Capillary inlets, types

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... 

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. 

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. 

There are several types of nebulisers, for example the concentric quartz system (Fig. 3.9) or cross-flow system (Fig. 3.10) the tips of which are made from synthetic material or precious stones. The first system can be subject to blockage with solutions containing as little as 0.1% of dissolved salts due to its small capillary inlet. The second system is less fragile and is resistant to corrosion from solutions containing hydrofluoric acid. 

Interfacing micro-LC and MS via a capillary inlet interface coimected to a GC-MS jet separator was described in 1978 by Takeuchi et al. [55]. In the period until 1982, this system was subsequently developed towards a vacuum nebuhzer, in which the column effluent is pneumatically nebulized into a modified jet-separator type of device [56-57]. The instrumental developments of the vacuum nebulizer interfaces are discussed in Ch. 4.3. Pneumatic nebulization of column effluents directly into the Cl somce was described by a number of groups [58-61]. A so-called helium interface for the introduction of organic solvents was described by Apffel et al. [59]. It was primarily applied to the analysis of pesticides in aqueous samples. Although the system was commercially available, it did not find wide application. 

Fig. 6.11 A schematic drawing of new ion attachment mass spectrometer with the capillary sample inlet and a vacuum envelope with a wall separating ELS chamber fiom mass analyzer chamber. This capillary inlet is fixed on the front flange of the vacuum envelope. 1C ionization chamber, ELS electrostatic lens system, QMS quadrupole mass spectrometer, TMP turbomolecular pump, RP rotary pump. The vacuum envelope is pumped by a single 230 L sec" turbomolecular pump with two ISO-100 inlet flanges (Pfeiffer-Vacuum TMH 261-250-010) plus a 250 mL min" rotary pump. Ionization chamber is closed-type, with a 1 mm < ) aperture through which ionic species are passed. The typical operating conditions are IS pressure with nitrogen gas used as a buffer gas, 40 Pa pressure of ELS chamber, 8x10" Pa, pressure of the QMS chamber, 8 xlO"" Pa. (Reprinted with permission from Ref. [93]. 2012, Springer)...

Sample injection in CE requires the introduction of very small amounts of analyte at the capillary inlet with high precision. All commercial instruments offer electromigration injection and at least one type of displacement injection. 

Fig. 3a-e. Supermolecular structures of polymers crystallized in various force fields a structure of the shish-kebab type, b structure formed during crystallization in a capillary with a conical inlet and c structure of a polymer crystallized at hydrostatic compression at 4 x 108 Pa... 

The use of NMR for studying chemical reactions began about 30 years ago. In 1972, Asahi and Mizuta [11] reported a study of the performance of five different types of flow cells used in NMR studies of chemical reactions (a) a straight glass tube, (b) a pipette-type tube, (c) a spiral capillary in a conventional sample tube, (d) a jet in the base of a conventional tube, and (e) a conventional spinning tube with an inlet at the base and an outlet at a height of about 50 mm. The best results were... 

Different types of instrumentation have been developed to introduce Hquid samples into the MS. Since Fenn has shown that molecular ions can be formed from liquids sprayed at atmospheric pressure in high electric fields, electrospray ionization (ESI) MS has gained increasing popularity for the analysis of biological samples [56]. In an electrospray inlet, the liquid sample is usually emitted as a spray from a capillary at a high potential compared to the mass analyzer into the electric field in front of the mass analyzer (Fig. 8). 

Figure 6.13. Inlet techniques for capillary columns (Hewlett-Packard Co.-Multipurpose glass inlet system). (A) Splitter type. (b) Splittless type with septum purge. ...

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