Current total electrospray

Figure 1.7 (a) Total electrospray current (ampere) with increasing concentration of analyte morphine hydrochloride. Because of the presence of impurity ions (Na and NH ) at 10 M, /total remains constant up to the point where the analyte reaches concentrations above 10 M. (b) Analyte MorH ion intensity (corrected for mass-dependent ion transmission, Tm, of... 

Fig. 3 LCMS Analysis of Fusion rCRALBP (A) RP-HPLC ultraviolet profile ( 220nm) froHi analysis of 1.5 (ig fusion human rCRALBP on a 50- X Vydac C18 column (lx 250 mm) at 50 lL/min usmg the indicated gradient. Solvent A was 0 1% trifluoracetic acid (TFA) and solvent B was 84% acetonitrile, containing about 0.07% TFA. (B) Reconstructed total ion current from electrospray-mass spectral analysis of the fusion rCRALBP liquid chromatography shown in A. (C) Electrospray-mass spectrum of fusion human rCRALBP indicating the presence of a protein of = 39,114 4 (calculated = 39,110). The deconvoluted spectrum is shown in the inset.

The fundamental piece of information on which the subsequent spectral analysis is based is the total-ion-current (TIC) trace. Such a trace, obtained from the LC-MS analysis of a pesticide mixture, is shown in Figure 3.13, together with the UV trace recorded simultaneously. For the purposes of this discussion, the HPLC and MS conditions used to generate the data, other than the fact that electrospray ionization was used, are irrelevant. 

Figure 5.27 Selective detection of lactolated peptides from a tryptic digest of / -lacto-globulins by LC-electrospray-MS-MS, showing (a) the total-ion-cnrrent trace in full-scan mode, and (b) the total-ion-current trace in neutral-loss-scanning mode. Figure from Selective detection of lactolated peptides in hydrolysates by liquid chromatography/ electrospray tandem mass spectrometry , by Molle, D., Morgan, F., BouhaUab, S. and Leonil, J., in Analytical Biochemistry, Volume 259, 152-161, Copyright 1998, Elsevier Science (USA), reproduced with permission from the publisher.

Figure 13 Detection of 6 ppm (w/v) of a mixed ethoxylated amine by ESI (electrospray) LC-MS. Total ion current (TIC) trace.

Fig. 5.8 Analysis of a Narcissus extract by HPLC coupled to the MS-based AChE assay. MS instrument Q-ToF2 (Waters) equipped with a Waters Z-spray electrospray (ESI) source, (a) Total ion current (TIC) (b) product trace (choline) m/z 104 (c) substrate trace (acetylcholine) m/z 146 (d)...

Fig. 7A-D. SFC/ELSD/CLND/MS analysis of an equimolar mixture of Tolbutamide, Fmoc-Ile-OH, Mebendazole, and Prednisolone. The column flow rate was 5 ml/min. A portion of the column effluent was split to each of the three detectors (CLND, 200 pl/min ELSD,200 pl/min MS, 100 pl/min). A makeup flow of 50/50 MeOH/H20 (300 pl/min) was added to the flow stream diverted to the mass spectrometer ion source. Mass spectra were acquired using electrospray ionization with no special modifications to the ion source A total ion current chromatogram showing two of the four components ionize efficiently under electrospray ionization conditions B ELSD chromatogram of the four components, all showing comparable response C UV chromatogram (254 nm) shows some selectivity in detection as does D D CLND detection. Reprinted from [7] with permission from D.B. Kassel...

To verify that this library was successfully synthesized, a portion of the resin was removed, and the compounds were cleaved from the polymer with trifluoroacetic acid and analyzed with HPLC electrospray ionization mass spectrometry. All the compounds shown could be identified. On cyclo-addition of the maleimides, endo/exo isomers and -in the case of the vinylsulfones - regioisomers were obtained. This led to complex chromatograms of isomeric compound mixtures co-elution often occurred. Quantification of the single compounds was not possible, and the peak area in the UV trace (detection at 214 nm) did not correlate with those of the total ion current chromatogram in the mass spectrum. 

