On-column Injection Technique Research Articles

Analysis of thermally labile pesticides by on-column injection gas chromatography in fruit and vegetables

Thermally labile pesticides (captafol, captan, dicofol, and folpet) are highly prone to suffer thermal degradation during sample introduction into a gas chromatograph (GC) to tetrahydrophthalimide (THPI), 4,4'-dichlorobenzophenone (DCBP), and phthalimide (PI), respectively, mainly produced in the glass liner of the injector. This undesired behavior leads to inaccurate qualitative and quantitative results. Direct on-column injection (OCI) technique is evaluated as an alternative to avoid or minimize compound alteration during the analysis. This configuration was studied and evaluated for the determination of this group of thermally troublesome pesticides. The OCI inlet was operated in "track oven" temperature and connected to a wide-bore deactivated guard column that is itself connected to a capillary GC analytical column. This technique has demonstrated to be useful for avoiding degradation generated in the hot inlet. Limitations observed for OCI in routine analysis were injection volume, guard column length, and maintenance issues. Analytical standards spiked in vegetable solutions were injected in OCI, not observing any thermal degradation rate. On the contrary, classical splitless injection (SLI) produced high degradation rates in all cases. This OCI approach was validated in citrate QuEChERS extracts of tomato, apple, and orange matrices for these four compounds and their corresponding transformation products (THPI, DCBP, and PI), evaluating recoveries, repeatability, linearity, and matrix effect. This set-up enabled the correct identification and quantitation for most compounds at LOQs of 0.010mg/kg in fruit and vegetable samples. The OCI grants evident differentiation between metabolites naturally occurring in food and thermal degradation products created during the analysis. Graphical abstract ᅟ.

Sample introduction in gas chromatography using a coiled wire filament

A simple device for field sampling and concentration of analytes for subsequent introduction into an injection port for gas chromatographic (GC) analysis has been developed. It consists of a tiny, coiled platinum wire filament (CWF) that is attached to a retractable plunger wire, which fits inside a syringe needle housing. Sampling is accomplished by dipping the end of the CWF in a liquid sample, which is drawn into the wire coil by capillary action, and introducing it into the injection port either before or after allowing the solvent to evaporate. The CWF can be used with or without a nonvolatile chemical coating. A major advantage of this sampling device is that nonvolatile sample matrix components remain on the wire coil, reducing the required injection port and liner cleaning frequency and contamination of the head of the chromatographic column. The coil itself can be easily cleaned between analyses by rinsing and/or burning off residual material in a small flame. The sampling coil facilitates specifically designed chemical reactions in the injection port, such as thermochemolysis and methylation. Applications demonstrated in this work include: (1) direct introduction of samples with little or no pre-treatment, (2) simultaneous thermochemolysis and methylation of lipid-containing samples such as bacteria and bacterial endospores for analysis of biomarkers, and (3) solid phase micro-extraction (SPME) using temporary wire coatings. The CWF allowed for significant reduction in sample preparation time, in most cases to less than a few minutes. The peak shapes examined for polycyclic aromatic hydrocarbon analytes (PAHs) were significantly better (asymmetry factors <1.3) when using the CWF sampling technique compared to splitless and on-column injection techniques (asymmetry factors >1.3). Extraction efficiencies for SPME (especially for high boiling point components such as PAHs) improved by an average of 2.5 times when using the CWF compared to the performance of commercially available SPME fibers. Coiled wire filaments and GC injection port liners were used for more than 100 Bacillus endospore thermochemolysis methylation analyses without the need for cleaning or replacement.

Performance of programmed temperature vaporizer, pulsed splitless and on-column injection techniques in analysis of pesticide residues in plant matrices

