A continuación incluyo los "abstracts" de mis publicaciones

 

Photolytic and transport effects produced by argon ion laser radiation on hexacyanoferrate(III) solutions.

Analytica Chimica Acta, 257 (1992) 217-221

R.M. Villanueva Camañas, J.M. Sanchis Mallols, E.F. Simó Alfonso and G. Ramis Ramos.

Dpto de Química Analítica, Facultad de Ciencias Químicas, Universidad de Valencia, E-46100 Burjassot (Spain).

When potassium hexacyanoferrate(III) solutions in a water ethanol or water-acetone medium are irradiated with Ar+ laser radiation, a precipitate is formed on the illuminated region of the cell back wall. The precipitate is probably due to iron(III) hydroxide formed photolytically and transported by the effect of the radiation pressure. Consequences of analytical interest are discussed.

Keywords: Hexacyanoferrate(III); Laser photolysis; Thermal lens spectrometry.

 

Determination of unconjugated catecholamine in urine as dopamine by thermal lens spectrometry.

Analyst, 117 (1992) 1367-1371

J. M. Sanchis-Mallols, R. M. Villanueva-Camañas and G. Ramis-Ramos.

Departamento de Ouimica Analitica, Facultad de Ouimica, Universitat de Valencia, 46100 Burjassot (Spain).

A thermal lens spectrometric (TLS) method to determine the sum of the concentrations of unconjugated catecholamines in urine, giving rise to a parameter with diagnostic value, the dopamine index, is proposed. After isolation with alumina, urinary catecholamines are oxidized with hexacyanoferrate(III), and the TLS signal is measured with a 100 mW argon ion laser-pumped spectrometer in ethanol-water (1 + 1). Limits of detection are about 1 µg cm-3, the repeatability is 2 % and the dynamic range extends up to 1 µg cm-3. The analysis of urine samples is performed by the standard additions method. The concentration of dopamine in urine is always much higher than the concentrations of other catecholamines, and catecholamine TLS sensitivities are similar, dopamine having an intermediate value. This makes dopamine an adequate standard, the expected systematic errors being within the ±5% range.

Keywords: Thermal lens spectrometry; catecholamine determination; urine.

 

Thermal lens spectrometric detection of catecholamines after oxidation to animochromes.

Analytical Letters, 25(8) (1992) 1425-1445

R.M. Villanueva Camañas, J.M. Sanchis Mallols, E.F. Simó Alfonso and G. Ramis Ramos.

Departament de Química Analítica, Facultat de Química, Universitat de Valencia, E-46100 Burjassot (Valencia}, Spain

Experimental conditions for the spectrophotometric and thermal lens spectrametric (TLS) detection of catechalamines after oxidation to aminochromes with hexacyanoferrate (III) are optimized. At the low concentrations used in TLS, and in a 0.07 M citrate buffer, catecholamine oxidation can be performed at pH 7 and is immediate, whereas a lower pH value is required in spectrophotometry to avoid aminochrome polymerisation, the oxidation reactions being much slower. Similar TLS sensitivities are obtained for all catechalamines which facilitates HPLC evaluation. Sensitivity can be enhanced using a 50% ethanol-water medium. The linear dynamic range extends over two orders of magnitude , the 1imit of detection being about 1 ng ml-1 with a reproducibility of 2%, indicating that TLS is adequate to detect catecholamines as aminchromes in physiological samples after HPLC separation. A chromatogram of a urine sample extract is given.

Keywords: Catecholamine determination; aminochromes; thermal lens spectrometry.

 

Modelling of the retention behaviour of solutes in micellar liquid chromatography with organic modifiers.

Journal of Chromatography, 639 (1993) 87-96

J.R. Torres-Lapasió, R.M. Villanueva-Camañas, J.M. Sanchis-Mallols, M.J. Medina-Hernandez and M.C. Garcia-Alvarez-Coque.

Departamento de Química Analítica, Facultad de Química. Universitat de València, 46100 Burjassot (Valencia) (Spain).

Most of the reported procedures for the determination of compounds by micellar liquid chromatography make use of micellar mobile phases containing an alcohol. The retention of a solute in a purely micellar eluent has been adequately described by the linear equation 1/lk' vs micelle concentration. This equation seems also to be valid for mobile phases with the same alcohol concentration and varying micelle concentrations. A model to describe the retention behaviour of solutes in any mobile phase of surfactant and alcohol is proposed, which makes use of the elution data in five mobile phases of surfactant with different amounts of alcohol. A function of the type l/k' = Aµ + Bj + Cµj + D, where µ and j are surfactant and alcohol concentration, respectively, proved to be satisfactory for different solutes (catecholamines, amino acids, phenols and other aromatic compounds).

