Flat Baselines Research Articles

Corrections to the Baseline Distortions in the OH-Stretch Region of Aqueous Solutions

The intensity gains or intensity losses of the OH-stretch vibrations and their changes of band shapes as observed in IR or Raman spectra of dilute aqueous solutions of carboxylic acids, amino acids, and amines were able to be simulated. The difference spectra of the type {sample solution} – {standard} x {empirical factor} displayed essentially flat baselines throughout the OH-stretch region of isotropic Raman scattering. Peaks of the solute spectra which had been hidden by the OH-stretch contour emerged from the background. At concentrations below 1 M, pure water was the standard. Distortions of the isotropic Raman spectra at higher solute concentrations (1 M to 4 M) could be mimicked by phosphoric acid or sulfuric acid solutions as standards. The influence of solutes on the reorientational motions of water molecules made baseline corrections of anisotropic Raman scattering and IR absorption of the more concentrated solutions difficult, if not impossible.

Practical Aspects of Recording Multidimensional NMR Spectra in Water with Flat Baselines

Practical Aspects of Recording Multidimensional NMR Spectra in Water with Flat Baselines

Perfectly flat baselines in 1D and 2D spectra with optimized spin-echo detection

Perfectly flat baselines in 1D and 2D spectra with optimized spin-echo detection

Universal liquid chromatographic methods : III. Sensitive, low-wavelength gradients with a novel injection-loading ion-pairing technique

This paper extends to the ion-pairing mode the “universal methods” previously reported for the reversed-phase mode. These methods offer savings of laboratory and customer time and cost as they often allow “first run problem solving”, reduce method development for each new problem and allow different separation problems to be run in sequence with no system changes. Major and minor components of unknown wide-polarity mixtures are analyzed with the near-universal detection possible at 210 nm. A new technique of injection loading an ion-pairing (IP) agent with an automated liquid chromatograph into simple buffered eluents is introduced. Full gradients from aqueous buffers to acetonitrile are achieved at 0.1 a.u.f.s. and 210 nm without ghost peaks or baseline shifts (less than 5%). Additioally, in three consecutive 12-min runs, the three liquid chromatographic modes (with different selectivities), viz., cation-pairing, anion-pairing and simple reversed-phase, can be explored in order to optimize the separation of a particular sample. The charge of the individual components at the eluent pH can be determined by the movement of peaks in consecutive runs. Other advantages of injection loading are that the pump and column life are preserved, only small amounts of clean ion-pairing agents are required and the effect of new ion-pairing agents on a sample can be investigated in one run. We also present a new technique for achieving flat 210-nm UV baselines. This is accomplished by bubbling a mixture of nitrous oxide (UV absorbing) with helium of a composition that varies the aqueous background UV absorption to match the second gradient eluent, acetonitrile.

Pyrolytically coated carbon cloth electrodes

The performance of carbon cloth electrodes with a pyrolytic graphite coating deposited on their surface is reported. Cyclic voltammograms recorded with treated and untreated cloth, in the −0·9 to +0·9 V (versus Ag/AgCl) potential range, are compared. The extremely high residual currents observed on untreated cloth electrodes are absent after pretreatment; the latter maintain flat base lines even after repeated potential cycling. Optimum conditions for the pyrolytic process are recommended.