Capillary inlets

We deal here with the stability of flow in a heated capillary tube when liquid is evaporating on the meniscus. The capillary, as shown in Fig. 11.1, is a straight vertical pipe with diameter d and length 1. The wall heat flux is uniform = const. The thermal conditions on the capillary inlet and outlet are ... 

Distance between syringe needle tip and capillary inlet... 

The simplest type of two-dimensional gas diromatography for heart cutting or trace enrichment using a packed precolumn and a capillary column is shown in Figure 8.16 [205]. Almost any modem gas chromatograph could be converted into a similar unit with the addition of a few auxiliary components. Preliminary separation t2dces place on the packed column, the effluent from which is directed either to a vent or to the capillary inlet by the Deans switch, nie effluent reaching the capillary inlet is split three ways. One portion passes to a detector used to monitor the preseparation, a second portion enters the cap Bry column and is... 

In CZE, the capillary, inlet reservoir, and outlet reservoir are filled with the same electrolyte solution. This solution is variously termed background electrolyte, analysis buffer, or run buffer. In CZE, the sample is injected at the inlet end of the capillary, and components migrate toward the detection point according to their mass-to-charge ratio by the electrophoretic mobility and separations principles outlined in the preceding text. It is the simplest form of CE and the most widely used, particularly for protein separations. CZE is described in Capillary Zone Electrophoresis. ... 

Sample injection is an event common to all modes of CE except CIEF, and the most relevant aspects of this step are described here. Because the total volume of the capillary is very low, sample injection in CE requires the precise introduction of very small amounts of analyte at the capillary inlet. There are two basic procedures for sample injection electromigration and hydraulic displacement. All commercial instruments offer electromigration, or electrophoretic, injection and at least one type of displacement injection. 

In electrophoretic injection, the capillary inlet is immersed in the sample solution and a voltage is applied for a determined period of time. The amount of sample introduced into the capillary depends on the voltage and the time it was applied. Sample injection is a compromise between detection and resolution, and its parameters are often best determined experimentally. If detection is not a problem, resolution can be greatly improved by maintaining the sample plug as narrow as possible. If EOF is present, sample ions will be introduced by a combination of electrophoretic mobility and EOF under these conditions, this injection mode is generally termed electrokinetic injection. 

Step 6 The sample is preferentially injected by hydrodynamic mode since in this way a representative amount of sample solution is introduced in the capillary inlet. The outlet of the capillary is maintained in the dip-vial. 

BGE dip After sample injection, dip in the capillary inlet into a BGE vial that is not the same vial as the run vial to reduce carryover and/or to increase peak symmetry. Check how often this dip vial needs to be replenished. 

Figure 3.7 Determination of the enantiomeric purity of SB-214857 API using CD-modified CE. Distomer content measured at 0.06% by area. (Conditions plain fused silica capillary, 50 cm effective length, 57 cm total length, 75 pm i.d. buffer lithium phosphate [pH 3.0, 100 mM] containing 0.05% (w/v) hydroxyethy[cellulose and 1.5 mM dimethyl- 8-CD voltage 30 kV temperature 20°C detection UV at 200 nm sample preparation 0.2 mg/ml in water sample introduction 5 s at 35 mbar, capillary inlet at anode.)...

The resulting spectra from El usually contain a number of fragments, providing extensive structural information about the analyte. A disadvantage of the observed fragmentation is eventually occurring isobaric overlay from different compounds in the analysis of sample mixtures, which often requires a separation step prior to the MS analysis. For this purpose the coupling of a GC with the ion source of the mass spectrometer via capillary inlet is a well established technique. Volatiles can be selectively introduced into El mass spectrometers via pervaporation membranes. The principle and application of this technique, called membrane introduction (MI) MS was recently reviewed [45]. The accuracy of intensity ratio measurements by El MS is about 0.1 -0.5% [4,8]. 

M NaOH if migration times become erratic. Buffer in both reservoirs should be replaced periodically because ions become depleted and electrolysis raises the pH at the cathode and lowers the pH at the anode. The capillary inlet should be 2 mm away from and below the electrode to minimize entry of electrolytically generated acid or base into the column.30 Stored capillaries should be filled with distilled water. 

Gas chromatograph (e.g., Model HP 6890, Hewlett Packard) fitted with a flame ionization detector and a dedicated cool on-column capillary inlet BPX-70 open tubular fused silica column (25 m long, 0.33 i.d., and 0.25-p.m film thickness SGE Chromatography Products)... 

There are several types of capillary inlets in use today which can be divided into two categories direct on-column injection and split/splitless injection techniques. 

J. Hinshaw, Capillary inlet systems for gas chromatographic trace analysis, J. Chromatogr. Sci., 26 142-145 (1988). 

---