Pantelis Rigas - Academia.edu (original) (raw)

Papers by Pantelis Rigas

Analytical Letters, 2016

ABSTRACT A postcolumn fluorescence reaction system for the high-performance liquid chromatographi... more ABSTRACT A postcolumn fluorescence reaction system for the high-performance liquid chromatographic (HPLC) determination of tetrodotoxin in the silver-cheeked toadfish Lagocephalus sceleratus is discussed theoretically and investigated experimentally. Ion-pair chromatography with volatile ammonium perfluoroheptanoate was used for the separation of tetrodotoxin and 4,9-anhydrotetrodotoxin. The postcolumn reaction was based on the tetrodotoxin conversion to a quinazoline fluorescent compound under strong alkaline conditions. All postcolumn parameters were optimized that affected the sensitivity, dispersion, and stability. Helically coiled and knitted open tubular reactors composed of polyetheretherketone were constructed and characterized in detail. The performance of these reactors was evaluated on the basis of sensitivity and dispersion. Their optimal design is reported. The knitted reactors were more efficient than the relevant helically coiled reactors when higher reaction times are required. A 1500-µL polyetheretherketone knitted coil with 0.010″ internal diameter was optimum exhibiting higher pressure tolerances than Teflon coils. The HPLC postcolumn reaction method was evaluated in terms of linearity, sensitivity, accuracy, precision, and ruggedness. The linear dynamic ranges for tetrodotoxin and 4,9-anhydrotetrodotoxin were 40–3000 and 80–3000 ppb, respectively. The limits of detection and quantification were 12 and 41 ppb, respectively, for tetrodotoxin and 26 and 85 ppb, respectively, for 4,9-anhydrotetrodotoxin. The accuracy was evaluated by recovery measurements and the values for tetrodotoxin were between 90.7 and 93.6%. The use of a volatile perfuorocarboxylic acid as an ion-pair reagent allows confirmation of analytes in sample matrix by liquid chromatography tandem mass spectrometry using identical mobile phase conditions.

Journal of Chromatography B: Biomedical Sciences and Applications, 1995

A high-performance liquid chromatographic analytical method was developed for the determination o... more A high-performance liquid chromatographic analytical method was developed for the determination of oxytetracycline in Artemia nauplii. A solid-phase extraction protocol was used to recover oxytetracycline and the internal standard tetracycline, from the Artemia samples. Oxytetracycline was analyzed using a 150 x 4.6 mm I.D. Hypersil-ODS column, a mobile phase of acetonitrile-tetrahydrofuran-0.01 M oxalic acid buffer (pH 3.0) (15:3:82, v/v), and an ultraviolet detection wavelength of 365 nm. The calibration curve of oxytetracycline in Artemia was linear (r 2-0.9998) from 0.1 to 6.4 /zg/g of tissue. Using a signal-to-noise ratio of 4:1 the oxytetracycline detection limit was 10 ng/g of tissue. Mean recovery of oxytetracycline amounted to 97%, while intra-assay variability was 1.5%. Quantitative data from an in-vivo feeding study indicated an excellent uptake of oxytetracycline by Artemia, as its levels reached 25.6/xg per g of nauplii.

Journal of Separation Science, 2009

A novel automated analytical scheme for the rapid determination of gemfibrozil in drug dissolutio... more A novel automated analytical scheme for the rapid determination of gemfibrozil in drug dissolution samples is reported. The procedure is based on direct coupling of a low pressure continuous flow technique such as sequential injection analysis (SI) to HPLC. SI performs automated dilution of the samples based on zone sampling and fills on-line the loop of the high pressure injection valve. Rapid separation of the analyte from the samples' matrix can be achieved in less than 1.0 min, by using a short RP monolithic column (25x4.6 mm id) at a flow rate of 2 mL/min. The SI and HPLC parts of the setup operate independently: during HPLC separation the next sample is treated by SI. This way a maximum throughput of 60 samples per hour is achieved allowing the complete analysis of a batch of six dissolution samples within 12-18 min based on the replicates. The proposed method was validated in terms of linearity, LOD and LOQ, precision, selectivity and accuracy. Its applicability was tested during quality control of four validation batches of a gemfibrozil-containing formulation. The results were in good agreement with the HPLC method proposed by the US Pharmacopeia.

