Biparametric multicommutated flow analysis system for determination of human serum phosphoesterase activity

A multicommutated flow analysis (MCFA) system constructed of microsolenoid valves and pumps offering simultaneous determination of activity of acid phosphatase (ACP) and alkaline phosphatase (ALP) in human serum samples has been developed. The MCFA system is based on optoelectronic flow-through detector made of two light emitting diodes and operating according to paired emitter detector diode (PEDD) principle. This photometric PEDD device has been dedicated for detection of p-nitrophenol (NP) generated in the course of enzymatic hydrolysis of p-nitrophenyl phosphate and optimized for the determination of NP in human serum samples. The developed PEDD-based MCFA system allows independent optimization of conditions for reaction and detection steps of photometric ACP and ALP bioassays. Moreover, it allows elimination of photometric interferences from serum matrix components according to two-points kinetic mode of measurement. The single measurement cycle takes 12 min, consists of four measurements (two for each phosphoesterase) and enables determination of serum ACP and ALP activities at physiological and pathological levels. The real analytical utility of the developed MCFA system has been confirmed by analysis of control sera as well as real human serum samples from healthy persons and oncological patients.     

Multicommutated flow analysis system for determination of creatinine in physiological fluids by Jaffe method

For the needs of photometric determination of creatinine according to Jaffe protocol a dedicated paired emitter detector diode (PEDD) detector has been developed. This PEDD device has been constructed in the compact form of flow-through cell (30 μL total volume and 7 mm optical pathlength) integrated with 505 nm LED-based emitter and 525 nm LED-based detector compatible with multicommutated flow analysis (MCFA) system. This fully mechanized MCFA system configured of microsolenoid valves and pumps is operating under microprocessor control. The developed analytical system offers determination of creatinine in the submillimolar range of concentrations with detection limit at ppm level. The throughput offered by the system operating according to multi-point fixed-time procedure for kinetic measurements is 15–40 samples per hour depending on the mode of measurements. The developed PEDD-based MCFA system has been successfully applied for the determination of creatinine in real samples of human urine as well as serum. The developed sampling unit used the system is free from effects caused by differences in sample viscosity.     

A new light emitting diode-light emitting diode portable carbon dioxide gas sensor based on an interchangeable membrane system for industrial applications

A new system for CO₂ measurement (0–100%) based on a paired emitter–detector diode arrangement as a colorimetric detection system is described. Two different configurations were tested: configuration 1 (an opposite side configuration) where a secondary inner-filter effect accounts for CO₂ sensitivity. This configuration involves the absorption of the phosphorescence emitted from a CO₂-insensitive luminophore by an acid–base indicator and configuration 2 wherein the membrane containing the luminophore is removed, simplifying the sensing membrane that now only contains the acid–base indicator. In addition, two different instrumental configurations have been studied, using a paired emitter–detector diode system, consisting of two LEDs wherein one is used as the light source (emitter) and the other is used in reverse bias mode as the light detector. The first configuration uses a green LED as emitter and a red LED as detector, whereas in the second case two identical red LEDs are used as emitter and detector. The system was characterised in terms of sensitivity, dynamic response, reproducibility, stability and temperature influence. We found that configuration 2 presented a better CO₂ response in terms of sensitivity.     

A windowless flow cell-based miniaturized fluorescence detector for capillary flow systems

A miniaturized fluorescence detector utilizing a three-dimensional windowless flow cell has been constructed and evaluated. The inlet and outlet liquid channels are collinear and are located in the same plane as the excitation paths, while the optical fiber used to collect the emission light is perpendicular to this plane. The straightforward arrangement of the flow path minimizes band dispersion and eliminates bubble formation or accumulation inside the cell. The use of high-brightness light-emitting diodes (LEDs) as the excitation source and a miniaturized metal package photomultiplier tube (PMT) results in a compact and sensitive fluorescence detector. The detection limit obtained from the system for fluorescein isothiocyanate (FITC) in flow injection mode is 2.6 nmol/L. The analysis of riboflavin and FITC by packed capillary liquid chromatography is demonstrated.      

Highly sensitive flow analysis determination of orthophosphate using solid phase enrichment of phosphomolybdenum blue without need for organic solvents in elution

In a flow analysis configuration, orthophosphate has been enriched as phosphomolybdenum blue on reversed phase polymers (styrene-divinylbenzene (DVB), methacrylate, dextran), recovered by an alkaline solution without added organic solvent, and measured photometrically at 700 nm. It was found that phosphomolybdenum blue is bound to those polymers mainly by fast adsorption but also partly by slow diffusion (which causes some carryover); the relative extent of both processes depends on the chemical nature of the polymer. With the enrichment column placed near the detector to minimize transport dispersion and an enrichment time of 120 s; a signal improvement factor of 30–50 was obtained using styrene-DVB.     