 

 

Determination of catecholamines as aminochromes by micellar liquid chromatography with thermal lens spectrophotometric detection.

Chromatographia, 38 (1994) 365-372

J. M. Sanchis Mallols, R. M. Villanueva Camañas and G. Ramis-Ramos.

Departamento de Química Analítica, Facultad de Quimica, Universitat de València, 46100 Burjassot, Valencia, Spain.

The determination of catecholamines (CAs) using micellar liquid chromatography with thermal lens spectrophotometric detection has been studied. CAs are oxidized with hexacyanoferrate(III) to aminochromes which are separated with a mobile phase of 0.05 M sodium dodecyl sulphate, 7% propanol and 0.03 M citrate buffer, pH 4.8, on a partially endcapped C18 column. The aminochrome-micelles and amino- chrome-stationary phase association constants are evaluated. Using the 488 nm line of an Ar+ laser with 250 mW pump power the limits of detection are about 4 ng mL-1. The technique is applied to the determination of unconjugated CAs in urine using isoproterenol as internal standard.

Keywords: Column liquid chromatography; micellar liquid chromatography; determination of catecholamines; aminochromes; thermal lens spectrometry.

Interpretive strategy for optimization of surfactant and alcohol concentration in micellar liquid chromatography.

Journal of Chromatography A, 677 (1994) 239-253

 

Interpretive strategy for optimization of surfactant and alcohol concentration in micellar liquid chromatography.

J.R. Torres-Lapasió, R.M. Villanueva-Camañas, J.M. Sanchis-Mallols, M.J. Medina-Hernandez and M.C. Garcia-Alvarez-Coque.

Departamento de Química Analítica. Facultad de Química, Universitat de Valencia, 46100 Burjassot, Valencia, Spain.

An interpretive procedure for optimization of the retention of the solutes in a mixture, eluted with mobile phases containing a surfactant and an alcohol in micellar liquid chromatography (MLC), is proposed. Three optimization criteria were used: positional resolution, valley-to-peak ratio and overlapping. Retention data from several phenols, aromatic compounds and catecholamines were used to test the procedure. The positional criterion, together with the retention model given by an equation of the type 1/k' = c0 + cl µ + c2j + c3µj , led to a reliable optimum resolution using the retention data for a few mobile phases. However, the resolution criteria that take into account both the position and the peak shape are preferable in MLC, where the chromatographic peaks are asymmetric and have a low efficiency.

 

Concentration gradient perturbations in micellar liquid chromatography with thermal lens spectrophotometric detection.

Analytical Letters, 27(10) (1994) 2011-2026

Jose M. Sanchis Mallols, Rosa M. Villanueva Camañas and Guillermo Ramis-Ramos.

Departamento de Química Analítica, Facultad de Quimica,Universitat de València, 46100 Buriassot, Valencia, Spain.

In HPLC with a sodium dodecyl sulphate micellar mobile phase, a perturbation of the sodium ion equilibrium gives rise to a refractive index gradient associated to a concentration gradient. This produces a loss of sensitivity and an increase of noise at a reproducible value of the retention time when thermal lens spectrometric detection is used. Baseline perturbations as this one produced by retained components of the mobile phase can overlap with the peaks of the analytes.

Keywords: Thermal lens spectrometry; Micellar liquid chromatography; Schlieren optics; Concentration gradients.

 

 

Determination of catecholamines in urine by micelar liquid chromatography with coulometric detection.

Chromatographia, 39 (1994) 591-596

J. M. Sanchis Mallols, J. R. Torres Lapasió, R. M. Villanueva Camañas and G. Ramis-Ramos.

Departamento de Química Analítica, Facultad de Quimica,Universitat de València, 46100 Buriassot, Valencia, Spain.

The determination of catecholamines by HPLC with a sodium dodecyl-sulphate (SDS), micellar mobile phase on a C18 column and with coulometric detection was studied. The eluate was conditioned at +0.25 and + 0.00 V, and the current at -0.16 V was recorded. A previously developed model which describes the chromatographic behaviour of solutes in HPLC with hybrid, micellar mobile phases was used to optimize the SDS and ethanol concentrations. A mobile phase of 0.l5 M SDS in a phosphate buffer of pH 3.4 and without ethanol is recommended. The limits of detection were 0.4-0.7 ng ml-l. The procedure was applied to the determination of unconjugated L-dopa, norepinephrine and dopamine in urine. Direct injection of the urine samples gave high results but the unconjugated catecholamines could be determined with a single solid-phase extraction step on an alumina column.

