Instrumentally simple flow detector for the determination of traces of electroluminescent compounds in aqueous solutions

A flow detector based on the observation of the cathodic electroluminescence at an oxide-covered aluminium electrode is described. The detector responds only to electroluminescent compounds in aqueous eluents, and additional selectivity can be achieved by making use of optical filters for wavelength discrimination. The optimum detection conditions were determined by using the cathodic electroluminescence induced by a polynuclear aromatic hydrocarbon in micellar solutions as the model electroluminescence. This instrumentally simple detector can be used to determine electroluminescent compounds in a wide concentration range with good precision. For instance, its detection limit, dynamic range and precision (i.e., relative standard deviation for 20 successive measurements of 1 × 10^?7 M samples) for the determination of micelle-encapsulated 9,10-diphenylanthracene were found to be 1 × 10^?8 M, four orders of magnitude and 7%, respectively.     

Specific determination of trace copper(II) by cathodic electroluminescence

Copper (II) stimulates cathodic electroluminescence at the oxide-covered aluminum electrode in the presence of hydrogen peroxide and 2,2′-bipyridine in 0.1 M sodium acetate. The detection limit is 5 × 10^?9 M; no other metal ions interfered. The mechanism of the reactions is discussed.     

Determination of polynuclear aromatic hydrocarbons in micellar solution by electrogenerated chemiluminescence

When polarized cathodically in aqueous acetate solution (pH 7.0) containing peroxodisulfate, a micelle-forming surfactant (Brij-35) and a polynuclear aromatic hydrocarbon, an oxide-covered aluminum electrode produces an intense electroluminescence where the emitting species is the micelle-encapsulated hydrocarbon. The detection limit is ca. 10^?8 M for 9,10- diphenylanthracene.     

Sensitive spectrophotometric detection of dopamine,levodopa and adrenaline using surface plasmon resonance band of silver nanoparticles

A simple and effective procedure is proposed for spectrophotometric determination of catecholamines; Dopamine (1), L-Dopa (2) and Adrenaline (3). It was found that the reduction of Ag⁺ to silver nanoparticles (Ag-NPs) by these catecholamines in the presence of polyvinylpyrrolidone (PVP) as a stabilizing agent produced very intense surface plasmon resonance peak of Ag-NPs. The plasmon absorbance of the Ag-NPs allows the quantitative spectrophotometric detection of the catecholamines. The calibration curves derived from the changes in absorbance at λ = 440 nm were linear with concentration of Dopamine, Levodopa and Adrenaline in the range of 3.2×10^?6? 2.0×10^?5 M, 1.6×10^?7 ? 1.0×10^?5 M, 1.5×10^?6? 4.0×10^?5 M, respectively. The detection limits (3σ) were 1.2×10^?6 M, 8.6 ×10^?8 M, 9.7 ×10^?7 M for the Dopamine, L-Dopa and Adrenaline, respectively. The method was applied successfully to the determination of catecholamines in Ringer’s injection serum.     

Simultaneous Determination of Antimony and Lead in Gunshot Residue by Cathodic Adsorptive Stripping Voltammetric Methods

Differential pulse cathodic adsorptive stripping (DPCAdSV) and square wave cathodic adsorptive stripping (SWCAdSV) voltammetric methods were developed for the determination of antimony and lead in gunshot residues. Linear working ranges for DPCAdSV and SWCAdSV methods were (2.0×10^?9–5.0×10^?7) M and (2.0×10^?9–7.0×10^?7) M for antimony and 2.0×10^?9–3.0×10^?7 M (both methods) for lead. The detection of antimony limits were found to be 1.3×10^?9 M for DPCAdSV and 7.3×10^?10 M for SWCAdSV while the corresponding values for lead were 3.0×10^?9 M and 5.8×10^?10 M. Antimony and lead contents obtained by these methods in gunshot residues are in good agreement with those obtained by graphite furnace atomic absorption spectrometric method within a confidence limit of 95%.     

Spectrophotometric and spectrofluorimetric determination of iodide by extraction of ICl−2 with rhodamine B

Iodide is determined after oxidation with nitrous acid in 5 M hydrochloric acid to ICl^?₂. The ion-pair formed with rhodamine B is extracted into toluene and measured spectrophotometrically (0.5–5 × 10^?5 M) or spectrofluorimetrically (1–10 × 10^?6 M). The relative standard deviations were 1.8% for the determination of 5 × 10^?6 M iodide (n = 5) by spectrofluorimetry and 2.3% (n = 50) for 1 × 10^?5 M iodide by spectrophotometry. Periodate, iodate and iodine responded exactly as iodide.     

