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Analytica Chimica Acta (v.579, #2)
Models and objective functions for the optimisation of selectivity in reversed-phase liquid chromatography by M.C. García-?lvarez-Coque; J.R. Torres-Lapasió; J.J. Baeza-Baeza (pp. 125-145).
Interpretive methodologies are the most efficient tools for finding the optimal conditions in chromatography. These methodologies are supported by models or algorithms able to infer the system behaviour upon changes in the experimental factors. Once the models are built with data obtained from sets of carefully designed experiments, molecular modelling or other approaches, they can be applied to predict the performance of new conditions. The different elements involved in these methodologies, for both isocratic and gradient elution, are given. Special attention is devoted to the description of retention, owing to its major impact on the prediction of chromatographic resolution. Several models considering the main factors affecting retention (i.e. organic modifiers, pH and temperature), and procedures that enhance the predictions, are presented. Both the existence of skewed peaks and the effect of elution conditions on peak profiles are considered. Finally, the assessment of resolution, as well as other secondary aims that affect the practical suitability of the optimal conditions, is discussed.
Keywords: Interpretive optimisation; Retention modelling; Peak modelling; Chromatographic objective functions
Models and objective functions for the optimisation of selectivity in reversed-phase liquid chromatography by M.C. García-Álvarez-Coque; J.R. Torres-Lapasió; J.J. Baeza-Baeza (pp. 125-145).
Interpretive methodologies are the most efficient tools for finding the optimal conditions in chromatography. These methodologies are supported by models or algorithms able to infer the system behaviour upon changes in the experimental factors. Once the models are built with data obtained from sets of carefully designed experiments, molecular modelling or other approaches, they can be applied to predict the performance of new conditions. The different elements involved in these methodologies, for both isocratic and gradient elution, are given. Special attention is devoted to the description of retention, owing to its major impact on the prediction of chromatographic resolution. Several models considering the main factors affecting retention (i.e. organic modifiers, pH and temperature), and procedures that enhance the predictions, are presented. Both the existence of skewed peaks and the effect of elution conditions on peak profiles are considered. Finally, the assessment of resolution, as well as other secondary aims that affect the practical suitability of the optimal conditions, is discussed.
Keywords: Interpretive optimisation; Retention modelling; Peak modelling; Chromatographic objective functions
HPLC-UV and HPLC-MS n multiresidue determination of amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl and azoxystrobin in surface waters by S. Polati; M. Bottaro; P. Frascarolo; F. Gosetti; V. Gianotti; M.C. Gennaro (pp. 146-151).
The paper presents a new HPLC method, with UV and MS n detection, for the determination of seven pesticides, including the sulfonylurea herbicides amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl, and the fungicide azoxystrobin characterised by a methoxyacrilate structure. The methodology consists of a preconcentration/SPE (solid phase extraction) step and HPLC-UV (240nm detection wavelength)-MS n analysis. Under the optimised conditions and after a 1000/1 preconcentration factor, the limits of detection were lower than 14.5ngL−1 for UV detection and lower than 8.1ngL−1 for MS detection. The limits of quantification were lower than 48.3ngL−1 in UV detection and than 26.9ngL−1 in MS n detection. The analysis of two samples, spiked with a mixture of the pesticides at threshold level concentrations, gave more than 60% recovery.
Keywords: Surface waters; Sulfonylurea herbicides; Azoxystrobin; High pressure liquid chromatography; Ultra-violet detection; Mass spectrometry detection Multiresidue determination
HPLC-UV and HPLC-MS n multiresidue determination of amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl and azoxystrobin in surface waters by S. Polati; M. Bottaro; P. Frascarolo; F. Gosetti; V. Gianotti; M.C. Gennaro (pp. 146-151).
The paper presents a new HPLC method, with UV and MS n detection, for the determination of seven pesticides, including the sulfonylurea herbicides amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl, and the fungicide azoxystrobin characterised by a methoxyacrilate structure. The methodology consists of a preconcentration/SPE (solid phase extraction) step and HPLC-UV (240nm detection wavelength)-MS n analysis. Under the optimised conditions and after a 1000/1 preconcentration factor, the limits of detection were lower than 14.5ngL−1 for UV detection and lower than 8.1ngL−1 for MS detection. The limits of quantification were lower than 48.3ngL−1 in UV detection and than 26.9ngL−1 in MS n detection. The analysis of two samples, spiked with a mixture of the pesticides at threshold level concentrations, gave more than 60% recovery.
