Voltage gradient, reproducibility

Fig. 2.15. Schematic automated isocratic and gradient elution nemo-liquid chromatograph/ capillary electrochromatograph according Alexander et al. (reproduced from Ref. [44] with permission of the publisher). 1, high-voltage power supply (negative polarity) 2, platinum electrode 3, outlet reservoir vial 4, UV detector with on-column flow cell 5, nanocolumn 6, two-position switching valve 7, jack stand 8, fused-silica make-up adapter (split device) 9, ground cable 10, internal loop micro-injection valve 11, plexiglas compartment 12, autosampler 13, dynamic mixer 14, micro-LC pumps.

Fig. 8.3. Isocratic (a) and gradient (b) separation of PTH amino acids. Column, 250 x 0.075 mm i.d. packed with 3.5 p.m/80 A Zorbax ODS eluents, (A) 2 mmol/1 ammonium acetate, pH 7.0, (B) 2 mmol/1 ammonium acetate, pH 7.0, 90% acetonitrile isocratic elution with 30% B in (a) gadient elution with 30-80% B in 5 min, followed by 80% for 5 min in (b) flow rate of mobile phase through inlet reservoir, 100 pl/min applied voltage, 15 kV Detection, ESI-MS, m/z 100-2000, 0.5 s/spectrum integration time sheath liquid, 1 mmol/1 ammonium acetate, pH 7.0, 90% methanol, 3 pl/min injection, electrokinetic, 2 kV, 2 s sample, PTH-asparagine, PTH-glutamine, PTH-threonine, PTH-glycine, PTH-tyrosine, PTH-alanine (in order of elution). (Reproduced from ref. [82] with permission of Elsevier Sciences B. V.).

Fig. 10.18. The separation of eighteen-amino-acids samples by pCEC. Column, PC-C18, 3 pm, 130 mm x 75 pm i.d. mobile phase (A), 50 mM sodium acetate-1% N,N-dimethyl-formamide, pH 6.4 (B), 50% acetonitrile in water linear gradient, 60-5% A in 6 min and kept at 5% 3,000V positive voltage across the column and 1,000 psi pressure were added on column during the separation flow-rate, 50 pl/min 20°C detection, 360 nm 20 nl injection. (A), 2 pg/ml of derived eighteen-amino-acids sample solution (B), 2 pg/ml of derived eighteen-amino-acids standard solution. Reproduced with permission from Ru et al. [197],...

Fig. 4 The total ion chromatography (TIC) of the separation of a tryptic digest of chicken ovalbumin with a sample injection amount of 12 pmol corresponding to the original protein [52]. Column length, 6 cm. Conditions 20 min, 0-40% acetonitrile gradient 1000 V applied voltage with a 40-bar supplementary pressure. (From Ref. 52 reproduced with permission of the authors and the American Chemical Society.)...

Figure 3.11 Chromatograms extracted from the TIC recorded in negative-mode of PCs and PAs dimers and trimers of a wine LC/ESI-MS analysis. Analytical conditions C18 (125 x 2 mm i.d., 3(r,m) narrow-bre column ion spray voltage —4000 V, orifice voltage —60 V. Binary solvent composed of A) aqueous 2% formic acid and B) acetonitrile/H20/formic acid (80 18 2v/v/v). Gradient program from 5% to 30% of B in 20min, 30-50% B in lOmin (flow rate 200p.L/min, flow rate in the ESI source 50p,L/min). (Reproduced from ]. Agric. Food (. hem., 1999, 47, 1023-1028, Fulcrand et al., with permission of American Chemical Society)...

Constant cun ents are not obtained in reasonable periods of time with a planar electrode in an unstirred solution because concentration gradients out from the electrode surface are constantly changing with time. In contrast, the DME exhibits constant reproducible currents nearly instantaneously after an applied voltage adjustment. This behavior represents an advantage of the DME that accounted for its widespread use in the early years of voltammetry. 

Figure 8 shows power output characteristics of FGM thermoelectric sample shown in Figure 7. Voltage-Current plot and Power-Current plot show the difference in the direction of temperature gradient applied to the sample. Output power with forward temperature gradient is 6% larger than that with reversed temperature gradient. The most likely explanation of this asymmetry can be found in a graded structure of the sample. But there is room for argument on this result because there seems a problem on reproducibility of both the material properties and the soldering technique. In this study the expected enhancement on conversion efficiency is rather small, it seems necessary to solve the problem mentioned above.

Figure 7.7 Schematic diagrams of a channel electron multiplier. (a) principle of operation of a CEM for detection of positive ions the electroding at each end consists of a thin band of metal deposited to provide electrical contact, and the potential gradient along the length of the device is developed from the external high voltage supply applied along the intrinsic resistance of the doped lead glass. Reproduced from Wiza, Nucl. Instrum. Methods 162,587 (1979), copyright (1979), with permission from Elsevier, (b) A cross-section of the surface structure of a CEM. Reproduced from literature provided by Burle ElectroOptics Inc, with permission.

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