Flow Injection Assembly Research Articles

Oxidized carbon nanotubes as sorbent for miniaturized solid-phase extraction of progestins from environmental water samples prior to their determination by HPLC-UV.

A solid-phase extraction method is presented for micro-extraction of three progestins (levonorgestrel, 19-norethisterone acetate and medroxyprogesterone acetate) from water samples. A mini-column was packed with 60mg of oxidized multiwalled carbon nanotubes and coupled to a flow injection assembly. The extraction parameters, such as washing solution, eluent type, eluent volume, flow rate and sample volume, were optimized. Separation and determination were performed by HPLC with UV detection. The method has a good linear range (0.90-9.0μgL-1), acceptable limits of detection (0.05-0.14μgL-1) and low RSDs (0.8-4.6%). Attractive features of the method include low consumption of organic solvents and preconcentration factors of up to 100. The method was applied to analyze stream, underground and effluent water samples, and recoveries between 74 and 121% were obtained. Graphical abstractSchematic representation of the flow injection assembly couples to an ox-MWCNTs extraction column used to perform the solid phase extraction procedure of progestins in environmental water samples.

Rapid automated method for on-site determination of sulfadiazine in fish farming: a stainless steel veterinary syringe coated with a selective membrane of PVC serving as a potentiometric detector in a flow-injection-analysis system

Sulfadiazine is an antibiotic of the sulfonamide group and is used as a veterinary drug in fish farming. Monitoring it in the tanks is fundamental to control the applied doses and avoid environmental dissemination. Pursuing this goal, we included a novel potentiometric design in a flow-injection assembly. The electrode body was a stainless steel needle veterinary syringe of 0.8-mm inner diameter. A selective membrane of PVC acted as a sensory surface. Its composition, the length of the electrode, and other flow variables were optimized. The best performance was obtained for sensors of 1.5-cm length and a membrane composition of 33% PVC, 66% o-nitrophenyloctyl ether, 1% ion exchanger, and a small amount of a cationic additive. It exhibited Nernstian slopes of 61.0 mV decade(-1) down to 1.0 × 10(-5) mol L(-1), with a limit of detection of 3.1 × 10(-6) mol L(-1) in flowing media. All necessary pH/ionic strength adjustments were performed online by merging the sample plug with a buffer carrier of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, pH 4.9. The sensor exhibited the advantages of a fast response time (less than 15 s), long operational lifetime (60 days), and good selectivity for chloride, nitrite, acetate, tartrate, citrate, and ascorbate. The flow setup was successfully applied to the analysis of aquaculture waters. The analytical results were validated against those obtained with liquid chromatography-tandem mass spectrometry procedures. The sampling rate was about 84 samples per hour and recoveries ranged from 95.9 to 106.9%.

Flow Injection Spectrophotometric Determination of 2,4‐D Herbicide

Abstract2,4‐Dichlorophenoxy acetic acid herbicide is spectrophotometrically determined by diazotization method in a flow injection assembly. The method is based on base hydrolysis of herbicides. The hydrolyzed product 2,4‐dichlorophenol is reacted with diazotized sulfanilic acid. The absorbance of the resulting coloured product was measured at 480 nm. The calibration graph is linear over the range of 0.2–20 μgmL−1, with a relative standard deviation of (RSD) of 7.2% and sample throughput of 90 samples h−1. The % recovery for determination of 2,4‐dichlorophenoxy acetic acid was found to be 92.0–95.3%. The method is easy, simple and faster than the established chromatographic method. The method was applied for determination of 2,4‐dichlorophenoxy acetic acid herbicide in commercial formulations and for residue determination in fruits and food samples.

Determination of Starane (Fluroxypyr) Herbicide Using Flow Injection Spectrophotometry

The starane herbicide was spectrophotometrically determined by the diazotization method in a flow injection assembly. Since starane is a substituted pyridyl compound the NH2 group at the p-position was exploited for diazotization. Starane was diazotized with nitrite and the diazotized product is coupled with beta-naphthol. The absorbance of the resulting azo dye was measured at 395 nm with a molar absorptivity of 1.5 x 10(4) L mol(-1) cm(-1). The calibration graph was linear over the range of 0.6 to 10 microg/mL, with a relative standard deviation (RSD) of 1.67% and a sampling through put of 60 samples h(-1). The % recovery for the determination of starane was found to be 96%. The method was successfully applied to the determination of the active ingredient of starane herbicide in its formulation as well as in food samples.

