Sequential Injection Analysis Method for the Determination of Glutathione in Pharmaceuticals.

A sequential injection analysis method for the determination of glutathione (GSH) in pharmaceuticals has been developed. It is based on the reduction of the Cu(II)-neocuproine complex by GSH and the formation of an orange-yellow colored Cu(I)-neocuproine complex with maximum absorbance at 458 nm. Under optimal conditions the method is characterized by a linear calibration range of 6.0 × 10-7-8.0 × 10-5 mol L-1 (Amax = 3270 CGSH - 0.0010; R2 = 0.9983), limit of detection of 2.0 × 10-7 mol L-1, limit of quantification of 6.7 × 10-7 mol L-1, repeatability (expressed as relative standard deviation) of 3.8%, and sampling rate of 60 h-1. The newly developed method has been successfully applied to the determination of GSH in pharmaceutical samples with no statistically significant difference between the results obtained and those produced by the standard Pharmacopoeia method.

Efficient derivatization-free monitoring of glycosyltransferase reactions via flow injection analysis-mass spectrometry for rapid sugar analytics.

The widespread application of enzymes in industrial chemical synthesis requires efficient process control to maintain high yields and purity. Flow injection analysis-electrospray ionization-mass spectrometry (FIA-ESI-MS) offers a promising solution for real-time monitoring of these enzymatic processes, particularly when handling challenging compounds like sugars and glycans, which are difficult to quickly analyze using liquid chromatography-mass spectrometry due to their physical properties or the requirement for a derivatization step beforehand. This study compares the performance of FIA-MS with traditional hydrophilic interaction liquid chromatography (HILIC)-ultra high-performance liquid chromatography (UHPLC)-mass spectrometry (MS) setups for the monitoring of the enzymatic synthesis of N-acetyllactosamine (LacNAc) using beta-1,4-galactosyltransferase. Our results show that FIA-MS, without prior chromatographic separation or derivatization, can quickly generate accurate mass spectrometric data within minutes, contrasting with the lengthy separations required by LC-MS methods. The rapid data acquisition of FIA-MS enables effective real-time monitoring and adjustment of the enzymatic reactions. Furthermore, by eliminating the derivatization step, this method offers the possibility of being directly coupled to a continuously operated reactor, thus providing a rapid on-line methodology for glycan synthesis as well.

Gold leaf electrochemical flow cell for determination of iodide in nuclear emergency tablets.

This work introduces an innovative gold-leaf flow cell for electrochemical detection in flow injection (FI) analysis. The flow cell incorporates a hammered custom gold leaf electrochemical sensor. Hammered gold leaves consist of pure gold and are readily available in Thailand at affordable prices (approximately $0.085 for a sheet measuring 40 mm × 40 mm). Four sensing devices can be made from a single sheet of this gold leaf, resulting in a production cost of approximately $0.19 per sensor. Each electrochemical sensor has the gold leaf as the working electrode, together with a printed carbon strip, and a printed silver/silver chloride strip as the counter and reference electrodes, respectively. Initial investigations using cyclic voltammetry of a standard 1000 µmol L⁻1 iodide solution in 60 mmol L⁻1 phosphate buffer (PB) solution at pH 5, demonstrated performance comparable to that of a commercial screen-printed gold electrode. The hammered gold leaf electrode was then installed in a commercial flow cell as part of an FI system. A sample or standard iodide solution (100 µL) is injected into the first carrier stream of phosphate buffer (PB) solution, which then merges to mix with the second stream of the same buffer solution before flowing into the flow cell for amperometric detection of iodide. The optimized operating conditions include a fixed potential of +0.39 V (vs Ag/AgCl), and a total flow rate of 3 mL min⁻1. A linear calibration is obtained in the concentration range of 1 to 1000 µmol L⁻1 I- with a typical equation of µA = (0.00299 ± 0.00004) × (µmol L-1 I-) + (0.021 ± 0.020), and R2 = 0.9994. Analysis of iodide using this gold leaf-FI system is rapid with sample throughput of 86 samples h⁻1 and %RSD of a sample of 100 µmol L⁻1 I⁻ of 1.2 (n = 29). The limit of detection, (calculated as 2.78 × SD of regression line/slope), is 27 µmol L⁻1 I-. This method was successfully applied to determine iodide in nuclear emergency tablets.

