Solvent extraction and extraction–voltammetric determination of phenols using room temperature ionic liquid

The phenolic compounds phenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitrophenol, 1-naphthol, 2-naphthol, and 4-chlorophenol are extracted nearly quantitatively from aqueous solution into the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF₆) in molecular form at pH<pK_a. Picric acid is extracted efficiently in anionic form. Recovery of pyrocatechol and resorcinol is much lower. The effect of pH, phenol concentration, and volume ratio of aqueous and organic phases were studied. Ionic liquid BMImPF₆ is shown to be suitable for extraction–voltammetric determination of phenols without back-extraction or addition of support electrolyte. The electrochemical window of BMImPF₆ at various electrodes was determined, and voltammetric oxidation of phenols and reduction of nitrophenols in BMImPF₆ was studied.     

Radiolysis of 1-naphthol in aqueous solutions

The effects of absorbed doses, initial pH and 1-naphthol concentration onto its radiolysis in aqueous sulphuric and hydrochloric acids by gamma rays from ⁶⁰Co were investigated. Under the experimental conditions, 1-naphthol degradation yields increased with increasing the absorbed doses (0.3–3.0 kGy) and with decreasing the initial 1-naphthol concentration (20–1 ppm). It was found out that the hydrated electrons did not play any significant roles in 1-naphthol radiolysis, as the degradation yields were higher at pH₀ ~ 0.46 compared to those at pH₀ ~ 2.0–5.0. The corresponding radiolytic yields G(−1-naphthol) were (6.13 ± 1.00)) × 10⁻² and (5.11 ± 0.22) × 10⁻² μmol/J in sulphuric acids, (15.61 ± 3.85) × 10⁻² and (4.76 ± 0.48) × 10⁻² μmol/J in hydrochloric acids. 1-Naphthol degradation rates could be described by the kinetic equations of pseudo-first-order reactions. An empirical relation between the observed reaction constants k _D and the initial 1-naphthol concentrations was established, enabling to predict the absorbed doses required for a given treatment efficiency. Three products of 1-naphthol degradation were revealed using an HPLC/UV procedure.     

Determination of lead in sediments and sewage sludge by on-line hydride-generation axial-view inductively-coupled plasma optical-emission spectrometry using slurry sampling

Among the “traditional” hydride-forming elements, lead is probably the most difficult, and its determination in this form has rarely been reported in the literature. In this paper a simple and rapid method, axial-view inductively-coupled plasma optical-emission spectrometry using on-line hydride generation (HG–ICP–OES) from samples prepared as slurry, is proposed for determination of lead in environmental samples. The samples (20–50 mg, particle size ≤120 μm) were treated with 1 mL aqua regia in a 40-kHz ultrasonic bath for 60 min. The slurry was diluted to a final volume of 50 mL with a 10% m/v solution of (NH₄)₂S₂O₈. The concentrations of NaBH₄, tartaric acid, and (NH₄)₂S₂O₈, used for on-line plumbane generation were optimized by means of a complete factorial analysis applied to an aqueous standard solution and to the slurry of a sediment certified reference material (CRM). External calibration against aqueous standards in the concentration range 10–100 μg L⁻¹ was used for analysis of six CRM—three marine sediments, one river sediment, and two sewage sludges. Analysis of the filtered slurry showed that Pb was only partially extracted into the liquid phase. Several major concomitants tested did not affect the Pb signal. The detection limit (3s, n = 10) for 20 mg sample in a final volume of 50 mL was 5.0 μg g⁻¹. Tin was the only other hydride-forming analyte that could be determined satisfactorily with Pb; for tin the detection limit was 1.0 μg g⁻¹. The values obtained for Pb and Sn were not significantly different from the certified concentrations, according to the t-test at the 95% confidence level. Nine river sediments collected locally were also analyzed and the concentrations were in agreement with results obtained after total digestion.     

Sensitive, selective spectrophotometric determination of phenols with periodic acid

A new spectrophotometric determination of phenols with periodic acid has been developed. The colored product of phenol periodic acid reaction has a λ_max 380 nm. The determination of phenol, pyrocatechol, α-naphthol, β-naphthol, quinol, p-cresol, m-cresol, 8-quinolinol, resorcinol, phloroglucinol, and gallic acid has been done. The effects of possible variables e.g., temperature, reagent, pH buffers have been studied. A study of interferences is made. Mechanism of the reaction is discussed.     