Development of integrated chemiluminescence flow sensor for the determination of adrenaline and isoprenaline

A novel integrated chemiluminescence (CL) flow sensor for the determination of adrenaline and isoprenaline is developed based on the enhancing effect of analytes on CL emission of luminol oxidized by periodate in alkaline solution. The analytical reagents luminol and periodate are immobilized on anion exchange resins, respectively, and packed in a glass tube to construct a reagentless sensor. The proposed sensor allows the determination of adrenaline and isoprenaline over the range from 2.0×10⁻⁸ to 1.0×10⁻⁵ g ml⁻¹ and 2.0×10⁻⁷ to 5.0×10⁻⁵ g ml⁻¹, respectively. The detection limits are 7.0×10⁻⁹ g ml⁻¹ for adrenaline and 5.0×10⁻⁸ g ml⁻¹ for isoprenaline with a relative standard deviation of 1.7% for the 1.0×10⁻⁷ g ml⁻¹ adrenaline (n=11) and 2.1% for 1.0×10⁻⁶ g ml⁻¹ isoprenaline (n=11). The sample throughput was 60 samples h⁻¹. The sensor has been successfully applied to the determination of adrenaline and isoprenaline in pharmaceutical preparations.     

Fluorimetric flow injection analysis of trace amount of formaldehyde in environmental atmosphere with 5,5-dimethylcyclohexane-1,3-dione

A simple and sensitive flow injection method with fluorimetry and 5,5-dimethylcyclohexane-1,3-dione (dimedone) was developed for the determination of formaldehyde. Formaldehyde reacted with dimedone in the presence of ammonium acetate to form a fluorescence compound, which has an excitation wavelength at 395 nm and an emission wavelength at 463 nm. A two-channel flow system was assembled. Distilled water and 0.3% dimedone buffered at pH 5.5 were delivered at 0.7 ml min⁻¹ and 100 μl of sample was injected into the carrier stream. The reaction was done in the reaction system designed newly, which consists of heating and cooling devices. The chemical reactivity with formaldehyde was excellent in the reaction system and selective. The calibration graphs were linear in the range of 25–100 and 5–10 ppb. RSDs (n=10) for 50 and 10 ppb formaldehyde were 0.6 and 3.4% and the LOD (S/N=3) was 0.9 ppb. The sample throughput was 20 h⁻¹. The method was applied to the determination of formaldehyde in gas sample evolved from adhesive agents and in living environmental indoor. The sensitive and selective method is useful for monitoring trace of formaldehyde in the environmental atmosphere.     

Determination of phosphate using a highly sensitive paired emitter-detector diode photometric flow detector

The use of a novel inexpensive photometric device, a paired emitter-detector diode (PEDD) has been applied to the colorimetric determination of phosphate using the malachite green spectrophotometric method. The novel miniaturized flow detector applied within this manifold is a highly sensitive, low cost, miniaturized light emitting diode (LED) based detector. The optical flow cell was constructed from two LEDs, whereby one is the light source and the second is the light detector, with the LED light source forward biased and the LED detector reversed biased. The photocurrent generated by the LED light source discharges the junction capacitance of the detector diode from 5 V (logic 1) to 1.7 V (logic 0) and the time taken for this process to occur is measured using a simple timer circuit.The malachite green (MG) method employed for phosphate determination is based on the formation of a green molybdophosphoric acid complex, the intensity of which is directly related to phosphate concentration. Optimum analytical parameters such as reaction kinetics, reagent to sample concentration ratio and emitter wavelength intensity were investigated for the spectrophotometric method. Linear calibration plots that obeyed the Beer-Lambert law were obtained for phosphate in the range of 0.02-2 μM. The dynamic range, sensitivity and limits of detection are reported.     

Low pressure ion chromatography with a low cost paired emitter-detector diode based detector for the determination of alkaline earth metals in water samples

The use of a low pressure ion chromatograph based upon short (25 mm × 4.6 mm) surfactant coated monolithic columns and a low cost paired emitter-detector diode (PEDD) based detector, for the determination of alkaline earth metals in aqueous matrices is presented. The system was applied to the separation of magnesium, calcium, strontium and barium in less than 7 min using a 0.15 M KCl mobile phase at pH 3, with post-column reaction detection at 570 nm using o-cresolphthalein complexone. A comparison of the performance of the PEDD detector with a standard laboratory absorbance detector is shown, with limits of detection for magnesium and calcium using the low cost PEDD detector equal to 0.16 and 0.23 mg L⁻¹, respectively. Finally, the developed system was used for the determination of calcium and magnesium in a commercial spring water sample.     