Precise evaluation of batch adsorption kinetics of plant total polyphenols based on a flow-injection online spectrophotometric method.

Efficient evaluation of adsorption kinetics of plant total polyphenols is essential for the design of adsorption separation of bioactive compounds. The conventional method uses manual sampling with poor reproducibility. Here, we developed a new method for on-line determination of total polyphenol content (TPC) in plant extracts by applying the Folin-Ciocalteu method in flow-injection analysis (FIA). The FIA parameters were optimized and a standard curve with excellent linearity was established. Precise determination of TPC with a satisfactory sample throughput of 20 h-1 was achieved for the adsorption kinetic study. The pseudo-second-order kinetic model was found to better describe the kinetic parameters of the batch adsorption/desorption process. The developed method proved to be accurate compared with the conventional method. The FIA method holds significant promise for studying and monitoring adsorption processes, due to its automatic on-line nature, low consumption of reagents and samples, and the ability to generate large quantities of highly accurate adsorption data.

Flow injection assays for NADH and ethanol using photosensitized rose bengal and luminol-copper (II) chemiluminescence system.

The online photoreaction of the rose bengal photosensitized luminol-copper (II) chemiluminescence (CL) system was used for the determination of ß-nicotinamide adenine dinucleotide (NADH) and ethanol (EtOH) in pharmaceutical formulations combined with a flow injection technique. NADH can significantly enhance the CL emission of the reaction. For EtOH, alcohol dehydrogenase in soluble form was utilized in the presence of nicotinamide adenine dinucleotide resulting in NADH production. The limit of detection (3σ blank, 𝑛 = 3) of 4.0 × 10-8 and 2.17 × 10-5  M, and linear range 1.3 × 10-7 to 2.5 × 10-5  M (R2  = 0.9998, n = 6) and 0.11-2.17 × 10-3  M (R2  = 0.9996, n = 6) were obtained for NADH and EtOH respectively. The injection rate was 100 h-1 with a relative standard deviation (n = 3) of 1.5-4.8% in the range studied for both analytes. The procedure was satisfactorily applied to pharmaceutical formulations with recoveries in the range 91.6 ± 3.0% to 110 ± 2.0% for NADH and 88 ± 3.0% to 95.4 ± 4.0% for EtOH. The results obtained were very consistent and did not differ considerably from the reported approaches at a 95% confidence limit. The possible mechanism of the CL reaction is also explained briefly.

Flow injection chemiluminescence determination of acetochlor and cartap-HCl in freshwater samples using an acidic KMnO4 -rhodamine-B reaction system.

A flow injection (FI) methodology using the acidic potassium permanganate (KMnO4 )-rhodamine-B (Rh-B) reaction with chemiluminescence (CL) detection was established to determine acetochlor and cartap-HCl pesticides in freshwater samples. Experimental parameters were optimized, and Chelex-100 cationic exchanger mini column and solid-phase extraction (SPE) were used as phase separation techniques. Linear calibration curves were observed for the standard solutions of acetochlor and cartap-HCl over the ranges 0.005-2.0 mg L-1 [y = 1155.8x + 57.551, R2  = 0.9999 (n = 8)] and 0.005-1.0 mg L-1 [y = 979.76x + 14.491, R2  = 0.9998 (n = 8)] with LODs and LOQs of 7.5 × 10-4 and 8.0 × 10-4  mg L-1 (3σ blank) and 2.5 × 10-3 and 2.7 × 10-3  mg L-1 (10σ blank), respectively, with an injection throughput of 140 h-1 . These methods were used to estimate acetochlor and cartap-HCl with or without the SPE procedure, respectively, in spiked freshwater samples. Results obtained were not significantly different at a 95% confidence level to those of other reported methods. Recoveries for acetochlor and cartap-HCl were obtained over the ranges 93-112% (RSD = 1.9-3.6%) and 98-109% (RSD = 1.7-3.8%), respectively. The most probable CL reaction mechanism was explored.