A programmed temperature vaporizer (PTV) injection technique has been recently implemented in our laboratory. In present paper its performance is compared with other GC injection techniques commonly used in trace analysis of organic contaminants. Twenty-six pesticides representing different chemical classes were selected for the study. This group comprised compounds typically subjected to discrimination in the injection port of the gas chromatograph, e.g., polar organophosphorus pesticides and thermolabile carbamates. In the first set of experiments standards in pure solvent were injected into GC systems employing different types of injection, i.e., (i) on-column, (ii) pulsed splitless, (iii) PTV solvent split, (iv) PTV splitless, and the responses of analytes were compared. Discrimination of troublesome compounds was significantly decreased with the application of PTV solvent split injection. In the second set of experiments repetitive injections of purified wheat samples were performed, with aims to evaluate the long-term stability of responses, as well as matrix effects in different stages of system contamination for each injection technique. The tolerance of the GC system to co-injected matrix components was increased in the order: on-column<pulsed splitless<PTV solvent split technique. As regards matrix effects, these were suppressed considerably with the PTV solvent split technique in comparison with pulsed splitless injection. With the latter technique after 66 injections of wheat samples relative responses (apparent recovery) reached as much as 450% for some compounds, while with the application of PTV matrix effects did not exceed 200% under the same conditions.

Gas Chromatographic Analysis in the Synthesis of Poly (Ethylene Oxide) Dimethyl Ethers

ABSTRACT Gas chromatography (GC) was used in the analysis of the synthesized oligomeric mixtures, involving poly(ethylene glycol)s, poly(ethylene oxide) monomethyl ethers, poly(ethylene oxide) dimethyl ethers and crown ethers. It was demonstrated that the samples could be successfully analyzed on the wide bore capillary column with cross-linked polar stationary phase (FFAP) without derivatization. An on-column injection technique is used to avoid possible sample distortion. Identification and quantitative analysis were achieved taking advantage of the GC homologues retention rule and the FID effective carbon number response rule, thus the limitations of some standard availability and purity problems were avoided. Much useful information such as average molecular weight, polydisperse distribution and so on were obtained by the established method, which is very important in the process monitoring and product quality control.

Direct analysis of several Fusarium mycotoxins in cereals by capillary gas chromatography–mass spectrometry

A method for qualitative and quantitative analysis of Fusarium mycotoxins by gas chromatography–mass spectrometry (GC–MS) using cold on-column injection was improved. Eight typical mycotoxins, including deoxynivalenol (DON), 3-acetyldeoxynivalenol (3ADN), fusarenon-X (FX), diacetoxyscirpenol (DAS), 15-monoacetylscirpenol (15MAS), T-2 toxin (T-2), scirpentriol (SCT), and zearalenone (ZEA) were subjected to GC–MS without chemical derivatization by means of the on-column injection technique. Chromatographic separation of the toxins extracted from barley was achieved as a single peak, and the specific EI mass spectra of each toxin were obtained. The fatty acids in the extract that interfere with measurements of the toxins on the gas chromatogram were removed by precipitation as an insoluble metal soap with zinc acetate. Additional clean-up was accomplished using a Bond Elut Florisil cartridge. The quantitative detection limit in barley ranged from 0.1 to 0.5 μg/g. The average recoveries of 93.1% for DON, 3ADN, 15MAS, DAS, T-2 and ZEA, and 46.0% for FX and SCT added to barley at the level of 1 μg/g were obtained.

Evaluation of gas chromatography with a flame photometric detector based on quartz surface-induced emission for determining the speciation of inorganic and methylgermanium compounds

Gas chromatography-flame photometric detection (GC-FPD) using quartz surface-induced germanium emission allows the sensitive determination of inorganic germanium (Ge i) and methylgermanium (MGe) compounds. Grignard pentylation is preferred to other derivative reactions as its products are suitable for the Chromatographic process. Pentylated organogermanium compounds are identified by gas chromatography-mass spectrometry (GC-MS). The typical germanium isotope patterns are obtained on loss of pentyl groups [M-Pe] + for all four tested compounds. Using the on-column injection technique and a HP-1 capillary column, all four organogermanium compounds are baseline-resolved within 10 min. The absolute detection limits (signals 3 times the standard deviation of baseline noise), for trimethylgermanium (TMGe), dimethylgermanium (DMGe), monomethylgermanium (MMGe) and germanium tetrachloride (TCGe) are 50, 70, 150, and 150 pg, respectively. The response range is linear over 3 orders of magnitude from detection limits up to 50 ng. The analytical figures of merit are compared with those for other techniques in the literature.

