On-column injection techniques

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]. 

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... 

H. Stan and H. Muller, Evaluation of automated and manual hot splitless, cold-splitless (PTV) and on-column injection technique us-... 

The ID has a direct influence on retention, efficiency, and capacity of the column. The on-column injection technique requires an ID of at least 0.30 mm. A narrow-bore column with an ID of 0.20 mm provides good resolving power with a minimum bleed. It is a good choice for MS analysis as it facilitates a proper adjustment of the carrier gas flow. Narrow-bore columns of limited capacity, however, may be a disadvantage for identification due to a fronting peak shape of overloaded peaks. Columns of an ID between 0.25-0.33 mm can be considered equal for the CWC-related chemicals. Columns of an ID 0.53 mm are useful if the sample contains a limited number of chemicals in widely different concentrations. 

The GC shall be capable of temperature programming and be equipped with all required accessories, such as syringes, gases, and a capillary column. The GC injection port shall be designed for capillary columns a splitless or an on-column injection technique is recommended. A 2 pL injection volume is assumed throughout this method however, with some GC injection ports, other volumes may be more appropriate. A 1 pL injection volume may be used if adequate sensitivity and precision can be demonstrated. 

The on-column injection techniques, in which the solvent is generally vaporized in a few meters of uncoated... 

For the assay of piperine in pepper, a 25 m by 0.5 mm I.D. glass capillary deactivated by high temperature silanization and coated with 0V-1 was used. The samples were injected by the on-column injection technique at 100°C, as described by Grob and Grob Jr.. The standard deviation of the whole procedure, sample preparation and chromatographic analysis, was 2.5 %. 

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

The high temperature of the injector, typically 250 °C, means that this method is not suitable for analytes that are subject to thermal degradation. For these materials, an on-column method is preferable, in which the solution of sample is injected directly into the narrow capillary column with a fine needle. On-column injection techniques are also more suitable for extremely dilute samples, as more sample is delivered to the column, but are less suitable for dirty samples containing non-volatile contaminants, which accumulate on the column. 

Figure 9. Analysis of triglycerides in whole butter on a 20 m X 0.30 mm SE-52 column with a stationary phase film thickness of 0.05 pm and the on-column injection technique. (12)...

Submicroliter samples are needed for the capillary on-column injection technique. To counter a general scepticism following the development of this injection technique, excellent quantitative results have been reported [42). The major advantages of this injection procedure seem to be in minimizing thermal decomposition of labile compounds as well as the lack of sample discrimination toward the later eluting components. This latter problem, observed frequently with the vaporizing injector... 

Bonilla, M., Enriquez, L. G., and McNair, H. M. (1995). Use of Cold On-Column Injection Technique for the Analysis of Putrescine and Cadaverine by Gas Chromatography. Pitteon 95. The Pittsburgh Conference. New Orleans, LA. 

While the potential exists for rapid growth in SFC and SFC-MS applications, practical problems remain to be resolved. Improved injection techniques are required and, in particular, on-column injection techniques which remove sample solvent prior to analysis and eliminate restrictions due to low sample solubility or limited injection volumes. The limitations for more polar materials are mostly unexplored. A large fraction of the compounds presently separated by HFLC can, in principle, be analyzed using SFC. In fact, it is not unreasonable to predict that essentially any compound soluble in an organic solvent should be amenable to SFC. 

One disadvantage is that trace analysis is limited since only a fraction of the sample enters the column. Consequently, splitless or on-column injection techniques are recommended for trace analysis. 

The on-column injection techniques, in which the solvent is generally vaporized in a few meters of uncoated deactivated capillary (retention gap) and vented via an early vapor exit valve, are of good accuracy and reproducibility.A schematic diagram for on-column injection is shown in Fig. 1. The on-column large-volume injection... 

Different sample introduction methods can be used in GC. If the sample is a liquid or a solid dissolved in an appropriate solvent, it may be introduced by a syringe into the injector. The choice of injection system depends on the column type and the sample composition. In packed columns, the sample is injected directly into the column inlet (Figure 2.3). In smaller inner diameter columns, split injection, splitless injection, and on-column injection techniques are used for liquid samples. 

For trace analysis, sample introduction without splitting part of the sample to a vent is the preferred mode for obtaining maximum sensitivity. This can be achieved with splitless or on-column injection techniques Schomburg, 1987). 

Successful derivatization is the key step for GC analysis of nonvolatile analytes. DPAA along with PAA have been derivatized using //-propanethiol under normal and acidic conditions [39, 40]. Thiol derivatization is a popular technique and allows for easy determination of the analyte. In a study done by Hanaoka et al. [39], the efficiency of a thiol derivatization was examined. For the degradation products, acidic conditions were required in order to properly facilitate a reaction. Most analytes had almost 100% recovery rates from the derivatization. The derivatization was also applied to a well water sample collected from Kamisu City. They were able to identify PAA that was present in the water (Figure 4.10). These workers also explored the possibility of analysing TPA by GC-FID without derivatization. Hanaoka et al. were able to use an on-column injection technique to... 

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