Determination of pioglitazone hydrochloride by flow injection chemiluminescence tris(2,2'-bipyridyl)ruthenium(II)-silver(III) complex system.

A novel flow injection-chemiluminescence (FI-CL) approach is proposed for the assay of pioglitazone hydrochloride (PG-HCl) based on its enhancing influence on the tris(2,2'-bipyridyl)ruthenium(II)-silver(III) complex (Ru(bipy)3 2+ -DPA) CL system in sulfuric acid medium. The possible CL reaction mechanism is discussed with CL and ultraviolet (UV) spectra. The optimum experimental conditions were found as: Ru(bipy)3 2+ , 5.0 × 10-5  M; sulfuric acid, 1.0 × 10-3  M; diperiodatoargentate(III) (DPA), 1.0 × 10-4  M; potassium hydroxide, 1.0 × 10-3  M; flow rate 4.0 ml min-1 for each flow stream and sample loop volume, 180 µl. The CL intensity of PG-HCl was linear in the range of 1.0 × 10-3 to 5.0 mg L-1 (R2 = 0.9998, n = 10) with limit of detection [LOD, signal-to-noise ratio (S/N) = 3] of 2.2 × 10-4  mg L-1 , limit of quantification (LOQ, S/N = 10) of 6.7 × 10-4  mg L-1 , relative standard deviation (RSD) of 1.0 to 3.3% and sampling rate of 106 h-1 . The methodology was satisfactorily used to quantify PG-HCl in pharmaceutical tablets with recoveries ranging from 93.17 to 102.77 and RSD from 1.9 to 2.8%.

Determination of thiram residues in fresh water using flow injection diperiodatonickelate(IV)-quinine chemiluminescence detection.

This study developed a simple flow injection (FI) method based on diperiodatonickelate(IV)-sulfuric acid reaction using chemiluminescence (CL) detection for the determination of thiram (THI) fungicide in fresh water using quinine as the sensitizer. The possible mechanism of the CL reaction was described using UV-Vis. absorption and CL spectra. Experimental variables were optimized by applying a univariate approach, and a linear calibration curve was obtained in the range of 1.0 × 10-3 -2.0 mg L-1 (R2 = 0.9994, n = 9) with a limit of detection of 5.0 × 10-4  mg L-1 (S/N = 3) and an injection throughput of 200 h-1 . This approach was successfully applied to determine THI in fresh water by using solid-phase extraction and achieved a good recovery rate of 94%-110% with a relative standard deviation of 1.9%-3.7% (n = 4). The results obtained were compared with the reported FI-CL and high-performance liquid chromatography-ultraviolet methods, and the three methods did not differ significantly at the 95% confidence limit.

The Determination Method of Total Polyphenol in Tea and Substitute Tea Based on [Ag(HIO6)2]5--Luminol Chemiluminescence System.

