Comparison of the sequential simplex method and linear solvent strength theory in HPLC gradient elution optimization of multicomponent flavonoid mixtures

Summary Using a camomile flavonoid extract as the sample and four different reversed-phase partition systems, the ability of the Simplex procedure to produce optimum gradient separation of unknown multicomponent mixtures was checked against the linear solvent strength (LSS) gradient elution theory. On the same partition systems the mean solvent strenghts were measured by experimentally determined logk vs. mobile phase composition plots. These mean solvent strengths are compared to those inferred from the optimum gradients and the usefulness of LSS theory in multicomponent mixture gradient elution optimization is discussed.Dadicated to Prof. Dr. A Liberti on the occasion of his 70th birthday.     

Retention behaviour of selected flavonoid compounds in NP-HPLC

Chromatographia - HPLC retention data for a number of flavonoid compounds have been evaluated on normal phase silica and cyano colums according to the Soczewinski-Snyder (S.-S.) model. On the...     

Reversed-phase ion-pair systems to predict partition coefficients of β-carbolines by HPLC and TLC

Summary A group of 17 β-carbolines was studied in HPLC and TLC systems in order to predict their partition coefficients (log P values). On account of the basic or acid character of some of these compounds, an ion pairing system gave the best results. Both HPLC and TLC data were comparable for log P prediction but severe pH conditions required the use of TLC plates. Retention data are quantitatively related to lipophilicity (expressed as the Hansch constant) and polarity (as the inductive constant) of the solute molecule.     

Trace-metal determination by second-harmonic alternating-current anodic stripping voltammetry

Second-harmonic alternating-current voltammetry can be used for the sequential determination of two electroactive species having very similar half-wave potentials (deltaE(1 2 ) < 50 mV). Since the concentrations of such metals in samples of special interest are often at trace levels, for their determination second-harmonic a.c. voltammetry (extremely selective but not sufficiently sensitive) can usefully be combined with the anodic stripping method, which has a very high analytical sensitivity. The determination of tin and lead as well as of indium and cadmium in 1M hydrochloric acid is described. The half-wave potentials are only 35 and 45 mV apart, respectively, for these systems. A three-electrode cell was used with a long-lasting sessile-drop mercury electrode as the working electrode, with a drop-time of 240-300 sec. The detection limit was found to be 10(-8)M for all four elements studied. The precision expressed as the relative standard deviation was 2-3% and the relative error was 1-2%.     

Undergraduate teaching of Analytical Chemistry at the Italian universities

Summary The present state of teaching Analytical Chemistry in Italian universities is described and proposals are made for general improvement.Presented at Euroanalysis III conference, Dublin, August 20–25, 1978     

Evaluation of the number of components in multi-component liquid chromatograms of plant extracts

Optimization of the chromatographic separation of flavonoid compounds in camomile extracts by the simplex method and the Monte Carlo method is described. Evaluation fo the number of peaks at unit resolution (R_s = 1) is used as the criterion of separation quality. The Davis-Giddings theory is applied in calculating the number of components and the results are validated by numerical simulations. Peak-purity checks for three identified compounds in commercial sample extracts are reported. Capacity factor patterns for 18 flavonoid and phenolic compounds over an extended range of methanol/aqueous buffer (pH 2.8) mobile phases are described.     

Determination of metals by second-harmonic alternating-current voltammetry with a semi-stationary mercury electrode

The simultaneous determination of tin(II) and lead(II) as well as of indium(III) and cadmium(II) by second-harmonic a.c. voltanunetry using a semi-stationary mercury electrode with a drop-time of 240-300 sec (the long-lasting sessile-drop mercury electrode) has been investigated. Under the best experimental conditions, concentration ratios in the ranges l:12 c(Sn):c(Pb) 15:1 and 1:15 c(In):c(Cd) 15:1 can be determined.     

Second harmonic a.c. anodic stripping voltammetry of metals at trace level: simultaneous determination of lead and thallium, and bismuth and antimony

Pairs of elements with very small differences in their half-wave potentials were determined at trace levels by second harmonic a.c. anodic stripping voltammetry. The simultaneous determination of lead and thallium as well as that of bismuth and antimony in 1M hydrochloric acid as supporting electrolyte was found to be possible in the range of concentration ratios: 7:1 > or = C(Pb):C(Tl) > or = 1:36 and 45:1 > or = C(Sb):C(Bi) > or = 1:35, with <5 % relative error due to mutual interference. The limit of detection was approximately 10(-8)M for all four elements, and the precision and error were 2-3%. The simultaneous determination of these metals in mixtures with concentration ratios outside the quoted ranges is still feasible by the standard-addition technique.     

Electrosorption of tert-butanol at the Hg/aqueous NaF solution interface

Electrosorption of tert-butanol (TBUOH) on Hg from aqueous NaF solution has been investigated by means of electrocapillary measurements. The results are analyzed in terms of isotherms at constant potential and constant electrode charge density. The Frumkin isotherm with an attractive interaction parameter is satisfactorily fitted at every potential and electrode charge investigated. The relevant adsorption parameters are also discussed.