A microfluidic flow injection system for DNA assay with fluids driven by an on-chip integrated pump based on capillary and evaporation effects

A miniaturized flow injection analysis (FIA) system integrating a micropump on a microfluidic chip based on capillary and evaporation effects was developed. The pump was made by fixing a filter paper plug with a vent tube at the channel end, it requires no peripheral equipment and provides steady flow in the mul min(-1) range for FIA operation. Valve-free sample injection was achieved at nanolitre level using an array of slotted vials. The practical applicability of the system was demonstrated by DNA assay with laser-induced fluorescence (LIF) detection. A precision of 1.6% RSD (10.0 ng mul(-1), n = 15) was achieved with a sampling throughput of 76 h(-1) and sample consumption of 95 nl.     

Determination of hydrogen peroxide in reactor moderator solutions by flow injection analysis

A flow injection analysis (FIA) method for the determination of hydrogen peroxide in reactor moderator water has been developed and installed at the Savannah River Site (SRS) Water Quality Laboratory. The mode of detection is amperometric and the technique has an analytical range of 0.10-2.50 mug/ml with a sampling rate of 40 samples/hour. The calibration curve is linear with a correlation coefficient of 0.999 and the relative standard deviation is at the 0.50% level for both 0.10- and 2.50-mug/ml standards. When the FIA procedure is compared to the manual method previously used at the SRS Water Quality Laboratory for hydrogen peroxide analysis, it demonstrates a minimum twenty minute reduction in analysis time per sample and the total liquid waste generated per sample analyzed is reduced by 95%.     

Indirect determination of tetrahydroborate (BH(-)(4)) by gas-diffusion flow injection analysis with amperometric detection

A rapid, indirect gas-diffusion flow injection analysis (FIA) method with amperometric detection has been developed for the selective and sensitive determination of tetrahydroborate (BH(-)(4)). The injected analyte reduces arsenic(III) to arsine. The arsine formed diffuses through the PTFE (polytetrafluoroethylene) membrane and is quantified amperometrically at a platinum working electrode. The precision of the technique was better than a relative standard deviation of 2.1% at 60 muM levels and better than 0.5% at 0.1 mM, with a throughput of 60 samples/hr. The detection limit of the method was found to be 1 muM (1.5 ng BH(-)(4)) with a linear range up to 1 mM. The dynamic range extends over five orders of magnitude in BH(-)(4) concentration. The effects of working potential, concentration of As(III) and HCl in the reagent stream, type and flow rate of the acceptor solution, temperature and interferents on the FIA signals were studied.     

Direct FIA-AS determination of potassium and magnesium in cement samples by use of the slurries approach

A direct procedure has been developed for the flame atomic determination of potassium and magnesium in cement samples. A 50-mg sample is dispersed in 25 ml of 0.13M nitric acid; 100 mul of this slurry is injected in a double channel FIA manifold simultaneously with 100 mul of a 10% (w/v) lanthanum solution. This procedure allows the rapid extraction of potassium and magnesium by leaching of the sample; nitric acid is not necessary if only potassium must be determined and the sample can be diluted with only distilled water. Aqueous standards are used. The manifold employed includes a well-stirred mixing chamber, which provides an adequate on-line dilution of the sample, in order to obtain emission or absorbance measurements in the dynamic range of the elements to be determined. The results obtained in the analysis of real samples agree with those found by flame atomic spectrometry after a previous alkaline fusion with lithium carbonate, and exhibit better precision. The limit of detection of the procedure is 0.007% for K(2)O and 0.01% for MgO and the precision of the entire procedure corresponds to a relative standard deviation of 1%.     

o-Dianisidine: a new reagent for selective spectrophotometric, flow injection determination of chlorine.

