Ammoniacal Buffer Research Articles

Fluorimetric determination of aqueous formaldehyde employing heating and ultrasound-assisted approach through its derivatization with a ß-diketone-nickel(2+) complex immobilized in a PMMA flow cell

Formaldehyde (FA) is a highly toxic substance present in many matrices, including freshwater as well as found in natural mechanisms such as rainfall and combustion of organic matter. Consumption of water contaminated with high levels of FA can cause severe short-term or long-term health problems. Due to these health risks, procedures are necessary to determine and quantify FA in aqua sources This paper reports on a study of fluorimetric determination of FA using a nickel(2 + )-diketonate coordination compound immobilized as a solid precursor. The compound was characterized by electronic absorption, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetry (TG), optical microscopy (OM), and scanner electron microscopy (SEM). The methodology was based on the reaction of the synthesized compound with an ammoniacal buffer generating a selective reagent for formaldehyde: fluoral-P. The product of the reaction generates 3,5-diacetyl-1,4-dihydrolutidine (DDL), which is responsible for the fluorescence of the system. Several parameters such as temperature, duration of heating time, and dilution effect with the best effects were studied to carry out FA determination. Under the optimum experimental conditions, a linear response ranging from 1.0 to 10.0 mg/L FA (R = 0.997 and n = 10), and a detection (3σ criterion) and quantification (10 σ criterion) limit estimated at 0.129 and 0.389 mg/L, respectively were achieved. The FA analysis was able to be conducted in 05 min with a relative standard deviation estimated at 1.10 %.

Capped cadmium telluride quantum dots fluorescence enhancement by Se(IV) and its application to dietary supplements analysis

A thioglycolic capped CdTe probe for Se(IV) detection was optimised by nanocrystal size, pH, buffer composition and concentration, and the order of reagent addition. A large increase in fluorescence (>90%) was observed upon sequential addition of Se(IV), buffer, and CdTe probe, caused by surface passivation due to the presence of singly charged Se(IV) in ammoniacal buffer (0.01 mol L–1) at pH 8.4. This result indicated the possibility of inorganic Se speciation. The method presented a detection limit of 60.5 μg L–1 with RSD ≤ 3.5% (n = 8) and was successfully applied to dietary supplements analysis.

Enhanced activity for non-enzymatic glucose biosensor by facile electro-deposition of cauliflower-like NiWO4 nanostructures

This work introduces simple electrodeposition of nickel tungstate nanostructures (NiWO4 NSs) as an electrocatalyst material for the development of a non-enzymatic glucose biosensor. We report a straightforward route for electrosynthesis of NiWO4 NSs on the glassy carbon electrode (GCE) surface by performing two electrochemical steps for the first time. In the first step, the Ni–W alloy was electrodeposited on carbon substrate at a constant potential of -1.4 V (vs. SCE) for 60 s in an ammoniacal buffer (pH = 8.0) containing an appropriate amount of NiSO4 and Na2WO4. 2H2O. In the next step, Ni–W alloy was converted to the cauliflower nanostructured NiWO4 by applying a cyclic voltammetric (CV) treatment in 1.0 M NaOH solution for 15 cycles at the scan rate 50 mV s−1. The surface morphology, elemental composition, crystal structure of NiWO4 NSs were studied by FESEM, EDX, and XRD analysis, respectively. The NiWO4 NSs/GCE nanosensor exhibited excellent electrocatalytic activity towards glucose in an alkaline medium. The proposed non-enzymatic glucose biosensor possessed excellent selectivity obtained at potential (0.6 V vs. SCE) in KOH 0.1 M, and outstanding long term stability. Furthermore, it showed a low detection limit of 0.15 µM with a high sensitivity of 1200 μA mM−1 cm−2 over the linear range of 0.5–280 µM in KOH 0.1 M. Finally, the practical application of the proposed sensor was successfully evaluated by determining the glucose concentration of human blood with the satisfactory results.

