Gas chromatography of plasma amino acids using a wide bore column: Comparison with packed and capillary columns

A procedure is described in which a wide bore glass capillary column is used as an alternative to the more traditional packed column in the analysis of amino acid levels in plasma. The coefficients of variation for all amino acids (with the exception of aspartic acid) were better than 11% with recoveries ranging from 81% to 122%. The data are compared with the corresponding results obtained using a packed column and show significant differences (p < 0.005) between values for glycine, serine, isoleucine, proline, methionine, aspartic acid, phenylalanine, and lysine. A similar comparison between results from the wide bore and the fused-silica open tubular (FSOT) column shows better agreement. Adjustment of chromatographic conditions for the wide bore analysis yields results in good agreement with those from FSOT analysis but which still differe significantly from the backed column data.     

Preparation of glass capillary columns

Summary Glass capillary column chromatography is the most rapidly growing part of gas chromatography. There are many complex new analytical tasks and they require special capillary columns. Fortunately there is a wide range of column preparation methods available, and they make the preparation of glass capillary columns a more varied job than that of packed columns. In this paper these methods are reviewed and suggestions are given for making task-oriented columns.     

On-line multidimensional chromatography using packed capillary liquid chromatography and capillary gas chromatography

The introduction of selected fractions from a liquid chromatograph into a gas chromatograph has been described; however, analyses were performed by off-line experiments requiring collection and reinjection of the separate fractions or by on-line procedures where disadvantageously, only a fraction of the separated peak or a well resolved component in a mixture could be introduced into a gas chromatograph. This disadvantage is overcome by the apparatus and method described in this paper, which utilizes a multidimensional chromatography system employing a high efficiency, packed capillary LC column coupled on-line to a capillary gas chromatograph. The liquid chromatograph (so designed) can act as a highly efficient clean-up or chemical class fractionation step prior to introduction into the gas chromatograph, significantly reducing sample preparation times in many applications. Thus minor components in a complex matrix can be determined without prior sample clean-up, an example of which is the determination of polychlorinated biphenyls in a complex hydrocarbon matrix.     

Gas chromatographic retention indices for alkenes on OV-101 and squalane capillary columns

Summary Gas chromatographic retention indices for 47 C₅ to C₈ alkenes on OV-101 dimethylsilicone at 50 and 70 °C were determined within a standard deviation of 0.3i.u. Data obtained on OV-101 are compared with those measured on squalane. The comparison of the retention index and dl/dT values from both columns is presented as linear regression equations with correlation coefficients greater than 0.98.     

Dynamic leaching of sodium-glass capillary columns

It is well known that removal of metal ions from the glass surface greatly improves both the thermal stability and the adsorption characteristics of glass capillary columns. Usually metal ions are removed from a glass surface by acid leaching; in particular, the static leaching procedure with hydrochloric acid is used very often for the preparation of glass capillary columns. This paper discusses the results of an investigation into dynamic leaching. Special attention is paid to those factors which affect the adsorption properties of the leached surface. The importance of the non-specific adsorptivity of the capillary surface due to changes of surface properties induced by the leaching process is pointed out.     

Direct injection of large sample volumes into capillary columns with packed column injector

A direct injection method for large volume samples which avoids severe tailing of the solvent peak has been developed using a packed column injector (up to 100 μl) leading into an ordinary capillary column (0.3 mm i.d.). Modifications are made to the cooler zones of the inlet port and on the carrier gas flow control system. This injection technique is based on the effective use of phase soaking and cold trapping using a retention gap. The large volume of solvent vapor is rapidly purged out of the injector with a higher flow of carrier gas while the solutes trapped at the head of the column are subsequently analyzed with another optimum flow rate. The proposed carrier gas flow regulation system is also compared with conventional split/splitless injection methods.     

Comparison of packed and capillary columns for quantitative gas chromatography of triglycerides in milk fat

Summary Quantitative gas chromatography of triglycerides in conjunction with established triglyceride formulae can be used to determine various milk fat parameters. Since the evaluation of, for example, iodine number or content of non-milk fats (foreign fats) in milk fat requires only the separation of triglycerides by carbon number and since repeatabilities, especially of the highboiling triglycerides, have been less acceptable with capillary columns in the past, packed columns have been used exclusively. There is, however, an increasing demand for the use of capillary instead of packed columns and to that end the present investigation has been carried out. To achieve a suitable resolution, with this particularly exacting high-temperature application, a short 5 m capillary column of extreme temperature stability has been used. As well as modification of various analytical conditions different injection techniques have been investigated. On-column, PTV and split injection were compared with regard to repeatability. The cold-on-column injection technique was found to produce the best results, being comparable to the excellent precision of a packed column. Thus, a method is now available by means of which the determination of milk fat parameters by the triglyceride formulae, such as the amount of foreign fats in milk fat, can now be carried out with a standardized capillary column.     

Comparison of different types of outlet frits in slurry‐packed capillary columns

Fused‐silica capillary columns for high‐performance liquid chromatography with 320 and 250 μm inner diameter were prepared by slurry packing with 5 and 3 μm Nucleosil C₁₈ stationary phase. Different types of mechanical and monolithic outlet frits were used and their influence on the resulting column performance was evaluated. Columns with quartz wool exhibited symmetrical peaks and low theoretical plate height, and the preparation time was short. The performance of monolithic frits varied based on type of monolith, length of the frit, and silanization procedure. The best frit performed similarly to the quartz wool ones, but the preparation took several hours. Their main advantage lies in the possibility of on‐column detection, because the detection window can be burnt immediately behind the frit.     

Glass capillary SCOT columns by a single-step coating method

A single-step coating method for the preparation of glass capillary SCOT columns is described. It is reproducible and less time-consuming than the well-known two-step coating procedures. Other methods attempted are discussed briefly. Both the flame ionization and electron capture detectors could be used in conjunction with temperature programming. The separations achieved with an “activity mixture”, phenols and phenolic acids, illustrate the resolution obtained. The columns are suitable for quantitative determinations and a comparison is made with a conventional packed column.     

Gas chromatographic separation of sugars by on-column injection on glass capillary columns

Sugars were separated gas chromatographically on short apolar glass capillary columns by using cold, on-column injection (OCI) techniques. After silylation, oligomers up to the hexasaccharides could be efficiently separated in resonable retention times. Response factors of silylated sugars were determined as a function of varying sample amounts and concentrations. The optimum injection amount was found to be 1 μl in heptane as solvent.     

Peak broadening in isothermal runs due to large retention gaps in capillary GC?

A simple formula is derived which allows estimation of the band broadening due to longitudinal diffusion in retention gaps for isothermal runs with the column held at the injection temperature. The broadening is strongly dependent on the linear gas velocity in the retention gap. If the internal diameters of the retention gap and the separation column are similar, the retention gap may have a length exceeding 100 m, even if the separation column is only 10 m long. A 0.5 mm I.D. retention gap attached to a 0.3 mm I.D. separation column (of interest for automatic on-column injection) may be several meters long. Retention gaps of 0.3 mm I.D. may be used for on-column injections into separation columns with I.D's. down to about 0.1 mm.