Keywords: Column liquid chromatography; Micellar liquid chromatography; Catecholamines in urine; Coulometric detection.

 

 

Analysis of pharmaceutical preparations containing catecholamines by micellar liquid chromatography with spectrophotometric detection

Analyst, 120 (1995) 1767-1772

Rosa M. Villanueva Camañas, Jose M. Sanchis Mallols, Jose R. Torres Lapasió and Guillermo Ramis-Ramos.

Departament de Química Analítica, Facultat de Química, Universitat de València, 46100 Burjassot, València, Spain.

An HPLC procedure for the determination of catecholamines (CAs) and other compounds which are associated with CAs in pharmaceutical preparations is described. A sodium dodecyl sulfate (SDS) micellar mobile phase, a C18 column and spectrophotometric detection at 280 nm were used. A mobile phase containing 0.1 mol l-1 SDS, 0.67 mol 1-1 (5% v/v) propanol and buffered with phosphate at pH 3 is recommended. The CAs gave limits of detection in the 4-7 ng ml-1 range. The procedure was applied to the determination of L-dopa, 2-methyldopa, epinephrine, dopamine and isoproterenol, as well as other compounds frequently associated with CAs in pharmaceuticals including phenylephrine, carbidopa and hydrochlorothiazide. The solute-micelle association constants and the partition constants of the CAs between the stationary phase and water in several media, and the protonation constants of L-dopa and 2-methyldopa. were evaluated from chromatographic data.

Keywords: Column liquid chromatography; Micellar liquid chromatography; Determination of catecholamines.

 

 

Quantitative retention - structure and retention - activity relationship studies of ionic and non-ionic catecholamines by micellar liquid chromatography.

Chromatographia, 46 (1997) 605-612

J. M. Sanchis Mallols, R. M. Villanueva Camañas, S. Sagrado, M. J. Medina-Hernandez.

Departamento de Química Analítica, Facultad de Farmacia. Universidad de Valencia, C/ Vicente Andrés Estellés s/n, 46100 Burjassot, Valencia, Spain.

When ionic surfactants are used as mobile phases in micellar liquid chromatography, MLC, the retention of compounds is governed by hydrophobic and electrostatic forces. In the absence of electrostatic effects, the hydrophobicity of compounds is the predominant factor affecting its retention and its interaction with micelles. Because both interactions should be considered for ionic compounds, a novel retention model is proposed which includes the hydrophobicity of a compound and the molar fraction of its charged form. High correlations between the logarithm of the capacity factors and structural parameters were obtained for ionic compounds with different degrees of ionization. The effect of the nature and composition of the mobile phase (pH, concentration of surfactant and modifier) was studied. The modelling of the retention of compounds as a function of physico-chemical parameters and experimental variables was established by means of multivariate regression methods (MLR, PLS). In addition, a predictive model for estimating the hydrophobicity of catecholamines is proposed. Finally, quantitative retention - activity relationships in MLC were also investigated for catecholamines.

Keywords: Column-liquid chromatography, Micellar liquid chromatography, Catecholamines, Retention-structure relationships.

 

 

Determination of phenylurea herbicides in drinking waters by hplc and solid phase extraction.

J. LIQ. CHROM. & REL. TECHNOL, 21(6), 869-881 (1998).

J.M. Sanchis-Mallols, S.Sagrado, M.J. Medina-Hernández, R. M. Villanueva Camañas and E. Bonet Domingo1.

Departamento de Química Analítica, Facultad de Farmacia, Universidad de Valencia. C/ Vicente A. Estellés s/n E-46100 Burjassot, València (Spain).1 General de Análisis Materiales y Servicios (GAMASER) S.L. Valencia. (Spain).

An HPLC procedure for determining phenylurea herbicides in waters is described. A LichroSpher RP select B octadecyl-silane analytical column and spectrophotometric detection at 247 nm were used. Adequate retention was achieved with a mobile phase containing ACN/H2O 35/55 (v/v) and 10-2 M phosphate (pH = 7). The herbicides were isolated from water samples by using a single solid phase extraction procedure with C18 solid-phase columns. An enrichment factor of 333 is achieved. The coefficients of variation of the method were lower than 8% at 3 µg l-1 herbicides concentration level. Recoveries ranged between 93 and 105%. The results obtained indicate that the proposed method is well suitable for monitoring phenylureas in compliance with the European Community standard for drinking water.

