ISSN:0935-6304    

DOI:10.1002/jhrc.1240130902

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThe analysis of residual accelerants in fire debris is commonly carried out by a three‐step procedure: sample preparation; separation and detection; and data interpretation. Each of these steps can be optimized individually but successful analysis requires that they are compatible with each other. The isolation of residual accelerant from fire debris requires that several methods are used to cover the range of fueis that are commonly used by arsonists. Since almost all incendiary fires are set with petroleum based fuels such as gasoline or heating oil, analysis is targeted toward hydrocarbons. Capillary column gas chromatography on apolar phases is now the overwhelmingly predominant method of separation. Data interpretation is commonly carried out by visual comparison of chromatograms.Fire debris analysis presents some unique challenges that are not often encountered in other fields. The analyte may be present at only trace levels and pyrolysis products from building materials or furnishings may dominate chromatographic patterns. Synthetic polymers may act as precursors to hydrocarbons that compete with substances typically found in petroleum based fuels. Exposure to heat and other environmental factors may also generate severe distortions in the chromatographic profiles of accelerants.Unfortunately, there is no simple solution to these problems. Methods are available to reduce some of the chemical noise introduced by interferences and thus enhance the recognizability of the target substances. Mass spectrometry, in combination with a modern data system, is the most effective approach to filter out unwanted substances. The interpretation of the analytical results is aided by scaling, side‐by‐side comparison, or stacking of chromatograms. An additional advantage of such computerized systems is the possibility of complete automation of the analysis.In this communication, we look at the interplay of chromatographic resolution, noise reduction by mass spectrometry, and automated data evaluation. Examples from model experiments and from simulated arson samples are pres

ISSN:0935-6304    

DOI:10.1002/jhrc.1240130903

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractCapillary columns of 0.3‐0.5 mm i.d. packed with 3‐ to 30‐μm silica‐based stationary phases for liquid chromatography were used for gas chromatographic separation of hydrocarbons. Column efficiencies were evaluated for various commercially available packing material. The best column efficiency was achieved with 5‐μm octadecyl group bonded silica gel, the surface of which was coated with a poly (dimethylsiloxane) film. The 30‐cm column produced 11,000 theor

ISSN:0935-6304    

DOI:10.1002/jhrc.1240130904

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA direct injection method for large volume samples which avoids severe tailing of the solvent peak has been developed using a packed column injector (up to 100 μl) leading into an ordinary capillary column (0.3 mm i.d.). Modifications are made to the cooler zones of the inlet port and on the carrier gas flow control system. This injection technique is based on the effective use of phase soaking and cold trapping using a retention gap. The large volume of solvent vapor is rapidly purged out of the injector with a higher flow of carrier gas while the solutes trapped at the head of the column are subsequently analyzed with another optimum flow rate. The proposed carrier gas flow regulation system is also compared with conventional split/splitless injection methods

ISSN:0935-6304    

DOI:10.1002/jhrc.1240130905

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA method has been developed for highly sensitive determination of haloperidol in human serum involving a simple extraction procedure followed by gas chromatographic separation. Target components were separated from the extracting solvents with a Van den Berg type solventless sample injector before introduction Into a DB‐1 capillary separation column. A surface ionization detector (SID), which has highly selective sensitivity for Substituted amines, was employed for quantitation using bromperidol as an internal standard. Chloroform proved to be the best extracting solvent, yielding a quantitative detection limit of 5 ng/ml (S/N= 2). Comparison of the response to target compounds obtained by the SID, FTD (flame thermionic detector), and FID (flame ionization detector) showed the SID to be superio

ISSN:0935-6304    

DOI:10.1002/jhrc.1240130906

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractA splitless injection method using make‐up flow was developed for SFC. Dilution of sample solvent with carbon dioxide mobile phase was very effective for focusing the solutes onto the column. Injection of a 4.5‐μl sample volume on a 100‐μm i.d. capillary column became p

ISSN:0935-6304    

DOI:10.1002/jhrc.1240130907

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractPolyacrylamide gel filled capillaries for electrophoresis can be improved in performance and stability by a specially optimized and reproducible production procedure. After surface pretreatment as described in this contribution, gels polymerized in capillaries are stable for long series of routine separations. Bubbles formation during gel polymerization can be avoided. The procedure is compared with those described by other authors. Separations of different oligonucleotide samples illustrate the quality of the gel capillaries obtained. The peak symmetry achieved proved to be better than that obtained without surface pretreatment.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240130908

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper reports the first investigation of electron capture ion mobility spectrometry as a detection method for capillary gas chromatography. In previous work with negative ion mobility detection after gas chromatography, the principal reactant ion species were O2−or hydrated O2−due to the presence of oxygen in the drift gas. These molecular reactant ions have a mobility similar to chloride and bromide ions, which are the principal product ions formed by most halogenated organics via dissociative ion‐molecule reactions. Oxygenated reactant ions thus interfere with the selective detection of chloride and bromide product ions. A recently described ion mobility detector design efficiently eliminated ambient impurities, including oxygen, from infiltrating the ionization region of the detector; consequently, in the negative mode of operation, the ionization species with N2drift gas were thermalized electrons. Thermalized electrons have a high mobility and their drift time occupies a region of the ion mobility spectrum not occupied by chloride, bromide, or other product ions. The result was improved selectivity for halogenated organics which ionize by dissociative electron capture. This was demonstrated by the selective detection of 4,4′‐dibromobiphenyl from the components of a polychlorinated biphenyl mixture (Aroc

ISSN:0935-6304    

DOI:10.1002/jhrc.1240130909

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractAlkyl chloroformates with methyl, ethyl, and 2‐chloroethyl substituents can instantaneously esterify fatty acids under proper reaction conditions. Apart from the formation of the corresponding alkyl esters, even the alkoxycarbonyl esters can be prepared. These derivatives are useful for the analysis of short‐chain fatty acids. As alkoxycarbonyl ester, even acetic acid can already be separated from the solvent peak. The reaction conditions were examined, and the Influence of solvent polarity and reagent concentration on the conversion was studied. Quantitative conversion of acids to their easters was achieved in non‐aqueous solutions, but even in the presence of water the yields were accep

ISSN:0935-6304    

DOI:10.1002/jhrc.1240130910

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractDuring some capillary zone electrophoresis (CZE) experiments, the baseline UV absorbance signal at 200 nm “jumped” from one stable level prior to the water plug (marking the flow of neutrals) to another stable level after the water plug. The phenomenon was further examined with distilled water as the sample and with different buffers, applied potentials, and salt concentrations in the buffer. It seems that there is an “isotachophoretic effect” on top of the CZE separations when running under stacking conditions. The effect results in a higher pH value of the buffer after the water plug compared to the pH prior to the plug. The nature of the buffer, the salt concentration in the buffer, and the applied potential all affect this phe

ISSN:0935-6304    

DOI:10.1002/jhrc.1240130911

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY