Automated flow-injection procedures for glycerol and triglycerides

An automated flow-injection manifold with stopped flow and merging zones is reported for the determination of triglycerides (50–250 mg dl^?1) and glycerol (5.0 × 10^?6?1.0 × 10^?2 M). In each case, a single reagent cocktain (20 μl) is synchronously merged with sample (20 μl) and the rate of formation of NADH monitored spectrophotometrically at 340 nm. For glycerol, the reagent contains glycerol dehydrogenase and NAD in Tris buffer, pH 8.0; for triglycerides, lipase in also included. The correlation coefficient for triglycerides over the range 50–250 mg dl^?1 was 0.971.     

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min^?1 providing a sample throughput of more than 15 samples h^?1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.     

Tiron as a spectrophotometric reagent for the estimation of osmium

A method for the spectrophotometric determination of osmium with tiron as a reagent has been described. The reagent forms a soluble and stable coloured complex on heating with osmium in the presence of sodium acetate. The regions of maximum and minimum absorptions are at 470 mμ and 410 mμ, respectively, and the system obeys Beer's law from 2 to 32 p.p.m. of osmium. But the optimum range, with the relative analysis error of 2.878% per 1% absolute photometric error, is from 8 to 24 p.p.m. of osmium. The sensitivity of the reaction is 0.033 μg/cm² (SANDELL) and the molar extinction coefficient is 5706. In solution, the complex is formed when the osmium and the reagent are in a ratio of l : 1 ; it has an instability constant equal to approximately 5.57? 10^-5.     

Determination of uranium using a flow system with reagent injection. Application to the determination of uranium in ore leachates

The determination of uranium by a flow system with reagent injection is based on the reaction of U(IV) with Arsenazo III in 3.6 M HCl; U(IV) is generated by reduction of uranyl ion in a lead reductor minicolumn installed in the sample channel of the manifold. The interference effect caused by several ions is studied. The calibration graph is linear up to 1.0 × 10^?5 M (2.4 mg l^?1) and the detection limit is 2.8 × 10^?8 M (6.6 μg l^?1). The modification of the manifold by including a second valve to by-pass the reducing column allows the measurement of the difference in peak heights, which makes the method specific for uranium.     

Spectrophotometric determination of trace amounts of beryllium using 1,8-dihydroxyanthrone as a new chromogenic reagent

A simple, rapid, and sensitive spectrophotometric method for the trace level determination of beryllium based on the formation of a 1:2 complex with anthralin (1,8-dihydroxyanthrone) as a new reagent is developed. A spectrophotometric method was used to determine the acidity constant and stepwise proton dissociation of the reagent. The experimental conditions for determining beryllium including the influences of pH, reagent concentration and time were evaluated and optimized. Under the optimum experimental conditions, the molar absorptivity of the complex is 0.47 × 10⁴ l mol^?1 cm^?1 at 545 nm. Calibration graph was linear in the range of 0.04–1.04 μg ml^?1 with a detection limit of 0.012 μg ml^?1 and a %RSD of 0.43%, for 5 replicate determinations at 0.48 μg ml^?1 of Be(II). The interferring effect of some cations and anions was also studied. The method was applied for the determination of beryllium in beryl, silicate rock and alloys. Ethylenediaminetetraacetic acid (EDTA) was used for masking interfering ions.     

A multicommuted flow system for sequential spectrophotometric determination of hydrosoluble vitamins in pharmaceutical preparations

A multicommuted flow system is proposed for spectrophotometric determination of hydrosoluble vitamins (ascorbic acid, thiamine, riboflavine and pyridoxine) in pharmaceutical preparations. The flow manifold was designed with computer-controlled three-way solenoid valves for independent handling of sample and reagent solutions and a multi-channel spectrophotometer was employed for signal measurements. Periodic re-calibration as well as the standard addition method was implemented by using a single reference solution. Linear responses (r=0.999) were obtained for 0.500-10.0 mg l⁻¹ ascorbic acid, 2.00-50.0 mg l⁻¹ thiamine, 5.00-50.0 mg l⁻¹ riboflavine and 0.500-8.00 mg l⁻¹ pyridoxine. Detection limits were estimated as 0.08 mg l⁻¹ (0.5 μmol l⁻¹) ascorbic acid, 0.8 mg l⁻¹ (2 μmol l⁻¹) thiamine, 0.2 mg l⁻¹ (0.5 μmol l⁻¹) riboflavine and 0.1 mg l⁻¹ (0.9 μmol l⁻¹) pyridoxine at 99.7% confidence level. A mean sampling rate of 60 determinations per hour was achieved and coefficients of variation of 1% (n=20) were estimated for all species. The mean reagent consumption was 25-fold lower in relation to flow-based procedures with continuous reagent addition. Average recoveries between 95.6 and 100% were obtained for commercial pharmaceutical preparations. Results agreed with those obtained by reference methods at 95% confidence level. The flow system is suitable for application in quality control processes and in dissolution studies of vitamin tablets.     

