Parallel spray interfaces

Another way to speed up HPLC that does not interfere with the existing gradient separation method is by parallel operation of several HPLC columns. The development in this direction started a couple of years ago when fast gradient separation was first combined with mass spectrometry-based detection. Parallel column operation was achieved by a single pumping system and a splitter tee that transferred the gradient flow onto two HPLC columns. The effluent of the two columns was simultaneously sprayed into a modified ion spray interface of a quadrupole mass spec-trometer. From the overlay chromatogram both desired and previously known compounds were identified after their molecular ions were filtered from the total ion current (TIC). In this first system, however, it was difficult to enhance the parallelization, and the detection system created a bottleneck. ... 

The solution to be electrosprayed is passed through the electrospray capillary (ESC) by means of a motor driven syringe. Some of the spray containing the ions then enters the pressure reducing capillary (PRC) leading to the forechamber (FCH) of the ion source. The exit tip of the PRC directs the gas jet in a direction parallel to the bottom of the FCH, i.e. across the interface plate (IN). An orifice of 4 mm diameter in the interface plate connects the FCH to the reaction chamber (RCH). The ions in the jet exiting from the PRC are deflected out of the jet towards this orifice and into the RCH by means of an electric field applied across the FCH. A weak field is also applied across the RCH. At the bottom of the RCH a small orifice, 100 pm diameter, allowed some gas and ions to leak into the vacuum of the mass... 

Figure 5.28 Cross-sectional SEM images of vacuum-plasma sprayed (VPS) coatings type Cl (a) and C2 (b) after immersion in HBSS for 7 days, showing a network of microcracks and debonding along macrocracks parallel to the interface (Vu and Heimann, 1996).

Coupling Other Modes of CE with MS Because of practical difficulties, the coupling of other modes of CE with MS is not very common. However, some attempts have been made to couple CIEE with ESI-MS [80,91], CEC-MS [92], CGE-MS [93], and MEKC-MS [83,94,95]. A simple MEKC-MS interface is described (Figure 5.15). This interface comprises two parallel capillaries, one for separation and the other for makeup liquid. Both have the dimensions 50 p,m i.d. X 155 p,m o.d. and have tapered ends. The capillaries are housed in a larger capillary (530 p,m i.d. x 690 tim o.d.) with a beveled edge. The larger capillary serves as a nano-ESI sprayer. A makeup liquid allows control of the composition of the spray solution. 

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