Keywords: Surface waters; Sulfonylurea herbicides; Azoxystrobin; High pressure liquid chromatography; Ultra-violet detection; Mass spectrometry detection Multiresidue determination
2,7-Dimethyl-3,8-dinitrodipyrazolo[1,5-a:1′,5′-d]pyrazine-4,9-dione: A new labelling reagent for liquid chromatographic analysis of amino acids by M.G. Gioia; B. Cacciari; A. Leoni; R. Gatti (pp. 152-157).
The use of 2,7-dimethyl-3,8-dinitrodipyrazolo[1,5-a:1′,5′-d]pyrazine-4,9-dione as pre-column reagent for LC analysis of amino acids is proposed. The compound reacts (30min at 68°C in presence of 0.04M triethylamine in a dimethylsulfoxide–water mixture) with primary and secondary amino function and the stable resulting adducts can be chromatographed under reversed-phase conditions and detected at λ=280nm. The derivatization conditions were optimized by a series of experiments. The effect of temperature, triethylamine concentration and reagent on the reaction was investigated. The yield of the glycine derivative was found to be quantitative at a reagent amino acid molar ratio of about 6 by comparison with an authentic specimen of synthesized glycine adduct. Application of the method to quality control of commercially available oral polyaminoacid formulations is described.
Keywords: Column liquid chromatography; Pre-chromatographic derivatization; 2,7-Dimethyl-3,8-dinitrodipyrazolo[1,5-a:1′,5′-d]pyrazine-4,9-dione; Amino acid determination
2,7-Dimethyl-3,8-dinitrodipyrazolo[1,5-a:1′,5′-d]pyrazine-4,9-dione: A new labelling reagent for liquid chromatographic analysis of amino acids by M.G. Gioia; B. Cacciari; A. Leoni; R. Gatti (pp. 152-157).
The use of 2,7-dimethyl-3,8-dinitrodipyrazolo[1,5-a:1′,5′-d]pyrazine-4,9-dione as pre-column reagent for LC analysis of amino acids is proposed. The compound reacts (30min at 68°C in presence of 0.04M triethylamine in a dimethylsulfoxide–water mixture) with primary and secondary amino function and the stable resulting adducts can be chromatographed under reversed-phase conditions and detected at λ=280nm. The derivatization conditions were optimized by a series of experiments. The effect of temperature, triethylamine concentration and reagent on the reaction was investigated. The yield of the glycine derivative was found to be quantitative at a reagent amino acid molar ratio of about 6 by comparison with an authentic specimen of synthesized glycine adduct. Application of the method to quality control of commercially available oral polyaminoacid formulations is described.
Keywords: Column liquid chromatography; Pre-chromatographic derivatization; 2,7-Dimethyl-3,8-dinitrodipyrazolo[1,5-a:1′,5′-d]pyrazine-4,9-dione; Amino acid determination
Proteomic profiling of human urinary proteome using nano-high performance liquid chromatography/electrospray ionization tandem mass spectrometry by Yu-Chang Tyan; How-Ran Guo; Chia-Yuan Liu; Pao-Chi Liao (pp. 158-176).
Urine, a blood filtrate produced by the urinary system, is an ideal bio-sample and a rich source of biomarkers for diagnostic information. Many components in urine are useful in clinical diagnosis, and urinary proteins can be strong indication for many diseases such as proteinuria, kidney, bladder and urinary tract diseases. To enhance our understanding of urinary proteome, the urine proteins were prepared by different sample cleanup preparation methods and identified by nano-high performance liquid chromatography electrospray ionization tandem mass spectrometry followed by peptide fragmentation pattern. The experimental results demonstrated that a total of 2283 peptides, corresponding to 311 unique proteins, were identified from human urine samples, in which 104 proteins with higher confidence levels. The present study was designed to establish optimal techniques to create a proteomic map of normal urinary proteins. Also, a discussion of novel approaches to urine protein cleanup and constituents is given.
Keywords: Abbreviations; HPLC-ESI-MS/MS; high performance liquid chromatography electrospray ionization tandem mass spectrometry; MARS; Multiple Affinity Removal System; NCBI; National Center for Biotechnology Information; TFF cartridge; tangential flow filtration cartridge; XCorr; cross-correlation valuesProteomics; Biomarker; Urinary proteome; Large-scale proteome; Protein identification
Proteomic profiling of human urinary proteome using nano-high performance liquid chromatography/electrospray ionization tandem mass spectrometry by Yu-Chang Tyan; How-Ran Guo; Chia-Yuan Liu; Pao-Chi Liao (pp. 158-176).