Flow-injection amplification for the spectrophotometric determination of iodide

A flow manifold is described in which iodide (0.05–15 μg ml^?1) in a 50-μl sample is oxidized by bromine water to iodate, most of the excess of bromine is reduced by formic acid, and the iodate is reacted with more iodide to form triiodide, which is determined spectrophotometrically. Six-fold amplification is achieved. The relative standard deviation is ca. 1%).     

Spectrophotometr1c determination of palladium : Bismuthiol i as an analytical reagent

The reagent, bismuthiol l, has been successfully utilized for the spectrophotometric determination of palladium. The colour reaction is instantaneous and the system is stable for at least 24 hours in the pH range 6 to 10 but shows no sharp peak of maximum absorption. The system obeys Beer's law at a palladium concentration of 0.8 μg to 8.0 μg per ml at any wavelength between 400 mμ and and 410 mμ giving a sensitivity of 0.08 μg of palladium per cm² (practical); 0.01 μg of palladium per cm² (sandell). Ethyl alcohol stabilizes the system against any deviation due to appearance of turbidity. A large excess of the reagent and almost all thc cations and anions, except platinum, gold, copper, chromium, iron, mercury, silver, thallium, uranium, vanadate and cyanide, do not interfere. By applying job's method of continuous variation it was found that the complex contains thc reactants in 1 : 1 ratio and that the average value of the dissociation constant of the complex is 3.2$\text{.}\text{?}$ 10^-5 at 25°.     

Factors affecting the detection limit of a flow- injection spectrophotometric procedure

Design criteria for manifolds to obtain adequated sensitivity and freedom from certain types of noise are discussed. For the determination of chloride by the mercury(II) thiocynate method, the mergin-streams manifold, needed to eliminated negative peaks at low concentrations and refractive index effects, increased the baseline noise because of inefficient mixing at the confluence point. Packed-bed reactors and single-bead-string reactors (SBSR) significantly improved the baseline noise. Refractive index effects caused by sample concentration gradients were eliminated by the injection of large volumes (>500 μl), so that the detector could view a homogeneous central part of the sample zone. This approach maximises the signal because the dispersion is governed only by the relative flow rates of the carrier and reagent streams. The detection limits for chloride were improved to 40 ng l^?1 in aqueous solutions of low ionic strength and to 1.3 mg l^?1 in 5.25% (w/v) potassium sulphate.     

Ion exchange in flow injection analysis: Determination of Ammonium Ions at the μg 1-1 level in Natural Waters with Pulsed Nessler Reagent

Ion exchange is incorporated in flow injection analysis by using a resin column in the sample loop of an electronically operated proportional injector. Effects of sample aspiration rate, sampling time, eluting agent concentration, pumping rate of the sample carrier stream, resin column size and sample acidity, were investigated to develop a preconcentration procedure for ammonium ion determination in natural waters at the μg 1^-1 level with pulsed Nessler reagent. The possibility of sample buffering before the adsorption step was studied. The proposed method is characterized by a precision of about 2%, a sampling rate of about 40 samples per hour. and a reagent consumption of 40 μl per sample, and is almost free of interferences. Recoveries from 95 to 105% were achieved in analysing rain-water samples with ammonium contents of less than 200 μg 1^-1. Alternative flow diagrams and the injector command unit are discussed.     

Flow characteristics in a segmented closed-tube design for ion-mobility spectrometry

Closed-tube design with unidirectional flow of drift gas in ion-mobility spectrometry (i.m.s) was found to provide residence times for analyte from 10 s to 10 min based on drift gas flow rate. The volume of drift gas necessary to restore reactant ions completely to the original intensity, after addition of excess (>900 mg l^?1) of analyte to the ion source, was three times the inner volume of the tube, regardless of flow rate. Contamination of the i.m.s. tube from analyte in the external atmosphere occurred readily in the open-tube design and in the closed-tube design with or without a slight vacuum attached to the tube. Rates of migration of analyte from outside to inside the tube were similar in all designs and the present closed-tube design was largely non-resistant to external contamination. Product-ion intensities for aromatic and polynuclear aromatic hydrocarbons were independent of drift flow rate from 100 to 800 ml min^?1 in the closed-tube design with no formation of artifacts. Plots of ion intensity vs. concentration of o-xylene were linear int wo ranges, 0.05–0.08 μg l^?1 and 0.1–2 μg l^?1, with slopes of 1.2 × 10^?9 A l μg^?1 in the first range and 1.0 × 10^?11 A l μg^?1 in the second range. No changes in mobility of aromatic product-ion peaks were seen with increases in concentration when the analyte was added to the drift gas rather than near the reaction region in unidirectional flow.     