Fluorimetric reaction detectors for high-performance liquid chromatography Part 2. Reactor materials and effects of variable dynamic dimensions

Summary Using selected steroid pairs some effects of the coupling of liquid chromatographic separations with derivatization after separation on band broadening are investigated. Derivatization with isonicotinoylhydrazid in organic solvents and the multi-step reaction of ketosteroids to form dihydrolutidin derivatives in aqueous solution are given as examples. The dependence of the resolution on the reactor materal, on the design of the reactor, on the linear velocity of the liquid stream in the reactor and on the ratio of the flow rate in the HPLC column and the reactor are examined.Part 1. Selection of Chemical reactions     

One-step straightfoward solid synthesis of high yield white fluorescent carbon dots for white light emitting diodes

Herein,we directly prepared white fluorescent CDs(W-CDs) using 1,6-dihydroxynaphthalene(1,6-DHN)and L-asparagine(L-Asn) as carbon sources through a simple solvent-free method.As-prepared W-CDs can be obtained in high yield(95%).A relative pure white LEDs(WLEDs) were fabricated with Commission Internationale de Eclairage(CIE) coordinates of(0.32,0.31).As-prepared W-CDs will have promising future for a wide range of optoelectronic devices.     

Stable deep blue organic light emitting diodes with CIE of y < 0.10 based on quinazoline and carbazole units

Achieving stable deep blue organic light emitting diodes (OLEDs) with narrow full width at half maximum (FWHM) and color gamut in the range of the commission International de L’Eclairage (CIE) of y ≤ 0.10 is still challenging in display and lighting applications. In this investigation, three donor-acceptor (D-A) deep-blue emitters were designed and synthesized via integrating asymmetric quinazoline (PQ) acceptor with weak donating carbazole (Cz) donor. The effect of the position and number of Cz group in PQ unit are investigated, which is also first examples for systematic research about the effect of different position of asymmetric PQ as acceptor on deep OLEDs. Their bandgaps of 3.12∼3.19 eV and the singlet state energy levels of 3.12∼3.19 eV were found to be sufficiently large to achieve deep blue light. As expected, these emitters-based OLEDs exhibit deep blue emission with the maximum wavelength ≤ 450 nm and narrow FWHM ≈ 60 nm. Especially, a CIE of y = 0.080 was achieved for 4PQ-Cz-based OLED. Significantly, the deep blue electroluminescence (EL) spectra of these three emitters-based OLEDs are very stable and the corresponding CIE coordinates deviation (ΔCIE (x, y)) can be negligible under the applied voltage ranging from 5 V to 9 V.     

Development of a tubular fluoride potentiometric detector for flow analysis: evaluation and analytical applications

In this work a construction procedure for tubular fluoride electrode to be used in flow systems is outlined. The electrode was constructed from a commercially available, LaF₃ single crystal. Principal advantages of the flow detector presented include simplicity of construction, robustness, durability, low cost and easy coupling into any point of a flow manifold.Evaluation of the intrinsic working characteristics of the potentiometric detector in a low dispersion manifold is presented with respect to analytical and dynamic parameters. The constructed detector has similar working characteristics to those of the conventional fluoride electrodes, namely the detection limit, lower limit of linear response and operational pH range.The analytical usefulness of the constructed device was assessed in a flow system developed for fluoride determination in toothpaste, tablet, collutory and water samples for which the reference procedures suggest the determination of fluoride ion with a conventional ion selective electrode.     

Non-aqueous capillary electrophoresis with red light emitting diode absorbance detection for the analysis of basic dyes

Non-aqueous capillary electrophoresis was evaluated for the separation of five hydrophobic basic blue dyes for application in forensic dye analysis. The use of a red light emitting diode as a high intensity, low-noise light source provided sensitive detection of the blue dyes while also allowing the evaluation of solvents that absorb strongly in the UV region. Excellent peak shapes and separation selectivity were obtained in methanol, ethanol, acetonitrile and dimethylsulfoxide, however water, tetrahydrofuran, dimethylformamide and acetone were unsuitable as solvents due to poor peak shapes and a lack of sensitivity, most likely due to adsorption onto the capillary wall. Due to the known compatibility of methanol with capillary electrophoresis–mass spectrometry, this solvent was examined further with the relative acidity/basicity of the electrolyte being optimised with an artificial neural network. The optimised method was examined for the separation of ink samples from 6 fibre tip and 2 ball point blue or black pens and showed that a unique migration time for the main dye component in seven of the eight pens could be obtained.     