Organosilica composite for preconcentration of phenolic compounds from aqueous solutions

A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO₂) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol) (TX). Under static conditions phenol was quantitatively extracted onto TX-SiO₂ in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO₂ for phenol is 2.4 mg g⁻¹ with distribution coefficients up to 3.4 × 10⁴ mL g⁻¹; corresponding data for 1-naphthol are 1.5 mg g⁻¹ and 3 × 10³ mL g⁻¹. The distribution coefficient does not change significantly for solution volumes of 0.025–0.5 L and adsorbent mass less than 0.03 g; 1–90 μg analyte can be easily eluted by 1–3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A ₅₄₀) and phenol concentration (C) in water was found according to the equation A ₅₄₀ = (6 ± 1) × 10⁻² + (0.9 ± 0.1)C (μmol L⁻¹) with a detection range from 1 × 10⁻⁸ mol L⁻¹ (0.9 μL g⁻¹) to 2 × 10⁻⁷ mol L⁻¹ (19 μL g⁻¹), a limit of quantification of 1 μL g⁻¹ (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical analysis. The detection limit of 1-naphthol with this method is 6 μL g⁻¹ while the quantification limit is 20 μL g⁻¹. A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08–3.2 mL g⁻¹.     

Application of dried blood spots combined with high-performance liquid chromatography coupled with electrospray ionisation tandem mass spectrometry for simultaneous quantification of vincristine and actinomycin-D

A sensitive, specific and efficient high-performance liquid chromatography-tandem mass spectrometry assay for the simultaneous determination of vincristine and actinomycin-D in human dried blood spots is presented. Dried blood spots were punched out of a collection paper with a 0.25-in.-diameter punch. The analytes were extracted from the punched-out disc using sonication during 15 min in a mixture of acetonitrile–methanol–water (1:1:1, v/v/v) containing the internal standard vinorelbine. Twenty-microlitre volumes were injected onto the HPLC system. Separation was achieved on a 50 × 2.1 mm ID Xbridge C₁₈ column using elution with 1 mM ammonium acetate–acetonitrile (70:30, v/v) adjusted to pH 10.5 with ammonia and run in a gradient with methanol at a flow rate of 0.4 mL/min. HPLC run time was 6 min. The assay quantifies vincristine from 1 to 100 ng/mL and actinomycine-D from 2 to 250 ng/mL using a blood sample obtained by a simple finger prick. Validation results demonstrate that vincristine and actinomycin-D can be accurately and precisely quantified in human dried blood spots with the presented method. The assay can now be used to support clinical pharmacologic studies with vincristine and actinomycin-D.     

Modulation of mobile phase composition in flow-injection/sequential-injection chromatography exploiting multisyringe flow analysis

In this paper, a time-based multicommutated flow system is proposed for appropriate selection and modulation of mobile phase composition in flow-injection (FI)/sequential-injection (SI) chromatography. The novel flow assembly involves the on-line coupling of a short monolithic reversed-phase chromatographic column with a multisyringe flow injection set-up furnished with a set of solenoid valves. The proposed hyphenated technique was applied to the simultaneous spectrophotometric determination of thiamine (B₁), pyridoxine (B₆) and cyanocobalamin (B₁₂) which were taken as model analytes. The separation method capitalizes on a dual isocratic elution protocol involving the use of a single forward stroke of the multisyringe pump for initial delivery of 50 mmol L⁻¹ ammonium acetate (pH 7.0) for 2.4 min followed by 50 mmol L⁻¹ ammonium acetate–methanol (80:20, v/v) for 6.4 min at 0.5 mL min⁻¹ and room temperature. Detection was performed at the maximum wavelength for each target vitamin—280 nm for B₁, 325 nm for B₆, and 360 nm for B₁₂. A first-order, two-level full-factorial design was utilized to ascertain the significant variables influencing the chromatographic separation and the magnitude of the interaction effects. The experimental design method revealed that resolution of the target vitamins is highly dependent on the pH, percentage of organic modifier, and their second-order interaction. The multisyringe flow-injection-based monolithic column separation method, which should be viewed as an expeditious and cost-effective alternative to the high-performance liquid chromatography counterpart, was applied to the separation and determination of B₁, B₆, and B₁₂ in different pharmaceutical dosage forms in less than 9 min. Statistical comparison of the results from the proposed procedure with those from the HPLC method endorsed by the US Pharmacopeia revealed there were no significant differences at the 95 % confidence level.     

Simultaneous determination of phenylenediamine isomers and dihydroxybenzene isomers in hair dyes by capillary zone electrophoresis coupled with amperometric detection

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE–AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CZE–AD were investigated. Under the optimum conditions the five analytes could be perfectly separated in 0.30 mol L⁻¹ borate–0.40 mol L⁻¹ phosphate buffer (pH 5.8) within 15 min. A 300 μm diameter platinum electrode had good responses at +0.85 V (versus SCE) for the five analytes. Their linear ranges were from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ and the detection limits were as low as 10⁻⁷ mol L⁻¹ (S/N = 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0–108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples. Figure Electropherograms obtained from 10 mg mL⁻¹ hair dye sample solutions at a platinum working electrode under optimum CZE–AD conditions: (a) natural black (I), (b) golden: (1) p-phenylenediamine, (2) m-phenylenediamine, (3) o-phenylenediamine, (4) resorcinol, and (5) catechol     

Über Reaktionen von Nitrosophenolen, 3. Mitt.: Reaktion von 2-Nitroso-1-naphthol mit Resorcin und Orcin

Zusammenfassung Die Reaktion von 2-Nitroso-1-naphthol mit Resorcin bzw. Orcin in Äther bei Anwesenheit von HNO₃ liefert Benzo[c]phenoxazon-(9) (I), Benzo[c]phenoxazon-(9)-12-oxid (II), Methyl-benzo[c]phenoxazon-(9) (III) sowie 11-Methyl-benzo[c]phenoxazon-(9)-12-oxid (IV). Die Struktur der isolierten Substanzen wurde durch Reduktion mittels TiCl₃ sowie durch die UV- und IR-Spektren gestützt.

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The reaction of 2-nitroso-1-naphthol with resorcinol and orcinol in ether solution in the presence of nitric acid has been studied. From the reaction mixture the benzophenoxazones I–IV have been isolated. Structures were assigned on the grounds of UV and IR spectra and partly by using TiCl₃ as a reducing agent.

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Mit 1 Abbildung     

Asymmetric Pd-catalyzed allylic amination of 1,3-diphenylallyl acetate with dipropylamine in ionic and molecular solvents

Asymmetric catalytic allylic amination of 1,3-diphenylallyl acetate with dipropylamine in an ionic liquid, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, and in THF and CH₂Cl₂ in the presence of palladium complexes of P-monodentate phosphite and phosphoramidite derivatives of S-1,1′-bis-2-naphthol was carried out. This gave a product with ee of up to 65%. The level of asymmetric induction is retained after three catalyst cycles. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2478–2481, November, 2005.     

Preparation of antibodies and development of a sensitive immunoassay with fluorescence detection for triazine herbicides

Specific polyclonal antibodies against s-triazine herbicides were obtained by preparing immunogens coupling home-synthesized haptens derivatives of simazine (6-chloro-N-ethyl-N′-ethyl-1,3,5-triazine-2,4-diamine) to lysine groups of hemocyanin from keyhole limpets and bovine serum albumin carrier proteins. Three highly sensitive rabbit antisera were obtained and evaluated with a battery of six enzyme tracers derived from triazine structures in an optimized ELISA format. The antiserum As8 and the HRP-2f tracer, which yield the best assay sensitivity for simazine (detection limit 0.11 ± 0.02 μg L⁻¹, IC₅₀ 0.88 ± 0.04 μg L⁻¹), were applied to the development of a sensitive flow-through immunoassay for the analysis of this herbicide. The automated assay was based on a direct competitive immunosorbent assay and fluorescence detection. The optimized method presents an IC₅₀ value of 0.35 ± 0.04 μg L⁻¹ with a detection limit of 1.3 ± 0.9 ng L⁻¹ and a dynamic range from 0.010 to 7.5 μg L⁻¹ simazine. The generic nature of the antiserum was shown by good relative cross-reactivities with other triazines such as atrazine (420%) or propazine (130%) and a lower response to terbutylazine (6.4%) and desethyl-atrazine (2.2%). No cross-reactivity was obtained for nonrelated pesticides such as 2,4-dichlorophenoxyacetic acid or linuron and the assay could be applied as a screening method for triazine herbicides. The total analysis time was 30 min per determination and the immunosensor could be reused for more than 150 cycles without significant loss of activity. The immunosensor has been successfully applied to the direct analysis of simazine in surface water samples at the nanogram per liter level. The results obtained by comparative analysis of the immunosensor with a chromatographic procedure for triazines showed a close correspondence.     