A continuous flow system combined with a sensing fluorimetric transductor for the determination of β-naphthol

A single automatic method for continuous flow determination of β-naphthol based on the enhancement of its native fluorescence once the analyte was transitorily retained on-line on a solid support (QAE A-25 resin) is reported. So, a flow-through optosensor was developed using a flow-injection analysis system with solid phase fluorimetric transduction. KCl (0.15 mol l⁻¹) at pH 12.0 was used as carrier solution. To obtain the optimum fluorescence signal the wavelengths chosen were 245 nm (excitation) and 420 nm (emission). The response of the sensor was directly proportional to the sample volume injected in the studied range 40-1500 μl. Approximately one higher order of magnitude is achieved in sensitivity when 1500 μl are used with respect to the use of 40 μl of sample. The sensor was calibrated for three different injection volumes: 40, 600 and 1500 μl, responding linearly in the measuring range of 2-60, 0.5-15 and 0.2-5 μg l⁻¹ with detection limits of 0.5, 0.09 and 0.05 μg l⁻¹, respectively. The relative standard deviation for ten independent determination is 0.6% (40 μl), 0.9% (600 μl) and 2.3% (1500 μl). A recovery study was performed onto three different spiked water samples at concentration levels from 1 to 2.5 μg l⁻¹ and the recovery percentage from the experimental data ranged between 101±2 and 105±5.     

Selective determination of cobalt in a strongly acidic medium by flow injection analysis

Summary A selective method for the FIA spectrophotometric determination of Co(II) based on the use of pyridoxal 4-phenylthiosemicarbazone as reagent was developed with the aid of a straightforward 4-line flow injection manifold. The physical variables involved in the process were optimized as follows: injected sample volume 260 l; reactor lengths 116 and 150 cm. The proposed method allows the determination of cobalt over the concentration range 0.4–14.4 g ml^–1 at a sampling rate of 48 samples h^–1. The method is subject to very few interferences thanks to the fact that the strongly acidic medium used prevents the formation of most of the complexes of the reagent with other ions. It was applied to the determination of cobalt in steels.     

Enzymatic determination of glucose in a flow system by catalytic oxidation of the nicotinamide coenzyme at a modified electrode

A chemically modified electrode for detection of dihydronicotinamide adenine dinucleotide (NADH) and dihydronicotinamide adenine dinucleotide phosphate (NADPH) is described. Graphite rods were modified by dipping them into solutions of-dimethylamino-1,2-benzophenoxzinium salt (Meldola blue). The modified electrodes were mounted in a flow-through cell in a flow-injection manifold. Samples (50 μl) of pure nicotinamide coenzymes produced strictly linear calibration graphs from 1 μM to 10 mM with a repeatability of 0.2–0.6% RSD. A packed-bed enzyme reactor (210 μl) containing immobilized glucose dehydrogenase was inserted in the manifold for glucose determinations. Oxidized coenzyme was also added to the carrier electrolyte. Straight calibration graphs were again obtained up to 1mM β-d-glucose. The detection limit was 0.25 μM β-d-glucose for 50-μl samples. The electrode was kept at ?50 to 0 m V vs. SCE which was low enough to avoid interferences from ascorbic acid, uric acid or quinones.     

Flow-injection spectrophotometric determination of aluminium based on chrome azurol S and cetylpyridinium chloride

Acidic aluminium solutions (120 μl) are injected into a buffered (pH 5.7) carrier stream and merge with a chrome azurol S/cetylpyridinium chloride stream; a 2.25-m reaction coil is used with a total flow rate of 4 ml min ^?1. Ethanol (30% v/v) in the reagent stream enhances the absorbance of the ternary complex; the molar absorptivity is then 1.34×10 ⁵ l mol ^?1 cm ^?1 at 625 nm. Calibration is linear over the range 0–400 ng ml^?1 aluminium; the limit of determination is 5 ng ml ^?1. Iron is masked in the usual way; fluoride is tolerated at ˇ1 mg l ^?1. The injection rate is about 45 h^?1. The procedure appears to be applicable to tap water.     

