Injection in split mode

Injection in the split mode is used for the analysis of concentrated solutions. The injection is performed at a high temperature, above the boiling points of the analytes and solvent. The sample is rapidly inserted in the injector where it is instantly vaporized and mixed with the carrier gas. A solenoid valve controls the proportion of the gas mixture (split ratio) that escapes through a leak. This procedure allows one to evacuate of part of the gas flow to decrease the amount of sample that enters the column, thus avoiding the saturation of the stationary phase (refer to Section 1.2.2.1). 

Although easy to put into place, the split mode presents an important discrimination problem when the solution to be analyzed contains compounds with very heterogeneous volatilities. The less well vaporized heavy products tend to escape through the leak whereas the light products mainly r ain in the injector. 

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Figure 1.6 ICH Class 2 solvents measured using GC. Purification of pravastatin sodium by preparative liquid chromatography. Reprinted from [15], copyright 2004, with permission from Elsevier. (Column 30 m X 0.53 mm i.d. 3 pm OVI-G43 (Supelco) carrier gas helium at 5 ml/min injection in split mode total flow 25 ml/min injector temperature 140 C flame ionization detector temperature 25C C and oven temperature 40°C for 20 min, to 240°C at 10°C/min, maintain at 240 C for 20 min. The components are 1 methanol, 3 acetonitrile, 4 dichloromethane, 5 hexane, 6 cw-l,2-dichloroeth-ylene, 7 nitromethane, 8 chloroform, 9 cyclohexane, 13 1,2-dimethoxyethane, 15 1,1,2-trichloroethyl-ene, 16 methylcyclohexane, 17 1,4-dioxane, 18 pyridine, 19 toluene, 20 2-hexanone, 21 chlorobenzene, 22 ethylbenzene, 23 m-xylene, 24p-xylene, 25 o-xylene, and 26 tetralin. The solvents are dissolved in DMF and heated at 80X for 60 min, and a sample of the headspace is injected.)...

Major volatile compounds were analyzed by direct injection (Sanchez-Palomo et al., 2006) of a HP-5890 GC with a FID detector, using a CP-Wax-57 capillary column (50 mx0.25mm i.d. 0.25 pm film thickness). The oven temperature program was 40 C (5 min)-4 °C/129 min-120 °C. Injector and detector temperature were 250 and 280 °C, respectively. One microliter (1 pi) was injected in split mode, spht ratio 1 15. Carrier gas was He (0.7 ml/min). 

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