Micro-traps

Efforts have been made, however, to extend the range or extent of samples that can be analysed by using a two-dimensional separation when used in heart-cut mode. This has been reported to include the use of numerous parallel micro-traps to essentially store the primary column eluent fractions ready for second-column separation, and the use of parallel second-dimension columns. 

Mitulovic, G., Smolnch, M., Chervet, J. R, Steinmacher, I., Kungl, A., and Mechtler, K., An improved method for tracking and redncing the void volnme in nano HPLC-MS with micro trapping columns. Analytical and Bioanalytical Chemistry 376(7), 946-951, 2003. 

An improved method for tracking and reducing the void volume in nano H PLC-M S with micro trapping columns. Anal. Bioanal. Chem. 376, 946-951. 

Due to the simple and open ion-trap structure, laser and molecular beams can be integrated more easily into the SCSI-MS technique (see Figures 10.2 and 10.3,[11]) than into a FT-ICR mass spectrometer with its large bulky super-conducting solenoid cooled cryogenically. Furthermore, because the SCSI-MS technique is compatible with micro-traps that are under development currently by the ion-trapping community (see for example Stick et al. [12]), this technique has the potential for possible future commercialization. 

These electrodes can be tested by appropriate software as SIMION [31] or other finite-element based programs. The suitability of the electrodes can be evaluated also by calculating their ability to store ions, in comparison with the ideal quadru-polar hyperboloidal geometry [32], to which the designers of micro traps aspire, and by dedicated experiment. 

We will now present some examples for often used micro-traps. 

The first example is a micro-trap within the evanescent field of a laser wave closely above the horizontal surface of a transparent solid at z = 0, illustrated in Fig. 9.22 [1161]. 

Since the conducting wires path can be produced as conductor paths on a microchip a micro-trap can be realized. In order to understand the trapping characteristics of such traps we will consider the form of magnetic fields for various wire configurations and start with the magnetic field... 

Another realization of a micro trap which consists of crossed linear conducting wires and as superimposed homogeneous magnetic field Boy in y-direction is shown in Fig. 9.27. The total magnetic field is similar to that shown in Fig. 9.26. The trap can be also realized as a micro trap with conducting wires deposited on a chip. The trap... 

A further realization of a micro-trap uses a specially formed magnetic field of a permanent magnet which has a minimum in the mid of the arrangement. 

The phase transition to EEC manifests itself by the sudden increase of the atomic density (Fig. 9.32), which can be monitored by measuring the absorption of an expanded probe laser beam (Fig. 9.33). As example of EEC in a magnetic trap Eig. 9.34 shows the spatial confinement of the atomic cloud in a Z-shaped Joffe-Pritchard micro-trap (see Sect. 9.1.8b), where a homogeneous magnetic field in y-direction is superimposed to the field produced by the current through the wire. The volume of the atomic cloud is an ellipsoid with rotational symmetry around the z-axis. 

Hold the tube horizontally and quickly seal this end in a micro-burner. Attach the tube (with the open end upwards) to a thermometer in the melting-point apparatus (Fig. i(c), p. 3) so that the trapped bubble of air in the capillary tube is below the surface of the bath-liquid. Now heat the bath, and take as the b.p. of the liquid that temperature at which the upper level of the bubble reaches the level of the surface of the batn liquid. 

Distillation of the ammonia. The ammonia which has been liberated quantitatively in the bulb F must now be distilled completely into the receiver J. The tap Ti on the steam-trap is therefore closed and tap T2 opened so that the steam is delivered into the bulb F, which at the same time is heated directly with the flame of a micro-Bunsen... 

Barrier Phenomenon. In red cell filtration, the blood first comes into contact with a screen filter. This screen filter, generally a 7—10-) m filter, does not allow micro aggregate debris through. As the blood product passes through the deeper layer of the filter, the barrier phenomenon continues as the fiber density increases. As the path becomes more and more tortuous the cells are more likely to be trapped in the filter. 

We have developed another bench for the measurement of the contrast value. Contrast measurement have been carried out on the MMA fabricated by Texas Instrument, in order to establish the test procedure (Zamkotsian et al., 2002a Zamkotsian et al., 2003). We can address several parameters in our experiment, as the size of the source, its location with respect to the micro-elements, the wavelength, and the input and output pupil size. In order to measure the contrast, the micro-mirrors are tilted between the ON position (towards the spectrograph) or the OFF position (towards a light trap). Contrast exceeding 400 has been measured for a 10° ON/OFF angle. Effects of object position on the micro-mirrors and contrast reduction when the exit pupil size is increasing have also been revealed. 

Han, j., Craighead, H. G., Separation of long DNA molecules in a micro-fabricated trap array. Science 288 (2000) 1026-1029. 

Figure 8.2 Different apparatus used for steu distillation. A aodified Gaman steam distillation apparatus A, steam generation flask B, sample chamber C, splash head D, condenser B, delivery tube F, separatory funnel. B = micro steam distillation apparatus A, boiling flask B, collection bulb C, water return arm D, Condenser. C - steam distillation apparatus using a Dean and Stark type trap. D = Nielsen-Kryger steam distillation apparatus.

The location of the position of double bonds in alkenes or similar compounds is a difficult process when only very small amounts of sample are available [712,713]. Hass spectrometry is often unsuited for this purpose unless the position of the double bond is fixed by derivatization. Oxidation of the double bond to either an ozonide or cis-diol, or formation of a methoxy or epoxide derivative, can be carried out on micrograms to nanograms of sample [713-716]. Single peaks can be trapped in a cooled section of a capillary tube and derivatized within the trap for reinjection. Ozonolysis is simple to carry out and occurs sufficiently rapidly that reaction temperatures of -70 C are common [436,705,707,713-717]. Several micro-ozonolysis. apparatuses are commercially available or can be readily assembled in the laboratory using standard equipment and a Tesla coil (vacuum tester) to generate the ozone. Reaction yields of ozonolysis products are typically 70 to 95t, although structures such as... 

Instrumental developments concern micro ion traps (sub-mm i.d.) [193], extension of the mass range, mass resolution and capture efficiency for ions generated externally. Fast separations at very low detection levels are possible by means of hybrid QIT/reToF mass spectrometry [194]. 

Fixed pathlength transmission flow-cells for aqueous solution analysis are easily clogged. Attenuated total reflectance (ATR) provides an alternative method for aqueous solution analysis that avoids this problem. Sabo et al. [493] have reported the first application of an ATR flow-cell for both NPLC and RPLC-FUR. In micro-ATR-IR spectroscopy coupled to HPLC, the trapped effluent of the HPLC separation is added dropwise to the ATR crystal, where the chromatographic solvent is evaporated and the sample is enriched relative to the solution [494], Detection limits are not optimal. The ATR flow-cell is clearly inferior to other interfaces. 

The possible mechanisms which one might invoke for the activation of these transition metal slurries include (1) creation of extremely reactive dispersions, (2) improved mass transport between solution and surface, (3) generation of surface hot-spots due to cavitational micro-jets, and (4) direct trapping with CO of reactive metallic species formed during the reduction of the metal halide. The first three mechanisms can be eliminated, since complete reduction of transition metal halides by Na with ultrasonic irradiation under Ar, followed by exposure to CO in the absence or presence of ultrasound, yielded no metal carbonyl. In the case of the reduction of WClfc, sonication under CO showed the initial formation of tungsten carbonyl halides, followed by conversion of W(C0) , and finally its further reduction to W2(CO)io Thus, the reduction process appears to be sequential reactive species formed upon partial reduction are trapped by CO. 

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