Evaluation of the Direct Interaction between Amino Acids and Glutathione-Coated CdTe Quantum Dots and Application in Urinalysis for Histidine Determination

The present work aimed to direct amino acid (AA) sensing by quantum dots (QD) and development of an analytical method for potential fast clinical tests. Notably, AA with a positive charge or neutral polar chains, namely L-histidine (His) and L-threonine (Thr), responded to glutathione-coated CdTe (GSH-CdTe) (ΔF ≤ 90%, variation of fluorescence intensity). However, in ammoniacal buffer (0.25 mol L-1) at pH 8.0, 2.2 nm GSH-CdTe responded only to His. Static quenching with complex association constant (Ksv) varying from 2.81 to 0.94 (10 L mol-1) as well as van der Waals forces and/or hydrogen bonding were predicted for His-QD quenching mechanism and binding type. Additionally, thermodynamic parameters as ΔH = -76.5 kJ mol-1 (enthalpy), ΔS = -227.4 J K-1 mol-1 (entropy) and ΔG from -9.8 until -6.4 kJ mol-1 (Gibbs free energy) at 20 to 35 °C were estimated by van’t Hoff equation. Under optimal conditions, the developed method presented a linear range from 0.42 to 35 mmol L-1 (with correlation coefficient (r) of 0.9970, n = 7), good precision (relative standard deviations (RSD) < 2.5% for 2.5 and 20 mmol L-1; n = 6) and limit of detection 1.6 × 10-4 mol L-1 (0.025 mg mL-1). Recovery tests were performed on artificial urine and human urine samples with recoveries ranging from 78.7 to 127.6%.

Electrodeposition and Electrooxidation of Bimetallic Systems Co–Ni and Cu–Ni

By means voltammetry method the characteristics of the electrodeposition and anodic oxidation processes of Cu, Ni, Co and Cu–Ni, Co–Ni were investigated in ammoniacal buffer supporting electrolyte using graphite electrode. The quantity, maximum currents and potentials of anodic peaks on the voltammetric curves in the case of binary system are defined by the ratio of metal ions concentration and electrodeposition procedure. The changes in the peaks parameters were attributed to the formation of bimetallic solid solutions with various contents of the components. It was shown that the result of coelectrodeposition of two metals on an inert substrate is determined not only the nature of the components of binary systems Co–Ni and Cu–Ni, but also features of the phase composition of bimetal in nano-state.

DEVELOPMENT OF FLOW INJECTION METHOD FOR ONLINE DETERMINATION OF THIOCYANATE BASED ON OXIDATION BY PERMANGANATE

The importance of developing method for thiocyanate becomes obvious, because thiocyanate can inhibit iodine uptake of thyroid gland leading to mumps disease. In this work, thiocyanate is oxidized by permanganate in the acid donor stream to cyanide, which is directly converted to hydrogen cyanide. Then, hydrogen cyanide diffuses through a Teflon membrane into acceptor stream containing nickel(II) in ammoniacal buffer to form tetracyanonickelate(II) which is detected spectrophotometrically at 267 nm. Analytical figures of merit were linear up to 50 mg L-1 for thiocyanate, with RSD of 1.34%, and detection limit of 0.07 mg L-1, respectively. Interfering anions were eliminated under stoichiometric amount of permanganate and sample throughput was 20 h-1. The method was validated for determining thiocyanate samples from synthetic and gold process waters with satisfactory results. Keywords: Thiocyanate, flow injection, permanganate, spectrophotometry

Silica-alumina-niobia (SiO2/Al2O3/Nb2O5) matrix obtained by the sol-gel processing method: new material for online extraction of zinc ions

In the present work, a new material, SiO2/Al2O3/Nb2O5 (designated as SiAlNb), was evaluated as an adsorbent in a flow injection spectrophotometric method for online preconcentration and determination of trace amounts of Zn2+ ions. The preconcentration method is based on Zn2+ adsorption onto the surface of SiAlNb in alkaline medium (pH 9.0). The elution step is carried out using HNO3 solution, followed by reaction of the Zn2+ ions with 1-(2-piridylazo)-2-naphtol (pan) in ammoniacal buffer solution (pH 9.3) containing Tween-80. The [Zn(pan)2] complex formed is determined at 560 nm. The method presented a linear range between 7.6 and 180.0 µg L-1 (r = 0.9992) and limits of detection and quantification of 2.3 and 7.6 µg L-1, respectively. According to the Langmuir linear model, the maximum adsorption capacity was found to be 7.0 mg of Zn2+ g-1 of SiAlNb. The proposed method was successfully applied to the Zn2+ determination in water samples (lake, mineral, tap) and certified reference material (TORT-2 Lobster Hepatopancreas).