Third-order Nonlinear Optical Properties of Octa-substituted Metal-free Phthalocyanine Thin Films

Third-order nonlinear optical susceptibility, χ⁽³⁾ of symmetrically octa-substituted metal-free phthalocyanine thin films measured by the third-harmonic generation technique are reported. The metal-free phthalocyanine has been found to show a χ⁽³⁾ (−3ω; ω,ω, ω) value as large as 7.73×10⁻¹² esu at 1.80 μm. The figure of merit, χ⁽³⁾/α, was estimated to be 4.17×10¹⁷ esu cm at 1.05 μm and 6.97×10¹⁶ esu cm at 1.65 μm. Both linear and third-order optical properties of liquid-crystalline metal-free phthalocyanines are discussed     

Solid-phase iodine as an oxidant in flow injection analysis: determination of ascorbic acid in pharmaceuticals and foods by background correction

A flow injection analysis (FIA)-background correction method comprising two solid-phase reactors and spectrophotometry for determination of ascorbic acid (AsA) is proposed. A polyethylene mini-column filled with solid iodine (30% m/m suspended on silica gel beads), reactor 1, and other column filled only with silica gel, reactor 2, which are then incorporated in a flow system so that solid iodine reagent in reactor 1 is affected as the sample passes through the column. The sample blank is produced by the oxidation of the AsA by iodine to form dehydroascorbic acid, insensitive to ultraviolet at 267 nm. AsA in samples is determined after injected in reactor 2; the difference in two analytical signal observed is related to amount of AsA. The linear range of the system is up to 50 μg ml⁻¹ with a detection limit of 0.08 μg ml⁻¹, R.S.D. of better than 1.0% and sampling frequency of 110 sample h⁻¹. The method is successfully applied to the determination of AsA in pharmaceuticals and foods.     

On-chip sample preparation by controlled release of antibodies for simple CD4 counting

We present a simple system for CD4 and CD8 counting for point-of-care HIV staging in low-resource settings. Automatic sample preparation is achieved through a dried reagent coating inside a thin (26 μm) counting chamber, allowing the delayed release of fluorochrome conjugated monoclonal antibodies after the filling of the chamber with whole blood by capillary flow. A custom-built image cytometer is used to capture fluorescence images representing more than 1 μl of blood. The thin layer of blood in combination with the large image area allows the use of whole blood from a finger prick without the need for dilution, lysis or cell enrichment. Automatic cell counting of CD4(+) and CD8(+) T-lymphocytes correlates well with results obtained by flow cytometry.     

Flow injection on-line acid digestion and pre-reduction of arsenic for hydride generation atomic absorption spectrometry-a feasibility study

A flow injection (FI) manifold is described which makes possible on-line microwave-assisted acid digestion, followed by pre-reduction of As(V) to As(III) and its determination by hydride generation atomic absorption spectrometry. The merging zone technique is used in order to reduce acid consumption for digestion. The efficiency of acid digestion is increased by pressure which is built up in-line by a flow restrictor. Flows for sample pretreatment and hydride generation can be optimized independently. L-cysteine was found superior to potassium iodide as the pre-reductant because much lower reagent and acid concentrations are required, much harsher conditions can be tolerated for acid digestion, and the integrated absorbance signals for arsenic in blood and standards are essentially identical, making possible the use of the standard calibration procedure.

The sampling frequency is 7–10/hr, depending on the conditions chosen, and the limit of detection, i.e. the concentration giving a signal equal to three times the standard deviation of the signal of the blank solution, is 0.25 μg/l for a 500 μl sample volume. The recovery of 10 μg/l As(V) added to a blood sample was 94 ± 2 and 98 ± 2% (n = 3) in absorbance and integrated absorbance, respectively.     

Hydrodynamic optical alignment for microflow cytometry

A microfabricated flow cytometer has been developed that is capable of detecting nearly all of the microparticles in an aqueous suspension. Current design allows for integrated coupling between an optical fiber-based detection system and the particle stream via hydrodynamic focusing. By adjusting the relative flow-rates at the auxiliary inputs of the focusing manifold, the particle stream can be steered out-of-plane relative to the illuminating laser, and similarly the particle stream can be squeezed or expanded. The microfabricated device was constructed in polydimethylsiloxane with cross-sectional microfluidic dimensions of 125 μm×125 μm. Using the present device and method, fluorescent microparticles in aqueous solution were counted at an absolute counting efficiency of 91±4%. The coefficient of variation of the fluorescence pulse-heights for far-red fluorescent microparticles was 15%. The device exhibited a linear response to fluorescence intensity calibration microparticles as shown by comparison with a commercial cytometer instrument.