Journal of Pharmaceutical and Biomedical Analysis, 2008

The first automated method for the determination of mexiletine hydrochloride - an antiarrhythmic ... more The first automated method for the determination of mexiletine hydrochloride - an antiarrhythmic agent - is reported. The method is based on the reaction of the analyte with o-phthalaldehyde (OPA) in the presence of sulfite in basic medium using a sequential injection (SI) manifold. The reaction product was monitored spectrofluorimetrically (lambda(ex)=350 nm/lambda(em)=446 nm). A simple and effective on-line dilution approach was adopted in order to expand the linearity and apply the method to assay, dosage uniformity and dissolution tests with minimum sample preparation. Chemical (pH, amount concentrations of OPA and sulfite) and instrumental variables (temperature, flow rate, injection volumes, etc.) that affected the determination were studied. The developed assay was validated in terms of linearity, range, limits of detection (LOD=3.4 mg L(-1)) and quantitation (LOQ=10 mg L(-1)), accuracy, precision (R.S.D.<3.4%) and selectivity. The method was applied successfully to the quality control of a mexiletine-containing formulation. The results were in good agreement with the US pharmacopoeia HPLC method.

Journal of Chromatography B, 2008

A new, sensitive method was developed for the determination of the neurotoxin domoic acid (DA) us... more A new, sensitive method was developed for the determination of the neurotoxin domoic acid (DA) using a reversed phase separation followed by post-column derivatization (PCD) with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) and subsequent fluorescence detection. The PCD conditions which involves a two-step reaction was fully optimized for the lowest detection limit. The first reaction occurs between DA and NBD-Cl while the second makes possible the detection of the derivative causing the destruction of the interfering fluorescent 4-hydroxy-7-nitrobenzo-2-oxa-1,3-diazole (NBD-OH) which is the hydrolysis product of NBD-Cl. Kainic acid a similar base structure compound with DA was used as an internal standard. The developed post-column method provides the ability for a fully automated analysis, low detection limits (LOD 25 ppb in real samples of mussel extracts), it requires less sample preparation, and it gives clean simple chromatograms without chromatographic interferences from coeluting compounds such as tryptophan. The method was successfully applied to for the quantitative determination of DA in mussel tissues at quantities as low as 75 microg/kg tissue.

Journal of Chromatographic Science, 1989

Iron(II) 1,10-phenanthroline, Fe(phen)3(2+), salts are used as mobile phase additives for the liq... more Iron(II) 1,10-phenanthroline, Fe(phen)3(2+), salts are used as mobile phase additives for the liquid chromatographic separation of alkyl sulfonates and sulfates on the reversed-phase PRP-1. As alkyl chain length increases retention increases. For a given chain length an alkyl sulfate is more retained than the corresponding alkyl sulfonate. Major elution variables that affect retention are mobile phase solvent and counteranion concentration. Indirect photometric detection is used to detect alkyl sulfonates and sulfates at 510 nm where Fe(phen)3(2+) salts absorb. Conditions for isocratic and gradient elution of multicomponent mixtures are described. Detection limits depending on analyte approached 0.1 nmol for isocratic elution and 3 nmol for gradient elution.

Instrumentation Science & Technology, 2012

Amino acid analysis (AAA) is widely used for determining the composition of proteins and their co... more Amino acid analysis (AAA) is widely used for determining the composition of proteins and their concentration in foods, biological fluids, and tissues. Because of the vast number of amino acids, the chromatographic techniques provide separations of them based either on the charge or on hydrophobicity differences. Several chromatographic techniques have been applied for this purpose, with the method of choice being ion-exchange chromatography followed by postcolumn derivatization, as a more rugged and reproducible method provides excellent amino acid separation with relative freedom from interferences. This review considers recent relative reviews, current separation techniques, the most popular post-column reactions for amino acid analysis, comparison with the pre-column methods, the strategies used to develop effective post-column methodology, instrumentation technology, and applications in food and clinical analysis. The focus of the article is on liquid chromatographic methods coupled with post-column derivatization in order to increase sensitivity and selectivity, illustrating the versatility of the post-column derivatization (PCD) instrumentation for practical analysis.