Simultaneous Square‐Wave Voltammetric Determination of Paracetamol,Caffeine and Orphenadrine in Pharmaceutical Formulations Using a Cathodically Pretreated Boron‐Doped Diamond Electrode

An electroanalytical method for the simultaneous determination of paracetamol (PAR), caffeine (CAF), and orphenadrine (ORPH) using the square‐wave voltammetry (SWV) and a cathodically pretreated boron‐doped diamond electrode was developed. The method exhibits linear responses to PAR, CAF, and ORPH in the concentration ranges 5.4×10^?7–6.1×10^?5 M, 7.8×10^?7–3.5×10^?5 M, and 7.8×10^?7–3.5×10^?5 M, respectively, with detection limits of 2.3×10^?7 M, 9.6×10^?8 M, and 8.4×10^?8 M, respectively. The proposed method was successfully applied in the simultaneous determination of these analytes in pharmaceutical formulations.     

Screening of chemiluminescent systems for the determination of some biologically important organic compounds

Screening tests are described for the development of chemiluminescence systems (oxidizing systems) capable of detecting biological organic compounds. The light emission depends strongly on the oxidizing systems employed. Acidic permanganate system gives rise to light emission for many compounds, including catechols, catecholamines, triphenols and indoles. The following oxidizing systems led specifically to chemiluminescence for hydroquinone, adrenaline or phenylpyruvic acid: 10^?1 M thiosulphate with 10^?1 M sodium hydroxide and 10^?4 M Ag (I), 0.3 % hydrogen peroxide with 10^?3 M sodium hydroxide/50% acetonitrile and 10^?4 M Fe (II), and 0.3% hydrogen peroxide with 10^?2 M sodium hydroxide/10^?2 M didodecyldimethylammonium bromide and 10^?4 M Co(II), respectively.     

Chemiluminescence determination of bufrenorphine hydrochloride by flow injection analysis

A direct, simple and rapid flow-injection method is described for determining buprenorphine hydrochloride (10^?8–10^?4 M) based on its chemiluminescent oxidation with potassium permanganate in polyphosphoric acid. The limit of detection is 1 × 10^?8 M (0.5 pmol per injection) and the log-log calibration is linear up to 1 × 10^?4 M; the r.s.d. is 0.7% for a 10 μg ml^?1 solution (n = 10). The method is directly applicable to aqueous solutions of tablets containing the drug (0.2 mg/tablet).     

Indirect Differential Pulse Voltammetric Determination of Aluminum Biological Samples in the Presence of 3, 4-Dihydroxyphenylalanine

ABSTRACT

Indirect differential pulse voltammetric (DPV) determination of aluminum in the presence of 3, 4-dihydroxyphenylalanine (L-dopa) with glass carbon electrode as working electrode has been described. The method relies on the decrease of DPV anodic peak current of L-dopa with the addition of Al^III The decreasing value of the peak current is linear with the increase of Al^III concentration. Under the optimum experimental conditions (pH 4.8, 6×10^?4 M L-dopa, 0.06M NaAc - HAc ¹buffer solution), the linear ranges are 4.0×10^?7 - 5.2×10^?6 M and 7.2×10^?6 - 4.5×10^?5 M. The relative standard deviation for 8×10^?6 M aluminum is 1.0% (n = 8) and the detection limit is 3.5×10^?7 M. A number of foreign species for interference have been studied. The method has been applied to determine aluminum in drinking water, synthetic renal dialysate and urine samples.     

Ionic liquids with an anion of N-lauroyl sarcosinate in membranes of ion-selective electrode

The study considers solubility in water, extractivity, and electrode properties of ionic liquids (IL), lauroyl tetrahexylammonium (THALS) and tetraoctylammonium lauroyl sarcosinate (TOALS). The values of solubility, found by potentiometry using ion-selective membranes of PVC-electrodes (ISE) have appeared to be 3.0 ± 0.4 mM and 0.011 ± 0.005 mM, for THALS and TOALS, respectively. Both IL quantitatively recover nitrophenol (99.9%) into chloroform from aqueous solutions in the pH range from 2 to 12. The application of IL as the active components of PVC-ISE enables the determination of lauroyl sarcosinate anion in the concentration range 1 × 10^?2?C1 × 10^?4 M for THALS and 1 × 10^?2?C1 × 10^?5 M for TOALS and the determination of mononitrophenols, 2,4-dinitrophenols and picrates (1 × 10^?2 M?C1 × 10^?5 M). A solid-state sensor based on screen-printed electrode modified by TOALS IL has been proposed. The electrode has been used for the determination of 4-nitrophenol in the concentration range 1 × 10^?2?C1 × 10^?5 M, the operational stability of the electrode is 10 days.     

