Cold-on-column injection

Adsorption or catalytic decomposition of labile substances by the syringe needle can be a problem for some compounds using hot vaporizing injectors [25]. For open tubular columns deactivated fused silica syringe needles and cold on-column Injection techniques are used to minimize this problem. Alternatively, syringes fitted with a needle shroud for cold-needle injection can be used [26]. 

Certainly, the precision and accuracy of the PTV techniques are generally superior to those of the classical hot split and splitless techniques and approach those obtained by cold on-column Injection [ 34,36,37, -54-57,62,64]. However, less is known concerning optimization of PTV injection and probably more parameters have to be considered than for cold on-column injection. The latter is, consequently, the preferred injection technique for most samples, except those contaminated by larg< amounts of involatile Impurities and for headspace vapors. 

Cold on-column injection differs from the vaporization techniques discussed above in that the sample is introduced directly as a liquid into the column inlet, where it is subsequently vaporized. In this way, discrimination is virtually... 

Haky, J.E., Leja, B. (1986) Evaluation of octanol-water partition coefficients using capillary gas chromatography with cold on-column injection. Anal. Lett. 19, 123-134. 

Like cold on-column injection the PTV has a low thermal mass, so can be heated and cooled quickly. However, unlike cold on-column the sample is injected into an injector liner and not direct onto the column. Unlike conventional split/spUtless injection, the aim is to make use of volatility selectivity of the system rather than to inhibit it. By selecting an appropriate starting temperature, the anal34es condense in the liner if desired the solvent may be flushed away through... 

It is frequently the case that organic peroxides, and the hydroperoxides in particular, cannot be analyzed by GLC in the usual way, as they undergo decomposition inside the instrument. A study on the thermal stability of various organic peroxides shows that on using the cold on-column injection technique, with the temperatures of the injection port and column as low as practically possible and applying slow heating rates, it is possible to... 

Coffee, instant, 610, 628 Cold on-column injection, thermal analysis, 684-5 Colorimetry... 

Cold on-column injection. In this approach, the sample is injected directly on-column and its vaporisation occurs after the injection. This requires a very special microsyringe. The needle (steel or silicone) has a diameter of approximately 0.15 mm and it penetrates the column, or pre-column, kept at 4 °C before raising it to its normal operating temperature. This approach, which is very difficult to master without the aid of an autosampler, is useful for thermolabile compounds (applications in... 

Various alkyl and aryltin compounds were determined in aquatic matrices, namely sediments, biota and water by means of gas chromatographic methods. In this work, comparisons of single or dual flame photometric detectors and electron capture detectors were reported (Tolosa et al., 1991). Sample preparations included acid digestion, extraction, formation of methyl derivatives and clean-up with alumina prior to gas chromatographic analysis. With the electron capture detector, cold on-column injection of organo-tin chlorides was studied. The conclusion was that a single or dual flame photometric detector equipped with a 600 nm interference filter yielded the best performance for determinations of tin species as methyl derivatives. Detection limits for the method using flame... 

Cold on-column injections allow the inlet and/or inlet section of the column to be cooled or maintained at lower temperatures than the oven. Cold on-column injection suffers from the possibility of sample zone band broading due to excessive solvent flooding. The advantage of cold on-column injection is that it reduces sample discrimination or sample loss, due to syringe needle heating during injection. 

Grob, K., Jr. (1981). Peak broadening or splitting caused by solvent flooding after splitless or cold on-column injection in capillary gas chromatography. ]. Chromatogr. 213, 3-14. 

Grob, K., Jr., and Neukom, H. P. (1980). Factors affecting the accuracy and precision of cold on-column injections in capillary gas chromatography. J. Chromatogr. 189, 109-117. 

In GC the injection may take place at a temperature that is lower than that of the column oven. The solute bands will be concentrated in a small volume and may be brought into the column by a subsequent heating of the cold zone. If this zone is part of the column itself we talk about cold (on-column) injection , if it is part of a separate injector unit we talk about cold trap injection. A similar band compression effect may be achieved in a different way by leaving the first part of the capillary column uncoated (i.e. no stationary phase present). The solute band will then be compressed at the point where the stationary phase starts to be present in the column. This band compression technique is usually referred to by the unfortunate term retention gap [706]. 

Figure 4.14 Sample injection ports, (a) Rash-vaporizer, (b) Split injector with septum purge for capillary columns, (c) Direct -cold on-column injection onto a capillary column showing rotating valve and insertion of needle into the base of the column. (Reproduced by permission of Dr Alfred I liithig Verlag from J. High Res. i hromuiogr., Chromalogr. Contniun., 2. 35.X (1979).)...

Cold on-column injection is an injection technique for GC which offers some advantages elimination of sample discrimination, elimination of sample alteration, and high analytical precision and accuracy. Peak splitting or peak distortion, which may occur as a result of polarity mismatches of solvent, stationary phase, and solutes, can be reduced by means of a retention gap. Today, the cold on-column technique using a retention gap is one of the most commonly employed techniques for large-volume injections. 

Verzele et al.2 concluded that the "cold on-column" injection, applied for the piperine assay, and the "falling needle" injection, applied for the quinine-quinidine assay, are the best alternative at the moment for quantitative capillary gas chromatography. They are applicable to high temperature capillary gas chromatography, but they also have their limitations. 

The development of the cold on-column injection technique and fused silica column with... 

GLASS CAPILLARY GC ANALYSIS WITH COLD ON-COLUMN INJECTION OF PIPERINE2 A = pure piperine and B = pepper extract. Internal standard (1) tetrahydropiperine, and piperine (2). Column 25 m x 0.5 m I.D. HTS-OV-1 column, 250°C isothermal. 

Capillary gas chromatography of cocaine has so far been scarcely done. Christophersen and Rasmussen analyzed a number of narcotic drugs, i.a. cocaine, on a glass capillary column coated with SE-30 using cold on-column injection (50°C). The oven temperature was programmed... 

---