Polyimide-coated fused silica capillarie

The concept of using decoupled coils has been developed further by Li et al. [19]. In this case, an RF switch was used for time-domain multiplexing of the signals into a single receiver channel. A four-coil system was constructed for operation at 6 T in a wide-bore (89 mm) magnet. Each coil was fabricated by using 17 turns of 50 pm diameter copper wire wrapped around a 180 pm i.d., 355 pm o.d., polyimide-coated fused silica capillary, giving an observe volume... 

Nebulizer sampie tube (polyimide coated fused silica capillary)... 

Proper cutting of the column and retention gap is critical. Square, clean cuts minimize flow disturbances. A cleaving tool for cutting polyimide-coated fused silica capillary tubing always should be used (Figure 20-33). Make the cuts after the ferrules have been installed onto the tubing. 

A PACE 5000 series Capillary electrophoresis instrument (Beckman, Fullerton, CA, USA) may be used for CE/MS. For CE, externally polyimide-coated fused-silica capillaries of 75 pm inside diameter (ID) and 375 pm outside diameter (OD) are recommended. These capillaries may be obtained from BGB Analytic Vertrieb (Essen, Germany). 

Capillary electrophoresis was carried out with a Capel 105 system (LUMEX, Russia) equipped with a UV monochromator (190-380 nm). A polyimide-coated fused silica capillary with an inner diameter of 75 jj.m, an outer diameter of 375 m and a total length of 61.5 cm (52 cm to the detector) was used. Data control was performed with personal computer software for Windows 95. The voltage used in all experiments was 20 kV (cathodic detection side). Between runs, the capillary was rinsed at high pressure for 3 min with 0.5 M NaOH and then with distilled water and flushed with the carrier buffer. 

We first consider the case of an open, but buffer-filled capillary column (Type A, shown schematically in Fig. 1), which is similar to that used in capillary electrophoresis. This is typically made of polyimide-coated fused silica. Let its length be L (cm) with an interior cross-sectional area as A (cm ). If a voltage, V (Volts), is applied across the ends of the column and the current I (Amps) is measured, the resistance, R (Ohms), of the buffer can be calculated from Ohm s law, as given in Eq. 1 ... 

Commercial instruments are mostly available with a UV-Vis detector and some with a fluorescence detector. When polyimidefused silica capillaries are used, the polyimide coating needs to be removed in the detection area. Fiber optics are used in most detectors. 

A third type of protective outer coating, stainless steel, for fused silica offers an alternative to aluminum-clad fused silica for elevated column temperatures. This technology is the inverse of that for polyimide-clad fused-silica capillary where a layer of fused silica is deposited on the inner surface of a stainless capillary. In Figure 3.19 scanning electron micrographs are displayed to compare the rough surface of stainless steel with the smooth surface of untreated fused silica and the surface of stainless steel after a micron meter layer of deactivated fused silica... 

Figure 28 Electrokinetic separation of the niacin derivatives in the presence of SDS. Conditions applied voltage, 15 kV sample injection, injected by raising the positive end of the capillary about 4 cm higher than the other end capillary, a polyimide-coated fused-silica (70 cm X 50 xm i.d.) micellar solution, 0.15 M SDS in 0.02 M borate-0.01 M KOH (pH 9.1) detection wavelength, 210 nm. 1, Isonicotinic acid hydrazide 2, Nam 3, pyri-dine-3-methanol 4, 6-AN 5, MNA 6, pyridine-3-aldehyde 7, pyridine 8, 3-acetylpyri-dine 9, thionicotinamide 10, NiA 11, pyridine-3-sulfonic acid 12, P-picoline 13, nicotinic acid ethyl ester. (From Ref. 71.)...

The most applied detectors are based on UV or fluorescence detection, both direct and indirect. For this purpose, a window has to be made on the polyimide coating of the fused silica capillary, simply by... 

Ti and To are the inner and onter radins of the fused-silica tnbe refers to the onter radins of the polyimide coating of the capillary tube Kj and are the thermal conductivities of the electrolyte solution and of the capillary wall, respectively... 

One can find 1-mm glass-lined stainless steel columns or fused silica capillary columns. Fused silica is available with 75-yU.m, 100-/xm, or 320-/xm internal diameter by 20-cm, 25-cm, or 30-cm length. Fused silica is a glass tubing with an outside polyimide coating to prevent breakage. 

Capillary electrophoresis is an instrumental technique for automating electrophoretic analyses.66 It is carried out in fused silica capillaries with internal diameters of 25-100 tm. The capillaries are coated with an external layer of polyimide for mechanical strength. The small internal diameter and high surface-to-volume ratio allow for efficient heat dissipation from the capillaries, enabling separations to be carried out at very high field strengths (up to 1000 V/cm). 

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