Say Goodbye to Either/Or Electrochemistry
Figure 5. Pharmacokinetic curve for the metabolism of penicillin G by the rat obtained using on-line in vivo measurement techniques. Metabolic curves in humans and dogs obtained by classical procedures are plotted for comparison. (Adapted from Reference 10.)
saturated aqueous oxalic acid/2,2'dithiodiethanol (49/49/1/1). The instrument used was a hybrid sector/ quadrupole type of the BEqQ design (i.e., the analyzer arrangement was magnet/electric sector/collision cell quadrupole/analyzer quadrupole). The transition followed was m/z 524 [(M + H) + for C-16 PAF] fragmenting to m/z 184. Thus the sectors were tuned to pass m/z 524 into the collision quadrupole where collision-activated decomposition occurred, and the analyzer quadrupole was set to pass the m/z 184 fragment. This technique is important for trace analysis because it eliminates much of the background chemical noise (except that at m/z 524) derived from glycerol or other matrix compounds used and significantly lowers the limit of detection. To achieve greater selectivity, one can also increase the resolution of the instrument above that required to give unit mass separation to help eliminate background at m/z 524. Figure 6 shows the first-stage MS analysis of several 50-pg injections of PAF obtained by monitoring m/z 524.37 at a resolution of 1500. This effectively eliminates a solvent background peak at m/z 524.07 that is approximately 50% of the relative intensity of the (M + H)+ ion of PAF. The points marked B in the figure are blank (water) injections, which show that none of the ion current recorded for the PAF samples was the result of background or injection artifacts.
is useful because of its high sensitivity, negligible memory effect, and applicability to a wide range of compounds. Unlike most other LC/MS interfaces, CF-FAB maintains the liquid nature of the eluate inside the ion source on a target surface and uses atom bombardment of this liquid to produce ions rather than nebulization and spray formation. A liquid flow interface for the combination of LC and FAB was first reported by Ito and co-workers (5) for the separation and analysis of bile acids using glycerol/acetonitrile/water (10:27:63) as the eluting solvent. They termed the technique frit-FAB because they used a stainless steel mesh or frit
ost electrochemical software is designed to do either sophisticated research or routine measurements. In the past, if your lab did both, you were stuck.
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LC/MS
Figure 6. Analysis of C-16 platelet activating factor (PAF) at trace levels using CF-FAB and MS/MS techniques.
A number of interfaces for combining LC and MS have been described, two of which—continuous-flow and the moving belt—use FAB ionization. CF-FAB
Approximately 50 pg of PAF were injected interspersed with blank (B) water injections. Data were obtained on a VG ZAB SEQ hybrid mass spectrometer. (Courtesy of S. J. Qaskell, Baylor University College of Medicine.)
EG&G PARC P.O. BOX 2565 • PRINCETON, NJ 08543-2565 (609) 530-1000 • FAX: (609) 883-7259
Circle 32 for literature. Circle 33 for a sales representative. ANALYTICAL CHEMISTRY,
VOL. 62, NO. 8, APRIL 15, 1990 • 481 A
