E. Marengo

Neural network and experimental design to investigate the effect of five factors in ion-interaction high-performance liquid chromatography

The effect of five experimental parameters on the ion-interaction chromatographic retention of pesticides characterized by different polarity was investigated by means of experimental design and artificial neural network treatments. The factors considered were: (1) the mobile phase pH; (2) N, the alkyl-chain length of the IIR (ion-interaction reagent); (3) CM, the organic modifier concentration in the mobile phase (4) CR, the concentration of IIR and (5) F, the flow-rate. The use of fractional design and Hoke design allowed useful information to be drawn about the retention mechanism involved and to build, through artificial neural network treatment (ANN), a model characterised by both descriptive and predictive ability. Four neurons and a bias unit were employed. The ANN proved to be a useful instrument in the optimisation of the chromatographic separation, as regards resolution and total analysis time: the experimental retention obtained in the optimal conditions always differed within 14% from the predicted ones.

Determination of aromatic amines at trace levels by ion interaction reagent reversed-phase high-performance liquid chromatography : analysis of hair dyes and other water-soluble dyes

Abstract A reversed-phase high-performance liquid chromatographic method, making use of interaction reagents, was developed for the separation and determination of aromatic amines. Different interaction reagents were used and compared. The use of octylammonium salicyte or octylammonium orthophosphate as the interaction reagent and a reversed-phase spherical 5μm RP-18 as the stationary phase, with spectrophotometric detection at different wavelengths, gave good results. The separation of up to seven aromatic amines (the three isomers of phenylenediamine, benzylamine, 2-phenylethylamine, 3-phenylpropylamine and aniline) was obtained with sensitivity levels ranging between 50 and 100 ppb. The method was applied to the analysis of water-soluble dyes such as fabric dyes, brown and blond hair dyes, black shoe dye and black fountain-pen ink. It was possible to detect and determine 1,4-phenylenediamine in commercial hair dyes. The results indicate that very large amounts of this amine are present in these products namely 7320 ppm for brown hair and 598 ppm for blond hair.

How chemometrics can helpfully assist in evaluating environmental data. Lagoon water

Abstract The seasonal dependence of inorganic anion composition of Venice lagoon water was investigated along the period June–November 1993. Monthly samples were collected in three different stations and nitrite, nitrate, iodide, bromide, chloride, sulfate, phosphate and silicate content was determined. Dissolved oxygen, temperature and conductivity were measured in situ. Unfortunately, in that period the weather behaved very atypically as concerns both rains and temperature and the raw data obtained for the variables considered do not allow direct correlations with the season. Only the chemometric treatment of principal component analysis permitted to characterize the samples as a function of seasonality and sampling site and allowed to select the significant discriminating factors.

Chemometrically Assisted Development of IP‐RP‐HPLC and Spectrophotometric Methods for the Identification and Determination of Synthetic Dyes in Commercial Soft Drinks

Abstract Two independent methods were developed to identify and determinate synthetic dyes and to follow their degradation processes. The IP‐RP‐HPLC method was optimised by the experimental design technique and the results obtained were compared with ones obtained by direct/derivative spectrophotometry. The dyes considered in this study that are representative of soft drink components, are: Tartrazine (E102), Quinoline Yellow (E104), Sunset Yellow (E110), Carmoisine (E122), Amaranth (E123), New Coccine (E124), Patent Blue Violet (E131), and Brillant Blue FCF (E133).

Classification of essential mint oils of different geographic origin by applying pattern recognition methods to gas chromatographic data

Abstract Pattern recognition techniques were applied to the classification of essential mint oils using their gas chromatographic data. A study has been completed on 59 samples of three different geographic origins: U.S.A., France and Italy. Principal component analysis provided new variables for an effective classification of the samples according to the different areas of origin. The pattern of the result was further analysed by means of a fuzzy clustering algorithm which permitted the quantification of the differences between the three classes. The chemical information contained in the gas chromatographic data was sufficient to characterize the geographic origin of the samples.

Investigation by experimental design and regression models of the effect of five experimental factors on ion-interaction high-performance liquid chromatographic retention

Abstract The effect on retention of simazine and atrazine of five experimental factors in ion-interaction chromatography is investigated by means of chemometrics. The factors are: (1) the chainlength of the ion-interaction reagent (N), (2) the concentration of the ion-interaction reagent (CR), (3) the pH of the mobile phase, (4) the flow rate (F) and (5) the organic modifier concentration (CM). Fractional and star experimental designs are employed. The effects of the factors and their interaction on retention are calculated and discussed: the results permit to draw out useful information concerning the interaction mechanisms involved. A regression model correlating the chromatographic retention to the factors, their second-order interactions and their squares with very good predictive ability (R2 > 97% and Rcv2 > 94%) is also calculated.

Simultaneous reversed-phase high-performance liquid chromatographic separation of mono-, di-and trichloroanilines through a gradient elution optimised by experimental design.

A new RP-HPLC method for the simultaneous determination of the 13 mono-, di- and trichloroanilines has been developed. In order to obtain the analyte resolution within an acceptable analysis time, a gradient elution program has been optimised through the use of an experimental design and a grid search algorithm. The optimized conditions provided the resolution of all the analytes in less than 80 min. The primary validation of the analytical method gave limit of detection values ranging between 0.02 and 0.06 mg/l and very good linearity of the calibration curves.

Analysis of vegetable and fish oils by capillary supercritical fluid chromatography with flame ionization detection

SummaryCapillary SFC with supercritical CO2 as mobile phase and flame ionization detection was adopted to separate and determine triacylglycerols in vegetable and fish oils. The effect on separation of many experimental variables has been checked along with the selectivity of several stationary phases of different polarity. A standard mixture of 13 triacylglycerols was used to optimize the procedure and their retention times were used as reference to identify peaks in real samples. In spite of the fact that many peaks remained unidentified, the chromatograms obtained were useful as fingerprint analyses of the real samples examined.

Retention Dependence on Organic Modifier and Interaction Reagent Concentration in Reversed-Phase Ion-Interaction HPLC

Abstract The effect played on ion-interaction chromatographic retention by the concentrations of the organic modifier and of the ion-interaction reagent as a function of the ionic strength is studied. Experiments are performed for a series of analytes characterized by different chemical properties (nitrate, nitrite, iodide, ascorbic, orotic and p-aminobenzoic acids, aniline, benzylamine, p- and m-aminophenol) in the absence and in the presence of organic modifiers (acetonitrile and methanol) and of sodium perchlorate to control the ionic strength (I=1.0 M). Concentrations of the ion-interaction reagent (octylammonium o-phosphate) ranging between 1.0 and 60.0 mM and of the organic modifier (methanol and acetonitrile) ranging between 0 and 45% are considered. Retention interdependence on the concentrations of ion-interaction reagent and of the methanol in the mobile phase is also studied. The results are discussed and compared with literature data and the relevant role played on the retention by ionic stren...

Retention of Anions as a Function of Mobile Phase PH in Ion-Interaction RP-HPLC

Abstract Retention of typical anions as a function of pH of the mobile phase in reversed-phase ion-interaction chromatography was studied. The different behaviours observed for anions of acids characterized by different pKa values were discussed, in comparison with literature results obtained in reversed-phase and in reversed-phase ion-pair chromatography.