On-column gas chromatographic-mass spectrometric assay for metabolic profiling of valproate in brain tissue and serum

A sensitive capillary gas chromatographic-mass spectrometric method for the determination of valproic acid and at least twelve of its metabolites in serum based on tert.-butyldimethylsilyl ( tBDMS) derivatives is described. Low detection limits are achieved by using a direct on-column injection technique. The addition of dry pyridine during the derivatization step now leads to uniform formation of 3-keto-VPA di- tBDMS derivatives and thereby avoids the necessity of a deuterated internal standard. A novel extraction procedure for metabolic profiling of valproate in brain tissue samples is presented. Using this method, (Z)-2-en-VPA was determined in rat brain tissue for the first time.

Flame ionization detection relative response factors of some polycyclic aromatic compounds: Determination of the main components of the coal tar pitch volatile fraction

The flame ionization detection (FID) relative response factors of some commercially available polycyclic aromatic compounds using split injection were determined and compared with other published FID relative response factors obtained using splitless and cold on-column injection technique. From these data FID relative response factors of some non-available polycyclic aromatic compounds were calculated in an approximate way. These factors were used in a quantitative study of the main components of a coal tar pitch volatile fraction. For this quantification the internal standard method and the absolute calibration with separate standard method were employed. Good reproducibility of the determinations using both methods was found.

Determination of felodipine and its metabolites in plasma using capillary gas chromatography with electron-capture detection and their identification by gas chromatography—mass spectrometry

A novel method for the determination of felodipine and its metabolites in plasma by capillary gas chromatography (GC) with electron capture detection was developed. Felodipine and its oxidized metabolite were assayed by capillary GC after solid-phase extraction with the aid of a cool on-column injection technique. Acid metabolites, methyl monoacid and ethyl monoacid and diacid, were extracted with diethyl ether and propylated with 1- n-propyl-3- p-tolyltriazene before being submitted to capillary GC. These methods were very sensitive and useful for the pharmacokinetic study of felodipine. Felodipine and its metabolites were identified by GC—mass spectrometry. The mass spectral patterns of the peaks of extracts from human plasma samples after oral administration of felodipine were in good agreement with those of reference compounds.

Simultaneous Determination of Morazone and Phenmetrazine in Rat Plasma and Urine Using an On-Column Injection Technique with Fused-Silica Capillary Column Gas Chromatography

The simultaneous determination of morazone and its major metabolite, phenmetrazine, using an on-column injection technique with fused-silica capillary column gas chromatography is described. The on-column injection technique prevents the decomposition of morazone. The limit of quantitation in 0.1 mL of rat plasma for morazone and phenmetrazine is 5 ng/mL and that in 1.0 mL of rat urine is 1 ng/mL. The within run precisions (%CV) at the concentration of 0.5 micrograms/mL are 3.27% for morazone and 3.09% for phenmetrazine.

Simultaneous determination of propoxyphene and norpropoxyphene in biological samples by gas chromatography using an on-column injection technique with a fused-silica capillary column

Simultaneous determination of propoxyphene and norpropoxyphene in biological samples by gas chromatography using an on-column injection technique with a fused-silica capillary column

Isolation and Identification of the Wax Esters from the Cuticular Waxes of Green Tobacco Leaf

Abstract Recent studies in our laboratory on the cuticular chemicals of green tobacco leaf have revealed the presence of wax esters, composed of fatty acids bound to fatty alcohols. Cuticular components of young green NC 2326 tobacco leaves were removed with methylene chloride, and partitioned between hexane and 80 % MeOH-H2O. The hexane-soluble fraction, which contained wax esters, paraffinic hydrocarbons, and fatty alcohols, was separated by silicic acid column chromatography, and the resulting wax ester fraction was further purified by lipophilic gel chromatography. Initial analyses of the wax ester fraction by capillary gas chromatography [GC] and capillary GC / MS, on a short fused silica [FS] SE-54 capillary column, indicated the presence of C30 - C52 wax esters. Application of the cold on-column injection technique and use of immobilized stationary phase, FS SE-54 capillary columns greatly improved the GC separation of the complex wax ester fraction and permitted the identification of individual wax ester isomers. Identification of wax ester isomers by GC/MS relied upon the presence of a molecular ion and ions characteristic of the acid and alcohol moieties. For the acid portion, these ions included the acid MW + 1 a.m.u. and MW - 17 a.m.u. ions, while for the alcohol, they were the alcohol MW - 18 a.m.u. and MW + 27 a.m.u. ions. Saponification of the wax ester fraction and subsequent analyses of the alcohols (as trimethylsilyl ethers) and acids (as methyl esters) revealed extensive iso- and anteiso-methyl branching of the acid moieties. The wax ester isomers with iso- and anteiso- methyl-branched acid moieties were separated from each other and from the normal straight-chain isomers by capillary GC and were identified by GC/MS, based upon characteristic ions resulting from the losses of the iso-branched (MW - 43 a.m.u.) and anteiso-branched (MW - 57 a.m.u.) groups from the molecular ion and from the acid moiety. One hundred and seventy individual wax esters were identified.

