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A study of quantitative analysis of some flavonoids in Satureja hortensis L. extracts is presented. The HPTLC analyses were performed in a normal chromatographic chamber on silica gel plates, with an appropriate mobile phase. Photodensitometric evaluation of the chromatographic plates was performed by UV-visible absorbance at 320 nm for rosmarinic acid and 349 nm for luteoline, after pulverizing with NTS reagent (diphenylboryloxyethylamine). Quantitative analyses of flavonoids were performed by use of calibration curves. The quantity of compounds extracted depends on the composition of the extraction solvent and on the extraction technique. The best results were obtained by heating under reflux with systems that contained 60–70% ethanol. Under these conditions it was found that this plant contained approximately 34 mg g -1 rosmarinic acid and 30 mg g -1 luteoline. The results obtained were compared and correlated with extraction method and confirm this plant contains important amounts of flavonoids and phenolic acids.

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Using RP-TLC with RP-18 F254s and a methanol-water mixture as the mobile phase, several new compounds (some plant growth stimulators, such as amido esters of ethanolamine and maleic and succinic acid derivatives) were studied. The log P values were calculated using fragmental constant or ACD/Labs Software database (Toronto, Canada). A good correlation was obtained between log P vs. RM0 and C0, respectively. These relationships can be used for prediction of the lipophilicity of similar compounds from the same structural group. The relationship between intercepts and slopes from TLC equations showed a very good correlation. The results obtained by RP-TLC demonstrated a basic feature of lipophilicity; that both series of compounds are two “congeneric” series.

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Two methods, one on the basis of relative error in yi (in that case wi should be taken as 1/yi2) (YWLS) and another on the basis of 1/xi2 as a weighting factor (XWLS), for the calculation of calibration function are reported and compared with conventional ordinary (OLS) and simple weighted least squares method (WLS). By these procedures the calibration functions for the TLC determination of some triazine herbicides are represented more strongly than by the ordinary least squares method mainly in the cases of heteroscedasticity. Instead of the coefficient of correlation, six coefficients of quality are used to characterize the quality of the calibration functions.

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Weighted least-squares spline functions are discussed and applied for calibration processes in analytical chemistry. Different weighting techniques are also considered, and for the evaluation of the results some quality coefficients are proposed. Depending upon the structure of the data, some weighting procedures may improve the results dramatically. Considering the results obtained in the case of TLC densitometry, it seems that nonlinear weighting procedures based upon the distance to the function are the best ones, with a plus for the y-distance type. It is difficult to give general rules regarding the optimal parameters of the weighted calibration splines function order (m), number (N) and distribution of knots, and weighting technique. These depend upon the structure of the data. However, higher order splines are not recommended since the result might become extremely unstable. The example used to illustrate the performances of the procedures discussed here involved only a single independent variable. The method is general and extends practically to any number of variables, thus resulting in a multivariate approach.

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The limit of detection (LOD) improvement in TLC determination of uranium and thorium in presence of other metal ions is presented in this paper. The mobile phase system contains iso-propyldithiophosphotic acid (i-PrDTP), as a complexing agent, in order to differentiate the studied species by modifying their retention. The paper reports the successful separation and the quantitative determination of uranium and thorium in the presence of other metal ions in the concentration range 2.5–30 µg/µl.

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A method for the determination of trace levels of triazines and organophosphorus pesticides in water is presented. The extraction method is based on a solid-phase extraction on C-18 bound silica SPE cartridges. A precolumn filled with Merck C-18 bound silica and home-made C-18 bound silica have been tested at a flow-rate of 3 ml/min with comparable preconcentration yields. A SIM-MS method using a 15N labelled internal standard has been developed for the organophosphorus pesticides. Detection limits lower than 1 µg/L have been obtained. Separations have been carried out on a conventional GC column OV 17 (1 m) and a capillary column OV 17 (25 m) with a temperature program from 150° C (2 min) to 300° C (rate of 6° C/min).

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