Reagent peak-free liquid chromatography–fluorescence analysis of carboxylic acids using a fluorous scavenging–derivatization method

We developed a fluorous scavenging–derivatization method for reagent peak-free liquid chromatography (LC)–fluorescence analysis of carboxylic acids. In this method, carboxylic acids were fluorescently derivatized with 1-pyrenemethylamine in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and 1-hydroxy-1H-benzotriazole. Residual excess unreacted reagent was tagged with 2-(perfluorooctyl)ethyl isocyanate and could be selectively removed by microfluorous solid-phase extraction before LC analysis. With use of this method, eight fluorescent derivatives of linear aliphatic carboxylic acids (C₁–C₈) can be separated within 30 min by reversed-phase LC with gradient elution. In the chromatogram obtained, the fluorous-tagged unreacted reagent peak is greatly decreased after microfluorous solid-phase extraction and does not interfere with the quantification of each acid. With use of microfluorous solid-phase extraction with 80% (v/v) aqueous methanol elution, over 99.9% of the unreacted fluorescent reagent was removed. The detection limits (signal-to-noise ratio of 3) for the carboxylic acids examined are 2.3–8.0 fmol per 10-μL injection. We also applied this method successfully to the analysis of highly polar carboxylic acids such as α-keto acids and tricarboxylic acid cycle metabolites.     

Covalent Attachment of Some Phenol Derivatives to the Silica Surface by Use of Single-stage Aminomethylation

The reaction conditions and component ratios were established for the attachment of 4-(2-pyridylazo)resorcinol (PAR), 1-(2-pyridylazo)-2-naphthol (PAN) and 8-hydroxyquinoline (8-HQ) to the silica surface by means of a single-stage Mannich reaction. The modified sorbents that were synthesized were characterized by an adsorption method, and DRIFT and UV spectroscopies. The concentrations of PAR, PAN and 8-HQ grafted to the silica surface that were attained were 2.8×10⁻⁵, 8.5×10⁻⁵ and 2.7×10⁻⁴ mol g⁻¹, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Simple sensor for simultaneous determination of dihydroxybenzene isomers

A simple sensor based on bare carbon ionic liquid electrode was fabricated for simultaneous determination of dihydroxybenzene isomers in 0.1 mol L⁻¹ phosphate buffer solution (pH 6.0). The oxidation peak potential of hydroquinone was about 0.136 V, catechol was about 0.240 V, and resorcinol 0.632 V by differential pulse voltammetric measurements, which indicated that the dihydroxybenzene isomers could be separated absolutely. The sensor showed wide linear behaviors in the range of 5.0 × 10⁻⁷–2.0 × 10⁻⁴ mol L⁻¹ for hydroquinone and catechol, 3.5 × 10⁻⁶–1.535 × 10⁻⁴ mol L⁻¹ for resorcinol, respectively. And the detection limits of the three dihydroxybenzene isomers were 5.0 × 10⁻⁸, 2.0 × 10⁻⁷, 5.0 × 10⁻⁷ mol L⁻¹, respectively (S/N = 3). The proposed method could be applied to the determination of dihydroxybenzene isomers in artificial wastewater and the recovery was from 93.9% to 104.6%.     