Urine, a blood filtrate produced by the urinary system, is an ideal bio-sample and a rich source of biomarkers for diagnostic information. Many components in urine are useful in clinical diagnosis, and urinary proteins can be strong indication for many diseases such as proteinuria, kidney, bladder and urinary tract diseases. To enhance our understanding of urinary proteome, the urine proteins were prepared by different sample cleanup preparation methods and identified by nano-high performance liquid chromatography electrospray ionization tandem mass spectrometry followed by peptide fragmentation pattern. The experimental results demonstrated that a total of 2283 peptides, corresponding to 311 unique proteins, were identified from human urine samples, in which 104 proteins with higher confidence levels. The present study was designed to establish optimal techniques to create a proteomic map of normal urinary proteins. Also, a discussion of novel approaches to urine protein cleanup and constituents is given.
Keywords: Abbreviations; HPLC-ESI-MS/MS; high performance liquid chromatography electrospray ionization tandem mass spectrometry; MARS; Multiple Affinity Removal System; NCBI; National Center for Biotechnology Information; TFF cartridge; tangential flow filtration cartridge; XCorr; cross-correlation valuesProteomics; Biomarker; Urinary proteome; Large-scale proteome; Protein identification
Determination of ethylenediaminetetraacetic acid, ethylenediaminedisuccinic acid and iminodisuccinic acid in cosmetic products by capillary electrophoresis and high performance liquid chromatography by L. Katata; V. Nagaraju; A.M. Crouch (pp. 177-184).
A capillary electrophoresis (CE) and a high performance liquid chromatography (HPLC) method are described for the simultaneous determination of ethylenediaminetetraacetic acid (EDTA), S, S′-ethylenediaminedisuccinic acid (EDDS) and R, S-iminodisuccinic acid (IDS) complexing agents as their Fe(III) complexes in cosmetics like shower cream and foam bath. The non-biodegradable EDTA is used in combination with biodegradable analogues like EDDS and IDS in many commercial products. The HPLC method involves separation by reversed-phase ion pair chromatography on a C18 column using methanol–formate buffer (20mM tetrabutylammonium hydrogen sulfate, 15mM sodium formate adjusted to pH 4.0 with formic acid) (10:90, v/v) as mobile solvent at a flow rate of 0.8mLmin−1 at 24°C using UV detection at 240nm. The CE separation was performed in a fused silica capillary of 50μm i.d. with the total length of 50cm with a 10mM MES and MOPSO (pH 5.5) at an applied voltage of −25kV. The samples were introduced by applying a 50mbar pressure for 2s. Absorbances at 215 and 225nm were monitored for the detection of the complexes. The methodology performance of the two methods was evaluated in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ) and reproducibility. The LOD values obtained from HPLC are low when compared with CE. The applicability of both the methods was demonstrated for the analysis of cosmetic products such as shower cream and foam bath. The results obtained by both CE and HPLC were found to be comparable and in good agreement.
Keywords: Ethylenediaminetetraacetic acid; S; ,; S; ′-Ethylenediaminedisuccinic acid; R; ,; S; -Iminodisuccinic acid; Capillary electrophoresis; Ion pair high performance liquid chromatography; Cosmetics
Determination of ethylenediaminetetraacetic acid, ethylenediaminedisuccinic acid and iminodisuccinic acid in cosmetic products by capillary electrophoresis and high performance liquid chromatography by L. Katata; V. Nagaraju; A.M. Crouch (pp. 177-184).
