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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 156-157 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; trichlorophenols ; ammonia ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No abstract
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 6 (1994), S. 369-372 
    ISSN: 1040-7685
    Keywords: capillary GC ; NPD ; aliphatic amines ; nitro and phosphorus compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of ammonia as a carrier gas and as a make-up gas on the response of the nitrogen phosphorus detector (NPD) was investigated. This study showed that the response of the NPD increased 2.2 to 10.3 fold for all studied aliphatic amines when 5% ammonia in nitrogen was used as a make-up gas. This increase was about 5.3 to 22.8 fold when ammonia was used as a carrier gas. The response of the NPD for nitro-aromatic compounds increased 1.8 to 3.1 fold using 5% ammonia as a make-up gas and 4.2 fold when ammonia was used as a carrier gas. The higher response obtained using ammonia as the carrier gas is related to improvements in the chromatographic performance (reduced tailing). The response of the NPD to phosphorus compounds was about 1.5 times higher using ammonia either as a carrier gas or as a make-up gas compared to nitrogen. Although the noise of the NPD increased, the signal-to-noise ratios for both amines and phosphorus compounds improved with the use of ammonia.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 537-542 
    ISSN: 1040-7685
    Keywords: capillary GC ; ammonia ; helium ; amines ; chlorophenols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A mixture of ammonia and helium was used as a carrier gas for capillary gas chromatographic analysis of aliphatic amines and dichlorophenols. The peak symmetry for aliphatic amines was drastically improved when the percentage of ammonia was 5-30%. The symmetry continued to improve, although less drastically, between 30-100%ammonia. The capacity factors of the amines decreased with increasing ammonia content up to 100%. 2,5-Dichlorophenol and 2,6-dichlorophenol could not be resolved when helium alone was used as the mobile phase with a column of intermediate polarity (cyanopropylmethylphenylsilicone). Complete separation was, however, achieved by increasing the ammonia content in the carrier gas to 50%. The ratio of the capacity factors (k'NH3/k'He) for the dichlorophenols increased linearly with increasing ammonia percentage up to 100% on the methylsilicone and cyanopropylmethylphenylsilicone columns.
    Additional Material: 6 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 14 (1991), S. 284-287 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Ammonia as carrier gas ; Chlorophenols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 252-256 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Ammonia ; Aliphatic amines ; Aromatic amines ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of ammonia as a carrier gas for the chromatography of aliphatic and aromatic amines has been investigated. As compared to nitrogen, ammonia gave drastically improved peak symmetry and lower capacity factors (k′) for primary and secondary amines on polar (Polyethylene glycol) and medium Polar (methylphenylcyanopropylsilicone) stationary Phases. The effect of ammonia was more Pronounced at low column temperatures. Considerably better detection limits of primary and secondary amines were obtained with ammonia as carrier gas than with nitrogen. No detrimental effects of using ammonia were observed on the gas chromatograph or on the columns over a period of about one year.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 723-726 
    ISSN: 0935-6304
    Keywords: Carrier gas ; Ammonia ; Helium ; Hydrocarbons ; Amines ; Ketones ; Alcohols ; Phenols ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of using ammonia as a carrier gas on the response of the flame ionization detector (FID) has been investigated. It was found that the FID response, calculated as the effective carbon number (ECN), increased for all the compounds studied when ammonia, rather than helium, was used. The change was 0-0. 9 carbon atom for hydrocarbons, one carbon atom for alcohols and diphenyl ether, and 0.4-1 carbon atom for phenols and ketones. The increase in ECN was larger for amines (0. 8-5 carbon atoms), but these numbers also reflected an improvement in chromatographic performance as a result of reduced adsorption on the column. The largest change in signal-to-noise ratio, a six-fold increase, was obtained for octyl-amine; ratios for hexyl methyl ketone, diisobutyl ketone, dihexyl-amine, dibutylamine, and N-methyloctylamine increased by a factor of 2-3 when ammonia was used as carrier gas. To determine the extent to which the effect on detector response was solely attributable to ammonia, a mixture of 5 % ammonia in nitrogen was used as detector make-up gas with helium as carrier gas. Under these conditions the noise in the FID increased but for most of the compounds studied the signal-to-noise ratio also increased.
    Additional Material: 3 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 757-759 
    ISSN: 0935-6304
    Keywords: CGC, ECD ; Ammonia, nitrogen ; Chlorophenols, nitro-aromatic compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of ammonia on the electron capture detector (ECD) response has been investigated. Nitrogen with different ammonia concentrations (5-20%) was used as make-up gas. Compared to pure nitrogen, the ECD response decreased when the ammonia concentration in the make-up gas was 5%. However, the response increased when the ammonia concentration was 20%. The response factor of 4-chlorophenol increased 4 fold when ammonia was 20%. Also, di- and tri-chlorophenols increased by 30-50%. The nitroaromatic compounds responses increased by about 2-3.7 times with 20% ammonia in the make-up gas. The signal-to-noise (S/N) increased when 20% ammonia in nitrogen was used as make-up gas compared to pure nitrogen. Also, the detector linearity increased by 50% with ammonia.