A flow injection analysis (FIA) procedure for the determination of free chlorine in industrial formulations and water samples is proposed. The manifold is provided with a gas-diffusion unit which permits the removal of interfering species and also the preconcentration of chlorine. The determination of chlorine is performed on the basis of the oxidation by o-dianisidine as a chromogenic reagent to a coloured product which can be monitored at 445 nm. The method (for a preconcentration step of 60 s) is linear over the range 0.04-1.00 mg l(-1) of chlorine, the limit of detection is 0.04 mg l(-1), the reproducibility of the procedure (as RSD of the slope) is 3.7% for a series of four independent calibrations, the precision (as RSD of a series of 30 continuous FIA peaks of 0.56 mg l(-1) of chlorine) is 1.4% and the sample throughput is 40 h(-1). A detailed comparative study of the analytical characteristics of a single mono-channel reverse FIA assembly and the same system but provided with a Fluoropore membrane filter of 0.5 microm pore size was performed to check the advantages of the new approach in terms of sensitivity, selectivity and limit of detection.     

Spectrophotometric determination of iron with ferrozine by flow-injection analysis

Two methods for the determination of iron by normal FIA and reversed FIA were developed using sodium 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine-4',4'-disulphonate (ferrozine). The reagent formed a chelate with Fe(II) in hexamethylentetramine buffered medium at pH 5.5. In one previous reaction coil Fe(III) was reduced to Fe(II) by ascorbic acid and in the other reaction coil the complexation reaction was developed. The linear range of the determination was 0.5-6 and 0.1-5 mug ml(-1) of iron for normal FIA and reversed FIA respectively. The proposed method was sensitive (detection limit 0.012 and 0.010 mug ml(-1)), rapid and reproducible (RSD 0.3 and 0.28%). The method was satisfactorily applied to the determination of iron in waste water, toadstool tissue, potato leaves, human hair and bauxites at a sampling rate of 90 and 50 samples h(-1) for normal FIA and reversed FIA respectively.     

Development and application of an integrated system for monitoring ethanol content of fuels

An automated flow injection analysis (FIA) system for quantifying ethanol was developed using alcohol oxidase, horseradish peroxidase, 4-aminophenazone, and phenol. A colorimetric detection method was developed using two different methods of analysis, with free and immobilized enzymes. The system with free enzymes permitted analysis of standard ethanol solution in a range of 0.05–1.0 g of ethanol/L without external dilution, a sampling frequency of 15 analyses/h, and relative SD of 3.5%. A new system was designed consisting of a microreactor with a 0.91-mL internal volume filled with alcohol oxidase immobilized on glass beads and an addition of free peroxidase, adapted in an FIA line, for continued reuse. This integrated biosensor-FIA system is being used for quality control of biofuels, gasohol, and hydrated ethanol. The FIA system integrated with the microreactor showed a calibration curve in the range of 0.05–1.5 g of ethanol/L, and good results were obtained compared with the ethanol content measured by high-performance liquid chromatography and gas chromatography standard methods.     

Selective Determination of Verapamil in Pharmaceutics and Urine Using a Boron‐doped Diamond Electrode Coupled to Flow Injection Analysis with Multiple‐pulse Amperometric Detection

This work presents a simple and low‐cost method for fast and selective determination of Verapamil (VP) in tablets and human urine samples using a boron‐doped diamond working electrode (BDD) coupled to a flow injection analysis system with multiple pulse amperometric detection (FIA‐MPA). The electrochemical behaviour of VP in 0.1 mol L⁻¹ sulfuric acid showed three merged oxidation peaks at around +1.4 V and upon reverse scan, one reduction peak at 0.0 V (vs. Ag/AgCl). The MPA detection was performed applying a sequence of three potential pulses on BDD electrode: (1) at +1.6 V for VP oxidation, (2) at +0.2 V for reduction of the oxidized product and (3) at +0.1 V for cleaning of the working electrode surface. The FIA system was optimized with injection volume of 150 μL and flow rate of 3.5 mL min⁻¹. The method showed a linear range from 0.8 to 40.0 μmol L⁻¹ (R>0.99) with a low limit of detection of 0.16 μmol L⁻¹, good repeatability (RSD<2.2 %; n=10) and sample throughput (45 h⁻¹). Selective determination of VP in urine was performed at+0.2 V due to absence of interference from ascorbic and uric acids in this potential. The addition‐recovery tests in both samples were close to 100 % and the results were similar to an official method.     

