H. Husmann

Preparation, performance and special applications of glass capillary columns

Abstract A simple procedure for the preparation of glass capillary with polar and non-polar stationary liquids, including prior etching and deactivation, is described. A dynamic method of depositing homogeneous solvent films on the capillary walls has been developed. Aspects of the assessment of galss capillary columns are discussed and supplementary proposals for a standardized test procedure with particular regard to temperature stability are made. An improved version of an automated double-column chromatograph for the execution of optimal qualitative and quantitative analyses of aqueous solutins is described.

Sampling techniques in capillary gas chromatography

Abstract Four different sampling methods for capillary gas chromatography, including split and splitless sampling, have been investigated with respect to precise and accurate qualitative and quantitative analysis. A new method of direct sampling for capillary columns is presented and compared with the known techniques with respect to resolution, reproducibility of retention, decomposition of sensitive sample components and discrimination of high-boiling components in quantitative analysis. Multi-dimensional arrangements using capillary columns for the “main” separation as the most flexible and efficient sampling devices are discussed. If by selective sampling in such set-ups only a partial analysis of those components is achieved, which are of real interest in a particular analytical problem, analysis time can be saved and the performance of the separation can be improved.

Aspects of double-column gas chromatography with glass capillaries involving intermediate trapping

Abstract The versatility of semi- and fully automated double-column systems containing one or two glass capillaries is improved considerably by the incorporation of intermediate trapping devices for the analysis of complex mixtures, including very dilute and aqueous solutions. For the main separation, glass capillaries are used exclusively in order to achieve optimum resolution of all interesting species as well as narrow peak profiles for low detection limits of trace components. A length of 10–50 mm of the glass capillary acts as the trap; cooling and heating is executed by using a simple stainless-steel mantle tube with two separate entrances for either blowing cool nitrogen generated from liquid nitrogen or blowing hot nitrogen generated by electrical heating. There are four advantages in the use of trapping techniques in double column systems: 1. Broad or distorted peak profiles generated at the pre-separation or during the elution from the pre-column and the transfer to the main column are eliminated; ideal plug injection of the on-column type is attained by this procedure. 2. Repetitive pre-separation and comulative trapping allow enrichment of trace components. 3. The main separation can be performed with an isothermal mode of operation for retention index identification with high reproducibility. 4. Two sets of independent retention index data are obtained when stationary liquids of different polarity are used in the two columns of the system and the re-injection procedure is adopted.

Alkylpolysiloxane glass capillary columns combining high temperature stability of the stationary liquid and deactivation of the surface

SummaryA new method of making alkylpolysiloxane (OV 1, OV 101, OV 17, Dexsil 400, SE 52, SE 54) columns with high stability at temperatures above 300°C of both the stationary liquid itself (low bleeding) and of the surface deactivation (no tailing of polar solutes with extended use at temperatures beyond 250°C) is described. The best results were achieved on dealkalinized alkali glass but also on borosilicate surfaces which have been additionally HF treated before coating in both cases. The procedure can also be applied to leached alkali and borosilicate surfaces successfully. The best deactivations of the glass surface are attained in a two step procedure: firstly by treatment with gaseous HF/N2 mixture and secondly by simple heating of the coated and closed column at temperatures between 350° and 450°C for several hours. The tailing behaviour of such columns for polar solutes is considerably improved by this procedure as shown by test chromatograms. The procedure can also be applied to leached alkali and borosilicate surfaces successfully.

Cross-linked poly(vinyl alcohol) as permanent hydrophilic column coating for capillary electrophoresis

A fast method for the generation of permanent hydrophilic capillary coatings for capillary electrophoresis (CE) is presented. Such interior coating is effected by treating the surface to be coated with a solution of glutaraldehyde as cross‐linking agent followed by a solution of poly(vinyl alcohol) (PVA), which results in an immobilization of the polymer on the capillary surface. Applied for capillary zone electrophoresis (CZE) such capillaries coated with cross‐linked PVA exhibit excellent separation performance of adsorptive analytes like basic proteins due to the reduction of analyte‐wall interactions. The long‐term stability of cross‐linked PVA coatings could be proved in very long series of CZE separations. More than 1000 repetitive CE separations of basic proteins were performed with stable absolute migration times relative standard deviation (RSD > 1.2%) and without loss of separation efficiency. Cross‐linked PVA coatings exhibit a suppressed electroosmotic flow and excellent stability over a wide pH range.