A Flow-Injection Biamperometric Method for Determination of Pantoprazole in Pharmaceutical Tablets

A flow-injection biamperometric method for determination of pantoprazole (PTZ) in pharmaceutical tablets is reported for the first time. The reversible redox couples Fe3+/Fe2+, Fe(CN)6(3-)/Fe(CN)6(4-), Ce4+/Ce3+, VO3(-)NO2+, and I2/I- were tested as indicating redox systems for biamperometric determination of PTZ in a flow-injection assembly with optimized flow parameters. The best results were obtained using V03(-)NO2+, which showed to be a selective and sensitive biamperometric indicating system for PTZ even in the presence of excipients and antioxidants that typically are found in drugs. The analytical graph was linear (r = 0.99945) in the range from 10 to 100 mg/L using 25 mmol/L VO3(-) as the reagent and water as the carrier stream and applying 100 mV between the 2 platinum wire electrodes. The limits of detection and quantitation were 200 and 667 microg/L, respectively, with a sensibility of calibration of 22.6 mV/mg/L. The proposed method was successfully applied to determine PTZ in commercial pharmaceutical tablets with a mean relative error of 1.60% (n = 5) and mean relative standard deviation of 3.10%. Recoveries close to 100% showed good agreement between the expected amount of PTZ in tablets (40 mg) and the results found by the application of the proposed method and demonstrated that the formulations used in the tablet compositions do not interfere in the PTZ analysis. The system had good stability, with a relative standard deviation of 3.80% for 9 sequential injections of a 60 mg/L PTZ solution. A sampling rate of about 100 samples/h was obtained.

Utility of copper(II) oxide as a packed reactor in flow injection assembly for rapid analysis of some angiotensin converting enzyme inhibitors

A new simple, sensitive, rapid and precise flow injection (FI) procedure based on the formation of copper complexes with some angiotensin converting enzyme (ACE) inhibitors has been developed and evaluated for the analysis of lisinopril (LN), enalapril maleate (EP), ramipril (RP) and perindopril tert-butylamine (PD). In this method, samples were injected into a flowing stream of distilled–deionized water, carried through the packed reactor of CuO for derivatization followed by ultraviolet (UV) detection. The flow rate was 1.5 ml min −1 and column temperature was ambient (25 °C). Lisinopril was injected directly into the flowing stream and the detector response was measured at 262 nm. The hydrolysis products of enalapril maleate, ramipril and perindopril tert-butylamine in 0.2N NaOH were injected after neutralization with 1N HCl and the detector response was measured at 272, 265 and 252 nm, respectively. The developed method was successfully applied to the determination of tested drugs in pharmaceutical preparations at a sampling rate of 60 samples h −1 and a recovery near 100% for all compounds.

Oxidation of adrenaline and noradrenaline by solved molecular oxygen in a FIA assembly

A simple and effective procedure is proposed for the study and simultaneous determination of adrenaline and noradrenaline. The fluorimetric determination of both substances is performed in a flow injection assembly and by oxidation of both drugs with the solved molecular oxygen. The influence of different parameters is empirically studied and the interpretation of the reaction mechanism is also added. The determination of adrenaline is monitored at 450 nm and the outputs at 520 nm correspond to the adrenaline and noradrenaline global amount; for both lectures λ exc 329 nm. The influence of temperature is relevant and analytical determination occurred at 55 °C by immersing the sample loop in a water bath. The linear range for adrenaline is over 0.5–20 μg ml −1, limit of detection for both compounds is 0.2 μg ml −1: the influence of foreign compounds as potential interferents is also tested; and, finally the procedure is applied to determination of both chatecolamines in synthetic samples.

