Problems in Qualitative Gas-Chromatographic Analysis of Steriods on Open-Hole Capillary Columns
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Problems in qualitative gas-chromatographic analysis of steriods on open-hole capillary columns Citation for published version (APA): Groenendijk, H. (1970). Problems in qualitative gas-chromatographic analysis of steriods on open-hole capillary columns. Technische Hogeschool Eindhoven. https://doi.org/10.6100/IR123356 DOI: 10.6100/IR123356 Document status and date: Published: 01/01/1970 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license above, please follow below link for the End User Agreement: www.tue.nl/taverne Take down policy If you believe that this document breaches copyright please contact us at: [email protected] providing details and we will investigate your claim. Download date: 04. Oct. 2021 .. PROBLEMS IN QUALITATIVE GAS CHROMATOGRAPHIC ANALYSIS OF STEROIDS ON OPEN-HOLE CAPILLARY COLUMNS PROEFSCHRIFT TER VERKRIJGING VAN DE GRAAD VAN DOCTOR IN DE TECHNISCHE WETENSCHAPPEN AAN DE TECHNISCHE HOGESCHOOL TE EINDHOVEN OP GEZAG VAN DE RECTOR MAGNIFICUS PROF. DR. IR. A. A. TH. M. VAN TRIER, HOOGLERAAR IN DE AFDELING DER ELEKTROTECHNIEK, VOOR EEN COMMISSIE UIT DE SENAAT TE VERDEDIGEN OP VRIJDAG 18 DECEMBER 1970 DES NAMIDDAGS TE 4 UUR DOOR HUlBERT GROENENDIJK GEBOREN TE MELISSANT DIT PROEFSCHRIFT IS GOEDGEKEURD DOOR DE PROMOTOR PROF. DR. IR. A. I. M. KEULEMANS Aan mijn vrouw Aan Richard en Natasha \ ? CONTENTS I. INTRODUCTION . 1.1. General . t .2. Gas chromatography 3 1.2.1. Basic concepts 3 1.2.2. Retention time 4 1.2.3. Relative retention 5 1.2.4. Plate theory 6 1.2.5. Rate theory 6 1.2.6. Resolution 8 1.2.7. Effect of temperature on retention time 9 1.2.8. Selectivity of stationary phases 11 1.3. Steroids . 12 1.3.1. Steroid classes . 13 1.3.2. Stereoisomerism 13 1.3.3. Nomenclature 15 References . 17 2. CHROMATOGRAPHIC ANALYSIS OF STEROIDS 18 2.1. Introduction . 18 2.2. Biological significance . 20 2.3. Conventional methods of steroid analysis 21 2.4. Pretreatment for gas-chromatographic steroid analysis . 22 2.4.1. Steroid conjugates 22 2.4.2. Hydrolysis 24 2.4.3. Extraction . 26 2.4.4. Sample preparation 26 2.4.5. The sample pretreatment adopted 27 2.5. Gas-chromatographic steroid analysis 28 2.5.1. Type of column .... 29 2.5.2. Column support 30 2.5.3. Liquid (stationary) phase 31 2.5.4. Preparation of columns 33 2.6. Steroid derivatives 34 2.7. Detection systems 38 References . 39 3. OPEN-HOLE CAPILLARY COLUMNS IN GAS-CHROMATO- GRAPHIC STEROID ANALYSIS 42 3.1. Introduction . 42 3.2. The gas-chromatographic system 43 3.3. Column material . 45 3.4. Factors determining the choice of column diameter and length . 45 3.4.1. Column efficiency . 45 3.4.2. Analysis time . 46 3.4.3. Pressure drop 47 3.4.4. Sample capacity 47 3.4.5. Linear carrier-gas velocity 48 3.4.6. Resolution . 48 3.4.7. Detection limit 48 3.4.8. Conclusion 48 3.5. Stationary phases . 49 3.5.1. Non-selective phases 49 3.5.2. Selective phases 53 3.5.3. Volatility 57 3.5.4. Stability . 59 3.6. Column preparation. 62 3.6.1. Column cleaning 62 3.6.2. Static coating method 62 3.6.3. Dynamic coating method 62 3.6.4. Modified static coating method 63 3.6.5. Column conditioning . 63 3.7. Comparison of packed and open-hole tubular columns. 64 3.7.1. The volumetric phase ratio 64 3.7.2. Column permeability . 65 3.7.3. Resolution . 65 3. 7.4. Number of theoretical plates required 67 3.7.5. Detection limit 73 3.8. Natural samples 73 References . 77 4. CARBON NUMBER, A NEW DEFINITION 78 4.1. Introduction . 78 4.2. Determination of column hold-up time 80 4.2.1. Direct measurement of t M 81 4.2.2. Indirect measurement of tM 81 4.2.3. Calculation of (v . 82 4.3. Linearity of the log plot 86 4.3.1. Testing the linearity of the log plot 86 4.3.2. Linearity of the C18-C32 region 86 4.3.3. Linearity of the CcC9 region 89 4.4. Carbon Index, a new concept . 98 4.4.1. Definition of the standards 98 4.4.2. Definition of the carbon index . 98 4.4.3. Equivalent definitions of the carbon index 100 4.5. Computer program 101 References 104 5. IDENTIFICATION 105 5.1. Introduction . 