We also studied12 the relationship between the thickness of the tip (apex angle = 90°) and the electrospray performance and found that the parylene thickness does not affect the spray performance. Spray performance from three tips was compared with different thicknesses (3, 5 and 7 pm) whose sizes were the same as the triangular tip in Figure 6.4. The monitored total ion currents for these three tips were 35.5 1.2 nA for the 3 pm thick tip, 35.3 1.5 nA for the 5pm thick tip and 35.8 1.4nA for the 7pm tip. Liquid droplets were confined to the tips in all cases. This indicates clearly that only the top surface of the triangular tip is involved in the ESI activity. 

Figure 6.7 Electrospray performance for coupling cyclo-olefin microchip to TOF mass spectrometer. The data are from 5 pM chicken cytochrome c dissolved in 50% methanol, 50% water with 0.1% formic acid. The electrospray voltage used was 2.5 kV and the flow rate was 300 nLmin. (A) Mass spectrum of chicken cytochrome c. (B) Total ion current of chicken cytochrome c for 10 min. (From ref. 12.)...

The electrospray stability of this device was studied with two different samples 1 pg mL 1 imipramine- 3 directly dissolved in 75% methanol, 25% water and 0.1% formic acid and extracted urine sample containing only methylphenidate-d3, which corresponds to the blank calibration standards. Figure 6.13A shows the total ion current of full mass range scan (m/z 250 to 350) of the imipramine-J3 sample over 15 min with a scan speed of 1.16 s per scan while Figure 6.13B shows the extracted ion current of the base peak (m/z 284.2) from Figure 6.13A. The RSD for the total ion current over the 15 min periods was 10.7% and the protonated molecule ion was even more stable with an RSD of 5.7%. Figure 6.13C shows the total selected ion current for the SRM data (m/z 234.2 > m/z 84.1, m/z 234.2 > m/z 84.1) from 150ngmL 1 methylphe-nidate-fi 3 sample. The SRM mode was also very stable with an RSD of 3.05% over a period of 5 min. 

Figure 6.13 Electrospray stability of the device. (A) Total ion current of m/z from 250 to 350 with solution of lpgmL-1 imipramine-d3 in 75% methanol, 25%water and 0.1 % formic acid. (B) Extracted ion current of imipramine-d3 (m/z 284.2) from (A). (C) Selected reaction monitoring of extracted urine sample containing 150ngmL 1 methylphenidate-<73 (from ref. 13).

Mixture of compounds from each well, which was chosen according to the scheme of cross sections, was analyzed by electrospray LC/MS. Ion currents corresponding to all 12 expected compounds were extracted from the total ion... 

FIGURE 3.11 Electrospray prototype corona ring, 1-cm diameter Rl, R2, R3, and R4 represent resistors at values of 1.25, 2.5, 6.2, 6.2, and 50 kH, respectively. Conditions to initiate spray were (A) 4,000 V, (B) 3,500 V, (C) 2,500 V, (D) 20 V, and (E) ground. Typical total current was 7 nA. (Taken from Shumate, An electrospray nebulization/ionization interface for liquid introduction into an ion mobility spectrometer, thesis, Washington State University, Pullman, 1989.)... 

Figure 5.27 (a) Pneumatically assisted electrospray source and API interface designed for LC/MS applications, (b) Total ion current (m/z 200-450) chromatogram observed in LC/MS analysis of a mixture of five monosulfonated azo dyes ( 20 ng of each injected on-column), and ESI mass spectrum of the last-eluting component. Separation was achieved using a 1 x 100 mm C,g column, operated in reverse phase isocratic mode with 40 jiL.min of a 30 70 mixture of acetonitrile and aqueous ammonium acetate (10 mol.L ). Reproduced from Bruins, Anal Chem. 59, 2642 (1987), copyright (1987), with permission of the American Chemical Society. 

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