    Additional Material: 2 Ill.
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  • 8
    Publication Date: 2019-03-27
    Description: In this study, a novel sort of sample preparation sorbent was developed, by preparing thin layer graphene oxide tablets (GO-Tabs) utilizing a mixture of graphene oxide and polyethylene glycol on a polyethylene substrate. The GO-Tabs were used for extraction and concentration of omeprazole (OME) in human saliva samples. The determination of OME was carried out using liquid chromatography-tandem mass spectrometry (LC–MS/MS) under gradient LC conditions and in the positive ion mode (ESI+) with mass transitions of m/z 346.3→198.0 for OME and m/z 369.98→252.0 for the internal standard. Standard calibration for the saliva samples was in the range of 2.0–2000 nmol L−1. Limits of detection and quantification were 0.05 and 2.0 nmol L−1, respectively. Method validation showed good method accuracy and precision; the inter-day precision values ranged from 5.7 to 8.3 (%RSD), and the accuracy of determinations varied from −11.8% to 13.3% (% deviation from nominal values). The extraction recovery was 60%, and GO-Tabs could be re-used for more than ten extractions without deterioration in recovery. In this study, the determination of OME in real human saliva samples using GO-Tab extraction was validated.
    Electronic ISSN: 1420-3049
    Topics: Chemistry and Pharmacology
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  • 9
    Publication Date: 2019-08-09
    Description: Due to their selectivity and chemical stability, molecularly imprinted polymers have attracted great interest in sample preparation. Imprinted polymers have been applied for the extraction and the enrichment of different sorts of trace analytes in biological and environmental samples before their analysis. Additionally, MIPs are utilized in various sample preparation techniques such as SPE, SPME, SBSE and MEPS. Nevertheless, molecularly imprinted polymers suffer from thermal (stable only up to 150 °C) and mechanical stability issues, improper porosity and poor capacity. The sol-gel methodology as a promising alternative to address these limitations allowing the production of sorbents with controlled porosity and higher surface area. Thus the combination of molecularly imprinted technology and sol-gel technology can create influential materials with high selectivity, high capacity and high thermal stability. This work aims to present an overview of molecularly imprinted sol-gel polymerization methods and their applications in analytical and bioanalytical fields.
    Electronic ISSN: 1420-3049
    Topics: Chemistry and Pharmacology
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  • 10
    Publication Date: 2019-10-11
    Description: A wooden stick coated with a novel graphene-based nanocomposite (Graphene oxide/polyethylene glycol (GO/PEG)) is introduced and investigated for its efficacy in solid phase microextraction techniques. The GO/PEG-stick was prepared and subsequently applied for the extraction of β-blockers, acebutolol, and metoprolol in human oral fluid samples, which were subsequently detected by liquid chromatography tandem mass spectrometry (LC-MS/MS). Experimental parameters affecting the extraction protocol including sample pH, extraction time, desorption time, appropriate desorption solvent, and salt addition were optimized. Method validation for the detection from oral fluid samples was performed following FDA (Food and Drug Administration) guidelines on bioanalytical method validation. Calibration curves ranging from 5.0 to 2000 nmol L−1 for acebutolol and 25.0 to 2000 nmol L−1 for metoprolol were used. The values for the coefficient of determination (R2) were found to be 0.998 and 0.996 (n = 3) for acebutolol and metoprolol, respectively. The recovery of analytes during extraction was 80.0% for acebutolol and 62.0% for metoprolol, respectively. The limit of detections (LODs) were 1.25, 8.00 nmol L−1 for acebutolol and metoprolol and the lower limit of quantifications (LLOQ) were 5.00 nmol L−1 for acebutolol and 25.0 nmol L−1 for metoprolol. Validation experiments conducted with quality control (QC) samples demonstrated method accuracy between 80.0% to 97.0% for acebutolol and from 95.0% to 109.0% for metoprolol. The inter-day precision for QC samples ranged from 3.6% to 12.9% for acebutolol and 9.5% to 11.3% for metoprolol. Additionally, the GO/PEG-stick was demonstrated to be reusable, with the same stick observed to be viable for more than 10 extractions from oral fluid samples.
    Electronic ISSN: 1420-3049
    Topics: Chemistry and Pharmacology
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