, a split injection system is necessary, a diagram of which is shown in figure 8. Figure 8 The Split Injection System The basic difference between the two types of injection systems is that the capillary column now projects into the glass liner and a portion of the carrier gas sweeps past the column inlet to waste. As the sample passes the column opening, a small fraction is split off and flows directly into the capillary column, ipso facto this device is called a split injector. The split ratio is changed by regulating the portion of the carrier gas that flows to waste which is achieved by an adjustable flow resistance in the waste flow line. This device is only used for small diameter capillary columns where the charge size is critical

) and these are values measured at atmospheric pressure with an inlet/outlet pressure ratio (g) of 2. Consequently, the sample volume at the inlet pressure will be proportionally smaller. The large column, however, can accept more reasonable sample volumes and at k'=5 on the 300 mm column a sample volume of nearly 8 ml can be tolerated. However, as the smaller columns provide both the fastest analysis and the greatest resolution, small sample volumes must be employed. This is achieved by using split injection systems. A diagram of a split injector is shown in figure 3. Figure 3 The Split Injector

basic drugs, but with a different set of operating conditions.. Its strong capability to be polarized by strong polar groups on the solute lead to strong polar-induced polar interactions that provided good relative retention ratios between the different components of the mixture and thus more than adequate resolution. The column was 25 m long, 0.22 mm I.D. and carried a film of stationary phase 0.25 mm thick. The initial temperature was 100ûC which was raised to 300ûC at a rate of 10ûC/min.. A split injector was used (split ratio 20:1) to place the sample on the column. Helium was used as the carrier gas at an inlet pressure of 150 kpa. The detector employed was, again, an FID maintained at a temperature of 380ûC. The results obtained for the neutral-acidic drug mixture is shown in figure 33. It is seen that again an excellent separation of the drugs is realized, with baseline separation obtained between all the components. In this case the separation is achieved in less than 25 min.

Drugs     The stationary phase used was BPX35 (also a proprietary product of SGE Ltd.) and consists of a dimethyl silicone polymer containing 35% of a phenyl derivative. The relatively high concentration of phenyl groups in this stationary phase, confers a strong interactive capacity for solute polar groups. The column was 25 m long, 0.22 mm I.D. and carried a film of stationary phase 0.25 mm thick. The initial temperature was 100ûC which was raised to 325ûC at a rate of 5ûC/min. A split injector was used (split ratio 20:1) and 0.5 ml of sample was placed on the column. Helium was used as the carrier gas at an inlet pressure of 150 kpa. The detector employed was an FID maintained at a temperature of 380ûC. The separation obtained is shown in figure 32   It is seen that more than adequate resolution of each drug was obtained and, thus, could be very useful for forensic purposes. The analysis time is a little long (cf 50 min.) but is, nevertheless acceptable considering

introduction of the diphenyl groups contributes more to phase temperature stability than it does to solute selectivity. The column was 30 m long, 250 mm I.D. carrying a film 0.25 mm thick of stationary phase. Helium was used as the carrier gas at a linear velocity of 25 cm/sec(set at 155˚C). The column was held isothermally for 8 min. at 75˚C and then programmed up to 200˚C at 4˚c/min. and finally held at 200˚C for 4 min. The sample volume was 0.5 ml which was split at 100:1 ratio allowing about 5 mg to be placed on the column. It is seen from figure 43 that a very good separation is obtained that convincingly confirms the complex nature of the essential oil. In practice, however, the net flavor or odor impact can often be achieved by a relatively simple mixture of synthetic compounds

to ensure the complete elution of the higher boiling components. An excellent separation is obtained giving clearly separated peaks for the marker compounds which are of importance in fuel evaluation. Nevertheless, due to the complexity of the sample, exceedingly high efficiencies were necessary and so, the analysis time was about 100 min. Long analysis times are directly related to the use of long columns The complete analysis was carried out using only 0.1 ml of gasoline with a split of 100:1 at 250˚C (ca 1 mg) confirming the remarkable sensitivity of the FID for general analysis