Central European Journal of Chemistry, 2012

The first HPLC method for the separation of three paraben preservatives (methyl-, ethyl- and prop... more The first HPLC method for the separation of three paraben preservatives (methyl-, ethyl- and propyl parabens) using a core-shell analytical column is reported in this study. The separation was completed in less than 8 min at a low flow rate of 0.4 mL min−1 and an isocratic mobile phase containing 20% acetonitrile as organic modifier. The backpressure was HPLC equipment. The proposed analytical procedure was validated for linearity (0.5–20 µg L−1), limits of detection (15–43 µg L−1) and quantification (50–142 µg L−1), selectivity, within day (1.3–1.5%) and day-to-day (3.4–4.6%) precision and accuracy. The proposed method has been applied to the determination of the selected paraben preservatives in commercially available hygiene wipes. The mean percent recoveries were found to be in the range of 98.0–98.4%.

Aquaculture, 1995

Large phospholipid vesicles loaded with the water soluble antibiotic oxytetracycline were formed ... more Large phospholipid vesicles loaded with the water soluble antibiotic oxytetracycline were formed using the reverse phase evaporation technique. Addition of cholesterol in the lipid phase and suspension of the liposomes in low pH solutions, greatly improved stability of the ...

Analytical Letters, 2011

In this study 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) is proposed as a postcolumn deriva... more In this study 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) is proposed as a postcolumn derivatization (PCD) reagent for the fluorescence detection of aliphatic primary and secondary amines after HPLC separation. Five primary (methylamine, isoamylamine, 2-phenylethylamine, putrescine, and histamine) and one secondary amine (dimethylamine) were separated isocratically on a cation-exchange column using HNO 3 (5 Â 10 À3 mol L À1) as the mobile phase. Post-column derivatization was based on two steps: 1) the derivatization of amines with NBD-Cl in alkaline medium, and 2) the acidification of the resulted mixture in order to minimize the background signal of the reagent and improve dramatically the sensitivity and determination range. The variables of the post-column reaction (concentration of NBD-Cl, buffer concentration and pH, reaction temperature, concentration of HCl, flow rates of the reagents) were thoroughly investigated. Critical chromatographic parameters such as the concentration of HNO 3 , the percentage of organic solvent, and the column temperature were also examined to achieve adequate separation. An internal standard of 1,7-diaminoheptane was used. The developed post-column method provides the ability for a fully automated analysis, low detection limits (LODs 20-100 lg L À1 with S/N ¼ 3), and it requires less sample preparation. The applicability of the proposed analytical scheme was demonstrated by the determination of histamine (HIS) in tuna fish tissues according to US Food and Drug Administration (FDA) guidelines.

Analytical Chemistry, 1988

Analytical Chemistry, 1988

Ruthenium(I I) 1,lO-phenanthrotlne and 2,2'-blpyridlne complexes are used as mobile phase additiv... more Ruthenium(I I) 1,lO-phenanthrotlne and 2,2'-blpyridlne complexes are used as mobile phase additives for the liquid chromatographic separatlon of inorganic and organic analyte anlons on Hamilton PRP-1. The Ru(I I) complexes act as ion interactlon reagents for analyte anion separations and, because the complexes are fluorescent, anions can be detected by Indirect fluorescence detectlon (IFD). Indirect photometric detectlon (IPD) is also posslble. Parameters affecting analyte anion retention are Ru(I I) complex concentratlon, type of ligand in the complex, analyte anion selectivity, type and concentration of counteranlon, pH, and type and concentration of buffer components. Complex mixtures of inorganlc and/or organic analyte anlons can be separated and detected. For IFD a linear detector response was found for an analyte anion (F-) concentratlon from 20 to 500 ng; the detection limit at a 2 1 slgnai:ndse ratlo was 10 ng of F-. IPD detection limlt for Fusing a Ru(bpy)t+ or a Ru(phen)t+ complex was about 0.8 and 0.4 ng, respectively.

Analytical Chemistry, 1986

Page 1. 2228 PRP-1 column (0.1-1.0 FgmL-') and on a C18 reversed phase (18-58 pgmL-1) were l... more Page 1. 2228 PRP-1 column (0.1-1.0 FgmL-') and on a C18 reversed phase (18-58 pgmL-1) were linear with a negative Yaxis intercept equivalent to 0.05 and 0.04 pgmL-' U(V1) respectively. Anal. Chem. 1988, 58, 2226-2233 ...