Spectrophotometric determination of nalidixic and pipemidic acids in a flow injection assembly with a solid-phase reactor as a highly stable reagent source

The flow-injection spectrophotometric determination of nalidixic (I) and pipemidic (II) acids were carried out by reaction with Fe(III) ions entrapped in a polymeric material and filling a packed-bed reactor; the released Fe(III) complexed with the quinolone is monitored at 426 nm. The method worked with a high reproducibility, even when using different reactors, days and solutions. Selectivity of the procedure was tested with different foreign compounds found in human urine as well as in pharmaceutical formulations containing both quinolones; no relevant interferences were observed. The calibration graph for (I) was linear over the range 1–250 μg ml −1 with a relative standard deviation of 0.7% at 100 μg ml −1 ( n=43). The calculated sample throughput was of 26 h −1. The LOD was ( s/ n=3) 0.1 μg ml −1. The calibration graph for (II) was linear over the range 10–500 μg ml −1 with a relative standard deviation of 1.1% at 150 μg ml −1 ( n=40). The calculated sample throughput was of 25 h −1 and the LOD was ( s/ n=3) 1 μg ml −1. The method was applied to determine the (I) in pharmaceutical formulations and of (II) in pharmaceutical formulations and human urine.

Determination of nitrite by inhibition of the chemiluminescence of acriflavine in a flow-injection assembly.

The indirect determination of nitrite was performed with a flow-injection assembly on the basis of the inhibition of the analytical output obtained in a luminometer by oxidation of acriflavine. The acriflavine solution merged with the nitrite and the resulting mixture was injected into a pure water stream. This solution merged with the oxidant solution (potassium permanganate in sulfuric acid medium) and the resulting chemiluminiscence was affected (inhibited) by the presence of nitrite after reaction with the aminoacridine. The method was applicable over the range 10-800 microg l(-1) of nitrite with a correlation coefficient of 0.9960. The relative standard deviation was 1.4% and the throughput was 76 samples h(-1). The influence of foreign substances was also tested. A solid-phase reactor, filled with Amberlite IRA-900, was inserted in the assembly for the on-line preconcentration of nitrite; the analytical output resulted in an increase of up to 11.5-fold. The method was applied to the determination of nitrites in residual waters, industrial formulations and soil samples.

Flow injection biamperometric determination of chloramine-T in environmental, pharmaceutical and veterinary samples

A flow injection assembly for the determination of chloramine-T is proposed. The sample (213 μl) is inserted into the carrier, de-ionized water flowing at 4.1 ml min −1. This carrier merges with a mixture of potassium iodide and sulphuric acid, and the resulting solution flows to the flow cell through a reactor 66 cm long. The chloramine-T oxidises the iodide to tri-iodide. The resulting iodide/iodine ratio is biamperometrically tested. The calibration graph is linear up to 65 μg ml −1 chloramine-T; the limit of detection is 0.5 μg ml −1; the relative standard deviation (r.s.d) of the calibration slope is 2.8% for a series of eight independent calibrations. The r.s.d. of a series of 74 peaks for 40 μg ml −1 chloramine-T) is 0.8%, and the sample throughput 220 h −1. Few foreign substances interfered. The method is applied to pharmaceutical, veterinary and waste water samples.

Enhanced chemiluminescent determination of chloramphenicol and related nitro compounds by 'on-line' photochemical reaction.

The viability of tandem photochemical reaction-chemiluminescence detection was studied for a heterogeneous family of nitro compounds using chloramphenicol as a test substance. The 'on-line' chemical photodegradation of chloramphenicol was performed in a flow injection assembly by using a photoreactor consisting of a 725 cm x 0.5 mm id piece of PTFE tubing coiled around an 8 W low-pressure mercury lamp. Photodegraded chloramphenicol was detected by oxidizing photo-fragments from the parent compound and their subsequent reaction with a luminol-Co(II) system. The calibration graph was linear up to 3 x 10(-5) mol l-1 chloramphenicol, the limit of detection was 3 x 10(-9) mol l-1, the relative standard deviation was 1.8% for 2 x 10(-6) mol l-1 of the drug and the sample throughput was 60 h-1. The proposed method was used to determine chloramphenicol in pharmaceutical formulations and its application to other related nitro compounds was studied.