DPASV Method for Determination of Trace Concentrations of Manganese in Non-Buffered Chloride Solutions by Addition of Cyanide as a Masking Agent

A highly sensitive, selective, and rapid differential pulse anodic stripping voltammetric method at HMDE is described for the determination of trace concentrations of Mn2+. The determination of Mn2+ in non-buffered chloride solution is seriously disturbed by the presence of Ni2+, Co2+, Cr3+, Zn2+ and Cu2+ due to intermetallic compound formation. The procedure is based on the addition of low amounts of cyanide as a masking agent. The interference of < 20 μgL−1 of Ni2+, Co2+ and Cr3+ and < 75 μgL−1 of Cu2+ and Zn2+ can thus be avoided, as the formed cyanide complexes prevent intermetallic compound formation during the short accumulation period. Thus, the addition of cyanide greatly improves the DPASV determination of manganese in non-buffered medium. A comparison between the determination of Mn2+ in the presence of a mixed cyanide/non-buffered chloride and in the ammoniacal buffer solution shows that the peak current of manganese in the presence of cyanide is four times higher with the same peak potential. The proposed method is shown to be applicable for the Mn2+ determination in both ground and tap water. A good agreement is obtained between the results by DPASV and AAS.

Mobilisation/purging of copper, chromium and arsenic ions from aqueous media into supercritical carbon dioxide

A series of complexometric extractions were performed to optimise the mobilisation/purging of metallic ions from samples of processing condensate of chromated copper arsenate (CCA). Whereas Cr(VI) and Cu(II) were rapidly mobilised into isobutylmethyl ketone-amended supercritical carbon dioxide (SC-CO 2) after reaction with dithiocarbamate or alkylxanthate, Cr(III) was appreciably less reactive under these conditions. For Cr(III), the pH of the derivatisation reaction was critical to the efficiency of complexation. It proved to be more efficient to form the complex and then to effect the mobilisation in a separate sequence rather than combining these unit operations into a single stage. Maximum derivatisation efficiencies with a variety of monovalent bidendate ligands were achieved in an ammoniacal buffer (NH 4Cl/NH 3) at pH≈8, then the crude product mixture was extracted complexometrically. An alternative approach involved a kinetically controlled precipitation of analyte Cr(III) from 0.35 M NaHCO 3, followed by a complexometric extraction of the filtrate. Some 88% of the substrate was removed from the aqueous medium with this filtration (∼50% removal) extraction (∼38% removal) combination. Complexometric extraction with a combination of diethyldithiocarbamate or alkylxanthate with methylthioglycolate reduced the aqueous metal burdens of CCA suspension (445.5±0.0% Cu, 771.0±1.1% Cr and 556.7 μg/ml±6.4% As) appreciably. In feasibility trials with CCA suspension that had been diluted 10-fold, optimised extraction procedures resulted in the mean removal of 99.9% Cu, 96.8% Cr and 86.0% As from the aqueous phase. Similar procedures with the undiluted suspension were approximately equally efficient (100% Cu, 98.7% Cr and 80.9% As). Although the solvent assisted complexometric extraction was virtually quantitative for Cu and efficient for Cr, the mobilisation of As would necessitate a subsequent treatment to remove residues of these ions.

Electrochemical studies of porphyrin interacting with DNA and determination of DNA

A voltammetric study of the interaction of TMAP with DNA on Hg electrode in ammoniacal buffer solution is described. Adding DNA in TMAP solution, the I p value of all three peaks of TMAP decreases, and E p of P 2 and P 3 shifts negatively, which is consistent with the results of decreasing TMAP concentration. In the presence of DNA, no new peaks appear, and the electrochemical parameters (standard rate constant k s , transfer coefficient α, diffusion coefficient D) of TMAP have no significant change. Electrochemically non-active complexes such as DNA-TMAP and DNA-2TMAP are formed when TMAP interacts with DNA. When DNA was added in 2 × 10 −6 mol l −1 TMAP solution, the I p1 of TMAP decreases in proportion to the DNA concentration from 5 × 10 −7 to 1 × 10 −5 mol l −1. The results of samples determination by electrochemical method are consistent with those by UV-spectroscopy.