Determination of epoxides by high-performance liquid chromatography following derivatization with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diethyldithiocarbamate

A reversed-phase, high-performance liquid chromatography (RP-HPLC) method that allows quantitation of low levels of epoxides has been described. The method involved derivatization of epoxides using 100- to 1,000-fold excess N,N-diethyldithiocarbamate (DTC) at 60 °C for 20 min at neutral pH. The unreacted DTC was then decomposed to CS₂ and diethyl amine by acidification of the reaction mixture to pH 2 using orthophosphoric acid. The first two steps could be performed in the same reaction vessel by sequential addition of reagents. In the final step, an aliquot (20 μL) of the derivatized sample was analyzed for the presence of stable esters of DTC by RP-HPLC using a Supelcosil LC-18-S (150 × 4.6-mm) column and a mobile phase consisting of 40% (v/v) acetonitrile in water at a flow of 1 mL min⁻¹. Using UV detection at 278 nm, the epoxides gave linear responses in the concentration range of 0.25 to 50 μM. The method is robust, and as low as 5 pmol of the analyte could be successfully detected and quantified with recoveries of ≥94%. Following a minimal pretreatment such as ultrafiltration (molecular weight cutoff 5,000 Da), the method is suitable for analysis of epoxides in complex physiological fluids (e.g., fetal bovine serum). The method has been rigorously evaluated and adapted in our laboratory for routine analysis and determination of stability of epoxides of 1,3-butadiene and other alkenes added to cell cultures.     

Quantification of Teicoplanin in Human Plasma by Liquid Chromatography with Ultraviolet Detection

A simple high-performance liquid chromatographic method was developed for determining five major components of teicoplanin, designated A2–1, A2–2, A2–3, A2–4 and A2–5, in human plasma. Using piperacillin sodium as internal standard, teicoplanin in plasma samples was extracted by coextractive cleanup procedure. The extracts were injected into a Nova-Pak C₁₈ column maintained at ambient temperature. The mobile phase consisted of acetonitrile–0.1% trifluoroacetic acid (27:73, pH = 2.2), at a flow rate of 1.0 mL min⁻¹. The analytes were detected at the UV wavelength of 218 nm. The method was found to be linear over the concentration range of 2.5–50 mg L⁻¹ for teicoplanin (r = 0.9993 ± 0.0038), which covered the clinically expected trough plasma levels. The percentage error of the analytical method was below 9%. The intra- and inter-day reproducibility was adequate with coefficients of variation less than 7%. The chromatographic running time was 11 min. Thus, the method can be effectively applied to measure teicoplanin concentrations in clinical samples.     

Simultaneous analysis of sarin, pyridostigmine bromide and their metabolites in rat plasma and urine using HPLC

Summary A method was developed for the separation and quantification of the warfare nerve agent sarin (O-isopropylmethylphosphonoflouridate), its metabolite methylphosphonic acid, the anti nerve agent drug pyridostigmine bromide (PB;3-dimethylaminocarbonyloxy-N-methyl pyridinium bromide) and its metaboliteN-methyl-3-hydroxypyridinium bromide in rat plasma and urine. The method involved using solid phase extraction and high performance liquid chromatography (HPLC) with reversed phase C₁₈ column, and UV detection at 280 nm. The compounds were separated using gradient of 1% to 55% acetonitrile in 0.1% triflouroacetic acid water solution (pH 3.20) at flow rate of 0.9 ml/min in a period of 15 min. The retention times ranged from 4.4–12.1 min. The limits of detection were 50 ng mL⁻¹ for PB andN-methyl-3-hydroxypyridinium bromide, and 10 μg mL⁻¹ for sarin and methylphosphonic acid, while limits of quantitation were between 100 ng mL⁻¹–12 μg mL⁻¹. Average percentage recovery of five spiked samples from plasma were 84.6±8.4, 86.5±9.0, 76.4±8.5, 81.3±8.2, and from urine 78.5±7.9, 76.4±7.8, 74.4±8.4, 80.6±6.8 for sarin, methylphosphonic acid, pyridostigmine bromide andN-methyl-3-hydroxypyridinium bromide, respectively. This method was applied to analyze the above chemicals and metabolites following combined administration in rats.     