Automation of the Photodegradation Spectrophotometric Method for the Determination of Diethylstilbestrol by Flow Injection

ABSTRACT An spectrophotometric determination of diethylstilbestrol is proposed on the basis of on-line photo-degradation and measurement at 330 nm. The procedure is accomplished by means of flow-injection assembly including a photo-reactor formed by a PTFE 168 cm long coil around a low-pressure mercury lamp 6 w; this photo-reactor was nested between the injection valve and the spectrophotometric flow-cell. The sample solution was injected into a carrier stream of aqueous di-potassium hydrogen ortophosphate flowing at 5.0 ml min−1. Influence of the physic-chemical and hydrodynamic parameters was studied and optimised. The calibration graph was linear up to 65 mg l−1, and the procedure presented a reproducibility (rsd of the calibration slope) 1.4%, and a sample throughput of 52 h−1. The influence of foreign compounds was tested.

Flow injection biamperometric determination of metronidazole with on-line photodegradation

The determination of metronidazole is performed in a flow injection assembly, provided with a 40 W low pressure mercury lamp and a home-made biamperometric flow-cell furnished with two platinum electrodes polarized at 100 mV. The sample solution after being irradiated is inserted into a pure water stream. It then merges with an in situ mixed solution containing potassium iodide in sulphuric acid. The calibration graph was linear over the range 0.2–8.0 mg l −1 metronidazole; the 3 σ limit of detection was 0.008 mg l −1; the relative standard deviation was 0.6% (for 4 mg l −1 n = 13) and the sample throughput 50 h −1. The influence of foreign compounds is slight and the method is applied for the determination of metronidazole in pharmaceutical and galenic formulations.

Study of various indicating redox systems on the indirect flow-injection biamperometric determination of pharmaceuticals

The reversible redox couples (Fe(III)/Fe(II); Ce(IV)/Ce(III); Fe(CN) 6 3–/Fe(CN) 6 4−; I 2/I −; Br 2/Br − and VO 3 −/VO 2+) were studied as indicating redox systems for biamperometric determination of paracetamol in a flow injection assembly. Considering the selectivity of assayed systems against excipients and antioxidants that typically are presented in pharmaceutical formulations (e.g. sucrose, glucose, ascorbic acid and hydrogen sulphite) the systems Fe(III)/Fe(II) and VO 3 −/VO 2+were selected for the determination of the drug. The sample was injected into a carrier which merged with the oxidant stream where the drug was oxidised by excess oxidant. The observed signal (current) showed a linear dependence on the concentration of reduced species. The calibration graphs were linear over the range 0.1–7 μg ml −1 of paracetamol for iron(III) and up to 20 μg ml −1 for metavanadate, with a relative standard deviation of 1.6 and 1.5% (5 μg ml −1 paracetamol; n = 20) and a sample throughput of 149 and 79 h −1 for iron(III) and metavanadate, respectively. Under flow optimal chemical and conditions for determining paracetamol both indicating systems were tested for different families compounds of pharmaceutical interest (phenothiazines, sulphonamides, nitrocompounds, epinephrine derivates, tetracyclines and pyridine derivates).

Flow injection-spectrophotometric determination of metoclopramide hydrochloride

The determination of metoclopramide hydrochloride is spectrophotometrically determined by the Bratton-Marshall method in a flow injection assembly. The required nitrite is prepared on-line in the flow assembly by reducing a nitrate solution with the aid of a copperised cadmium solid-phase reactor. The calibration graph is linear over the range 0.5–85 mg l −1, with a relative standard deviation (RSD) of 0.89%, and sample throughput of 51 samples h −1. The method is easy and simple, and it is applied to determination of metoclopramide in some pharmaceutical formulations. The method eliminates the need for frequent preparation of unstable nitrite solutions.

Spectrofluorimetric determination of vitamin K3 by a solid-phase zinc reactor immobilized in a flow injection assembly.