Vlaams Instituut voor de Zee. VLIZ. Informatie over marien en kustgebonden onderzoek & beleid in ... more Vlaams Instituut voor de Zee. VLIZ. Informatie over marien en kustgebonden onderzoek & beleid in Vlaanderen.

Analytical and Bioanalytical Chemistry, 2004

The present work reports for the first time a simple and rapid method for the spectrofluorimetric... more The present work reports for the first time a simple and rapid method for the spectrofluorimetric determination of lisinopril (LSP) in pharmaceutical formulations using sequential injection analysis (SIA). The method is based on reaction of LSP with o-phthalaldehyde (OPA) in the presence of 2-mercaptoethanol (borate buffer medium, pH=10.6). The emission of the derivative is monitored at 455 nm upon excitation at 346 nm. The various chemical and physical conditions that affected the reaction were studied. The calibration curve was linear in the range 0.3-10.0 mg L(-1) LSP, at a sampling rate of 60 injections h(-1). Consumption of OPA reagent was significantly reduced compared with conventional flow injection (FI) systems, because only 50 microL of OPA was consumed per run. The method was found to be adequately precise ( s(r)=2% at 5 mg L(-1) LSP, n=10) and the 3 sigma detection limit was 0.1 mg L(-1). The method was successfully applied to the analysis of two pharmaceutical formulations containing LSP. The results obtained were in good agreement with those obtained by use of high-performance liquid chromatography (HPLC), because the mean relative error, e(r), was <1.8%.

Analytica Chimica Acta, 2004

... 1. It comprised the following parts: a micro-electrically actuated 10-port valve (Valco, Swit... more ... 1. It comprised the following parts: a micro-electrically actuated 10-port valve (Valco, Switzerland), a spectrofluorimeter (Fasma 502, Rigas Labs, Thessaloniki, Greece) with a 18 ??l flow cell and a peristaltic pump (Gilson Minipuls3, Villiers-le-Bel, France). ...

Analytical and Bioanalytical Chemistry, 2013

Amino acid analysis (AAA) has always presented an analytical challenge in terms of sample prepara... more Amino acid analysis (AAA) has always presented an analytical challenge in terms of sample preparation, separation, and detection. Because of the vast number of amino acids, various separation methods have been applied taking into consideration the large differences in their chemical structures, which span from nonpolar to highly polar side chains. Numerous separation methods have been developed in the past 60 years, and impressive achievements have been made in the fields of separation, derivatization, and detection of amino acids (AAs). Among the separation methods, liquid chromatography (LC) prevailed in the AAA field using either pre-column or post-column labeling techniques in order to improve either separation of AAs or selectivity and sensitivity of AAA. Of the two approaches, the post-column technique is a more rugged and reproducible method and provides excellent AAs separation relatively free from interferences. This review considers current separations combined with post-column labeling techniques for AAA, comparison with the pre-column methods, and the strategies used to develop effective post-column methodology. The focus of the article is on LC methods coupled with post-column labeling techniques and studying the reactions to achieve optimum post-column derivatization (PCD) conditions in order to increase sensitivity and selectivity using various types of detectors (UV-Vis, fluorescence, electrochemical etc.) and illustrating the versatility of the PCD methods for practical analysis.

Journal of Chromatography B: Biomedical Sciences and Applications, 1995

A high-performance liquid chromatographic analytical method was developed for the determination o... more A high-performance liquid chromatographic analytical method was developed for the determination of oxytetracycline in Artemia nauplii. A solid-phase extraction protocol was used to recover oxytetracycline and the internal standard tetracycline, from the Artemia samples. Oxytetracycline was analyzed using a 150 x 4.6 mm I.D. Hypersil-ODS column, a mobile phase of acetonitrile-tetrahydrofuran-0.01 M oxalic acid buffer (pH 3.0) (15:3:82, v/v), and an ultraviolet detection wavelength of 365 nm. The calibration curve of oxytetracycline in Artemia was linear (r 2-0.9998) from 0.1 to 6.4 /zg/g of tissue. Using a signal-to-noise ratio of 4:1 the oxytetracycline detection limit was 10 ng/g of tissue. Mean recovery of oxytetracycline amounted to 97%, while intra-assay variability was 1.5%. Quantitative data from an in-vivo feeding study indicated an excellent uptake of oxytetracycline by Artemia, as its levels reached 25.6/xg per g of nauplii.