Rapid extraction and analysis of organic compounds from solid samples using coupled supercritical fluid extraction/gas chromatography

Direct coupling of supercritical fluid extractions with gas chromatography (SFE-GC) allows the extraction, concentration, and gas chromatographic analysis of organic analytes from solid samples to be performed in less than 1 h. Coupling of the supercritical fluid extraction step with a capillary gas chromatographic column is achieved using a standard on-column injector and requires no modification of the gas chromatograph. Maximum sensitivity is achieved and analyte degradation or loss is minimized since the extracted species are quantitatively transferred into the fusedsilica capillary gas chromatographic column where they are cryogenically focused prior to normal gas chromatographic analysis using flame ionization (SFE-GC/FID) or mass spectral (SFE-GC/MS) detection. SFE-GC analysis yields good chromatographic peak shapes that compare favorably with those obtained using standard on-column injection techniques. Class-selective extractions can be achieved by performing multiple SFE-GC analyses with different extraction pressures. The ability of coupled SFE-GC to yield rapid extraction and analysis of organic analytes is demonstrated for a variety of samples including polycyclic aromatic hydrocarbons (PAHs) from treated wood, urban dust, and river sediment, phenolic species from wood smoke particulates, nicotine from tobacco, biological markers from coal, and flavor components from food products.

Assay of the chiral organophosphate, soman, in biological samples.

The anticholinesterase, soman, (CH3)3CC(H)CH3O(CH3)P(O)F, consists of four stereoisomers assigned as C(+/-)P(+/-)-soman in which C stands for chirality in the pinacolyl moiety and P for chirality at phosphorus. The four stereoisomers are separated by gas chromatography on an optically active Chirasil-Val column, synthesized and coated in house, or on a Chirasil-Val column identical with the commercially available column when combined with a Carbowax 20M column. This method in combination with an assay based on acetylcholinesterase inhibition shows that the two isomers which do not have anticholinesterase activity, i.e. C(+/-)P(+/-)-soman, are rapidly degraded in rat blood due to hydrolysis by phosphorylphosphatases. Epimeric soman isomers, e.g. C(+/-)P(-)-soman, can be separately assayed on a Carbowax or a CPSil 8 column, using 2H-labeled soman isomers as internal standards. 2H-labeled soman stereoisomers serve as internal standards in GC-assay of all four stereoisomers on Chirasil-Val. For work-up of the four stereoisomers from rat blood the sample is first stabilized by acidification to pH 4.2 at 0 degree C to suppress hydrolysis by phosphorylphosphatases, addition of aluminum ions for complexation of fluoride ions to prevent regeneration of C(+/-)P(-)-soman by free fluoride ions from soman-inhibited carboxylesterase, and addition of (CH3)3CCH2O(CH3)P(O)F to occupy covalent binding sites for C(+/-)P(-)-soman, before extraction with a Sep-Pak C18 cartridge and elution with ethyl acetate. Using a splitless or on-column injection technique and alkali flame ionization detection, the minimum detectable concentration is 30 pg/3-ml blood sample.

Determination of polar organic solutes in methanol using hot on-column injection capillary gas chromatography

In an attempt to improve the analysis of methanolic extracts of atmospheric samples containing highly polar, water-soluble organic compounds using capillary gas chromatography, the hot on-column injection technique was chosen. Since the on-column injector used was not designed to be heated, the point of injection was inside the heated gas chromatograph oven. Preliminary analyses indicated solute peak splitting and distortion occurred when 0.4 ..mu..L was injected, severely limiting overall sensitivity. To overcome this limitation, the on-column injector was used together with a separately heated metal sheath that surrounded the first 7 cm of the capillary column. This modification allowed the injection of 4 ..mu..L of methanol, containing highly polar, water-soluble solutes, into the chromatographic system with no evidence of solute peak splitting or distortion. 15 references, 2 figures, 1 table.