A capillary electrophoresis (CE) and a high performance liquid chromatography (HPLC) method are described for the simultaneous determination of ethylenediaminetetraacetic acid (EDTA), S, S′-ethylenediaminedisuccinic acid (EDDS) and R, S-iminodisuccinic acid (IDS) complexing agents as their Fe(III) complexes in cosmetics like shower cream and foam bath. The non-biodegradable EDTA is used in combination with biodegradable analogues like EDDS and IDS in many commercial products. The HPLC method involves separation by reversed-phase ion pair chromatography on a C18 column using methanol–formate buffer (20mM tetrabutylammonium hydrogen sulfate, 15mM sodium formate adjusted to pH 4.0 with formic acid) (10:90, v/v) as mobile solvent at a flow rate of 0.8mLmin−1 at 24°C using UV detection at 240nm. The CE separation was performed in a fused silica capillary of 50μm i.d. with the total length of 50cm with a 10mM MES and MOPSO (pH 5.5) at an applied voltage of −25kV. The samples were introduced by applying a 50mbar pressure for 2s. Absorbances at 215 and 225nm were monitored for the detection of the complexes. The methodology performance of the two methods was evaluated in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ) and reproducibility. The LOD values obtained from HPLC are low when compared with CE. The applicability of both the methods was demonstrated for the analysis of cosmetic products such as shower cream and foam bath. The results obtained by both CE and HPLC were found to be comparable and in good agreement.
Keywords: Ethylenediaminetetraacetic acid; S; ,; S; ′-Ethylenediaminedisuccinic acid; R; ,; S; -Iminodisuccinic acid; Capillary electrophoresis; Ion pair high performance liquid chromatography; Cosmetics
Simultaneous separation of five fluoroquinolone antibiotics by capillary zone electrophoresis by Adriana F. Faria; Marcus V.N. de Souza; Mauro V. de Almeida; Marcone A.L. de Oliveira (pp. 185-192).
A novel methodology has been developed for simultaneous separation of ciprofloxacin (CPFLX), gatifloxacin (GTFLX), levofloxacin (LVFLX), moxifloxacin (MFLX) and sparfloxacin (SPFLX) fluoroquinolone antibiotics (FQs), using capillary zone electrophoresis (CZE) with UV detection at 282nm. Electrolyte composition was optimized through the variation of the Tris/hydrochloride and sodium tetraborate buffer mixture. The electrolyte consisted of a 25mmolL−1 Tris/hydrochloride and 15mmolL−1 sodium tetraborate buffer mixture resulting in pH 8.87. All analytes were separated in less than 3min. The proposed method was applied to the separation of FQs in pharmaceutical formulations, and the assay results were within 95–105% of the label claim.
Keywords: Capillary electrophoresis; Fluoroquinolones; Pharmaceutical formulations
Simultaneous separation of five fluoroquinolone antibiotics by capillary zone electrophoresis by Adriana F. Faria; Marcus V.N. de Souza; Mauro V. de Almeida; Marcone A.L. de Oliveira (pp. 185-192).
A novel methodology has been developed for simultaneous separation of ciprofloxacin (CPFLX), gatifloxacin (GTFLX), levofloxacin (LVFLX), moxifloxacin (MFLX) and sparfloxacin (SPFLX) fluoroquinolone antibiotics (FQs), using capillary zone electrophoresis (CZE) with UV detection at 282nm. Electrolyte composition was optimized through the variation of the Tris/hydrochloride and sodium tetraborate buffer mixture. The electrolyte consisted of a 25mmolL−1 Tris/hydrochloride and 15mmolL−1 sodium tetraborate buffer mixture resulting in pH 8.87. All analytes were separated in less than 3min. The proposed method was applied to the separation of FQs in pharmaceutical formulations, and the assay results were within 95–105% of the label claim.
Keywords: Capillary electrophoresis; Fluoroquinolones; Pharmaceutical formulations
Separation and determination of trace amounts of zinc, lead, cadmium and mercury in tap and Qaroun lake water using polyurethane foam functionalized with 4-hydroxytoluene and 4-hydroxyacetophenone by N. Burham; S.M. Abdel-Azeem; M.F. El-Shahat (pp. 193-201).
A stable chelating sorbent was synthesized by covalently linking 4-hydroxytoluene or 4-hydroxyacetophenone with the polyurethane foam (PUF) through –NN– group. The synthesized chelating sorbents were characterized by IR and UV/vis measurements. The modified foams show excellent stability towards various solvents. Factors influencing the extraction process of Zn(II), Pb(II), Cd(II) and Hg(II) were studied and evaluated as a function of pH of metal ion solution and equilibration shaking time. The values of sorption capacity of metal ions (μgg−1) were determined with the two types of bonded foams. The two phenolic bonded foams were studied comparatively. The potential applications of the two newly synthesized foams for the removal and separation of the examined metal ions from two natural water samples (drinking tap water and Qaroun lake water at Fayoum City, Egypt) were investigated. Precision (assessed as a relative standard deviation, R.S.D.) was also evaluated and found to be ≤7.3% ( N=5) with a detection limit under 0.46μgL−1.