BACKGROUND: Scientific, accurate, and rapid detection of the composition and content of tea polyphenols is an important basis for their rational use and giving full play to their physiological effect. The spectrophotometric assays for total polyphenols have poor selectivity. Therefore, there is a need to develop a simple and reliable method for the determination of the total polyphenolic level in tea products. OBJECTIVE: The aim of this research was to develop a flow injection chemiluminescence (FI-CL) method based on the Ag(III)-luminol system for the total polyphenol content analysis of tea and substitute tea. METHOD: Through Box-Behnken experimental design, we selected the optimum determination condition. The Ag(III) concentration was 5 × 10-5 mol/L, and the luminol concentration was 3 × 10-7 mol/L (including 0.15 mol/L NaOH). The peristaltic pump is 25 r/min, and the photomultiplier voltage is 600 v. Sample extracts were diluted 100 000 times for the FI-CL assay. RESULTS: Under optimal conditions, CL intensities were proportional to total polyphenol content (in terms of gallic acid concentrations) in the range of 0.1∼100 µg/L. The LOD and LOQ were 0.03 µg/L and 0.1 µg/L. The recovery values were in the range of 86.3-111.0% with a RSD of 1.04∼2.62%. The polyphenolic content of 12 teas and 6 substitute teas was determined, and the results of the developed method and Folin-Ciocalteu method were highly correlated (r = 0.9493 for tea and r = 0.8533 for substitute tea). CONCLUSIONS: The proposed method is better than the Folin-Ciocalteu method in terms of selectivity, sensitivity, and accuracy. It is suitable for the determination of polyphenol content not only in tea, but also in substitute tea. HIGHLIGHTS: We developed a new flow-injection analysis method for polyphenolic content determination based on the Ag(III)-luminol chemiluminescence system. It is simple, rapid, sensitive, and accurate. It is suitable for the determination of polyphenols content not only in tea, but also in substitute tea.

Improving Harmonization and Standardization of Expanded Newborn Screening Results by Optimization of the Legacy Flow Injection Analysis Tandem Mass Spectrometry Methods and Application of a Standardized Calibration Approach.

BACKGROUND: Newborn screening (NBS) laboratories in the United Kingdom adhere to common protocols based on single analyte cutoff values (COVs); therefore, interlaboratory harmonization is of paramount importance. Interlaboratory variation for screening analytes in UK NBS laboratories ranges from 17% to 59%. While using common stable isotope internal standards has been shown to significantly reduce interlaboratory variation, instrument set-up, sample extraction, and calibration approach are also key factors. METHODS: Dried blood spot (DBS) extraction processes, instrument set-up, mobile-phase composition, sample introduction technique, and calibration approach of flow injection analysis-tandem mass spectrometry (FIA-MS/MS) methods were optimized. Inter- and intralaboratory variation of methionine, leucine, phenylalanine, tyrosine, isovaleryl-carnitine, glutaryl-carnitine, octanoyl-carnitine, and decanoyl-carnitine were determined pre- and postoptimization, using 3 different calibration approaches. RESULTS: Optimal recovery of analytes from DBS was achieved with a 35-min extraction time and 80% methanol (150 µL). Optimized methodology decreased the mean intralaboratory percentage relative SD (%RSD) for the 8 analytes from 20.7% (range 4.1-46.0) to 5.4% (range 3.0-8.5). The alternative calibration approach reduced the mean interlaboratory %RSD for all analytes from 16.8% (range 4.1-25.0) to 7.1% (range 4.1-11.0). Nuclear magnetic resonance analysis of the calibration material highlighted the need for standardization. The purities of isovaleryl-carnitine and glutaryl-carnitine were 85.13% and 69.94% respectively, below the manufacturer's stated values of ≥98%. CONCLUSIONS: For NBS programs provided by multiple laboratories using single analyte COVs, harmonization and standardization of results can be achieved by optimizing legacy FIA-MS/MS methods, adopting a common analytical protocol, and using standardized calibration material rather than internal calibration.

Nickel oxide hollow microsphere for the chemiluminescence determination of tuberculostatic drug isoniazid.