105 5.2. General identification parameters 107 5.2.1. Isothermal relative retention parameters 107 5.2.2. Programmed-temperature retention parameters 108 5.2.3. Boiling-point index . 109 5.2.4. Other identification parameters . 109 5.3. Parameters used for the identification of steroids . 109 5.3.1. Definition of steroid-identification parameters 110 5.3.2. Comparison of reference sets . 112 5.4. Temperature dependence of retention parameters 117 5.4.1. Temperature-retention-time relationships . 117 5.4.2. Plea for a new identification parameter 120 5.5. Molecular-structure-retention-behaviour relationships 121 5.5.1. Survey of the literature . 123 5.5.2. Structure-retention relationships for the carbon index. 126 5.6. Computer program IDENTIFICATION 129 5.6.1. Reliability of identification 130 5.6.2. Reference carbon indices 132 5.6.3. Procedure 132 References 134 6. DIRECT INJECTION INTO CAPILLARY COLUMNS 136 6.1. Introduction . 136 6.2. Direct injection of liquid samples 137 6.2.1. Direct injection without a cold zone 137 6.2.2. Direct injection with a cold zone . 140 6.3. Direct injection ofliquid samples with solvent elimination 143 6.4. Direct injection of solid samples . 146 6.5. Quantitative evaluation of the injection devices 153 6.5.1. Removal of the solvent . 153 6.5.2. Trap efficiency . 154 6.5.3. Influence on retention quantities 155 6.5.4. Contribution to peak-broadening 157 References . 161 Summary 163 Samenvatting. 165 Dankbetuiging 167 Levensbericht . 168 1- 1. INTRODUCTION 1.1. General Gas-chromatographic (GC) steroid analysis has grown rapidly since the early 1 1 investigations reported by Eglinton et al. in 1959 - ). Although the retention times in this work were very long, gas chromatography had proved its usefulness in the separation of compounds of low volatility and since that time steroid analysis in the vapour phase has become common practice. Today, the number of publications on the analysis of steroids, steroid hormones and sterols, both as pure compounds and in fairly complex mixtures, is quite considerable. One of the most interesting applications is steroid analysis in body fluids, which is extremely important for clinical purposes. Although steroids in body fluids constitute mixtures of fair complexity, in which steroids are present in a scale of concentrations together with numerous other compounds of biological origin, only packed columns have been used up till now. The lack of interest in the high resolving power of capillary columns as compared to packed columns may be due basically to some practical problems inherent in operating capillary columns at "high" temperatures. These practical problems chiefly concern the: Preparation of efficient columns The preparation of efficient columns appeared to constitute a considerable problem. It is very difficult to prepare columns that possess sufficient efficiency at the elevated temperatures required for gas-chromatographic steroid analysis. In particular, the preparation of columns with selective phases appeared to be cumbersome and once a good column was obtained, it degraded fairly quickly, resulting in a short column lifetime. This is mainly due to the lack of surface active agents stable at these high temperatures. Sample requirements The sample requirements of open-hole capillary columns present another practical problem. Apart from the limitation imposed on the construction of an injection device, the small amounts of material involved in GC analysis on capillary columns exclude the possibility of an additional identification. Samples can hardly be collected from the effluents of a capillary column. More over, established techniques such as u.v. and i.r. analysis of column effluents are not accessible to capillary columns. The only additional identification tool capable of handling the small sample sizes eluting from a capillary column is a gas-chromatograph- mass-spectrometer combination. Apart from practical problems involving the coupling between the gas chromatograph aud the mass spectrometer, the latter instrument is still fairly expensive.