Electrochemical behavior of mutagenic nitro and amino derivatives of carbazole

AbstractThe electrochemical behavior of nitro and amino carbazole derivatives has been investigated. In aprotic medium, both in reduction and oxidation, the electrochemical process is complicated by “father‐son” protonation reactions. In protic medium, the hydroxylamines resulting from 4‐electron reduction of nitrocarazoles are unstable in very acidic medium, but relatively stable in acetic or ammoniacal buffer, except for 3‐hydroxyl‐aminocarbazole; reduction of amino‐nitrocarbazoles leads to unstable hydroxylamines. Oxidation of aminocarbazoles is a 2‐electron process, the 2‐amino compounds being more difficult to oxidize than the 3‐amino derivatives. The relationships between these electrochemical behaviors and mutagenic properties of the studied compounds are also discussed.

Electrochemical access to functionalized dihydrothiopyran derivatives. Part 1: electroreduction of tetraactivated 4H-thiopyrans

Electroreduction of tetraactivated 4H-thiopyrans leads selectively to diastereoisomers of dihydrothiopyrans. The relative percentages depend on the experimental conditions (electrolysis in sulfuric medium, ammoniacal buffer). The preferred conformations of the end-products are determined in solid state by X-ray crystallography and in solution by 1H NMR spectroscopy, then compared with molecular modelling results. The relative conformations of the diastereoisomers and their ratio are established by 1H NMR spectroscopy.

Indirect ultraviolet determination of silver with nickelocyanide ion by flow injection analysis

A flow-injection method for the ultraviolet spectrophotometric determination of silver, based on its reaction with nickelocyanide ion, Ni(CN) 2− 4, in ammoniacal buffer medium (pH 10) and subsequent measurement of the decrease in the absorption of the Ni(CN) 2− 4 complex at 275 nm is described. The calibration graph is linear in the range 10–400 μm silver. At a sampling rate of about 60 samples h −1 with 35 μl sample injections, precision was about 1% relative standard deviation. The proposed method was successfully applied to the determination of silver in some common silver minerals.

Electrochemical reduction of o-nitrophenylthioacetic derivatives. Production of 2H-1,4-benzothiazines

Comparative studies of the electrochemical reduction of 2-( o-nitrophenylthio)-acetic acid and its methyl ester in aqueous media of different acidity show that reduction of the ester in an ammoniacal buffer is the best adapted for electrosynthesis of 4-hydroxy-2H-1,4-benzothiazin-3(4H)-one. The electrochemical behaviours of the corresponding phenylhydroxylamines and azoxy compounds are also investigated.

Determination of trace metals in Nile River and ground water by differential pulse stripping voltammetry

The determination of trace metals in river water and ground water by DPSV is seriously disturbed by the presence of organic complexes. The influence of these substances can be eliminated by acidification of the samples with acids. Cd, Pb and Cu were determined at pH 1.1 (HNO3 medium) and Zn, Cd, Pb and Cu at pH 2 (HCl medium), in both the Nile river and ground water. Zn was determined at pH 3.5 in HCl and pH 4.5 in HNO3, after neutralizing the samples with NH3/NH4Cl buffer. Manganese could then be determined, after further addition of ammoniacal buffer solution up to pH 7.5 and 8.5. Ni and Co were determined in the adsorptive mode after formation of dimethylglyoximates at pH 9.2. The effect of pH on the stripping peaks of manganese was studied. Good agreement was observed between DPSV and AAS results for Zn, Cd, Pb, Cu and Mn, but the concentrations of Ni and Co were below the detection limits for AAS. Good agreement was obtained between DPSV results in HCl and HNO3 for Ni and Co. The results indicate that decomposition of organic complexes by acidification with HNO3 is better than in the case with HCl for Zn, Pb, Cu, Ni and Co, but HCl is better than HNO3 for Cd and Mn.