Use of a copper electrode in alkaline medium as an amperometric sensor for sulphite in a flow-through configuration

A flow injection analysis (FIA) method has been developed for the determination of sulphite in beverages. The method is based on the amperometric detection (0.60 V vs Ag/AgCl (sat. NaCl)) of the analyte at a copper surface in an alkaline medium (1 M NaOH solution) with a manifold that incorporates flow extraction of sulphite as SO2 through a PTFE membrane. Under optimal experimental conditions the peak current response increases linearly with sulphite concentration over the range from 1.0 to 5.0 mM. The repeatability of the electrode response in the FIA configuration was evaluated as 4% ( n =20), the limit of detection of the method was 0.04 mM (S/N =3) and the analytical frequency was 50 h(-1). Since ethanol is also electroactive and permeates through the PTFE membrane, a strategy involving in a first step measurements of only ethanol by manipulating the pH of the donor stream was employed for wine samples. Then, both ethanol and sulphite were measured at the copper electrode at 0.40 V vs Ag/AgCl (sat. NaCl) and the sulphite concentration was determined by difference. Results for 3 different beverage samples (alcoholic and non-alcoholic) showed excellent agreement with the ones obtained by using a recommended procedure for sulphite analysis.     

Sensitive determination of a glyoxal-DNA adduct biomarker candidate by column switching capillary liquid chromatography electrospray ionization mass spectrometry

A method based on column switching packed capillary liquid chromatography electrospray mass spectrometry has been developed for the determination of the adduct glyoxal-deoxyguanosine, a biomarker candidate for the assessment of glyoxal exposure, in DNA hydrolysate solutions. Microgram amounts of DNA were isolated and enzymatically hydrolyzed to deoxyribonucleosides, prior to ultrafiltration and subsequent dilution to a sample solution consisting of water-acetonitrile-formic acid (98 : 2 : 0.2, v/v). The sample solution was loaded onto a 1 mm I.D. x 5 mm Hypercarb (5 mum) porous graphitic carbon trap column for analyte enrichment using an injection volume of 200 mul, and was subsequently back-flushed onto a 0.30 mm I.D. x 150 mm Lichrospher diol (5 mum) analytical column. The samples were loaded with a flow rate of 40 mul min(-1) and glyoxal-deoxyguanosine was desorbed from the trap column and eluted with an isocratic mobile phase consisting of water-acetonitrile-formic acid (50 : 50 : 0.2, v/v) at a flow rate of 5 mul min(-1). Mass spectrometric determination of glyoxal-deoxyguanosine was obtained by multiple reaction monitoring of the transition [M + H](+)m/z 326 --> m/z 210. The method was evaluated over the concentration range 0.25-50 ng ml(-1) of glyoxal-deoxyguanosine in the hydrolysate of 5 mug DNA. The method was linear with a correlation coefficient of 0.9998 in this range. The within-day (n = 6) and between-day (n = 6) precisions were determined as 1.2-11% and 1.4-11% RSD, respectively, and the recovery was close to 100%. The mass limit of detection was 15 pg, corresponding to a concentration limit of detection of 75 fg mul(-1) DNA hydrolysate solution, corresponding to 48 adducts per 10(6) normal nucleosides. The method was applied for the determination of glyoxal-deoxyguanosine in DNA hydrolysate solutions of calf thymus DNA and cell cultures after reaction or incubation with glyoxal.     

