ISSN:0935-6304    

DOI:10.1002/jhrc.1240091202

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

年代:1986

数据来源: WILEY

摘要:

AbstractSamples, representative of certain classes of “high molecular weight” and/or less volatile substances, were analyzed by gas chromatography utilizing a new generation of aluminum clad flexible fused silica glass capillary columns containing thin films of a methyl polysioxane stationary phase capable of being operated isothermally to 400–425°C and temperature programmed to 425–440°C. The results obtained here were compared with those described in the literature discussing the latest advances in Supercritical Fluid Chromatography (SFC) in the analysis of precisely the same types of samples. In all instances, the gas chromatographic method provided superior speed of analysis, superior column efficiency, and superior resolution of the component bands. This was due to fundamental factors, favoring the diffusivity of the solutes in both the gas and liquid phases in this process at these high temperatures. Under these circumstances, it is thought that the strength of SFC mainly lies in the analysis of thermally labile samples until the advocates of this technique make more definitive strides in the handling of still higher molecular weight substances well beyond the newly expanded range of gas chrom

ISSN:0935-6304    

DOI:10.1002/jhrc.1240091203

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe capillary gas chromatographic analysis of complex naturally occurring and food‐product triglyceride mixtures is accomplished qualitatively and quantitatively on columns coated with methyl and methyl‐phenyl (65%) silicones using programmed‐temperature split/splitless and on‐column injection. Faster analysis times are achieved using elevated initial column oven temperatures with cold initial injector tempe

ISSN:0935-6304    

DOI:10.1002/jhrc.1240091204

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

年代:1986

数据来源: WILEY

摘要:

AbstractA procedure is suggested for preparation of reproducible and stable galss capillary Apiezon LH+KF columns for the determination of organic compounds containing different functional groups. The advantage of the universal equation over the linear equation for calculation of retention indices for any homologs, including the first members of the series, is shown using the following five homologous series as examples: fatty acid methyl esters, methyl ketones, secondary and tertiary aliphatic amines, andN‐alkyl piperidines. The accuracy of the calculation enables the universal equation to be used in computer‐assisted identificat

ISSN:0935-6304    

DOI:10.1002/jhrc.1240091205

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe reaction of Cab‐O‐Sil, a highly dispersed vitreous quartz, with hexamethyldisilazane (HMDS) was studied in the temperature range 380–500°C, using29Si solid state NMR and other techniques. Such studies are of importance in view of deactivation procedures of fused silica at high temperatures in capillary GC.The commonly accepted reaction equation:\documentclass{article}\pagestyle{empty}\begin{document}$$ \left({{\rm Me}_{\rm 3} {\rm Si}} \right)_2 {\rm NH } + {\rm 2}\equiv {\rm SiOH} \to {\rm 2} \equiv {\rm SiOSiMe}_{\rm 2} + {\rm NH}_{\rm 3} $$\end{document}predominates only belowca. 400°C. Aboveca. 400°C the intermediate cleavage product Me3SiNH2reacts with surface silanol groups to form SioSiMe2NH2+ CH4. At higher temperatures these groups may ultimately form (SiO)3SiNH2groups (analogously to the formation of bi‐and tridentate linkages starting from SiOSiMe3groups), but (SiO)3SiNH2groups are also directly formed at lower temperatures, simultaneously with the SiOSiMe3groups, probably by reaction with siloxane bridges:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Me}_3 {\rm SiNH}_2 + \equiv {\rm SiOSi} \equiv\; \to \;\equiv SiNH_2 + \equiv SiOSiMe_3 $$\end{document}.The reactions of the trimethylsilylamine part of HMDS with Cab‐O‐Sil were confirmed by an independent series of silylations usingN,N‐dimethyltrimethylsilylamine instead of HDMS. The presence of amino groups as SiNH2was confirmed by FT‐IR. This may be one of the reasons why very high temperature silylation with disilazanes does not provide a satisfactory deactivation of fused silica GC columns: the active SiOH groups are “replaced” by active SiNH2groups. However, such a material may be of interest in LC. Silylation with silazanes atca. 350°C in humid atmosphere and/or after extensive hydroxylation (leaching) of the surface should yield sufficiently deactivated surfaces with

ISSN:0935-6304    

DOI:10.1002/jhrc.1240091206

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe behavior of heavy solutes present in a sample injected on the precolumn has not been clarified in on‐column injection onto gas chromatograph having a capillary column coupled to an uncoated precolumn in an oven. To investigate this point, an on‐column gas chromatograph has been developed which is constructed with a heatable precolumn outside the oven. Some experiments were carried out in order to evaluate the performance. As a result, it was found that heavy solutes reach the first part of the main capillary column after the solvent has gone, resulting in sharp peaks without solvent effects. The reason why sharp peaks appear for the heavy solutes is also discussed. The cold‐trapping effect has been shown to play an important role in narrowing the band width of the heavy solutes. Some of the advantages of the gas chromatograph developed are also pres

ISSN:0935-6304    

DOI:10.1002/jhrc.1240091207

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe need for faster and more efficient separations of complex mixtures of organic compounds by gas chromatography has led to the development of small inner diameter open tubular columns. Owing to their decreased plate height, extremely narrow peaks are obtained. When differently sized columns with equal plate numbers are compared, injection of a fixed amount of a solute will give the highest detector signals for the smallest bore columns. When P is defined as the ratio of the column inlet and outlet pressures, it can be seen from theory that under normalized chromatographic conditions the minimum detectable amount (Qº) for a mass flow sensitive detector increases proportionally to the square of the column diameter for P = 1. In the situation of greater interest in the practice of open tubular gas chromatography where P is large, a linear relationship is derived between Qºand the column diameter.It is a widespread misunderstanding, however, that narrow bore capillary columns should be used for this reason in trace analysis. If a fixed relative contribution of the injection band width to the overall peak variance is allowed, a decreased plate height drastically restricts the maximum sample volume to be injected. It is shown that the minimum analyte concentration in the injected sample (Cº) is inversely proportional to the column inner diameter when a mass flow sensitive detector is used. For actual concentrations less than Cº, sample preconcentration is required. The effect of peak resolution and selectivity of the stationary phase in relation to Cºand Qºwill be discussed as well. The validity of the given theory is experimentally investigated. Minimum analyte concentrations and minimum detectable amounts are compared using columns with different inner dia

ISSN:0935-6304    

DOI:10.1002/jhrc.1240091208

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

年代:1986

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240091210

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

年代:1986

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240091211

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

年代:1986

数据来源: WILEY

ISSN:0935-6304    

DOI:10.1002/jhrc.1240091212

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

年代:1986

数据来源: WILEY