 

 

Determination of phenoxyacid herbicides in drinking waters by hplc and solid phase extraction.

J. LIQ. CHROM. & REL. TECHNOL, 21(12), 1871-1882 (1998).

J.M. Sanchis-Mallols, S.Sagrado, M.J. Medina-Hernández, R. M. Villanueva Camañas and E. Bonet Domingo1.

Departamento de Química Analítica, Facultad de Farmacia, Universidad de Valencia. C/ Vicente A. Estellés s/n E-46100 Burjassot, València (Spain).1 General de Análisis Materiales y Servicios (GAMASER) S.L. Valencia. (Spain).

An HPLC procedure for determining phenoxy acid herbicides in waters is described. A LichroSpher RP select B octadecyl-silane analytical column and spectrophotometric detection at 230 nm were used. Adequate retention was achieved with a mobile phase containing MeOH/H2O/PnOH 50/42/8 (v/v) and 10-2 M phosphate (pH = 2.5). The herbicides were isolated from water samples by using a single solid phase extraction procedure with C18 solid-phase columns. An enrichment factor of 500 is achieved. The coefficients of variation of the method were lower than 6.5% at 0.4 µg l-1 herbicides concentration level. Recoveries ranged between 93 and 118%. The results obtained indicate that the proposed method is well suitable for monitoring phenoxy acid herbicides in compliance with the European Community standard for drinking water.

 

Chromatographic quantification of hydrophobicity of ionic compounds by using micellar mobile phases.

Journal of Chromatography A 823, 549 - 559 (1998).

L. Escuder Gilabert, J.M. Sanchis Mallols, S. Sagrado, M.J. Medina-Hernández y R.M. Villanueva-Camañas.

Departamento de Química Analítica, Facultad de Química, Universidad de Valencia. C/ Vicente A. Estellés s/n E-46100 Burjassot, València (Spain).

Many biologically active compounds of interest in structure-activity relationships are ionic at physiological pH. However, ionic organic compounds are only weakly or not retained in conventional RPLC which impides the chromatographic estimation of their hydrophobicity and the development of quantitative retention-activity relationship studies. The use of micellar mobile phases allows the retention of ionic compounds. Hydrophobic and electrostatic forces govern the retention of ionic compounds in micellar liquid chromatography. In this paper three different retention models log k-log P for ionic compounds are tested (p = partition coefficient). The retention model (log k = a log P +bα + c) which includes the hydrophobicity and the molar total charge of compound at given pH value has proven to be valid for all types of compounds tested, catecholamines, local anesthetics, diuretics and o-phthalaldehyde-N-acetyl-L-cysteine amino acid derivatives.

Keywords: Hydrophobicity, retention models, Micellar liquid chromatography, Catecholamines, Anesthetics, Diuretics, Amino acids.

 

A new mathematical function for describing electrophoretic peaks.

Electrophoresis  26, 2076 - 2085 (2005).

María C. García Álvarez-Coque, Ernesto F. Simó-Alfonso, José M. Sanchis-Mallols y Juan J. Baeza-Baeza.

Departamento de Química Analítica, Facultad de Química, Universidad de Valencia, E-46100 Burjassot, València (Spain).

A new model is proposed for characterizing skewed electrophoretic peaks, which is a combination of leading and trailing edge functions, empirically modified to get a rapid recovery of the baseline. The peak model is a sum of square roots and is called thereby "combined square roots (CSR) model". The flexibility of the model was checked on theoretical and experimental peaks with asymmetries in the range of 0-10 (expressed as the ratio of the distance between the center and the trailing edge, and the center and the leading edge of the chromatographic peak, measured at 10% of peak height). Excellent fits were found in all cases. The new model was compared with other three models that have shown good performance In modelling chromatagrapnlc peaks: the empirically transformed Gaussian, the parabolic Lorentzian-modified Gaussian, and the Haarhoff-van der Linde function. The latter model was proposed recently to describe electrophoretic peaks. The CSR model offered the highest flexibility to describe electrophoretic peak profieles, even those extremely asymmetrical with long tails. The new function has the advantage of using measurable parameters that allow the direct estimation of peak areas, which is useful for quantitative purposes.

Keywords: Capillary electrophoresis, Electrophoretic peaks, Peak modelling.