In this article, nickel(II) oxide (NiO) hollow microspheres (HMSs) were fabricated and used to catalyze chemiluminescence (CL) reaction. The studied CL reaction is the luminol-oxygen reaction that was used as a sensitive analytical tool for measuring tuberculostatic drug isoniazid (IND) in pharmaceutical formulations and water samples. The CL method was established based on the suppression impact of IND on the CL reaction. The NiO HMSs were produced by a simple hydrothermal method and characterized by several spectroscopic techniques. The result of essential parameters on the analytical performance of the CL method, including concentrations of sodium hydroxide (NaOH), luminol, and NiO HMSs were investigated. At the optimum conditions, the calibration curve for IND was linear in the range of 8.00 × 10-7 to 1.00 × 10-4  mol L-1 (R2  = 0.99). A detection limit (3S) of 2.00 × 10-7  mol L-1 was obtained for this method. The acceptable relative standard deviation (RSD) was obtained for the proposed CL method (2.63%, n = 10) for a 5.00 × 10-6  mol L-1 IND solution. The mechanism of the CL reaction was also discussed.

Multicommutation flow analysis system for non-enzymatic lactate determination based on light-driven photometric assay.

A fully-mechanized bioanalytical system for the photometric light-driven lactate determination is presented. The system is based on highly integrated four diode flow-through cell in which two UV-LEDs are used for the photochemical reduction of Fe(III) in the presence of lactate whereas LED-photodiode system allows the photometric detection of Fe(II)-Ferrozine complex to be registered. The developed multicommutation flow analysis system consisting of bifunctional optoelectronic device (photodegradation of Fe(III)-lactate complex and detection), solenoid micropumps and microvalves, is fully controlled and powered by the Arduino-compatible electronics. In consequence, independent and precise control of crucial parameters of the assay, including irradiation time and current supplying UV-LEDs is possible. Under optimized condition the system is useful for the lactate determination in the sub-milimolar range of concentration (6.0-300.0 µmol/L) with satisfactory sensitivity (597.1 AU·L/µmol) and detection limit (3.4 µmol/L), significant reduction of sample and reagents consumption (1.25 µL or 0.5 µL for 40- and 100-fold dilution of human serum samples, respectively) and high sample flow throughput (24 detections per hour). As the system offers the monitoring of detection process, the kinetic discrimination of effects from potential interferents is possible, improving the assay selectivity. The practical utility of the designed system was confirmed by its used for analysis of human serum standards. The recovery values were in the range of 92.1-104.2%. As the limit of quantitation offered by the system is significantly lower than physiological lactate levels, the serum samples have to be diluted what results in further decrease of both sample volume required for analysis and nonselective effects from matrix.

Determination of lansoprazole in pharmaceuticals using flow injection with rhodamine 6G-diperiodatoargentate(III) chemiluminescence detection.

A chemiluminescence (CL) method based on rhodamine 6G (R6G)-diperiodatoargentate(III) (silver(III) complex) reaction in acid solution is reported for the determination of lansoprazole (LNP) combined with a flow injection (FI) technique. The most likely mechanism for CL reaction was elucidated considering reported data, spectrophotometric and spectrofluorimetric studies. The weak CL reaction between R6G and silver(III) complex could be magnanimously increased in the presence of LNP with a limit of detection (LOD) of 0.002 mg L-1 (S/N = 3), a linear range of 0.01 to 10 mg L-1 (R2 = 0.9997, n = 7), a relative standard deviation (RSD) of 1.2 to 3.2% (n = 4) and an injection throughput of 140 h-1 . No interference activity of commonly found excipients in LNP was detected. After LNP extraction from pharmaceutical samples, the recovery rate ranging from 93 to 110% (RSD, 1.4-3.3%, n = 4) was calculated. The results of the proposed flow CL method were assessed with a spectrophotometric approach applying paired Student's t-test and the calculated value (0.178) was lower than the distributed value (2.20) at a 95% confidence limit.

Improving the measurement of total dissolved sulfide in natural waters: A new on-site flow injection analysis method.

