Cemaldi

As with cLC-MALDI-MS, CE-MALDI-MS is still under development and several designs have been reported. Offline deposition onto a continuously moving target was one of the earliest designs used.[7] In another type of off-line coupling, a piezoelectric flow-through microdispenser was connected to a CE system.[8] Pressure pulses cause the microdispenser to eject droplets with volumes of 60100 pL collected at the target plate. This decreased the spot size to ~ 400 pm in diameter, compared to a diameter of 1-4 mm for the dried-droplet method. The sensitivity increased as well as the detection limits (100 attomol for peptides).

More recently, on-line interfacing has been performed by depositing the capillary effluent onto a moving surface under vacuum inside the MS. Moving surfaces used include a rotating ball,[9] a wheel,[10] and a moving tape.[11] In the moving-tape design (Fig. 3), the CE capillary outlet is juxtaposed with an infusion capillary in a liquid junction. The liquid junction allows the circuit for the electrophoresis to be separated from the MS. In addition, the gap in the capillaries is used to mix matrix with capillary effluent. Flow from the separation capillary across the junction is maintained by electroosmosis (100400 nL/min). The infusion capillary transfers sample and matrix mixture into the vacuum of the mass spectrometer and is in contact with the tape. Small volumes of deposited solvent are rapidly evaporated within the vacuum region, leaving fractionated sample crystallized with matrix deposited as a continuous trace 40 pm wide on the tape. The tape transfers the sample to the laser irradiation region for analysis by MALDI-TOF-MS. The laser spot is wider (100 x 100 pm) than the deposited trace; therefore, a full segment of the trace is irradiated with each shot. This arrangement yields extremely high sensitivity; detection limits of 10 _18 mol for peptide standards demonstrated. In addition, the reproducibility of 15% was very good when compared to 20-90% for conventional MALDI experiments. The instrument is robust enough to operate for 24 hr without interruption. In principle, this

ION SOURCE CHAMBER repeller

PEEK -V liner

| repeller center (tape guide)

^propelled shaft

Fig. 3 Schematic of the on-line coupling of CE to MALDI. (From Ref. [11].)

| repeller center (tape guide)

^propelled shaft

Fig. 3 Schematic of the on-line coupling of CE to MALDI. (From Ref. [11].)

system could also be operated in parallel with multiple capillaries and the laser directed toward different traces on the same tape.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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