Inlet systems split inlets

Inlet System, (splitting type)—Split injection is necessary to maintain the actual chromatographed sample size within the limits required for optimum column efficiency and detector linearity. 

General texts on GC are numerous [118,119] narrow-bore GC was addressed by van Es [120]. Sample introduction techniques and GC inlet systems have been reviewed [25,90] and split/splitless [121] and on-column injection [122] were considered specifically. Stationary phases [123], multiple detection [103], derivatisation [124,125], and quantitative analysis in GC [109] have been described. High-speed GC has recently been reviewed [126]. For a compendium of GC terms and techniques, see Hinshaw [127]. 

In early GC-MS with paeked GC columns eluting several tens of milliliters per minute most of the flow had to be separated before entering the ion source to prevent the vacuum system from breakdown. [4,29,34] This was either effected by a simple split to divide the effluent in front of the inlet system by a faetor of about 1 100 or by means of a more elaborate separator, the jet separator being the best... 

Septum bleed is worse than in split mode because all the flow goes through the column. Most of the splitless inlet systems that are presently available use a vented septum technique to avoid this problem. 

Fig. 15. Schematic layout of the HPLC chip a layout of the channel system, b cross section along the channel axis, c cross section along the detector cell axis. IS sample and mobile phase inlet, S split injector, OS outlet for rejected sample and mobile phase, C separation channel, F frit, D optical detector cell, OD outlet to waste, P positioning grooves for optical fibers (reprinted with permission from [84]. Copyright 1995 John Wiley)...

Fig. 12. Schematic illustration of hydrodynamic relaxation achieved in a split inlet system (iabove) and a frit inlet system (below). Reproduced from [160] with kind permission of the American Chemical Society...

Another popular and efficient inlet system for the LC/MS combination is the atmospheric pressure chemical ionization process. This system has some similarity to the electrospray interface and can also cope with flow rates of up to 2 ml/min. and thus the total column eluent can be utilized without splitting the flow. 

Figure 6-11 Flow diagram of a GC inlet system for split injection.The head pressure and total flow are adjusted to achieve a desired flow rate in the column and a fractional spilt between the column and the spilt vent. GC, Gas chromatography.

Phthalates can be present in the chromatographic system. The most important contamination is located in the inlet and gas supply system. Split or splitless inlets may contain septa, liners and o-rings that are contaminated with phthalates. Another critical factor is the quality of caps for autosampler vials. These caps can also contain phthalates. 

Because of the variety of columns and samples that can be analyzed by GC, several injection techniques have been developed. The packed inlet system is designed mainly for packed and wide-bore columns. However, an adapter can be used to enable capillary columns to be used. When injection is carried out in the on-column mode, glass wool can be used for packing the injector. For capillary GC, spht technique is most common, which is used for high concentration samples. This technique allows injection of samples virtually independent of the selection of solvent, at any column temperature, with httle risk of band broadening or disturbing solvent effects. The sphtless technique, on the other hand, is used for trace level analysis. The so-called cold injection techniques (on-column, temperature programed vaporization, cooled needle split) have also been recently developed. " " ... 

On using split inlet systems the injection of small sample volumes will provide very go results however, direct injection without splitting was not successful. 

As mentioned previously, when a known sample size is required, as in the external standardization technique, the measurement of that sample size will generally be the limiting factor in the analysis. However, improper sample injection can introduce into the analysis errors other than those pertaining to sample size. Thus it will be beneficial to examine the various methods of sample injection and both types of error associated with them. A common error source in split-injection systems comes from the discrimination of components in the mixture on the basis of their boiling point differences. The problem can be attributed to in-needle fractional distillation, nonevaporative transport (mist) that bypasses the column inlet, or poor mixing with the mobile phase when low split ratios are used. Errors associated with the inlet system are covered in detail in Chapter 9, Inlet Systems for Gas Chromatography. ... 

When using a split inlet, there are several flows that provide the exact injected sample amount. The most important of these is the split ratio, which is the ratio of the volumetric flowrate at the split purge vent to the volumetric flowrate in the GC column. Classically, this was measured manually, using a flowmeter to obtain the purge vent flow and by injecting a nonretained substance to obtain the column flowrate. With electronically controlled systems, these values are... 

A HP-5790A gas chromatograph equipped with a split/splitless capillary inlet system and a flame ionization detector are used. A fused-silica capillary column with crosslinked 5% phenyhnethylsilicone gum phase HP-5, 25 m x 0.20 mm i.d., 0.33 pm film thickness, is used. Nitrogen is used as a carrier gas at an inlet pressure of 100 kPa. The oven is operated isothermally at 60°C for 0.5 min after injection, heated at 30°C/min to 200°C, then at 60°C/min to 250°C, and then... 

Programmed-temperature vaporizer, an inlet system designed to perform a temperature programmed injection, a cold injection system for direct liquid injection for split or splitless injection, solvent spHt technique and cryo-enrichment. 

Sample Met System—The sample inlet sy m must be capable of operating continuously at a temperature up to the maximum column temperature employed. A splitting iqjector is recommended, capable of splitiess or accurate split control in the range of 10 1 to 50 1. An automated gas sampling valve is also recommended. The inlet system must be well conditioned and evaluated frequently for compatibility with trace quantities of reactive sulfur compounds. 

Sample Introduction System—Any system capable of introducing a representative 0.1 to 1.0-pL liquid sample into the split inlet device of the gas chromatograph. Microlitre syringes, autosamplers, and liquid sampling valves have been used successfully. The split injector should be capable of accurate split control in the range from 10 1 to 500 1. 

Make-up gas Make-up gas rate Splitless mode Purge off Purge on Purge vent Split vent Sample injection Injector inlet system Detector... 

A differential pressure controller acts in split range on the inlet control valve and the bypass valves. The differential pressure governor is retained as the standby and backup system. 

Figure 16-16 shows the performance characteristic of a split-shaft turbine where the only power output limitation is the maximum allowable temperature at the inlet of the turbine section. In actual practice a torque limit, increased exhaust temperature, loss of turbine efficiency, aud/or a lubrication problem on the driven equipment usually preclude operating at very low power turbine speeds. The useful characteristic of the split-shaft engine is its ability to supply a more or less constant horsepower output over a wide range of power turbine speeds. The air compressor essentially sets a power level and the output shaft attains a speed to pnivide the required torque balance. Compressors, pumps, and various mechanical tinvc systems make very good applications for split-shaft designs. 

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