Keywords: Preconcentration; Separation; 4-Hydroxytoluene; 4-Hydroxyacetophenone; Bonded polyurethane foam; Water analysis
Separation and determination of trace amounts of zinc, lead, cadmium and mercury in tap and Qaroun lake water using polyurethane foam functionalized with 4-hydroxytoluene and 4-hydroxyacetophenone by N. Burham; S.M. Abdel-Azeem; M.F. El-Shahat (pp. 193-201).
A stable chelating sorbent was synthesized by covalently linking 4-hydroxytoluene or 4-hydroxyacetophenone with the polyurethane foam (PUF) through –NN– group. The synthesized chelating sorbents were characterized by IR and UV/vis measurements. The modified foams show excellent stability towards various solvents. Factors influencing the extraction process of Zn(II), Pb(II), Cd(II) and Hg(II) were studied and evaluated as a function of pH of metal ion solution and equilibration shaking time. The values of sorption capacity of metal ions (μgg−1) were determined with the two types of bonded foams. The two phenolic bonded foams were studied comparatively. The potential applications of the two newly synthesized foams for the removal and separation of the examined metal ions from two natural water samples (drinking tap water and Qaroun lake water at Fayoum City, Egypt) were investigated. Precision (assessed as a relative standard deviation, R.S.D.) was also evaluated and found to be ≤7.3% ( N=5) with a detection limit under 0.46μgL−1.
Keywords: Preconcentration; Separation; 4-Hydroxytoluene; 4-Hydroxyacetophenone; Bonded polyurethane foam; Water analysis
Simultaneous quantification of 17 trace elements in blood by dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS) equipped with a high-efficiency sample introduction system by S. D’Ilio; N. Violante; M. Di Gregorio; O. Senofonte; F. Petrucci (pp. 202-208).
A quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) equipped with a dynamic reaction cell (DRC) and coupled with a desolvating nebulization system (APEX-IR) was employed to determine 17 elements (Al, As, Ba, Cd, Co, Cr, Li, Mn, Mo, Ni, Pb, Sb, Se, Sn, Sr, V, and Zr) in blood samples. Ammonia (for Al, Cr, Mn, and V) and O2 (for As and Se) were used as reacting gases. Selection of the best flow rate of the gases and optimization of the quadrupole dynamic bandpass tuning parameter (RP q) were carried out, using digested blood diluted 1+9 with deionized water and spiked with 1μgL−1 of Al, Cr, Mn, V and 5μgL−1 of As and Se. Detection limits were determined in digested blood using the 3 σ criterion. The desolvating system allowed a sufficient sensitivity to be achieved to determine elements at levels of ngL−1 without detriment of signal stability. The accuracy of the method was tested with the whole blood certified reference material (CRM), certified for Al, As, Cd, Co, Cr, Mn, Mo, Ni, Pb, Sb, Se, and V, and with indicative values for Ba, Li, Sn, Sr, and Zr. The addition calibration approach was chosen for analysis. In order to confirm the DRC data, samples were also analyzed by means of sector field inductively coupled plasma mass spectrometry (SF-ICP-MS), operating in medium ( m/Δ m=4000) and high ( m/Δ m=10,000) resolution mode and achieving a good agreement between the two techniques.
Keywords: Trace elements; Blood; Dynamic reaction cell inductively coupled plasma mass spectrometry; Desolvating system
Simultaneous quantification of 17 trace elements in blood by dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS) equipped with a high-efficiency sample introduction system by S. D’Ilio; N. Violante; M. Di Gregorio; O. Senofonte; F. Petrucci (pp. 202-208).
A quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) equipped with a dynamic reaction cell (DRC) and coupled with a desolvating nebulization system (APEX-IR) was employed to determine 17 elements (Al, As, Ba, Cd, Co, Cr, Li, Mn, Mo, Ni, Pb, Sb, Se, Sn, Sr, V, and Zr) in blood samples. Ammonia (for Al, Cr, Mn, and V) and O2 (for As and Se) were used as reacting gases. Selection of the best flow rate of the gases and optimization of the quadrupole dynamic bandpass tuning parameter (RP q) were carried out, using digested blood diluted 1+9 with deionized water and spiked with 1μgL−1 of Al, Cr, Mn, V and 5μgL−1 of As and Se. Detection limits were determined in digested blood using the 3 σ criterion. The desolvating system allowed a sufficient sensitivity to be achieved to determine elements at levels of ngL−1 without detriment of signal stability. The accuracy of the method was tested with the whole blood certified reference material (CRM), certified for Al, As, Cd, Co, Cr, Mn, Mo, Ni, Pb, Sb, Se, and V, and with indicative values for Ba, Li, Sn, Sr, and Zr. The addition calibration approach was chosen for analysis. In order to confirm the DRC data, samples were also analyzed by means of sector field inductively coupled plasma mass spectrometry (SF-ICP-MS), operating in medium ( m/Δ m=4000) and high ( m/Δ m=10,000) resolution mode and achieving a good agreement between the two techniques.
Keywords: Trace elements; Blood; Dynamic reaction cell inductively coupled plasma mass spectrometry; Desolvating system
New reliable Raman collection system using the wide area illumination (WAI) scheme combined with the synchronous intensity correction standard for the analysis of pharmaceutical tablets by Minjung Kim; Hoeil Chung; Youngah Woo; Mark Kemper (pp. 209-216).
A novel and reliable Raman collection system for the non-destructive analysis of pharmaceutical tablets has been proposed. The main idea was to develop and utilize the wide area illumination (WAI) scheme for Raman collection to cover a large surface area (coverage area: 28.3mm2) of solid tablet to dramatically improve the reliability in sample representation and the reproducibility of sampling due to less sensitivity of sample placement with regard to the focal plane. Simultaneously, the effective and synchronous standard configuration using isobutyric anhydride was harmonized with the WAI scheme to correct the problematic variation of Raman intensity from the change of laser power. To verify the quantitative performance of the proposed scheme, the compositional analysis of active ingredient in naproxen tablet has been performed. The average sample composition was successfully represented by using the WAI scheme compared to the conventional scheme with a much smaller illumination area. After the intensity correction using the non-overlapping peak of isobutyric anhydride standard and area normalization, a partial least squares (PLS) model was developed using an optimized spectral range and the concentrations of naproxen in tablets were accurately predicted. The prediction accuracy was not sensitive to changes in laser power or tablet position within ±2mm. Additionally, the prediction accuracy was repeatable without systematic drift or need for re-calibration.
Keywords: Raman spectroscopy; Tablet analysis; Naproxen; Non-destructive analysis
New reliable Raman collection system using the wide area illumination (WAI) scheme combined with the synchronous intensity correction standard for the analysis of pharmaceutical tablets by Minjung Kim; Hoeil Chung; Youngah Woo; Mark Kemper (pp. 209-216).
A novel and reliable Raman collection system for the non-destructive analysis of pharmaceutical tablets has been proposed. The main idea was to develop and utilize the wide area illumination (WAI) scheme for Raman collection to cover a large surface area (coverage area: 28.3mm2) of solid tablet to dramatically improve the reliability in sample representation and the reproducibility of sampling due to less sensitivity of sample placement with regard to the focal plane. Simultaneously, the effective and synchronous standard configuration using isobutyric anhydride was harmonized with the WAI scheme to correct the problematic variation of Raman intensity from the change of laser power. To verify the quantitative performance of the proposed scheme, the compositional analysis of active ingredient in naproxen tablet has been performed. The average sample composition was successfully represented by using the WAI scheme compared to the conventional scheme with a much smaller illumination area. After the intensity correction using the non-overlapping peak of isobutyric anhydride standard and area normalization, a partial least squares (PLS) model was developed using an optimized spectral range and the concentrations of naproxen in tablets were accurately predicted. The prediction accuracy was not sensitive to changes in laser power or tablet position within ±2mm. Additionally, the prediction accuracy was repeatable without systematic drift or need for re-calibration.
Keywords: Raman spectroscopy; Tablet analysis; Naproxen; Non-destructive analysis
Automatic identification of terpenoid skeletons by feed-forward neural networks by Vicente P. Emerenciano; Sandra A.V. Alvarenga; Marcus Tullius Scotti; Marcelo J.P. Ferreira; Ricardo Stefani; Jean-Marc Nuzillard (pp. 217-226).