Total dissolved sulfide (TDS) plays multiple important roles in the aquatic environments. However, the determination of trace levels of TDS in natural waters is challenging because TDS is vulnerable to oxidation and volatilization. In this study, a fully automated flow injection analysis spectrophotometric system, incorporating a hollow fiber membrane contactor (HFMC) and a long path length liquid waveguide capillary cell, was fabricated to facilitate the on-site measurement of trace TDS in natural waters. The HFMC was used for matrix separation and analyte preconcentration. The measurement was based on the reaction of sulfide and N,N-dimethyl-p-phenylenediamine in the presence of FeCl3 under acidic conditions to yield methylene blue (MB). The proposed method was highly sensitive, with detection and quantification limits of 0.57 and 1.90 nmol L-1, respectively. The linear working range was from 1.90 to 150 nmol L-1, with a correlation coefficient of 0.9995. The repeatability, expressed as the relative standard deviation, was less than 0.86% (n = 15) and the recoveries varied from 76.2 ± 0.1% to 103.9 ± 0.6% (n = 3) for spiked samples. This method was applied to conduct a field analysis of TDS in a reservoir, giving results aligned with those obtained using a standard MB method. This work demonstrates that the new method for determining TDS was effective for both laboratory analysis and on-site measurement.

Development, validation, and clinical application of an FIA-MS/MS method for the quantification of lysophosphatidylcholines in dried blood spots.

BACKGROUND: Lysophosphatidylcholine (LPC) plays pivotal roles in several physiological processes and their disturbances are closely associated with various disorders. In this study, we described the development and validation of a reliable and simple flow injection analysis-tandem mass spectrometry (FIA-MS/MS)-based method using dried blood spots (DBS) for quantification of four individual LPC (C20:0, C22:0, C24:0, and C26:0). METHODS: Lysophosphatidylcholines were extracted from 3.2 mm DBS with 85% methanol containing 60 ng/ml internal standard using a rapid (30 min) and simple procedure. The analytes and the internal standard were directly measured by triple quadrupole tandem mass spectrometry in multiple reactions monitoring mode via positive electrospray ionization. RESULTS: Method validation results showed good linearity ranging from 50 to 2000 ng/ml for each LPC. Intra- and inter-day precision and accuracy were within the acceptable limits at four quality control levels. Recovery was from 70.5% to 107.0%, and all analytes in DBS were stable under assay conditions (24 h at room temperature and 72 h in autosampler). The validated method was successfully applied to assessment of C20:0-C26:0LPCs in 1900 Chinese neonates. C26:0-LPC levels in this study were consistent with previously published values. CONCLUSION: We propose a simple FIA-MS/MS method for analyzing C20:0-C26:0LPCs in DBS, which can be used for first-tier screening.

Multisyringe Flow Injection Analysis of Tropomyosin Allergens in Shellfish Samples.

This paper presents the development and the application of a multisyringe flow injection analysis system for the fluorimetric determination of the major heat-stable known allergen in shrimp, rPen a 1 (tropomyosin). This muscle protein, made up of 284 amino acids, is the main allergen in crustaceans and can be hydrolyzed by microwave in hydrochloric acid medium to produce glutamic acid, the major amino acid in the protein. Glutamic acid can then be quantified specifically by thermal conversion into pyroglutamic acid followed by chemical derivatization of the pyroglutamic acid formed by an analytical protocol based on an OPA-NAC reagent. Pyroglutamic acid can thus be quantified between 1 and 100 µM in less than 15 min with a detection limit of 1.3 µM. The method has been validated by measurements on real samples demonstrating that the response increases with the increase in the tropomyosin content or with the increase in the mass of the shrimp sample.

Research on the internal flow and macroscopic characteristics of a diesel fuel injection process.

The internal flow and macroscopic spray behaviors of a fuel injection process were studied with schlieren spray techniques and simulations. The injection pressures(Pin)and ambient pressures(Pout)were applied in a wide range. The results showed that increasing the Pin is likely to decrease the flow performance of the nozzle. Furthermore, increasing the Pin can increase the spray tip penetration. However, the effect of Pin on the spray cone angle was not evident. The spray cone angle at an injection pressure of 160MPa was 21.7% greater than at a pressure of 100MPa during the initial spraying stage. Additionally, the discharge coefficient increased under high Pout, and the decrease in Pout can promote the formation of cavitation. Finally, increasing the Pout can decrease the penetration, while the spray angle becomes wider, especially at the initial spray stage, and high Pout will enhance the interaction of the spray and the air, which can enhance the spray quality.