Liquid-state mercury(II) ion-selective electrode based on N-(O,O-diisopropylthiophosphoryl)thiobenzamide

A liquid ion-exchange electrode containing a complex of mercury(II) with N-(O,O-diisopropylthiophosphoryl)thiobenzamide in carbon tetrachloride is described. The electrode shows excellent sensitivity and good selectivity. The slope of the calibration graph is 29.0 mV/pHg²⁺ in the pHg²⁺ in the pHg²⁺ range 2–15.2 in mercury(II) ion buffers. The electrode can be used for determination of 5 × 10^?5–10^?2 M Hg(II) in the presence of 10^?2 M Cu(II), Ni(II), Co(II), Zn(II), Pb(II), Cd(II), Mn(II), Fe(III), Cr(III), Bi(III) or Al(III) ions and in the presence of 10^?3 M Ag(I) ions. It can bealso used for end-point detection in titrations with EDTA of 10^?3–10^?4 M mercury(II) at pH 2.     

Flow-injection determination of paraoxon by inhibition of immobilized acetylcholinesterase

Two flow-injection methods (continuous-flow and stopped-flow) are proposed for the determination of paraoxon, applying the dual-injection technique and spectrophotometric detection. They are based on the inhibition of the acetylcholinesterase-catalysed hydrolysis of α-naphthyl acetate and subsequent reaction of the α-naphthol produced with p-nitrobenzenediazonium fluoroborate. For the continuous-flow system the calibration graph was linear from 5 × 10^?7 to 1.5 × 10^?5 M, the relative standard deviation (r.s.d.) (n=6) for an 8 × 10^?6 M standard was 1.4%, the limit of detection (3σ) was 4 × 10^?7 M and the sample throughput was ca. 60 h^?1. For the stopped-flow system the linear range was from 1 × 10^?8 to 4 × 10^?7 M, the r.s.d. for a 2.5 × 10^?7 M standard was 0.9%, the limit of detection was 8 × 10^?9 M and the sample throughput was 30 h^?1.     

Effect of biogenic photochromic electron acceptors on chlorophyll fluorescence

It is shown that the photophysical properties of chlorophyll a (Chl) depend on the nature and relative amounts of 2-methyl-1,4-naphthoquinone (MNQ) and nicotinamide adenine dinucleotide phosphate (NADP). Photoinduced charge separation occurs in aqueous ethanol solutions of Chl (1 × 10^?5 M) and NADP (5 × 10^?6–5 × 10^?4 M), resulting in the dynamic quenching of Chl fluorescence. Coordination interaction between Chl and NADP is established at an NADP concentration of ≥5 × 10^?4 M. The nonlinear Stern-Volmer dependence in this range is due to the input from static quenching. It is shown that the quenching of Chl fluorescence in an MNQ solution at Chl and MNQ concentrations of 1 × 10^?5 M and 6.7 × 10^?5–1 × 10^?4 M, respectively, is described by a linear dependence in the Stern-Volmer coordinates; no complex formation is observed for Chl and MNQ under these conditions, and electron transfer is of the dynamic type. Static or mixed-type energy transfer from MNQ to Chl dominates at elevated MNQ concentrations.     

A multivariate calibration procedure for the tensammetric determination of detergents

A multivariate calibration procedure based on singular value decomposition (SVD) and the Ho-Kashyap algorithm is used for the tensammetric determination of the cationic detergents Hyamine 1622, benzalkonium chloride (BACl), N-cetyl-N,N,N-trimethylammonium bromide (CTABr) and mixtures of CTABr and BACl. The sensitivity and accuracy depend strongly on the nature of the detergent. Acceptable accuracy is obtained with a two-step calculation procedure in which calibration constants for the total concentration range of interest are used to guide the choice of a more specific set of calibration constants which are valid for a much smaller concentration span. For Hyamine 1622, concentrations in the range 5 × 10^?6?2 × 10^?4 M could be determined with an accuracy of ± 10^?6 M. For CTABr, these numbers were 3 × 10^?6?2 × 10^?4 M and ± 5 × 10^?7 M; for BACl, they were 2 × 10^?3?9 × 10^?2 g l^?1 and ± 1 × 10^?3 g l^?1. In the mixtures of CTABr and BACl, the accuracies were ± 3 × 10^?6 M and × 1 × 10^?3 g l^?1, respectively.     

