Automated derivatization and fluorimetric determination of biogenic amines in milk by zone fluidics coupled to liquid chromatography.

A novel zone-fluidics/high pressure liquid chromatographic (ZF-HPLC) method is described for the simultaneous determination of six biogenic monoamines, in the presence of hexylamine as internal standard. Automated on-line derivatization of the analytes with naphthalene-2,3-dicarboxaldehyde/cyanide ions was performed using the ZF concept and the derivatives were injected on the HPLC column for separation/detection. The influence of the ZF operation conditions on the derivatization reaction was investigated.

Zwitterionic hydrophilic interaction chromatography coupled with post-column derivatization for the analysis of glutathione in wine samples.

In this study the development, validation and application of a new chromatographic method for the determination of glutathione (GSH) in wine samples is presented. The separation of the GSH was carried out using a sulfobetaine-based hydrophilic interaction chromatography (HILIC) analytical column whereas its detection was carried out spectrofluorimetrically (λext/λem=340/455 nm) after post-column derivatization with o-phthalaldehyde. GSH was separated efficiently from matrix endogenous compounds of wines by using a mobile phase of 15 mmol L(-1) CH3COONH4 (pH=2.

Selective fluorimetric method for the determination of histamine in seafood samples based on the concept of zone fluidics.

In the present article we report our results on the development of a selective automated method for the determination of histamine in seafood using the concept of zone fluidics. The method is based on the sequential on-line reaction of the analyte with o-phthalaldehyde in the absence of a nucleophilic reagent, followed by acidification. The careful selection of the chemical and instrumental variables enabled the determination of the analyte with adequate sensitivity at the low micromolar level and with specificity against other biogenic amines and amino acids such as histidine.

Determination of glutathione and cysteine in yeasts by hydrophilic interaction liquid chromatography followed by on-line postcolumn derivatization.

In the present study, we report a new method for the determination of two primary thiols, cysteine (CYS) and glutathione (GSH), by hydrophilic interaction LC. The polar analytes are separated isocratically using a mobile phase consisting of 65% acetonitrile/35% ammonium acetate (15 mmol/L, pH 2.0) and are detected at 285 nm following on-line postcolumn derivatization by the thiol-selective reagent methyl propiolate.

On-line cleavage of disulfide bonds by soluble and immobilized tris-(2-carboxyethyl)phosphine using sequential injection analysis.

Reduction of disulfide bonds is - in many cases - a critical pretreatment step for the determination of thiols in real samples. This study reports the first systematic investigation of the potentials of the on-line reduction of disulfide bonds under flow conditions in a sequential injection setup. One of the most promising reducing agents, tris-(2-carboxyethyl)phosphine (TCEP) was selected for this purpose while the Ellman's disulfide (DTNB) was used as model compound.

Automated determination of total captopril in urine by liquid chromatography with post-column derivatization coupled to on-line solid phase extraction in a sequential injection manifold.

The present study reports a new liquid chromatographic (HPLC) method for the determination of the anti-hypertension drug captopril (CAP) in human urine. After its separation from the sample matrix in a reversed phase HPLC column, CAP reacts with the thiol-selective reagent ethyl-propiolate (EP) in a post-column configuration and the formed thioacrylate derivative is detected at 285 nm. Automated 4-fold preconcentration of the analyte prior to analysis was achieved by an on-line solid phase extraction (SPE) step using a sequential injection (SI) manifold.

Automated pre-column derivatization of thiolic fruit-antibrowning agents by sequential injection coupled to high-performance liquid chromatography using a monolithic stationary phase and an in-loop stopped-flow approach.

The present study reports the very first application of ethyl propiolate (EP) as an advantageous pre-column derivatization reagent for the determination of thiols by liquid chromatography (LC). Cysteine (CYS), glutathione (GSH) and N-acetylcysteine (NAC) were derivatized online under stopped-flow conditions in a sequential injection (SI) system coupled to HPLC. The formed derivatives were separated isocratically with a monolithic stationary phase (100×4.