Flow-injection on-line oxidizing fluorimetry and solid phase extraction for determination of thioridazine hydrochloride in human plasma

A simple, sensitive and specific fluorimetric method has been developed for the determination of thioridazine hydrochloride in human plasma involving solid phase extraction (SPE). In a flow-injection system, thioridazine hydrochloride is on-line oxidized into a strongly fluorescent compound with a lead dioxide solid-phase reactor and the fluorescence intensity is measured with a fluorescence detector (λ_ex = 349 nm, λ_em = 429 nm). A comparison of plasma sample pretreatment between SPE procedure and precipitation method was made and the results showed that SPE procedure was better than precipitation method. Under the optimum conditions, the fluorescence intensity is proportional to the concentration of thioridazine hydrochloride in the range from 0.015 to 2.000 μg mL⁻¹. The detection limit is 5.5 ng mL⁻¹ of thioridazine hydrochloride and the relative standard deviation is 1.06%. This method has been applied to determination of thioridazine hydrochloride in real patients plasma samples with the results compared with those obtained by HPLC method.     

Nephelometry and turbidimetry with paired emitter detector diodes and their application for determination of total urinary protein

Two miniature and compact optoelectronic devices fabricated by means of integration of light emitting diodes have been developed for turbidimetric and nephelometric measurements. These devices are operating according to paired-emitter-detector-diode (PEDD) principle. The detectors have been characterized using bovine serum albumin and Exton protein assay as a model analyte and a model analytical method, respectively. The developed detectors have been adapted for measurements under conditions of flow injection analysis (FIA). Under optimized conditions the turbidimetric flow system offers the range of linear response up to 400 mg L⁻¹ with the detection limit at 20 mg L⁻¹. The linear range and detection limit found for optimized nephelometric FIA system are 15–500 mg L⁻¹ and 8 mg L⁻¹, respectively. The PEDD-based FIA systems with the detector operating according to both modes of measurements have been successfully applied for urinalysis offering total protein determination at physiological and pathological levels with high throughput (over 60 injections per hour).     

Using on-line solid phase extraction for flow-injection spectrophotometric determination of salbutamol

In the proposed procedure, the determination of salbutamol with Folin-Ciocalteau reagent (FC) using a flow injection analysis technique (FIA) with spectrophotometric detection at 750 nm is described. The lab-made FIA system consisted of a peristaltic pump Gilson Minipulse 3 equipped with Tygon tubes, double 6-port external Vici Valco sample injector and S 2000/SAD500 fiber optic spectrophotometer. It was controlled by a PC with use of originally compiled LabVIEW^®—supported software containing the mathematical library with various statistical functions for off-line data evaluation. Concentration, volume of reagents and flow rate were optimised by a simplex method. The proposed system was used for the direct determination of salbutamol sulphate in the tablets and the human urine without preliminary pre-treatment of the sample. The negative effect of interfering substances (excipients of the tablets and matrix of the urine) is overcome by a solid phase extraction (SPE), when salbutamol is adsorbed on the solid phase in the microcolumn, which is integrated directly into the flow system. Pre-treatment of the sample takes place directly in the flowing stream. The sample throughput without carryover of on-line SPE was 60-80 samples per hour. With the SPE column (Baker—carboxylic acid), salbutamol was determined in the linear range from 1 to 15 μg ml⁻¹ (R.S.D.=1.2%), with detection limit (3σ) 0.1 μg ml⁻¹ and a frequency of 40-60 samples per hour in the water solutions. The salbutamol was determined in the linear range from 2 to 20 μg ml⁻¹ (R.S.D.=1.7%), with detection limit (3σ) 1 μg ml⁻¹ and a frequency of 30 samples per hour in the samples of the human urine.     

A novel amperometric sensor and chromatographic detector for determination of parathion

A novel amperometric sensor and chromatographic detector for determination of parathion has been fabricated from a multi-wall carbon nano-tube (MWCNT)/Nafion film-modified glassy-carbon electrode (GCE). The electrochemical response to parathion at the MWCNT/Nafion film electrode was investigated by cyclic voltammetry and linear sweep voltammetry. The redox current of parathion at the MWCNT/Nafion film electrode was significantly higher than that at the bare GCE, the MWCNT-modified GCE, and the Nafion-modified GCE. The results indicated that the MWCNT/Nafion film had an efficient electrocatalytic effect on the electrochemical response to parathion. The peak current was proportional to the concentration of parathion in the range 5.0×10^–9–2.0×10^–5 mol L^–1. The detection limit was 1.0×10^–9 mol L^–1 (after 120 s accumulation). In high-performance liquid chromatography with electrochemical detection (HPLC–ED) a stable and sensitive current response was obtained for parathion at the MWCNT/Nafion film electrode. The linear range for parathion was over four orders of magnitude and the detection limit was 6.0×10^–9 mol L^–1. Application of the method for determination of parathion in rice was satisfactory.