Urinary steroid profiles in pregnancy by capillary column gas chromatography

A qualitative and quantitative method for the estimation of urinary steroids during pregnancy by capillary column gas chromatography has been developed. Steroid conjugates were hydrolysed by enzymes and free steroids isolated by extraction using SEP-PAK C 18 cartridges. Methoxime-trimethylsilyl derivatives of the steroids were characterized by packed column gas chromatography-mass spectrometry and subsequently by their retention indices on capillary column gas chromatography. Of the 48 peaks resolved on the profiles about 35 were identified as steroids. The retention indices of reference steroids were very reproducible in the short term showing a mean coefficient of variation of 0.015%. The columns allowed 95% valley resolution of steroids whose retention indices differed by only 7 units. The use of an on-column injection technique contributed to the high precision for replicate injections (coefficient of variation < 1%) while for reference steroids, and well-resolved peaks in the urine profile, the mean coefficient of variation for the complete assay was less than 10%. To the best of our knowledge this is the first report concerning the quantitation, with good precision, of a large number of steroids in pregnancy urine.

Extraction and enrichment of chlorinated phenols from surface waters for the determination by capillary-GC/FTIR-spectroscopy

A method is presented for the separation and substance-specific determination of chlorinated phenols at trace level in surface waters using capillary-GC/FTIR-spectroscopy. Since an injected amount of at least 100 ng is required to obtain well-structured IR spectra, the extraction and enrichment procedure must provide a concentration factor of 104 and simultaneously high recoveries. The separation of the complete range of chlorinated phenols is performed without derivatisation on a SE54 fused silica WCOT column; the degree of decrease in separation efficiency introduced by the FTIRS detection system is discussed. The applicability of an on-column injection technique using a thermodesorption- and cold trap injector with solvent removal is tested, which allows the injection of large volums of concentrate. Proceeding form 1 l water volume and a 10 ppb concentration level the chlorophenols are correctly identified by their IR spectra and the mean recovery is in the 90% range. Furthermore, the possibility is discussed to obtain information on the identity of matrix components based on IR data only.

Determination of Picogram Nitroglycerin Plasma Concentrations Using Capillary Gas Chromatography with On-Column Injection

A specific, sensitive, and precise capillary gas chromatographic (GC) assay capable of analyzing picogram concentrations of nitroglycerin in human plasma was developed. The analytical procedure involves a double extraction of 1mL of plasma with pentane, after the addition of internal standard (1ng of 2,6-dinitrotoluene), followed by evaporation and reconstitution in 50 μL of heptane. The extract (1 μL) was injected onto a capillary column using the on-column injection technique. The GC oven temperature was programmed from 120°C to 180°C at a rate of 5°C/min. The oven temperature was then programmed to 250°C and was maintained for 10min. The nitroglycerin and internal standard retention times were 8.6 and 11.4 min, respectively. The position of the end of the capillary column inside the detector is a critical determinant of sensitivity: the column exit must be positioned such that nitroglycerin adsorption to the detector is minimized (i.e., sensitivity maximized). The assay limit of quantitation was 25 pg/mL (CV = 7.6%) using 1mL of plasma. This GC assay, specific for nitroglycerin in the presence of its metabolites, isosorbide dinitrate, and several other drugs, may be used to quantitate plasma levels obtained after therapeutic nitroglycerin doses.

Evaluation of automated splitless and manual on-column injection techniques using capillary gas chromatography for pesticide residue analysis

Evaluation of automated splitless and manual on-column injection techniques using capillary gas chromatography for pesticide residue analysis

An Evaluation of Splitless and On-Column Injection Techniques for the Determination of Priority Micropollutants

Splitless and on-column injectors were evaluated for use in quantitative multi-residue analysis of priority micropollutants by wall-coated open-tubular gas chromatography. Under limited conditions some splitless injectors yield quantitative results. However, on-column injection devices have a broader range of applicability and yield better precision and accuracy. For quantitation of wide boiling range mixtures, such as polychlorinated biphenyls, at picogram levels, on-column injection devices are the only ones which yield satisfactory results.