPD, sulfur-specific flame photometric detector, and mass-selective detector (MSD) have also been used. The MSD has the additional advantage of providing structural identification of the individual components. 

Conventional gum phases, methylpolysiloxanes (SE-30, OV-1), 5% phenylmethylpolysiloxane (SE-52), 5% phenyl-95 % dimethylpolysiloxane, and 5% phenyl-1% vinylmethylpolysiloxane (SE-54) are popular stationary phases in capillary column GC, by which separation of PAHs up to coronene (relative molecular mass = 300) may be achieved. The stationary phase giving the best separation for a maximum number of PAHs, however, is SE-54 bonded to fused silica capillary columns. It is a slightly more selective stationary phase than SE-30, its selectivity arising from the polarizability of its phenyl groups. 

The separation of essential oil components is usually carried out by GC with fused-silica capillary columns. The information obtained from high-resolution GC analysis of the volatile fraction of essential oils must be enough to determine any adulteration or loss of quality. Therefore a selective and accurate separation is absolutely necessary in the case of industrial analysis. 

Formerly, a GC method with nitrogen-phosphorus selective detector (NPD) was developed for the determination of HCAs with the advantage of the high response of these compounds in the detector due to the nitrogen atoms present in the structure of the HCAs. Kataoka and Kijima developed a simple and rapid derivatiza-tion method for GC analysis of HCAs. Ten HCAs were converted into their A-dimethylaminomethylene derivatives with A,A-dimethylformamide dimethylac-etal and measured by GC with NPD using two connected fused silica capillary columns in order to improve the separation of HCAs [115]. The structures of the HCAs derivatives were confirmed by GC-MS. 

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