Feed-forward neural networks (FFNNs) were used to predict the skeletal type of molecules belonging to six classes of terpenoids. A database that contains the13C NMR spectra of about 5000 compounds was used to train the FFNNs. An efficient representation of the spectra was designed and the constitution of the best FFNN input vector format resorted from an heuristic approach. The latter was derived from general considerations on terpenoid structures.
Keywords: Artificial neural networks; 13; C NMR; Spectroscopy; Terpenoids; Steroids
Automatic identification of terpenoid skeletons by feed-forward neural networks by Vicente P. Emerenciano; Sandra A.V. Alvarenga; Marcus Tullius Scotti; Marcelo J.P. Ferreira; Ricardo Stefani; Jean-Marc Nuzillard (pp. 217-226).
Feed-forward neural networks (FFNNs) were used to predict the skeletal type of molecules belonging to six classes of terpenoids. A database that contains the13C NMR spectra of about 5000 compounds was used to train the FFNNs. An efficient representation of the spectra was designed and the constitution of the best FFNN input vector format resorted from an heuristic approach. The latter was derived from general considerations on terpenoid structures.
Keywords: Artificial neural networks; 13; C NMR; Spectroscopy; Terpenoids; Steroids
Voltammetric studies on the electrochemical determination of methylmercury in chloride medium at carbon microelectrodes by F. Ribeiro; M.M.M. Neto; M.M. Rocha; I.T.E. Fonseca (pp. 227-234).
Electroanalytical techniques have been used to determine methylmercury at low levels in environmental matrices. The electrochemical behaviour of methylmercury at carbon microelectrodes in a hydrochloric acid medium using cyclic, square wave and fast-scan linear-sweep voltammetric techniques has been investigated. The analytical utility of the methylmercury reoxidation peak has been explored, but the recorded peak currents were found to be poorly reproducible. This is ascribed to two factors: the adsorption of insoluble chloromercury compounds on the electrode surface, which appears to be an important contribution to hinder the voltammetric signal of methylmercury; and the competition between the reoxidation of the methylmercury radical and its dimerization reaction, which limits the reproducibility of the methylmercury peak. These problems were successfully overcome by adopting the appropriate experimental conditions. Fast-scan rates were employed and an efficient electrochemical regeneration procedure of the electrode surface was achieved, under potentiostatic conditions in a mercury-free solution containing potassium thiocyanate—a strong complexing agent. The influence of chloride ion concentration was analysed. Interference by metals, such as lead and cadmium, was considered. Calibration plots were obtained in the micromolar and submicromolar concentration ranges, allowing the electrochemical determination of methylmercury in trace amounts. An estuarine water sample was analysed using the new method with a glassy carbon microelectrode.
Keywords: Methylmercury determination; Carbon microelectrodes; Square wave voltammetry; Fast-scan linear-sweep voltammetry; Water analysis
Voltammetric studies on the electrochemical determination of methylmercury in chloride medium at carbon microelectrodes by F. Ribeiro; M.M.M. Neto; M.M. Rocha; I.T.E. Fonseca (pp. 227-234).
Electroanalytical techniques have been used to determine methylmercury at low levels in environmental matrices. The electrochemical behaviour of methylmercury at carbon microelectrodes in a hydrochloric acid medium using cyclic, square wave and fast-scan linear-sweep voltammetric techniques has been investigated. The analytical utility of the methylmercury reoxidation peak has been explored, but the recorded peak currents were found to be poorly reproducible. This is ascribed to two factors: the adsorption of insoluble chloromercury compounds on the electrode surface, which appears to be an important contribution to hinder the voltammetric signal of methylmercury; and the competition between the reoxidation of the methylmercury radical and its dimerization reaction, which limits the reproducibility of the methylmercury peak. These problems were successfully overcome by adopting the appropriate experimental conditions. Fast-scan rates were employed and an efficient electrochemical regeneration procedure of the electrode surface was achieved, under potentiostatic conditions in a mercury-free solution containing potassium thiocyanate—a strong complexing agent. The influence of chloride ion concentration was analysed. Interference by metals, such as lead and cadmium, was considered. Calibration plots were obtained in the micromolar and submicromolar concentration ranges, allowing the electrochemical determination of methylmercury in trace amounts. An estuarine water sample was analysed using the new method with a glassy carbon microelectrode.
Keywords: Methylmercury determination; Carbon microelectrodes; Square wave voltammetry; Fast-scan linear-sweep voltammetry; Water analysis