Trace Detection of Mercury(II) Using Gold Ultra‐Microelectrode Arrays

The electroanalytical detection of trace mercury(II) at gold ultra‐microelectrode arrays is reported. The arrays consist of 256 gold microelectrodes of 5 μm in diameter in cubic arrangements which are separated from their nearest neighbor by 100 μm. The array was utilized in nitric acid using linear sweep voltammetry where a linear response from mercury additions over the range 10 μg L^?1?200 μg L^?1 (10^?8?10^?6 M) was observed with a sensitivity and detection limit of 0.11 nC/μg L^?1 and 3.2 μg L^?1 (16 nM) respectively from using a deposition time of 30 s at ?0.2 V (vs. SCE). This methodology was explored in 0.1 and 1 M chloride media over the mercury range 10 μg L^?1?200 μg L^?1 (5×10^?8?10^?6 M) where similar sensitivities of 0.087 nC/μg L^?1 and 0.078 nC/μg L^?1 were observed with an identical detection limit. The protocol is demonstrated to be useful for the determination of mercury for analysis of environmental water samples.     

Determination Of Amino Acid Based On A Series Piezoelectric Quartz Crystal Sensor

ABSTRACT

A series piezoelectric quartz crystal (SPQC) sensor has been applied to detect L-glutamic acid and L-lysine acid. The effect of formaldehyde solution on the frequency shift was studied. Two methods were discussed. For the calibration curve method, in a neutralized formaldehyde medium, the linear ranges for determining L-glutamic acid and L-lysine acid were from 7.1×10^?6M to 6.5×10^?4M and from 6.9×10^?6 M to 7.4×10^?4 M, respectively, with the detection limit being 7.1×10^?6 M and 6.9×10^?6 M, the recoveries were 99.2% and 100.1%, the R.S.D were 1.63% (n=6) and 1.83%(n=6), respectively. Frequencimetric tiration method was also described and the lowest titratable concentrations were 8.3×10^?5M and 5.5×10^?5 M, respectively.     

Axially Chiral TADF‐Active Enantiomers Designed for Efficient Blue Circularly Polarized Electroluminescence

The use of a chiral, emitting skeleton for axially chiral enantiomers showing activity in thermally activated delayed fluorescence (TADF) with circularly polarized electroluminescence (CPEL) is proposed. A pair of chiral stable enantiomers, (?)‐(S)‐Cz‐Ax‐CN and (+)‐(R)‐Cz‐Ax‐CN, was designed and synthesized. The enantiomers, both exhibiting intramolecular π‐conjugated charge transfer (CT) and spatial CT, show TADF activities with a small singlet–triplet energy difference (ΔE_ST) of 0.029 eV and mirror‐image circularly polarized luminescence (CPL) activities with large g_lum values. Notably, CP‐OLEDs based on the enantiomers feature blue electroluminescence centered at 468 nm with external quantum efficiencies (EQEs) of 12.5 and 12.7 %, and also show intense CPEL with g_EL values of ?1.2×10^?2 and +1.4×10^?2, respectively. These are the first CP‐OLEDs based on TADF‐active enantiomers with efficient blue CPEL.     

Method for determination of fluoroquinolones based on the plasmonic interaction between their fluorescent terbium complexes and silver nanoparticles

We report on a fluorometric method for the determination of the fluoroquinolones levofloxacin (LEV) and moxifloxacin (MOXI). It is based on the Tb(III)-sensitized luminescence that is plasmonically enhanced by silver nanoparticles (Ag NPs). The emission of the Tb(III) complexes has maximum at 545?nm after excitation at 284?nm and is strongly enhanced in the presence of the colloidal Ag NPs. Under optimum experimental conditions, luminescence intensity increases linearly with the concentration in the range from 4.16?×?10^-17-3.59?×?10^-15?M of LEV, and from 4.98?×?10^-17-2.49?×?10^-15?M for MOXI with correlation coefficients of 0.9996 and 0.9996, respectively. The limits of detection are 7.19?×?10^-18?M and 8.47?×?10^-18?M, respectively, and the relative standard deviations are 1.3 and 1.5% for 5 replicate measurements at 6.08?×?10^-14?M of LEV and 5.48?×?10^-14?M of MOXI. The method was successfully applied to the determination of LEV and MOXI in pharmaceutical samples, in urine and in serum.

Polarographic waves of tri-n-butyl phosphate and polarographic determination of uranium in the presence of tri-n-butyl phosphate

The results of a study on the polarographic behaviour of TBP and its influence on the determination of uranyl ions is presented. The half-wave potential of the adsorption wave of TBP depends on the concentration of TBP, type of supporting elec trolyte and its concentration. In the presence of TBP the polarographic wave of U(VI) ion is changed. Below 7·10^?5 M TBP the polarographic wave of U(VI) is not affected, between 7·10^?5 and 2·10^?4 M TBP the shape, height and half-wave potential of U(VI) waves are changed and above 2·10^?4 M, up to saturated solution of TBP, the waves of U(VI) do, not change further. The bes supporting electrolytes for the determination of U(VI) are KNO₃ or NaClO₄ in concentrations of 0.1 to 0.5 M, pH 1–2 and TBP concentrations from 3·10^?4 to 1.2·10^?3 M.