Ruthenium Oxide Hexacyanoferrate Modified Electrode for Hydrogen Peroxide Detection

A sensor for H₂O₂ amperometric detection based on a Prussian blue (PB) analogue was developed. The electrocatalytic process allows the determination of hydrogen peroxide at 0.0 V with a limit of detection of 1.3 μmol L^?1 in a flow injection analysis (FIA) configuration. Studies on the optimization of the FIA parameters were performed and under optimal FIA operational conditions the linear response of the method was extended up to 500 μmol L^?1 hydrogen peroxide with good stability. The possibility of using the developed sensor in medium containing sodium ions and the increased operational stability constitute advantages in comparison with PB‐based amperometric sensors. The usefulness of the methodology was demonstrated by addition‐recovery experiments with rainwater samples and values were in the 98.8 to 103% range.     

Flow injection analysis of imidacloprid in natural waters and agricultural matrixes by photochemical dissociation, chemical reduction, and nitric oxide chemiluminescence detection

A flow injection analysis (FIA) to quantify imidacloprid was developed based upon (1) ultraviolet (254 nm) photochemical dissociation of imidacloprid to produce nitrite, (2) chemical reduction of the nitrite to nitric oxide by iodide in acid, (3) removal of gas-phase nitric oxide from the aqueous stream using a membrane separator, and (4) detection of the nitric oxide by chemiluminescent reaction with ozone. The cross-reactivity of imidacloprid with eight metabolites of imidacloprid was determined using a commercial ELISA kit and the FIA method. While the ELISA kit demonstrated varying degrees of cross-reactivity, cross-reactivity in the FIA method was observed for only the N-nitro and N-nitroso metabolites. The optimized analytical FIA method, FIA provides a linear response in imidacloprid concentration over four orders of magnitude, has a limit of detection of 5.6 pmol (1.5 ng) of imidacloprid, and exhibits an inter-day precision of 0.4%. Spike-recoveries by FIA demonstrated excellent recovery of imidacloprid in natural waters, hemlock xylem fluid, honey, and grapes with little to no interference from the matrix.     

Ultrasensitive and Simple Method for Determination of N‐Acetyl‐L‐Cysteine in Drug Formulations Using a Diamond Sensor

A boron‐doped diamond (BDD) electrode coupled to flow injection analysis (FIA) was firstly developed for determination of N‐acetyl‐L ‐cysteine (NAC) in drug formulations. The effects of experimental parameters including pH, applied potential and scan rate on the response were investigated. FIA amperometry was applied as an automatic method for the quantitative detection of trace amounts of NAC. A wide linear range of 0.5–50 µmol/L and a low detection limit of 10 nmol/L were obtained. The results of amperometric determinations show a very good reproducibility, and the RSD for the measurement based on 10 measurements was <3.7 % and <4.1 % for intra‐ and inter‐day, respectively. The benefits of the proposed method are fast, simple, sensitive and no requirement of complicated operational steps.     

Determination of cyanide by a flow injection analysis-atomic absorption spectrometric method

A new flow injection analysis (FIA) procedure is proposed for the indirect atomic absorption spectrometric determination of cyanide. The FIA manifold is based on the insertion of the sample into a distilled water carrier, then the sample flows through a solid-phase reactor filled with silver iodide entrapped in polymeric resin beads. The calibration graph is linear over the range 0.2-6.0 mg l-1 of cyanide (correlation coefficient 0.9974), the detection limit is 0.1 mg l-1, the sample throughput is 193 h-1 and the RSD is 0.8%. The method is simple, quick and more selective than other published FIA procedures. The reproducibility obtained by using different solid-phase reactors and solutions is in the range 2.2-3.1% (RSD). The method was applied to the determination of cyanide in commercial samples such as pharmaceutical formulations and industrial electrolytic baths.     

Flow injection near-infrared determination of ethanol in chloroform

A simple and direct flow injection (FIA) procedure has been developed for the determination of the stabilizing agent ethanol in chloroform samples. The procedure is based on the use of the absorbance band of ethanol in the near-infrared (NIR) region at 2272 nm, measured in front of a reference sample of chloroform stabilized with amylene. The method developed provides a limit of detection of 0.0045% (v/v) and a dynamic range until 10% (v/v) with a typical variation coefficient of 0.4% for six independent analysis of a real sample containing approximately 1% (v/v) of ethanol. The sample injection frequency allowed by the method is 78 h^–1.     