Rapid determination of methylxanthines in real samples by high-performance liquid chromatography using the new FastGradient narrow-bore monolithic column.

The present study reports one of the very first analytical applications of the new narrow-bore monolithic column, FastGradient Chromolith (50mm x 2.0mm i.d.

Automated zone-sampling dilution by coupling sequential injection analysis to high-throughput HPLC for the direct determination of gemfibrozil.

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.

Ethyl-propiolate as a novel and promising analytical reagent for the derivatization of thiols: study of the reaction under flow conditions.

The present investigation demonstrates the potentials of ethyl-propiolate (EP), a novel derivatizing reagent for thiols. To the best of our knowledge this is the first systematic study of EP in analytical chemistry. The reaction was investigated under flow conditions using sequential injection (SI) analysis and UV detection at 285 nm.

Automated sample preparation coupled to sequential injection chromatography: on-line filtration and dilution protocols prior to separation.

Sequential injection chromatography (SIC) is a valuable tool in analytical chemistry as it can combine the automation capabilities of low pressure continuous flow techniques and the separation power of HPLC into a single instrumental configuration. The present study reports an automated SI setup allowing on-line filtration and dilution of the samples before separation through a short monolithic column. The applicability of the procedure was evaluated by studying the behavior of acyclovir formulations under forced degradation conditions.

Hybrid sequential injection-flow injection manifold for the spectrophotometric determination of total sulfite in wines using o-phthalaldehyde and gas-diffusion.

A new automated spectrophotometric method for the determination of total sulfite in white and red wines is reported. The assay is based on the reaction of o-phthalaldehyde (OPA) and ammonium chloride with the analyte in basic medium under SI conditions. Upon on-line alkalization with NaOH, a blue product is formed having an absorption maximum at 630 nm.

Selective determination of cyanides by gas diffusion-stopped flow-sequential injection analysis and an on-line standard addition approach.

A highly selective sequential injection (SI) method for the automated determination of weak-acid-dissociable cyanides is reported. The analytical procedure is based on the on-line reaction of the analyte with ninhydrin in carbonate medium to form a coloured product (lambda(max)=510 nm). Cyanides are removed from sample matrix by acidification through a gas-diffusion step incorporated in the SI manifold.

Separation and determination of nimesulide related substances for quality control purposes by micellar electrokinetic chromatography.

A micellar electrokinetic chromatography (MEKC) method has been developed and validated for the determination of nimesulide related compounds in pharmaceutical formulations. Electrophoretic separation of six European Pharmacopoeia (EP) impurities (A-F) was performed using a fused silica capillary (L(eff.)=50 cm, L(tot.

Flow injection direct spectrophotometric assay for the speciation of trace chromium(III) and chromium(VI) using chromotropic acid as chromogenic reagent.

A new rapid and sensitive FI assay is reported for the simultaneous direct spectrophotometric determination of trace Cr(VI) and Cr(III) in real samples. The method is based upon the reaction of Cr(VI) with chromotropic acid (CA) in highly acidic medium to form a water-soluble complex (lambda(max)=370nm). Cr(III) reacts with CA only after its on-line oxidation to Cr(VI) by alkaline KIO(4).

Flow injection spectrophotometric determination of fosfestrol, following on-line thermal induced digestion and using an orthophosphate calibration graph.

A novel flow injection (FI) system for the spectrophotometric determination of diethyl stilbestrol diphosphate (fosfestrol) in pharmaceutical formulations is described. On-line thermal induced digestion of the analyte by peroxodisulfate ion was performed and the orthophosphate ion generated was determined spectrophotometrically (lambda(max)=690 nm) using a molybdenum blue based FI approach. As the achieved conversion of the analyte was quantitative, an orthophosphate calibration graph can be used for its determination as well.