“Direct” (on-column) sampling into glass capillary columns : Comparative investigations on split, splitless and on-column sampling

Abstract On-column (direct) sampling is superior to other techniques of sampling into capillary columns, especially for analyses with quantitative objectives, for example the precise and accurate determination of relative response factors. Discrimination by volatility of sample constituents is minimal and only slightly dependent on solvent volatility and column inlet temperature, but is independent of the type of carrier gas. Prior heating of the sample for vaporization before entering the column is avoided and decomposition of labile sample components is reduced to a minimum. The performances of two different on-column sampling techniques for quantitative analysis were compared. A new construction of an on-column sampling device for very low sample volumes (columns loads) is described, which allows for the introduction of volumes as low as a few nanolitres of samples into capillary columns.

New developments and experiences with glass capillary column production and sampling techniques

SummaryAn introductory discussion is given on the manufacture of glass capillary columns, including details of the methods of column testing and of the properties of the inner surfaces of glass capillaries. As a result a simple method for the testing of various kinds of support surfaces is presented which allows stepwise control of the column making procedure. A new kind of pretreatment of soft glass surfaces with HCl and HF at 450°C is described which allows the production of non-polar columns with much improved tailing behaviour for strongly polar solutes. Concerning capillary column sampling a new technique of “direct” sampling without previous vaporisation of the sample outside the column is presented together with a double column system for “selective” sampling of complex mixtures.

Capillary column gas chromatography of compounds of low volatility : Temperature stabilityt of stationary liquids on various glass surfaces

Abstract Several probles relating to gas—liquid chromatography in glass capillaries at high temperatures are discussed. Studies on the temperature stability of stationary liquid and solutes in the temperature range 250–390° were concerned with the parameters that influence column bleeding, especially of silicone phases from glass capillaries. The following parameters proved to be important: • Type of glass (alkali or borosilicate) with special regard to the alkali content: methylsilicones such as OV-101 and SE-30 are more stable on borosilicate and less on alkali glass. • Surface properties after roughening and/or deactivation: most deactivations are not stable at temperatures above 240°. Barium carbonate deos not decrease the decomposition of methylsilicones; an increase in decomposition was observed instead. Treatment with hydrogen chloride decreases but does not completely prevent the decomposition of methylsilicones. • Type and origin of methylsilicone: SE-30 and OV-1 proved to be much more stable than OV-101, even on alkali glass surfaces. In the standardized bleeding measurements, the column length, carrier gas flow rate and film thickeness were kept constant. The separation efficiency, tailing behaviour and decompositon or adsorption of methyl stearate as a more polar standard compound were controlled in paralled during the bleeding measurements. POLY S 179 (sulphonated polyphneyl ether) proved to be the most stable polar stationary liquid in glass capillary column work and could be used even on alkali glass surfaces at temperatures up to 390°. The most important appliacation for which columns with improved temperature stability have been developed was the rapid separation of the polynuclear aromatic hydrocarbons in coal tar with high resolution.

A GC-based method for high-throughput screening of enantioselective catalysts

By combining two gas chromatography instruments (each containing a column with a chiral stationary phase) with the proper robotics and software, it is possible to construct an instrumental configuration which makes possible high-throughput screening of the enantioselectivity of a given catalytic reaction. As an example, the acylation-based catalytic kinetic resolution of racemic 2-phenyl-1-propanol catalyzed by mutant lipases can be about assayed, 700 exact E- and ee-determinations being possible per day. The method is, therefore, of interest in the directed evolution of enantioselective enzymes and/or in the combinatorial search for asymmetric transition metal catalysts.

Crosslinking of alkylpolysiloxane filsm on various types of glass surfaces including fused silica using γ-radiation of a60cobalt-source. Comparison to crosslinking by thermal peroxid treatment

SummaryCrosslinking of alkylpolysiloxane stationary phases, especially in thick film capillary columns, is useful for the homogenous coating of fused silica and pretreated alkaliglass surfaces. The films of the stationary liquid are immobilized against solvent rinsing using CH2Cl2, pentane, and acetone, and maintain homogenity even at high temperature. Various doses of γ-radiation from a60Co. source were used for the crosslinking instead of the thermal peroxid treatment recently described by other authors. The effect of the γ-radiation crosslinking-procedure was investigated in comparison to the peroxid method in regard of: decrease of stationary phase content by solvent rinsing, separation efficiency, tailing behaviour, and bleeding of the columns obtained. Similar results as with the cumylperoxid-treatment were achieved using the γ-radiation-method. By γ-radiation no polar functional groups or moleculs are introduced into the stationary phase, however, as with the peroxid method. Less than 20% of the various stationary liquids are usually removed from the columns by solvent rising after crosslinking using both methods depending on the doses of radiation and the cumylperoxid concentration applied respectively.