摘要:

AbstractThe occurrence of the highly toxic non‐orthosubstituted (planar) chlorobiphenyls (CBs) at low levels in wildlife, (human) fat, and fish generates the need for a routine analytical procedure. The use of a fully automated system for the separation of planar and non‐planar CBs, consisting of a gel permeation chromatography system, a sample preparation system employing extraction columns, and a porous graphitic carbon HPLC column is described, and tested with horse fat. Gas chromatography on capillary columns, with electron‐capture or high resolution mass spectrometric detection, is used for quantitation of th

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131202

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

年代:1990

数据来源: WILEY

摘要:

AbstractMany uncoated precolumns, and to a lesser extent separation columns, strongly retain some of the solvent. Retarded release of such solvent elevates the baseline after the solvent peak and causes ugly “humps” of eluted solvent as the temperature is increased. The problem is probably a result of retention by a porous surface, e.g. surfaces obtained by leaching or hydrothermal treatment of capillaries prior to silylation. It is assumed that other problems with capillary columns can be explained by the same mechanism, including: a kind of adsorption including apolar compounds, and “ghost” peaks as well as “memory” effects. Fused silica capillaries are superior to glass, but even for these special procedures are required in order to achieve thorough deactivation of the internal surface without introduci

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131203

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe deactivation of fused silica capillary columns with a laboratory‐made poly‐diphenylvinylmethylhydrosiloxane copolymer has been investigated. The deactivation obtained at different temperatures and reaction times is characterized with a dual column capillary GC system [1]. In parallel, the effect of the silylation temperatures and reaction times on the nature, the structure, and the chemical properties of the deactivation layer has also been studied by solid‐state29Si NMR spoctroscopy. A fumed silica, Cab‐O‐Sil M5, was used as a model substrate for these spectroscopic studies.The deactivated fused silica capillaries show an excellent thermal stability (up to 400°C), a high resistance to solvolysis, and a minimal interaction to various critical test components. A good wettability of the fused silica capillary columns deactivated with this reagent was confirmed by successful subsequent coating with polysiloxanes with different pheny

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131204

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

年代:1990

数据来源: WILEY

摘要:

AbstractMartin'sadaption ofRaoult'sLaw has been shown to describe partition phenomena in normal phase HPLC. Thus, in the separation of fatty acid pentaflorobenzyl esters and of triacylglycerols in dichloromethane or acetonitrile in half‐water‐saturated hexane, the natural logarithm of the corrected retention volume is proportional to the number of double bonds that these solutes contain. By extendingMartin'sadaption ofRaoult'sLaw with activity coefficients, evidence was obtained that deviations observed for the homologous series of saturated fatty acid pentafluorobenzyl esters from C2to C5could be accounted for by a diminution of adsorption by the inductive effect. For chain lengths longer than C5, it appeared that there were additional field and inductive effects from the methyl end of the hydrocarbon chains.Thus, with these half‐water‐saturated solvent systems, the silica surface is probably covered with a bilayer of water which, in the dynamic situation in an HPLC column, attracts several layers of the polar organic component of the mobile phase by dispersive interactions. This stationary phase surface may, then, be considered to be immiscible with the predominantly hexane mobile phase due to these dispersive interactions and thus partition can occur between these two phases. Solutes that enter the stationary phase are then free to interact with the underlying aqueous phase by ads

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131205

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper shows that the liquid chromatography (LC) methods so far described in the literature for iso‐alpha acids analysis are unsatisfactory. The main reasons for this are the failure of the advocated eluent systems to completely suppress trace metal activity of commercial LC columns and the lack of a stable reference iso‐alpha acid.The trace metal problem can be solved by using a column packing material specifically designed for “Hop Acid” analysis and by adding ethylenediaminetetraacetate (EDTA) to the eluent. The reference problem is more difficult, but possibly a formulation of the iso‐alpha acids in their acid form may be the answer.Chromatographic conditions changing the elution pattern of the individual iso‐alpha acids are studied. This leads to better control of their co‐elution in the analyti

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131206

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

年代:1990

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131207

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

年代:1990

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131208

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

年代:1990

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131209

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

年代:1990

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131210

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

年代:1990

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240131211

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

年代:1990

数据来源: WILEY