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ANALYTICAL CURRENTS
Adhesion-based AFM measurements correlate with chemical reaction Atomic force microscopy (AFM) provides nanoscale spatial resolution and has been used to study interfacial materials. Its use, however, would increase if it provided chemical composition information concurrently with the visual image. Previous efforts to include chemical details have focused on friction and adhesion measurements, which depend on the interactions of the functional groups within a few angstroms of the sample surface. Marc Porter and co-workers at Iowa State University/Ames Laboratory have applied adhesion measurements to the realtime monitoring of the electrochemical transformation of an 11-mercaptoundecyl ferrocenecarboxylate monolayer chemisorbed at a Au(lll) electrode using an AFM probe tip modified with an octade-
Analytical alphabet soup analyzes hemoglobin from a single cell Although techniques that are capable of analyzing the components of a single cell would allow comparisons between individual cells and the identification of biomarkers indicative of aberrant cell morphology, such endeavors make huge sensitivity demands on the instruments. Richard Smith of Pacific Northwest National Laboratory, Andrew Ewing of Pennsylvania State University, and their colleagues had previously obtained spectra of a and P chains of hemoglobin by injecting 10 human erythrocytes (red blood cells) into their CE/ESI-FT-ICR instrument Now theVve oneUDDed themselves and tained mass spectra of a- and
could be correlated with the electrochemical reactions of the ferrocenyl group. Fad curves, defined as the probe tip displacement versus the vertical displacement of the sample state, were collected while the sample stage was moved vertically at 10 um/s and the applied potential was scanned from-0.47 V to+0.25 V. The Fad decreased after ~ 10-20% of the ferrocenyl was oxidized, and plots of Fad versus potential and of the fractional coverage of the reduced form of the ferrocenyl group have strikingly similar sigmoidal shapes. The authors plan further experiComparison of plots of (a) Fad and (b) fractional ments to determine if the change coverage of the reduced form of the ferrocenyl group in Fad can be attributed to surversus applied potential. The potential was scanned face tension changes generated from -0.47 V to +0.25 V. by the redox of ferrocenyl, to the uptake of counterions and water, or to a canethiolate monolayer. Using this tipcombination of both. (J. Phys. Chem. sample combination, they showed that 1996 100 13342-45) changes in the force of adhesion (Fad) P-chain hemoglobin from a single human erythrocyte (~ 450 amol hemoglobin) by incorporating selective ion accumulation techniques based on quadrupolar excitation over the m/z range 1250-1450.
The erythrocyte was electroosmotically injected into the capillary, and the end of the capillary was placed in a vial of CE running buffer; the osmotic shock of exposure to the running buffer lysed the cell. The 1-m capillary was modified with aminopropylsilane to prevent protein adsorption and to provide sufficient flow for stable operation of the ESI source. TheFT-ICRMSwas based on a 7-T superconducting magnet and was equipped with an external ESI source. Because of the limited resolution of the CE separation and the relatively long ion injection interval (5-s injection and 1-s "cleanup event"), the a and 3 chains appear in the single-scan mass spectrum, which has a mass resolution >45 000. (Rapid Commun. Mass ESI-FT-ICR mass spectrum of multiply charged hemoglobin species Spectrom 1996 10 acquired following injection, ,n-column lysing, and CC separation of o single 919-22) human erythrocyte. .Adapted with permission of John Wiley & Sons.) Analytical Chemistry News & Features, October 1, 1996 5 9 3 A
