ISSN:0935-6304    

DOI:10.1002/jhrc.1240150702

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

年代:1992

数据来源: WILEY

摘要:

AbstractIon mobility monitoring has been used for detection in gas, supercritical fluid, and liquid chromatography, illustrating its potential as a method of detection for unified chromatography. Applications presented include GC‐IMD of dioxins in fly ash, SFC‐IMD of vitamin E, and HPLC‐IMD of alkylamines.Ion mobility spectra of several mixed supercritical fluid mobile phases are also presented. Use of methanol, acetonitrile, and dichloromethane as modifiers of supercritical carbon dioxide, and use of supercritical dichlorodifluoromethane and chlorodifluoromethane as mobile phases had little effect on the reactant ion pattern at the flow rates and concentrations used in this study. Only when acetone was used as a modifier of carbon dioxide did the positive reactant ions change significantly. No effect of modifiers or mobile phase was observed for the negative reactant

ISSN:0935-6304    

DOI:10.1002/jhrc.1240150703

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

年代:1992

数据来源: WILEY

摘要:

AbstractRare earth elements have been separated by HPLC on octadecyl‐bonded silica gel, dynamically modified with ammonium dodecylsulfate, using aqueous solutions of α‐hydroxyisobutyric acid as mobile phase.The requirements and characteristics of post‐column reaction with xylenol orange and cetylpyridinium bromide were investigated and optimized, and the reaction found to be highly sensitive and sufficiently rapid. The absorbance of the complex at 598 nm was not affected by the presence of α‐hydroxyisobutyric acid at concentrations of the latter up to 150 mmol/l; at higher concentrations of the acid, the absorbance decreased slightly.For most of the rare earth elements the response was linear up to 0.2 mmol/l; the relative standard deviation of peak area was, typically, ∼1 %. The sensitivity of the method was usually better than 1 μg/ml.The results obtained from the determination of lanthanum, cerium, praseodymium, and neodymium in samples of apatite and bastnesite were in a good agreement with those obtaine

ISSN:0935-6304    

DOI:10.1002/jhrc.1240150704

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe gas chromatographic separation of the components of a complex mixture of industrial solvents, not possible on a single stationary phase owing to coelution of some of the compounds, has been achieved on two serially connected wide bore capillary columns of different polarity.The analysis of a mixture of twenty five compounds was optimized using the serial gas chromatography theory ofPurnellandWilliams. The capacity factors of sample components measured with the two columns coupled in series were found to agree with those predicted by theory, regardless of the order in which they were connected.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240150705

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

年代:1992

数据来源: WILEY

摘要:

AbstractA dry‐packing method has been developed which enables the preparation of packed capillary columns for micro HPLC from 250 μm i.d. tubing and 5 μm packing materials. Pressurized gases, such as hydrogen and argon, were used to transport the packing media, and ethanol or methanol were used as discharge agents. By changing the gas pressure, the packing density could be easily adjusted. It was found that, within experimental limits, the higher the packing density, the greater the column efficiency. Comparison between dry‐ and slurrypacked columns showed that the former had greatly improved stability; the efficiency of dry‐packed columns was about the same as, or even better than, that obtained by slurry

ISSN:0935-6304    

DOI:10.1002/jhrc.1240150706

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

年代:1992

数据来源: WILEY

摘要:

AbstractA fully automated system, comprising a liquid chromatograph (LC) coupled on‐line to a gas chromatograph (GC) by means of a loop interface, has been constructed for clean‐up and analysis of polycyclic aromatic hydrocarbons (PAH). An autosampler was utilized for sample injection into the LC. By the use of a back‐flush technique in conjunction with an ordinary analytical aminopropylsilica column, PAH could be isolated by LC: a concurrent solvent evaporation injection technique was then used for on‐line transfer of the PAH fraction to the GC, where the PAH analysis was completed.Compared with ordinary off‐line LC clean‐up followed by GC analysis, the sensitivity has been increased by a factor of 50–100, yielding a detection limit for individual PAH of a few nanograms per sample when using flame ionization detection. Further, irreproducible losses of low molecular weight PAH as a result of solvent evaporation steps in off‐line clean‐up procedures have been eliminated. Reproducibility of retention times and relative peak areas is high, facilitating automatic peak identification and calculation of concentrations, and the system can thus be used for automatic sample evaluation. The total time required for clean‐up and analysis is only 1.5 hours, and the demand on personnel time for the analysis of PAH has been drastically reduced.The technique has been demonstrated with samples of urban air and of used automobile eng

ISSN:0935-6304    

DOI:10.1002/jhrc.1240150707

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

年代:1992

数据来源: WILEY

摘要:

AbstractExploitation of the full potential of selector‐modified polysiloxanes as chromatographic stationary phases is limited because conventional methods of silicone synthesis involve strong acids or strong nucleophiles such as water or bases; under these conditions many potentially useful selectors decompose. The general approach to polysiloxane synthesis presented herein gives access to functionalized polysiloxanes under mild conditions. The functional groups incorporated can serve as chromatographic selectors or as electrophilic sites for secondary modification or cross‐link

ISSN:0935-6304    

DOI:10.1002/jhrc.1240150708

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

年代:1992

数据来源: WILEY

摘要:

AbstractEnsemble or signal averaging, and the use of the technique for the solution of some unique problems with minimum sample handling, have previously been reported. The capability of the technique has been evaluated with microbore gas chromatography for the fast handling of a large number of analyses:ca20–30 replicate injections are easily attainable in a reasonable analysis time. The implementation of the signal averaging technique with other concentration techniques for improving detection limits is also demonstrate

ISSN:0935-6304    

DOI:10.1002/jhrc.1240150709

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

年代:1992

数据来源: WILEY

摘要:

AbstractMixtures of several basic proteins have been used to test CZE capillaries with surfaces modified by new pretreatment procedures; the performance obtained has been compared with that achieved using capillaries treated by procedures described in the literature.It has been shown that addition of non‐ionic polyvinylalcohols (PVA) to CZE buffer solutions deactivates even bare,i.e.untreated, fused silica surfaces and renders them suitable for separations of basic proteins. The performance obtained from such surfaces was comparable with that of capillaries modified by the more elaborate procedures of etching, silanol derivatization, and/or adsorptive coating (again with polymers).A home‐made device is described which enables derivatization and coating reactions to be performed on fused silica capillaries under an inert atmosphere,i.e.one free from oxygen and wa

ISSN:0935-6304    

DOI:10.1002/jhrc.1240150710

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

年代:1992

数据来源: WILEY

摘要:

AbstractThe influence of the pressure drop on the efficiency and speed of analysis in packed and open tubular supercritical fluid chromatography (SFC) is described: methods previously developed to describe the effects of mobile phase compressibility on the performance of open tubular columns in SFC have been extended to packed columns.TheHorvathandLinequation has been used to elucidate the influence of variations in velocity, diffusivity, and capacity factor along the column on the overall efficiency of packed column SFC. In packed columns, in contrast with the situation in open tubular columns, because the increase in velocity is no longer compensated by an increase in diffusion coefficients, the increase in both linear velocity and capacity factor which result from a significant pressure drop cause the plate height to increase along the column.The effect of fluid decompression along the length of the column on the speed of analysis in SFC has been studied and numerical expressions derived which enable calculation of compressibility correction factors for the plate height. Both thef1andf2correction factors remain very close to unity for acceptable pressure drops, which means that the pressure drop has virtually no effect on the number of plates generated per unit time for an unretained component. For retained species, the decompression of the mobile phase across the column causes the capacity factor to increase and hence leads to increased analysis times.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240150711

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

年代:1992

数据来源: WILEY