C. Abrigo

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.

Separation of phenylurea pesticides by ion-interaction reversed-phase high-performance liquid chromatography Diuron determination in lagoon water

An ion-interaction HPLC method is developed for the separation of the phenylurea herbicides asulam, diuron, isoproturon, linuron and monuron. C18 was used as stationary phase and octylammonium phosphate as ion-interaction reagent, in the presence of methanol or acetonitrile as organic modifier. Detection limits lower than 9 μg/l can be obtained without preconcentration steps. The method was applied to the analysis of diuron in a sample of lagoon water. Using liquid-liquid extraction, a diuron concentration of 42 μg/l was found.

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.

The Role of pH of the Mobile-Phase in Ion-Interaction RP-HPLC

Abstract The dependence of retention on pH of the mobile phase is investigated in reversed-phase ion interaction chromatography, being the mobile phase an aqueous solution of 5.0 mM octylammonium and ortho-phosphoric acid at different pH values. The analytes considered were amines, diamines, amides, and species characterized by different functionalities. The behaviour of retention as a function of pH is discussed with comparison with literature data and correlation with pka values is shown. The optimization of separation and resolution in a mixture of acids and amines through pH variations is also presented.

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.

A Selective Determination of Azide by Ion-Interaction Reversed-Phase HPLC

Abstract A method is presented for the analysis of sodium azide, based on the use of ion-interaction reversed-phase HPLC chromatography. A C-18 reversed-phase is the stationary phase and octylammonium ortho-phosphate at different pH values is the interaction reagent Spectrophotometric detection at 230 nm is employed. The analysis is free from interference by acetate, carbonate, chloride, fluoride, sulphite, hydrazine, hydroxylamine, nitrate, bromide, iodide, sulphide, thiocianate and nitrite. A good correlation (r2 = 0.9782) is obtained between peak area and concentration in the range between 1 and 250 ppb. Samples of tap water spiked with sodium azide (in the range within 25 and 250 ppb) gave per cent average recovery of 98%. The method sensitivity, expressed as signal to noise ratio equal to 3, is 50 ppb when the pH of the interaction reagent is equal to 3.0, 30 ppb for pH 6.4 and 10 ppb at pH 8.0.

Determination of fluoxetine and norfluoxetine in human plasma by ion-interaction RP-HPLC

Abstract The paper reports a sensitive Ion-Interaction Reverse Phase HPLC-UV method for the separation and determination of fluoxetine ((±)N-methyl-(4-(trifluoromethyl)phenoxy) benzene-propanamine) in human plasma. An ODS silica-based column is used as the stationary phase and the mobile phase consists of 5.00 mM octylamine in water/acetonitrile (60/40 v/v), at pH = 6.4, with UV detection at 230 nm. The method is selective towards potentially interferent drugs, such as paroxetine, amylsulpride, fluvoxamine, mianserin, imipramine, amitryptiline, cromipramine, maprotiline, haloperidol, flunitrazepam and diazepam. The proposed method was successfully applied to the determination of fluoxetine and norfluoxetine in plasma of some patients being treated for obsessive-compulsive disorders.

Ortho-Phosphate of Aromatic Amines as the Interaction Reagents in Reversed-Phase HPLC Chromatography. Direct Spectrophotometric Detection of non Absorbing Anions

Abstract This paper shows that in the ion-interaction-reagent reversed-phase HPLC chromatography here employed anions too, like amines, are retained through the formation of ion-pairs and that under this form they are also released. Experiments were performed with spectrophotometric detection and with the use of interaction reagents composed by an anion which does not absorb at the detection wavelength and an amine which on the contrary does. The formation of the characteristic system peaks was discussed and explained, in agreement with previously obtained results. The method here developed permits the spectrophotometrical detection of non-absorbing anions, through the absorbance properties of the hetaeron amine.

Determination of nitrite, nitrate, iodide, bromide, chloride, sulfate, in venice lagoon‐water by reversed‐phase ion‐interaction HPLC. The effect of the geographical position

Abstract The paper reports analytical data concerning water samples in Venice lagoon collected in different geographical sites, characterized by different salinity and kind of pollution. Chloride, iodide, bromide, sulfate, nitrite, nitrate were determined by means of ion‐interaction chromatography, while phosphate determination was performed spectrophotometrically. The results are discussed with reference to literature data.