Basic Eluent Research Articles

Determination of guanidino compounds by anion-exchange chromatography and amperometric detection

Guanidino compounds were separated and determined by anion-exchange chromatography and electrochemical detection using a basic aqueous eluent and a nickel working electrode. It was found necessary to use a sample clean-up procedure prior to chromatographic analysis of uremic dialysate and serum samples. The effect of eluent hydroxide concentration on the retention of guanidino compounds was studied. Quantitative calibration showed that working curves were non-linear. Electrochemical detection for guanidino compounds with a nickel working electrode, while not selective, has high detection sensitivity. Detection limits for guanidino compounds ranged from 3 to 12 pmol.

Non-linearity of calibration in the determination of anions by ion-chromatography with suppressed conductivity detection

Traces of simple inorganic anions may be determined by chromatographic separation with an alkaline eluent and conductimetric detection, which involves “suppressing” the background conductivity of the eluent by neutralization to form a sparingly dissociated species. Over a wide range of determinand concentration, e.g., two decades, non-linearity of the calibration may become evident, leading to errors of up to 100% at lower concentrations if linearity is assumed (a linear fit of the data usually gives a correlation coefficient >0.99, which may lead to false confidence). The curvature arises from displacement of eluent ions by the determinand and the consequent re-equilibration of the conjugate acid in the suppressed eluate. Even if the distribution of determinand in the peak is ideally Gaussian, the observed conductivity peak may be distorted and calibration will then be non-linear. The best linearity is obtained with the most strongly basic eluent, but other characteristics must also be considered, e.g., run time, peak separation. With a carbonate eluent, the curvature is demonstrated empirically for chloride, nitrate and sulphate calibrations. A second-order fit gives errors of < 10%. With a more strongly basic borate eluent, the deviation from linearity is negligible, but elution times are longer and may be inconvenient in some circumstances.

Polymer coated stationary phases for liquid chromatography

Polymethyloctylsiloxane-coated stationary phases have been prepared for liquid chromatography, by thermal reaction. The influence of the reaction conditions on retention and efficiency of test substances with different structures has been discussed. The materials have good stability in both acidic and basic eluents.

Purification of 3H‐dihydroalprenolol by two dimensional thin layer chromatography

AbstractA two dimensional thin‐layer chromatographic method developed for the purification and analysis of (‐)‐[3H]dihydroalprenolol, by using an acidic mobile phase (butanol/water/acetic acid 25:10:4, v/v) in one direction and a basic eluent (chloroform/acetone/tri‐ethylamine 50:40:10, v/v) in another direction.

Separation of trace metal complexes for analysis of samples of high salt content by inductively coupled plasma mass spectrometry

An on-line sample treatment method has been developed to separate analyte metals from alkali and alkaline-earth elements and anions for inductively coupled plasma mass spectrometry (ICP-MS). The reagent bis(carboxymethyl)-dithiocarbamate is used to complex, V, Cr, Ni, Co, Cu, Mo, Pt, Hg, and Bi. These complexes are adsorbed into a polystyrene-divinylbenzene resin column at acidic conditions. The interfering matrix ions are not complexed and pass through the column unretained. The metal complexes are then removed from the column with a basic eluent. No organic solvent is necessary to displace the metal complexes. The technique is applied successfully to standard samples of urine and seawater. Detection limits are in the range 8-80 ng L/sup /minus/1/.

Mechanism of ion-pair liquid chromatography of amines, neutrals, zwitterions and acids using anionic hetaerons

The basis of retention in reversed-phase ion-pair chromatography is examined using C 18, C 10 and C 12 alkyl sulphates as hetaerons (pairing species) with a range of cations, neutrals, zwitterions and anions as solutes. The basic eluent comprises water—methanol (80:20) containing 20m M phosphate buffer pH 6.00 and 50m M sodium ion. Measurements were made of k′ (column capacity ratio) as a function of hetaeron concentration in the mobile ( C m) and stationary phases ( C 5) the latter being determined by the break-through method. While the adsorption isotherms were non-linear, plots of k′ versus surface concentration of hetaerons were essentially linear for cations up to a level at which the hetaeron formed micelles in the eluent whereupon k′ declined. k′ for neutrals fell slightly as C 5 increased as did k′ for small zwitterions; k′ for anions fell drastically as C 5 increased whereas small peptides behaved like cations. k′ values for all types at any given surface concentration (molar) were more or less independent of the chain length of the hetaeron. It is concluded that the degree of retention is directly related to the surface charge arising from the adsorbed hetaeron and that under most practical conditions ion-pair formation in the eluent is unimportant.