Absorbance detectors trends

Figure 19.10 Peak areas and system peaks. (Reproduced by permission of Elsevier Science Publishers BV from G. Sehili and J. Crommen, Trends Anal. Chem., 6, 111 (1987).) The two peaks indicated by Sare system peaks. Sample, racemate of bupivacaine (equal amounts of both isomers) stationary phase, EnantioPac (aq-acid glycoprotein on silica) mobile phase, phosphate buffer (pH 7.2)-isopropanol (92 8), UV detector, 215 nm (the mobile phase shows some absorbance at this wavelength).

Figure 7.41. Unpolarized difference ATR spectra of galena electrode-electrolyte interface at potentials starting at -0.5 V. Electrolyte is 8 x 10 M potassium n-butyl xanthate solution in borate buffer (pH 9.18) at N2 atmosphere. Spectra were obtained with Perkin-Elmer 1760X FTIR spectrometer with MCT detector. Each spectrum is average of 200 scans with 4 cm resolution and is represented relative to spectrum measured one step before. Horizontal lines indicate zero absorbance. Additional features of spectrum baselines are upward sloping in long-wavelength part of spectra (marked with dotted lines) due to hole absorption and downward trend in short-wavelength part of spectra (>1500 cm ) at potentials from -0.1 to -E0.1 V, attributed to recharging of surface states and defect levels. Reprinted, by permission, from I. V. Chernyshova, J. Phys. Chem. B 105, 8185 (2001), p. 8187, Eig. 2. Copyright 2001 American Chemical Society.

With increasing sensitivity in the sequencing process there is a trend toward the use of narrow-bore (2.1-mm-i.d.) and microbore (1.0-mm-i.d.) columns. These columns provide for higher analyte detection sensitivity and considerably smaller peak elution volumes (Simpson et al., 1989). With 1.0-mm-i.d. columns peptides can be recovered in as little as 30 fA of liquid and collected at the detector outlet directly onto the sequencing support, thus eliminating any sample losses due to sample absorption to the surface of the plastic tube. Quantitation of the collected polypeptide is provided by the signal size as detected by UV absorbance. 

---