Reversed flow-injection manifold for the spectrophotometric determination of captopril based on its inhibitory effect on the Co(II)-2,2'-dipyridyl-2-pyridylhydrazone complex formation.

The present work reports a new, simple and rapid reversed flow-injection (r-FI) method for the accurate and precise spectrophotometric determination of captopril (CPL) in pharmaceutical formulations. The method is based on the inhibitory effect of CPL on the complex formation of Co(II) with 2,2'-dipyridyl-2-pyridylhydrazone (DPPH). The chemical and FI variables were studied and optimized.

Optimization and validation of a dissolution test for selegiline hydrochloride tablets by a novel rapid HPLC assay using a monolithic stationary phase.

The present study reports the optimization and validation of a dissolution test for selegiline.HCl tablets using a new high-performance liquid chromatographic (HPLC) method. Rapid separation of the analyte from sample matrix was achieved in less than 60s using a Cromolith RP-18e monolithic column using UV detection at 220 nm.

Enzymatic chemiluminescent assay of glucose by sequential-injection analysis with soluble enzyme and on-line sample dilution.

This work reports a sequential-injection analysis (SIA) method for the enzymatic assay of glucose with soluble glucose oxidase (GOD) and on-line sample dilution with chemiluminescence (CL) detection. A zone of sample was aspirated in the holding coil of the SIA manifold and, if necessary, was diluted on-line by means of an auxiliary dilution conduit. Then, a zone of GOD was aspirated adjacent to the sample zone and a stopped-flow period was applied to allow the enzymatic reaction to proceed with production of hydrogen peroxide.

Highly selective flow injection spectrophotometric determination of gold based on its catalytic effect on the oxidation of variamine blue by potassium iodate in aqueous N,N-dimethylformamide medium.

A highly selective and simple flow injection method is reported for the determination of Au(III) in jewel samples. The method is based on the catalytic effect of Au(III) on the oxidation of 4-amino-4'-methoxydiphenylamine hydrochloride (Variamine Blue B base, VB) by KIO(3). The colored reaction product was monitored spectrophotometrically at 546nm.

Review of recent applications of flow injection spectrophotometry to pharmaceutical analysis.

Pharmaceutical analysis is one of the most important fields in analytical chemistry. The discovery of new drugs and the on-going update of international regulations for the safety and efficacy of pharmaceutical formulations demand the continuous development of new analytical methods. Inevitably, automation plays an important role, especially when a lot of samples have to be analyzed in the minimum of time.

Development and validation of a high-throughput high-performance liquid chromatographic assay for the determination of caffeine in food samples using a monolithic column.

The present study reports the development and validation of a high-throughput high-performance liquid chromatographic (HPLC) assay for the determination of caffeine in food samples. The analyte was separated rapidly from sample matrix using a short monolithic column (50 mm x 4.6 mm i.

Selective stopped-flow sequential injection method for the spectrophotometric determination of titanium in dental implant and natural Moroccan phosphate rock.

The present work reports the first sequential injection (SI) method for the spectrophotometric determination of Ti(IV). The method is based upon the reaction of Ti(IV) with chromotropic acid (CA) in acidic medium to form a water-soluble complex (lambda(max)=420nm). The chemical and instrumental variables of the system that affected the reaction were studied.

Automated determination of flutamide by a validated flow-injection method: application to dissolution studies of pharmaceutical tablets.

The first flow-injection (FI) method for the determination of flutamide--a potent antiandrogen used for the treatment of prostate cancer--is reported. The method is based on the direct measurement of the absorbance of the analyte at 310 nm under flow conditions. Parameters affecting the determination such as detection wavelength, sample injection volume and flow rate were studied and optimized.

High-throughput HPLC assay of acyclovir and its major impurity guanine using a monolithic column and a flow gradient approach.

Acyclovir and its major impurity guanine are determined rapidly by the incorporation of a monolithic column (100 mm x 4.6 mm i.d.