Analytical Letters, 2016

ABSTRACT A postcolumn fluorescence reaction system for the high-performance liquid chromatographi... more ABSTRACT A postcolumn fluorescence reaction system for the high-performance liquid chromatographic (HPLC) determination of tetrodotoxin in the silver-cheeked toadfish Lagocephalus sceleratus is discussed theoretically and investigated experimentally. Ion-pair chromatography with volatile ammonium perfluoroheptanoate was used for the separation of tetrodotoxin and 4,9-anhydrotetrodotoxin. The postcolumn reaction was based on the tetrodotoxin conversion to a quinazoline fluorescent compound under strong alkaline conditions. All postcolumn parameters were optimized that affected the sensitivity, dispersion, and stability. Helically coiled and knitted open tubular reactors composed of polyetheretherketone were constructed and characterized in detail. The performance of these reactors was evaluated on the basis of sensitivity and dispersion. Their optimal design is reported. The knitted reactors were more efficient than the relevant helically coiled reactors when higher reaction times are required. A 1500-µL polyetheretherketone knitted coil with 0.010″ internal diameter was optimum exhibiting higher pressure tolerances than Teflon coils. The HPLC postcolumn reaction method was evaluated in terms of linearity, sensitivity, accuracy, precision, and ruggedness. The linear dynamic ranges for tetrodotoxin and 4,9-anhydrotetrodotoxin were 40–3000 and 80–3000 ppb, respectively. The limits of detection and quantification were 12 and 41 ppb, respectively, for tetrodotoxin and 26 and 85 ppb, respectively, for 4,9-anhydrotetrodotoxin. The accuracy was evaluated by recovery measurements and the values for tetrodotoxin were between 90.7 and 93.6%. The use of a volatile perfuorocarboxylic acid as an ion-pair reagent allows confirmation of analytes in sample matrix by liquid chromatography tandem mass spectrometry using identical mobile phase conditions.

Journal of Chromatography B: Biomedical Sciences and Applications, 1995

A high-performance liquid chromatographic analytical method was developed for the determination o... more A high-performance liquid chromatographic analytical method was developed for the determination of oxytetracycline in Artemia nauplii. A solid-phase extraction protocol was used to recover oxytetracycline and the internal standard tetracycline, from the Artemia samples. Oxytetracycline was analyzed using a 150 x 4.6 mm I.D. Hypersil-ODS column, a mobile phase of acetonitrile-tetrahydrofuran-0.01 M oxalic acid buffer (pH 3.0) (15:3:82, v/v), and an ultraviolet detection wavelength of 365 nm. The calibration curve of oxytetracycline in Artemia was linear (r 2-0.9998) from 0.1 to 6.4 /zg/g of tissue. Using a signal-to-noise ratio of 4:1 the oxytetracycline detection limit was 10 ng/g of tissue. Mean recovery of oxytetracycline amounted to 97%, while intra-assay variability was 1.5%. Quantitative data from an in-vivo feeding study indicated an excellent uptake of oxytetracycline by Artemia, as its levels reached 25.6/xg per g of nauplii.

Journal of Separation Science, 2009

A novel automated analytical scheme for the rapid determination of gemfibrozil in drug dissolutio... more A novel automated analytical scheme for the rapid determination of gemfibrozil in drug dissolution samples is reported. The procedure is based on direct coupling of a low pressure continuous flow technique such as sequential injection analysis (SI) to HPLC. SI performs automated dilution of the samples based on zone sampling and fills on-line the loop of the high pressure injection valve. Rapid separation of the analyte from the samples' matrix can be achieved in less than 1.0 min, by using a short RP monolithic column (25x4.6 mm id) at a flow rate of 2 mL/min. The SI and HPLC parts of the setup operate independently: during HPLC separation the next sample is treated by SI. This way a maximum throughput of 60 samples per hour is achieved allowing the complete analysis of a batch of six dissolution samples within 12-18 min based on the replicates. The proposed method was validated in terms of linearity, LOD and LOQ, precision, selectivity and accuracy. Its applicability was tested during quality control of four validation batches of a gemfibrozil-containing formulation. The results were in good agreement with the HPLC method proposed by the US Pharmacopeia.