Incorporation of hydroxamic acid ligands into Nafion film electrodes

This paper describes studies on Nafion-coated glassy carbon electrodes incorporating hydroxamic acids. Desferrioxamine, a trihydroxamic acid, and glycine hydroxamate, a monohydroxamic acid, can be incorporated by ion exchange into the Nafion film. These ligands were detected in the film visually, after reaction with iron(III), and electrochemically, by voltammetric oxidation. The complex of iron(III) with desferrioxamine was electrochemically active at the iron(III) centre in the Nafion film. The electrochemistry of this complex in the film agrees well with the solution electrochemistry reported by other workers: irreversible at low pH and reversible at high pH. The ability of the modified electrode to act as a sensor for iron(III) was assessed. Complexation of iron(III) from dilute solution into the polymer film was possible, and 5 × 10–7 mol l–1 iron(III) could be detected after a 10 min preconcentration, with differential-pulse voltammetric detection in pH 10 ammoniacal buffer.

Hematin as a peroxidase substitute in hydrogen peroxide determinations.

Hematin can substitute for horseradish peroxidase (HRP) as the catalyst in the determination of hydrogen peroxide using phenolic substrates such as p-hydroxyphenylacetate or p-cresol. Although the peroxidatic activity of hematin from bovine blood is not as great as HRP in terms of unit iron content, the activity per unit weight is substantially greater. Hematin is 500 times less expensive than HRP per unit peroxidatic activity. In hematin-catalyzed systems, reaction development and fluorescence measurement can both be conducted optimally in the same ammoniacal buffer. Hydroxyalkyl hydroperoxides are rapidly hydrolyzed to H2O2 at this pH and are also determined. On the other hand, for methyl hydroperoxide, hematin exhibits only approximately 10% of the sensitivity exhibited by HRP. Hematin is significantly more stable in solution than HRP. The use of hematin as catalyst and p-cresol as the substrate leads to a particularly inexpensive and sensitive system, permitting a limit of detection (LOD) of 7 nM H2O2 in a flow-injection configuration.

Réduction électrochimique de 4H-1,3-thiazines: obtention de 6H-1,3-thiazines et (ou) de pyrroles substitués

Controlled potential electroreduction (protic medium, mercury cathode) of substituted 2-ethoxy and 2-phenyl-4H-1,3-thiazines leads to 6H-1,3-thiazines and (or) pyrroles. The nature of the isolated products appears strongly dependent on pH of the medium and type of substitution: pyrrole formation takes place in acidic medium (0.5 mol L−1 H2SO4) and is favoured by phenyl and alkoxycarbonyl groups at positions 2 and 4, respectively; formation of 6H-1,3-thiazines and their reduction products (substituted thiobenzamides, carbamates and 2-thiazoline) occurs in weakly acidic (acetate buffer) or basic (ammoniacal buffer) medium. Keywords: electrochemical reductions, substituted 4H- and 6H-1,3-thiazines, pyrroles, 2-thiazoline, cyclic regression.

Some observations on the electrochemical reduction of pyridazin-3-ones

Controlled potential electroreduction of three pyridazin-3-ones has been investigated in protic medium. Whatever the acidity, the first reduction always takes place at the 4,5-double bond. In an ammoniacal buffer, further reduction leads to the tetrahydro derivative. In acidic medium, reduction of N-2 unsubstituted 4,5-dihydropyridazine-3-ones gives N-amonipyrrolidin-2-ones, whereas 2-methyl 4,5-dihydropyridazin-3-one leads to a pyrrolin-2-one.

Indirect ultraviolet determination of cyanide by flow injection analysis using absorption of the Hg-EDTA complex at 250 nm

The flow injection principle was used in the determination of cyanide ion by the decrease in the ultraviolet absorption of the Hg-EDTA complex at 250 nm. The decrease in the absorbance is linear with cyanide concentration in the range of 0.5–52 ppm. A manifold consisting of two lines was used. The EDTA carrier and the Hg-EDTA reagent streams were buffered at pH 10 (ammoniacal buffer). The method has a detection limit of 0.5 ppm cyanide. At a sampling rate of ca.60 samples per hour with 100-μl sample injections, precision was about 1% relative standard deviation. The effects of the concentration of the Hg-EDTA reagent, pH, sample volume, flow rate, coil length, and anion interference on the FIA-ultraviolet signals are reported.