Split Injector Research Articles

Comparison of two injection systems to be used with 5 μm I.D. open-tubular columns

The split injection system and the pressure pulse-driven stopped-flow injection system (PSI) were compared in terms of band broadening and sample injection volume reproducibility for 5 μm I.D. open-tubular columns. It was found that the PSI injector has a better injection profile factor than the split injector, maximum column efficiency being obtained with higher injection volumes (ten times) using the PSI injector. The repeatability of the injected volumes obtained with the PSI injector is twice as good as that with the split injector. The peak efficiency reproducibility is similar with both injectors (R.S.D. = 3–4%).

Split injector for capillary zone electrophoresis

A split injector is described for capillary zone electrophoresis. It consists of a pump for delivery of the medium, a rotary injector, an interface, and a fused-silica capillary connected between the interface and the rotary injector. Several factors affecting split injection are examined, such as geometrical configuration of the interface and sample loop volume. The use of this split injector is demonstrated for both rectangular capillaries with large cross-sectional areas and the more conventional circular capillaries. The present injection method requires no interruption of the applied voltage.

Split injection into a capillary column at very low split ratios

The solute zone in the inlet liner of a split injector at very low split ratios are split because of significant differences between the mean linear velocities in the capillary and in the liner. As the frontal part of the split zone of the solute moves through the liner with a velocity comparable with that in the capillary, radial diffusion is the limiting process. Given the diffusion coefficient of the solute, the radial mixing of the frontal part of the solute zone can he improved both by the inlet liner and the zone extension.

Development of a method for the determination of phthalate esters in sewage sludge including chromatographic separation from polychlorinated biphenyls, pesticides and polyaromatic hydrocarbons

A method was developed that allows phthalate esters (PEs) to be determined in sewage sludge samples by use of gas chromatography (GC) with electron-capture detection. Discrimination of the PEs in the split injector of the GC system was detected and the resulting problems are discussed. The ultrasonic technique was optimised for extraction time and number of extractions and compared with the Soxhlet extraction technique. It was shown that extraction efficiency is slightly better with ultrasonication than using Soxhlet extraction. The Soxhlet extraction also yielded much higher blank levels. The extract clean-up was carried out by dual column liquid chromatography with neutral alumina and Florisil. In this way separation of polychlorinated biphenyls, pesticides and polyaromatic hydrocarbons from the PEs was attained. This procedure was used successfully to determine PEs in several sewage sludge samples.

Simultaneous quantification of total medium- and long-chain fatty acids in human milk by capillary gas chromatography with split injection

Four different quantification methods for the capillary gas chromatographic determination of medium-chain fatty acids (6:0-12:0) and myristic acid in human milk samples, using a split injector, were compared. Odd-carbon-numbered fatty acids (5:0-17:0) were added as internal standards. Each medium-chain fatty acid and myristic acid was calculated on the basis of: (1) the peak area of the internal standard with one methylene group less; (2) the peak area of the internal standard with one methylene group more; (3) half the sum of the peak areas of the internal standards with one methylene group less and more (bracketting method); (4) the peak area of 17:0. The peak-area ratio of each analyte and 17:0 in a standard was found to be subject to an unacceptably high coefficient of variation. From the methods using internal standards with one methylene group more and less, the bracketting method was found to be the best, resulting in recoveries close to 100%, with the lowest coefficients of variation. The method was applied for the determination of the fatty acid composition of mature milk samples of 47 Curaçaoan women.

Injectors for open-tubular column liquid chromatography with 10 6 theoretical plates at retention times in the minute range

A pressure pulse-driven stopped-flow injection system for use in open-tubular column liquid chromatography is described and is compared with a conventional split injector. For a non-retained sample component 10 6 theoretical plates are obtained in 220 s using a 1.3 m × 3.5 μm I.D. column. The loss of 25% in the number of theoretical plates corresponds to an injection volume of ⩽ 8 pl.

Sampling onto capillary columns. Difficulties with various types of samples a simple accessory to split injectors for avoidance of discrimination

The quantitation problems arising by discrimination at split sampling onto capillary columns due to selective vaporization from the syringe needle after extrusion of the adjusted volume of the liquid sample into the vaporization chamber and/or due to malfunction of the splitting itself can be avoided by a simple accessory to the common injector constructions in order to arrange for cooling of the entire syringe needle except the tip. It could be proved that the discrimination which is usually observed does not originate from the splitting itself, if the temperature of the split region is not changed appreciably during the sampling procedure.

Glass wool in the inserts of split injectors for capillary GC?

AbstractIt has been reported that glass wool packed tightly into the glass liner of a vaporizing injector used in the splitting mode considerably reduces the standard deviation of the results obtained, because of improved evaporation of the sample prior to reaching the split point at the capillary column entrance. This finding could not be reproduced on using the same sample composition as reported in the literature, i.e. methanol/2‐ethyl‐1‐hexanol (1:1).The standard deviations obtained were between 3 and 10% (depending on the conditions selected) and were not influenced significantly by the introduction of glass wool.The peak area ratio (methanol/2‐ethyl‐1‐hexanol) was found to depend on a number of parameters, such as: injector temperature; glass liner internal diameter; syringe handling technique; the relative position of the syringe needle exit and capillary column entrance; the sample volume injected; and the packing of the glass liner. Generally, the area ratio deviated further from the correct one (determined by cold on‐column sampling) when the glass liner was packed with glass wool.On the basis of the results, it is speculated that either a complete evaporation of the sample should be achieved (which appears to be impossible under the conditions we used) or, alternatively, the sample should be given the least possible opportunity to evaporate, thus allowing it to enter the column in the form of droplets. The results were worse in terms of precision and accuracy the greater the partition of sample components between the liquid (droplet) and vapor phase. It is concluded that the use of evaporation aids such as glass wool cannot be generally recommended.

Pressure and flow changes in vaporizing GC injectors during injections and their impact on split ratio and discrimination of sample components

AbstractThe effect of pressure changes in the vaporizing GC injectors on the split ratio is investigated. It is shown that the true split ratio depends on a number of parameters and may strongly differ from the split ratio expected from the flows set before injection. Quantitation with split injection based on external standards has to be carried out very carefully (or should be replaced by the method with internal standard). The split ratio may strongly change during the splitting of the sample. There are a number of mechanisms causing some sample components to be retarded and hence to be split by a different ratio. The split injector is a device which still requires further development.