摘要:

AbstractReduction of the column diameter has proved to be a highly efficient tool to increase the speed of analysis. Unfortunately, the requirements for instrumental design with respect to sample input band width, low dead volume interfacing, and time constants of detection and registration systems are the more critical the smaller the inside diameter.Recently we reported input band widths as low as 1 ms [1] for gaseous samples at ppm concentration levels, without any preconcentration, in a study with narrow bore columns and thermal conductivity detection.In this study a simple versatile micro on‐column cold trap/thermodesorption enrichment system for narrow bore columns is introduced and evaluated. The combination of considerable sample enrichment and preservation of the compatibility of the required input band width with column dimensions is critically examined. The process of thermodesorption (reinjection) which is the most critical step, is particularly emphasized.The system consists of a short aluminum coated fused silica or metal capillary with a low mass and a low cost electrical heating. Input band widths down to 1 ms are obtained without extreme demands on electrical power (300 watt). The potential of the system is illustrated with some extremely fast separation

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111202

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

年代:1988

数据来源: WILEY

摘要:

AbstractAn innovative solvent delivery method termed solvent modulation has been developed to control solute retention in liquid chromatography. Solvent modulation is the technique whereby individual solvent zones are introduced onto the chromatographic column in a known random orrepeating sequence. Because the solvent zones are of constant composition and are spatially separated from one another, solute retention is controlled independently in each zone. Hence, the overall retention of a solute is a time‐weighted average of the capacity factors in the solvent zones it has encountered. Solvent modulation offers a simple, versatile, and accurately modeled means to control and predict solute retention in liquid chromatograph

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111203

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

年代:1988

数据来源: WILEY

摘要:

AbstractExpressions for the minimum detectable amount Qoand the minimum analyte concentration Coas functions of the chromatographic parameters are derived for both mass and concentration sensitive detectors. The effects of pressure drop, column inner diameter, and film thickness are given.The minimum analyte concentration for mass flow sensitive detectors, Com, can be reduced considerably by selecting the carrier gas velocity well above its optimum value (related to Hmin), however, at the cost of long columns and long analysis times. For Qothe improvements can be neglected, and so the analysis can best be performed at uopt.When the flow rate in the detector, Fd, is equal to the column flow rate Fc, the maximum permissible detector volume of concentration sensitive detectors is proportional to dc2up to dc3, and so narrow bore columns require detectors of extremely small volume. Make‐up gas has to be added when the actual volume is too large, thus worsening the detectability. Another approach, vacuum operation of the detector cell, appears to be very attractive. On the other hand, when wide bore columns are used in combination with small volume concentration sensitive detectors, very small values of Qocand Cocare obtainable when the abundant carrier gas can be removed before entering the detector cell.Digital noise filtering can further reduce the obtainable Qoand Covalues, especially for broad peaks and thus for wide bore column

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111204

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

年代:1988

数据来源: WILEY

摘要:

AbstractA gas chromatographic method for volatile organic chemicals in which an aqueous sample is purged directly to a cryogenically cooled, fused silica column uses a Nafion tube drier between the purge vessel and GC column. The Nafion strips water from the gas stream during the purge step while allowing volatile halocarbons and aromatics to continue to the GC column. Examples of this technique are presented on 0.53 mm and 0.25 mm fused silica columns coated with a variety of stationary phases.

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111205

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

年代:1988

数据来源: WILEY

摘要:

AbstractA method is described for the quantitative determination of linear alkylene oxide‐fatty alcohol condensates, nonionic surface active agents in water. Surface active agent is extracted from water samples with benzene. Surfactant is further extracted by salting out into chloroform. Capillary, supercritical fluid chromatography allows the separation and quantitative determination of oligometric constituents using carbon dioxide as a supercritical fluid. In this case, a fingerprint of the surfactant is obtained. Analysis time, however, is approximately 60 minutes. In the second case, the ether groups of ethylene oxide fatty alcohol condensates are cleaved by reaction with 50 percent hydrobromic acid in glacial acetic acid in sealed ampoules. The resulting alkyl bromides are extracted with carbon disulfide and chromatographed by both the supercritical fluid, capillary column chromatography (SFC) and high resolution open tubular column gas chromatography (OTC – HRGC). Results are in good agreement between these two techniq

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111206

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

年代:1988

数据来源: WILEY

摘要:

AbstractLaser induced fluorescence is used for the detection of labeled amino acids. A preliminary comparison is made of three fluorescence pre‐column labeling reagents,ortho‐phthaldialdehyde, naphthalene dicarboxaldehyde, and fluorescein isothiocyanate, and data on phenylalanine detection limits are gi

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111207

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

年代:1988

数据来源: WILEY

摘要:

AbstractA commercially available silanol terminated silicone stationary phase, OV‐61‐OH (33% phenyl), and two phenyl‐substituted siloxane/silarylene copolymers, Sila 3 (27% phenyl) and 4 (35% phenyl), have been evaluated for use as stationary phases in fused silica capillary columns for gas chromatography.Ulterations in column adsorptive activity, separation efficiency, stationary phase film thickness and selectivity after column conditioning for 50 h at 370°C have been studied. A high thermal stability was experienced with the stationary phases tested here. For OV‐61‐OH, the best thermal stability was obtained when coated on untreated fused silica, which illustrates the importance of grafting reactions here. The heat treatment resulted in some deactivation of adsorptive sites in the column. A higher degree of column deactivation was achieved when surface silylation was performed prior to coating. High thermal stability was achieved with Sila 3 when coated on such surfaces. Sila 3 would thus be preferred in cases when high thermal stability in combination with high dsorptive inertness is desired.Sila 4 showed low column bleeding at 370 °C, but prolonged heating at this temperature resulted in the broadening of n‐alkane peaks when eluted at 90 °C. This indicates that excessive crosslinking has taken place during the heat treatment and the minimum allowable column operation temperature is thereby increased to ca. 120 °C. The separation of aza‐arenes and of triglycerides are show

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111208

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

年代:1988

数据来源: WILEY

摘要:

AbstractIn this study, the cold split‐splitless injector recently introduced by Carlo Erba was optimized for the trace analysis of polycyclic aromatic hydrocarbons. Injections of hundreds of microliters of hexane solutions were performed in the solvent split mode using an autosampler programmed for large volume injection. Injection parameters such as type of insert, initial oven temperature, split time, and flow are shown to play important roles in defining the conditions for obtaining quantitative results. The loss of early eluting compounds can be minimized by achieving a solvent trapping effect, making use ofn‐octane as co‐solvent inn

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111209

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

年代:1988

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111210

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

年代:1988

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240111211

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

年代:1988

数据来源: WILEY