Journal of Pharmaceutical and Biomedical Analysis, 2008

The first automated method for the determination of mexiletine hydrochloride - an antiarrhythmic ... more The first automated method for the determination of mexiletine hydrochloride - an antiarrhythmic agent - is reported. The method is based on the reaction of the analyte with o-phthalaldehyde (OPA) in the presence of sulfite in basic medium using a sequential injection (SI) manifold. The reaction product was monitored spectrofluorimetrically (lambda(ex)=350 nm/lambda(em)=446 nm). A simple and effective on-line dilution approach was adopted in order to expand the linearity and apply the method to assay, dosage uniformity and dissolution tests with minimum sample preparation. Chemical (pH, amount concentrations of OPA and sulfite) and instrumental variables (temperature, flow rate, injection volumes, etc.) that affected the determination were studied. The developed assay was validated in terms of linearity, range, limits of detection (LOD=3.4 mg L(-1)) and quantitation (LOQ=10 mg L(-1)), accuracy, precision (R.S.D.<3.4%) and selectivity. The method was applied successfully to the quality control of a mexiletine-containing formulation. The results were in good agreement with the US pharmacopoeia HPLC method.

Journal of Chromatography B, 2008

A new, sensitive method was developed for the determination of the neurotoxin domoic acid (DA) us... more A new, sensitive method was developed for the determination of the neurotoxin domoic acid (DA) using a reversed phase separation followed by post-column derivatization (PCD) with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) and subsequent fluorescence detection. The PCD conditions which involves a two-step reaction was fully optimized for the lowest detection limit. The first reaction occurs between DA and NBD-Cl while the second makes possible the detection of the derivative causing the destruction of the interfering fluorescent 4-hydroxy-7-nitrobenzo-2-oxa-1,3-diazole (NBD-OH) which is the hydrolysis product of NBD-Cl. Kainic acid a similar base structure compound with DA was used as an internal standard. The developed post-column method provides the ability for a fully automated analysis, low detection limits (LOD 25 ppb in real samples of mussel extracts), it requires less sample preparation, and it gives clean simple chromatograms without chromatographic interferences from coeluting compounds such as tryptophan. The method was successfully applied to for the quantitative determination of DA in mussel tissues at quantities as low as 75 microg/kg tissue.

Journal of Chromatographic Science, 1989

Iron(II) 1,10-phenanthroline, Fe(phen)3(2+), salts are used as mobile phase additives for the liq... more Iron(II) 1,10-phenanthroline, Fe(phen)3(2+), salts are used as mobile phase additives for the liquid chromatographic separation of alkyl sulfonates and sulfates on the reversed-phase PRP-1. As alkyl chain length increases retention increases. For a given chain length an alkyl sulfate is more retained than the corresponding alkyl sulfonate. Major elution variables that affect retention are mobile phase solvent and counteranion concentration. Indirect photometric detection is used to detect alkyl sulfonates and sulfates at 510 nm where Fe(phen)3(2+) salts absorb. Conditions for isocratic and gradient elution of multicomponent mixtures are described. Detection limits depending on analyte approached 0.1 nmol for isocratic elution and 3 nmol for gradient elution.

Instrumentation Science & Technology, 2012

Amino acid analysis (AAA) is widely used for determining the composition of proteins and their co... more Amino acid analysis (AAA) is widely used for determining the composition of proteins and their concentration in foods, biological fluids, and tissues. Because of the vast number of amino acids, the chromatographic techniques provide separations of them based either on the charge or on hydrophobicity differences. Several chromatographic techniques have been applied for this purpose, with the method of choice being ion-exchange chromatography followed by postcolumn derivatization, as a more rugged and reproducible method provides excellent amino acid separation with relative freedom from interferences. This review considers recent relative reviews, current separation techniques, the most popular post-column reactions for amino acid analysis, comparison with the pre-column methods, the strategies used to develop effective post-column methodology, instrumentation technology, and applications in food and clinical analysis. The focus of the article is on liquid chromatographic methods coupled with post-column derivatization in order to increase sensitivity and selectivity, illustrating the versatility of the post-column derivatization (PCD) instrumentation for practical analysis.