Immunosensors for pollutants working in organic media. Study of performances of different tracers with luminescent detection

A comparative study of enzymatic and non-enzymatic labels combined with luminescence detection, developed for immunosensing of pesticide residues (carbaryl, 1-naphthol, irgarol 1051) in organic media, is presented. Peroxidase and alkaline phosphatase enzymes with fluorogenic (3-p-hydroxyphenylpropanoic acid) and luminogenic (AMPPD derivative) substrates, respectively, were assessed as enzymatic markers. As an alternative, terbium(III) chelate, with time-resolved fluorescence detection, was evaluated as a non-enzymatic label. The best sensitivity was achieved by use of alkaline phosphatase in an immunocomplex capture assay format (I ₅₀ values 0.06, 0.27, and 7.45 μg L⁻¹ in buffer, 1:1 methanol–buffer, and methanol, respectively). Results were also good (I ₅₀ 1.00 and 6.30 μg L⁻¹ for water and aqueous–organic mixture, respectively) for Tb(III) chelate in an immobilized conjugate assay format. Use of alkaline phosphatase label to measure carbaryl (100 ng L⁻¹) in different spiked river water samples, after solid-phase extraction and analyte elution with an ethyl acetate–methanol mixture, resulted in recoveries ranging from 81 to 98%, with acceptable precision (CV 4–14%, n=4).     

D<Subscript>2</Subscript>O Isotope Effects on the Ionization of <Emphasis Type="Italic">β</Emphasis>-Naphthol and Boric Acid at Temperatures from 225 to 300 °C using UV-Visible Spectroscopy

The deuterium-isotope effects on the ionization constants of β-naphthol (2-naphthol) and boric acid, Δlog ₁₀ K=[log ₁₀ K _D2O−log ₁₀ K _H2O], have been determined from measurements in light and heavy water at temperatures from 225 °C≤t≤300 °C and pressures near steam saturation. β-Naphthol is a thermally-stable colorimetric pH indicator, whose ionization constant lies close to that of H₂PO₄⁻ (aq), the only acid for which Δlog ₁₀ K is accurately known at elevated temperatures. A newly designed platinum flow cell was used to measure UV-visible spectra of β-naphthol in acid, base, and buffer solutions of H₂PO₄⁻/HPO₄²⁻ and D₂PO₄⁻/DPO₄²⁻, from which the degree of ionization at known values of pH and pD was determined. Values of the ionization constants of β-naphthol in light and heavy water were calculated from these results, and used to derive a model for and over the experimental temperature range with an estimated precision of ±0.02 in log ₁₀ K. The new values of K _H2O and K _D2O allowed us to use β-naphthol as a colorimetric indicator, to measure the equilibrium pH and pD of the buffer solutions B(OH)₃/B(OH)₄⁻ and B(OD)₃/B(OD)₄⁻ up to 300 °C, from which the ionization constants of boric acid were calculated. The magnitude of the deuterium isotope effect for H₂PO₄⁻ (aq) is known to fall from Δlog ₁₀ K=−0.62 to Δlog ₁₀ K=−0.47, on the “aquamolal” concentration scale, as the temperature rises above 125 °C, but then remains almost constant. Although the temperature range is more limited, the new results for β-naphthol and boric acid appear to show a similar trend.     

Zinc-cobalt alloy: electrodeposition and characterization

Zinc-cobalt alloy electrodeposits offer enhanced corrosion protection to steel, compared to zinc deposits. A near neutral zinc-cobalt alloy sulfate bath was developed. In the absence of β-naphthol and sodium lauryl sulfate (SLS), only a light grey and non-uniform deposit was obtained. Addition of boric acid yielded a grey and uniform deposit. To obtain the grey uniform alloy deposit, the optimum bath composition was: 0.5 M ZnSO₄, 0.5 M CoSO₄, 40 g/L H₃BO₃, 0.865 g/L SLS and 0.345 g/L β-naphthol. The current efficiency for alloy deposition was 50% in the current density range 0.5–2.5 A/dm². X-ray fluorescence studies on the alloy deposit formed on steel revealed 58–75% zinc on the surface. Anodic stripping voltammetric studies were carried out on zinc-cobalt alloy films formed on glassy carbon to identify the phases formed in the alloy. Zn-Co alloy film dissolution peaks suggested the existence of β, β₁ and γ phases of the alloy. Electronic Publication