The spectrofluorimetric determination of vitamin K3 (menadione) using a flow injection (FI) assembly provided with a solid-phase reactor with immobilized zinc is described. The naphthohydroquinone was produced by means of two coupled steps in the FI system: hydrolysis of the sodium sulfite derivative of the menadione in a basic medium and reduction of the generated menadione in the zinc reactor in an acidic medium. The fluorescent product was monitored spectrofluorimetrically (lambda ex 325 nm; lambda em 425 nm). The calibration graph was linear over the range 0.1-18 micrograms ml-1 with a reproducibility of 1.6%; the limit of detection was 0.005 microgram ml-1 and the sample throughput was 70 h-1. The influence of foreign compounds was studied and the procedure was applied to the determination of vitamin K3 in three different pharmaceutical formulations.

The use of solid phase reactors as the source of a catalytic solution. the indirect flow-injection spectrophotometric determination of amino acids

The indirect determination of amino acids is carried out in a flow-injection assembly by means of a solid-phase reactor containing cupric salts, immobilized in polyester resin beads. A pharmaceutical substance is forced through the reactor and the released cupric ions (complexed by the pharmaceutical substance) act as a catalyst for the subsequent reaction between Fe(III) and sodium thiosulfate. The calibration graph is linear over the range 0.1-3.0 µg mL-1 glycine, the RSD was 2.3%, and the sample throughput was 28 h-1. The influence of foreign substances was studied and the method was applied to the determination of glycine in two different pharmaceutical formulations.

Integrated Automatic Determination of Nitrate, Ammonium and Organic Carbon in Soil Samples

An automated photometric method for the sequential determination of nitrate, ammonium and organic carbon in soils by use of a single-line flow injection assembly is reported, but differently programmed for the assay of the individual analytes. These analytes, which are determined by using suitable photometric reagents, are directly related to the nutritional properties of soil. A filtration probe was used for the continuous filtration of soil extract. The precision, expressed as RSD, was 2.0, 2.6 and 2.1% for nitrate, ammonium and organic carbon, respectively. The proposed method features a high throughput and low reagent consumption, and requires minimal sample handling. Its performance was tested in routine analyses of soil samples, all with satisfactory results.

FLOW INJECTION ANALYSIS FOR METHANOL WITH ALCOHOL OXIDASE AND CHEMILUMINESCENT DETECTION

A highly sensitive flow injection system was developed for the methanol determination. The system is based on the oxidation of methanol in the presence of alcohol oxidase to yield formaldehyde and hydrogen peroxide. The concentration of the hydrogen peroxide produced was determined by luminol chemiluminescence. A four-line flow injection assembly was used. The sample was injected into a flow of phosphate buffer at pH 9 that merged with a flow containing alcohol oxidase. The enzymatic reaction takes place in a coiled tube, 2 meters · long and 0.8 mm i.d. Just in front of the chemiluminescence cell, the flow containing the sample merged with a flow of luminol (1.5 mM) and potassium ferricyanide (20 mM). The injected volume was 50 pL and the total flow rate 1.6 mL min·1 The determination range was 5x10"4 -1x10'2 %(v/v) methanol. The throughput was 40 samples per hour. From 20 tested substances, only L-cysteine generated a signal comparable with that of methanol. The others, at concentrations equal to those of methanol, either gave no signal at all (n-butanol, cyclo-hexanol, glycine, L-threonine, L-proline, copper sulphate) or gave signals much smaller than that of methanol.

Fia-spectrophotometric determination of thiamine after UV-irradiation

The determination of thiamine was carried out by UV-photodegradation in a single-line flow-injection assembly. The UV-photodegradation of thiamine was carried out in the coil of the injection valve, constituted of a PTFE tubing, half of its length being helically coiled around a UV lamp. A peak with two adjoining maxima was produced by injection, corresponding to the absorbance of the irradiated and non-irradiated sample. The analytical parameter is the difference between the two peaks, measured at 264 nm. The calibration graph is linear over the 1.2–30 μg/ml range of thiamine hydrochloride in 0.1 M HCl. The influence of certain admixed substances was studied and the method was tested for the determination of thiamine in tablets.