Central European Journal of Chemistry, 2012

The first HPLC method for the separation of three paraben preservatives (methyl-, ethyl- and prop... more The first HPLC method for the separation of three paraben preservatives (methyl-, ethyl- and propyl parabens) using a core-shell analytical column is reported in this study. The separation was completed in less than 8 min at a low flow rate of 0.4 mL min−1 and an isocratic mobile phase containing 20% acetonitrile as organic modifier. The backpressure was HPLC equipment. The proposed analytical procedure was validated for linearity (0.5–20 µg L−1), limits of detection (15–43 µg L−1) and quantification (50–142 µg L−1), selectivity, within day (1.3–1.5%) and day-to-day (3.4–4.6%) precision and accuracy. The proposed method has been applied to the determination of the selected paraben preservatives in commercially available hygiene wipes. The mean percent recoveries were found to be in the range of 98.0–98.4%.

Aquaculture, 1995

Large phospholipid vesicles loaded with the water soluble antibiotic oxytetracycline were formed ... more Large phospholipid vesicles loaded with the water soluble antibiotic oxytetracycline were formed using the reverse phase evaporation technique. Addition of cholesterol in the lipid phase and suspension of the liposomes in low pH solutions, greatly improved stability of the ...

Analytical Letters, 2011

In this study 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) is proposed as a postcolumn deriva... more In this study 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) is proposed as a postcolumn derivatization (PCD) reagent for the fluorescence detection of aliphatic primary and secondary amines after HPLC separation. Five primary (methylamine, isoamylamine, 2-phenylethylamine, putrescine, and histamine) and one secondary amine (dimethylamine) were separated isocratically on a cation-exchange column using HNO 3 (5 Â 10 À3 mol L À1) as the mobile phase. Post-column derivatization was based on two steps: 1) the derivatization of amines with NBD-Cl in alkaline medium, and 2) the acidification of the resulted mixture in order to minimize the background signal of the reagent and improve dramatically the sensitivity and determination range. The variables of the post-column reaction (concentration of NBD-Cl, buffer concentration and pH, reaction temperature, concentration of HCl, flow rates of the reagents) were thoroughly investigated. Critical chromatographic parameters such as the concentration of HNO 3 , the percentage of organic solvent, and the column temperature were also examined to achieve adequate separation. An internal standard of 1,7-diaminoheptane was used. The developed post-column method provides the ability for a fully automated analysis, low detection limits (LODs 20-100 lg L À1 with S/N ¼ 3), and it requires less sample preparation. The applicability of the proposed analytical scheme was demonstrated by the determination of histamine (HIS) in tuna fish tissues according to US Food and Drug Administration (FDA) guidelines.

Analytical Chemistry, 1988

Analytical Chemistry, 1988

Ruthenium(I I) 1,lO-phenanthrotlne and 2,2'-blpyridlne complexes are used as mobile phase additiv... more Ruthenium(I I) 1,lO-phenanthrotlne and 2,2'-blpyridlne complexes are used as mobile phase additives for the liquid chromatographic separatlon of inorganic and organic analyte anlons on Hamilton PRP-1. The Ru(I I) complexes act as ion interactlon reagents for analyte anion separations and, because the complexes are fluorescent, anions can be detected by Indirect fluorescence detectlon (IFD). Indirect photometric detectlon (IPD) is also posslble. Parameters affecting analyte anion retention are Ru(I I) complex concentratlon, type of ligand in the complex, analyte anion selectivity, type and concentration of counteranlon, pH, and type and concentration of buffer components. Complex mixtures of inorganlc and/or organic analyte anlons can be separated and detected. For IFD a linear detector response was found for an analyte anion (F-) concentratlon from 20 to 500 ng; the detection limit at a 2 1 slgnai:ndse ratlo was 10 ng of F-. IPD detection limlt for Fusing a Ru(bpy)t+ or a Ru(phen)t+ complex was about 0.8 and 0.4 ng, respectively.

Analytical Chemistry, 1986

Page 1. 2228 PRP-1 column (0.1-1.0 FgmL-') and on a C18 reversed phase (18-58 pgmL-1) were l... more Page 1. 2228 PRP-1 column (0.1-1.0 FgmL-') and on a C18 reversed phase (18-58 pgmL-1) were linear with a negative Yaxis intercept equivalent to 0.05 and 0.04 pgmL-' U(V1) respectively. Anal. Chem. 1988, 58, 2226-2233 ...