Sequential Injection Analysis for Automation and Evaluation of Drug Liberation Profiles: Clotrimazole Liberation Monitoring.

A fully automated sequential injection system was tested in terms of its application in liberation testing, and capabilities and limitations were discussed for clotrimazole liberation from three semisolid formulations. An evaluation based on kinetic profiles obtained in short and longer sampling intervals and steady-state flux values were applied as traditional methods. The obtained clotrimazole liberation profile was faster in the case of Delcore and slower for Clotrimazol AL and Canesten cream commercial formulations. The steady-state flux values for the tested formulations were 52 µg cm-2 h-1 for Canesten, 35 µg cm-2 h-1 for Clotrimazol AL, and 7.2 µg cm-2 h-1 for Delcore measured in 4 min sampling intervals. A simplified approach for the evaluation of the initial rate based on the gradient between the second and third sampling points was used for the first time and was found to correspond well with the results of the conventional methods. A comparison based on the ratio of the steady-state flux and the initial rate values for Canesten and Clotrimazol AL proved the similarity of the obtained results. The proposed alternative was successfully implemented for the comparison of short-term kinetic profiles. Consequently, a faster and simpler approach for dissolution/liberation testing can be used.

Multicommutated Flow Analysis System for Determination of Horseradish Peroxidase and Its Inhibitors.

A fully mechanized multicommutated flow analysis (MCFA) system dedicated to determining horseradish peroxidase (HRP) activity was developed. Detection was conducted using a flow-through optoelectronic detector-constructed of paired LEDs operating according to the paired emitter-detector diode (PEDD) principle. The PEDD-MCFA system is dedicated to monitoring the enzyme-catalyzed oxidation of p-phenylenediamine (pPD) by a hydrogen peroxide. Under optimized conditions, the presented bioanalytical system was characterized by a linear response range (33.47-200 U/L) with a detection limit at 10.54 U/L HRP activity and 1.66 mV·L/U sensitivity, relatively high throughput (12 signals recordings per hour), and acceptable precision (RSD below 6%). Additionally, the utility of the developed PEDD-MCFA system for the determination of HRP inhibitors allowing the detection of selected thiols at micromolar levels, is demonstrated. The practical utility of the flow system was illustrated by the analysis of some dietary supplements containing L-cysteine, N-acetylcysteine, and L-glutathione.

Photometric Determination of Iron in Pharmaceutical Formulations Using Double-Beam Direct Injection Flow Detector.

In this work, an innovative, flow-through, double-beam, photometric detector with direct injection of the reagents (double-DID) was used for the first time for the determination of iron in pharmaceuticals. For stable measurement of the absorbance, double paired emission-detection LED diodes and a log ratio precision amplifier have been applied. The detector was integrated with the system of solenoid micro-pumps. The micro-pumps helped to reduce the number of reagents used and are responsible for precise solution dispensing and propelling. The flow system is characterized by a high level of automation. The total iron was determined as a Fe(II) with photometric detection using 1,10-phenanthroline as a complexing agent. The optimum conditions of the propose analytical procedure were established and the method was validated. The calibration graph was linear in the range of 1 to 30 mg L-1. The limit of detection (LOD) was 0.5 mg L-1. The throughput of the method was 90 samples/hour. The repeatability of the method expressed as the relative standard deviation (R.S.D.) was 2% (n = 10). The method was characterized by very low consumption of reagents and samples (20 µL each) and a small amount of waste produced (about 540 µL per analysis). The proposed flow method was successfully applied for determination of iron in pharmaceutical products. The results were in good agreement with those obtained using the manual UV-Vis spectrophotometry and with values claimed by the manufacturers. The flow system worked very stably and was insensitive to bubbles appearing in the system.