Fluorimetric determination of uranium(VI) in waters by flow-injection analysis after preconcentration on a silica gel microcolumn

A method was developed for the selective determination of trace concentrations of uranium(VI) by flow-injection analysis (FIA) with fluorimetric detection. Uranium(VI) is selectively separated and/or pre-concentrated from a volume up to 20 ml on an activated silica gel microcolumn (2 x 40 mm) from a medium of 0.03M EDTA, 0.06M tartrate, and/or 0.05M NaF at pH = 9.3. After washing the column the uranium is eluted with a mixture of 1.33M sulphuric and phosphoric acids and determined with a relative standard deviation not exceeding 6% for concentrations in the range 10-250 mug/l. The detection limit was estimated to be 0.1-0.2 mug of uranium. The method has been verified on artificial water samples with high content of the interfering elements and applied to analysis of waste and natural waters.     

New Electrochemical Sensor of Prolonged Application for Metformin Determination Based on Hydrated Ruthenium Dioxide‐Carbon Black‐Nafion Modified Glassy Carbon Electrode

Metformin (MET) is an antidiabetic drug most commonly used in treatment of diabetes mellitus type 2 (T2D). Adsorptive stripping voltammetric method using carbon black – hydrated ruthenium dioxide – Nafion modified glassy carbon electrode (CB‐RuO₂‐Nafion GC electrode) have been developed for metformin determination in pharmaceutical formulations. By using ruthenium dioxide, electrode's lifespan was extended to at least 3 weeks (change of metrological parameters estimated as 3–4 %) what is an excellent result concerning other solutions previously described in the literature. Moreover the fabrication of the sensor is simple and fast. Deposition step was carried out at the potential 0 mV for 15 s. The best results were obtained in 0.05 M acetate buffer (pH 4.6). Important aspect was fixed MET : Cu(II) ratio equal to 1 : 8, otherwise linear dependence between register current and MET concentration could not be obtained. In addition, a significant improvement in the parameters of the calibration curve was obtained. Limit of detection was equal to 0.7 μM. Developed method was successfully applied in analysis of 2 pharmaceuticals products and in wastewater and river water. Accuracy of the method was estimated using recoveries, which were in the range 101–110 %. In order to adapt developed system into hydrodynamic conditions, amperometry in hydrodynamic transport conditions and flow injection analysis (FIA) measurements have been conducted. Conducted FIA measurements prove that developed method has potential for application in automized flow systems without frequent calibration.     

用流动注射在线富集分离荧光分光光度计测定垃圾渗出液中的苯胺

建立了用荧光分光光度计作为流动注射分析的检测器,用自动研制的流通池测定垃圾渗出液中苯胺的新方法。方法的线性范围为０．０７～０．５ｍｇ／Ｌ,检出限为０．０５ｍｇ／Ｌ。用于垃圾渗出液的测定,结果与ＨＰＬＣ法无显著性差异,回收率在９６％～１０４％之间,该法具有选择性好、灵敏度高、重现性好的特点。     

FIA titrations of phenothiazine derivatives in aqueous micellar and non-aqueous media

New methods of flow injection analysis (FIA) neutralization titrations of phenothiazine derivatives in aqueous micellar medium of a cationic surfactant using potentiometric and spectrophotometric detection were proposed; titrations with a mixing gradient chamber and high-speed titrations were compared. The FIA titration method in non-aqueous media based on an official method of determination (titration with perchloric acid in anhydrous acetic acid) was also developed. Under optimized reaction conditions and flow-through parameters, the calibration range and equations, the sensitivity, and the repeatability of all methods were found and discussed. All titrations were assayed for medicinal forms.