Vlaams Instituut voor de Zee. VLIZ. Informatie over marien en kustgebonden onderzoek & beleid in ... more Vlaams Instituut voor de Zee. VLIZ. Informatie over marien en kustgebonden onderzoek & beleid in Vlaanderen.

Analytical and Bioanalytical Chemistry, 2004

The present work reports for the first time a simple and rapid method for the spectrofluorimetric... more The present work reports for the first time a simple and rapid method for the spectrofluorimetric determination of lisinopril (LSP) in pharmaceutical formulations using sequential injection analysis (SIA). The method is based on reaction of LSP with o-phthalaldehyde (OPA) in the presence of 2-mercaptoethanol (borate buffer medium, pH=10.6). The emission of the derivative is monitored at 455 nm upon excitation at 346 nm. The various chemical and physical conditions that affected the reaction were studied. The calibration curve was linear in the range 0.3-10.0 mg L(-1) LSP, at a sampling rate of 60 injections h(-1). Consumption of OPA reagent was significantly reduced compared with conventional flow injection (FI) systems, because only 50 microL of OPA was consumed per run. The method was found to be adequately precise ( s(r)=2% at 5 mg L(-1) LSP, n=10) and the 3 sigma detection limit was 0.1 mg L(-1). The method was successfully applied to the analysis of two pharmaceutical formulations containing LSP. The results obtained were in good agreement with those obtained by use of high-performance liquid chromatography (HPLC), because the mean relative error, e(r), was <1.8%.

Analytica Chimica Acta, 2004

... 1. It comprised the following parts: a micro-electrically actuated 10-port valve (Valco, Swit... more ... 1. It comprised the following parts: a micro-electrically actuated 10-port valve (Valco, Switzerland), a spectrofluorimeter (Fasma 502, Rigas Labs, Thessaloniki, Greece) with a 18 ??l flow cell and a peristaltic pump (Gilson Minipuls3, Villiers-le-Bel, France). ...

Analytical and Bioanalytical Chemistry, 2013

Amino acid analysis (AAA) has always presented an analytical challenge in terms of sample prepara... more Amino acid analysis (AAA) has always presented an analytical challenge in terms of sample preparation, separation, and detection. Because of the vast number of amino acids, various separation methods have been applied taking into consideration the large differences in their chemical structures, which span from nonpolar to highly polar side chains. Numerous separation methods have been developed in the past 60 years, and impressive achievements have been made in the fields of separation, derivatization, and detection of amino acids (AAs). Among the separation methods, liquid chromatography (LC) prevailed in the AAA field using either pre-column or post-column labeling techniques in order to improve either separation of AAs or selectivity and sensitivity of AAA. Of the two approaches, the post-column technique is a more rugged and reproducible method and provides excellent AAs separation relatively free from interferences. This review considers current separations combined with post-column labeling techniques for AAA, comparison with the pre-column methods, and the strategies used to develop effective post-column methodology. The focus of the article is on LC methods coupled with post-column labeling techniques and studying the reactions to achieve optimum post-column derivatization (PCD) conditions in order to increase sensitivity and selectivity using various types of detectors (UV-Vis, fluorescence, electrochemical etc.) and illustrating the versatility of the PCD methods for practical analysis.

Journal of Chromatography B: Biomedical Sciences and Applications, 1995

A high-performance liquid chromatographic analytical method was developed for the determination o... more A high-performance liquid chromatographic analytical method was developed for the determination of oxytetracycline in Artemia nauplii. A solid-phase extraction protocol was used to recover oxytetracycline and the internal standard tetracycline, from the Artemia samples. Oxytetracycline was analyzed using a 150 x 4.6 mm I.D. Hypersil-ODS column, a mobile phase of acetonitrile-tetrahydrofuran-0.01 M oxalic acid buffer (pH 3.0) (15:3:82, v/v), and an ultraviolet detection wavelength of 365 nm. The calibration curve of oxytetracycline in Artemia was linear (r 2-0.9998) from 0.1 to 6.4 /zg/g of tissue. Using a signal-to-noise ratio of 4:1 the oxytetracycline detection limit was 10 ng/g of tissue. Mean recovery of oxytetracycline amounted to 97%, while intra-assay variability was 1.5%. Quantitative data from an in-vivo feeding study indicated an excellent uptake of oxytetracycline by Artemia, as its levels reached 25.6/xg per g of nauplii.