Septum injection

Fig. 5.18. Reservior inlet of a JEOL JMS-700 sector instrument with the septum injection port opened. The operation valve switches between evacuation, isolation and admission of the sample a needle valve allows regulation of the sample flow. The GC transfer line crosses in the upper background from the GC (left) to the ion source housing (upper right).

Samples are injected into the vaporizer by a metering pump or manually with septum injection the manual injection procedure is intended for method development. The sample gas mixture then passes through the chromatographic column where the sample compounds separate. Fractions pass through the thermal conductivity detector and then to a condenser collection manifold where up to five fractions can be collected. Complete control of the system is achieved via a mini-computer. 

The trend toward automatic injection will become predominant with increasing routine application. Currently, satisfactory injection devices are only available for GC septum injection from Hewlett-Packard, Varian, etc. These have been adapted to HPLC with good results [6] within the general limitations of septum injection. Automatic injection usually results in better reproducibility with relative standard deviations of less than 1% and external standardization can be used [6]. Automatic systems based on loop injection have been announced by several manufacturers, e.g. DuPont, Varian, Altex. 

Septum injection, pneumatic high-pressure syringe injection and v.alve injection are the usual kinds of sampling devices. The stop-flow injection technique is also used. Automated sampling devices based on high-pressure syringe injection or valve injection are already available. 

The early design of HPLC injector systems was strongly influenced by those used in gas chromatography (GC). This is obvious when one considers that, although septum injection is still popular in GC, it has been almost totally supplanted in HPLC by high pressure injection... 

Bonded-phase wide-bore capillary columns permit relatively large-volume septum injections and can offer advantages of improved efficiency, reproducibility, and reliability. A 60 m x 0.53 mm i.d. fused silica capillary coated with the dimethylpolysiloxane SPB-1 (5 pm film thickness) programmed from 40°C to 200°C offers many advantages over packed column and PLOT systems. Improved resolution of very volatile compounds is obtained and, even with an initial temperature of 40°C, the total analysis time can be reduced to 26 min, and good peakshapes can be obtained even for alcohols (Figure 1). Moreover, splitless septum injections of up to 300 pi headspace can be performed with no noticeable effect on column efficiency hence, sensitivity is at least as good as that attainable with a packed column. Indeed, nowadays packed and PLOT columns are only used in specific applications or if a capillary GC is not available. 

Insert the tip of the needle barely through the septum. Inject S.O cm of gas into the instrument at a constant rate so that IS s is required for the injection. Determine the sulfur concentration by the procedure described in 10.2 to 10.7. 

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