Flow injection determination of bismuth in urine by successive retention of Bi(III) and tetrahydroborate(III) on an anion-exchange resin and hydride generation atomic absorption spectrometry

Bismuth as BiCl₄⁻ and BH₄⁻ ware successively retained in a column (150 mm × 4 mm, length × i.d.) packed with Amberlite IRA-410 (strong anion-exchange resin). This was followed by passage of an injected slug of hydrochloric acid resulting in bismuthine generation (BiH₃). BiH₃ was stripped from the eluent solution by the addition of a nitrogen flow and the bulk phases were separated in a gas–liquid separator. Finally, bismutine was atomized in a quartz tube for the subsequent detection of bismuth by atomic absorption spectrometry. Different halide complexes of bismuth (namely, BiBr₄⁻, BiI₄⁻ and BiCl₄⁻) were tested for its pre-concentration, being the chloride complexes which produced the best results. Therefore, a concentration of 0.3 mol l⁻¹ of HCl was added to the samples and calibration solutions. A linear response was obtained between the detection limit (3σ) of 0.225 and 80 μg l⁻¹. The R.S.D.% (n = 10) for a solution containing 50 μg l⁻¹ of Bi was 0.85%. The tolerance of the system to interferences was evaluated by investigating the effect of the following ions: Cu²⁺, Co²⁺, Ni²⁺, Fe³⁺, Cd²⁺, Pb²⁺, Hg²⁺, Zn²⁺, and Mg²⁺. The most severe depression was caused by Hg²⁺, which at 60 mg l⁻¹ caused a 5% depression on the signal. For the other cations, concentrations between 1000 and 10,000 mg l⁻¹ could be tolerated. The system was applied to the determination of Bi in urine of patients under therapy with bismuth subcitrate. The recovery of spikes of 5 and 50 μg l⁻¹ of Bi added to the samples prior to digestion with HNO₃ and H₂O₂ was in satisfactory ranges from 95.0 to 101.0%. The concentrations of bismuth found in six selected samples using this procedure were in good agreement with those obtained by an alternative technique (ETAAS). Finally, the concentration of Bi determined in urine before and after 3 days of treatment were 1.94 ± 1.26 and 9.02 ± 5.82 μg l⁻¹, respectively.     

Electrochemiluminescence sensor using tris(2,2′-bipyridyl)ruthenium(II) immobilized in Eastman-AQ55D–silica composite thin-films

An electrochemiluminescence (ECL) sensor with good long-term stability and fast response time has been developed. The sensor was based on the immobilization of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) into the Eastman-AQ55D–silica composite thin films on a glassy carbon electrode. The ECL and electrochemistry of Ru(bpy)₃²⁺ immobilized in the composite thin films have been investigated, and the modified electrode was used for the ECL detection of oxalate, tripropylamine (TPA) and chlorpromazine (CPZ) in a flow injection analysis system and showed high sensitivity. Because of the strong electrostatic interaction and low hydrophobicity of Eastman-AQ55D, the sensor showed no loss of response over 2 months of dry storage. In use, the electrode showed only a 5% decrease in response over 100 potential cycles. The detection limit was 1 μmol l⁻¹ for oxalate and 0.1 μmol l⁻¹ for both TPA and CPZ (S/N=3), respectively. The linear range extended from 50 μmol l⁻¹ to 5 mmol l⁻¹ for oxalate, from 20 μmol l⁻¹ to 1 mmol l⁻¹ for TPA, and from 1 μmol l⁻¹ to 200 μmol l⁻¹ for CPZ.     

Determination of nanomolar concentrations of phosphate in freshwaters using flow injection with luminol chemiluminescence detection

A simple and rapid flow injection (FI) method is reported for the determination of phosphate (as molybdate reactive P) in freshwaters based on luminol chemiluminescence (CL) detection. The molybdophosphoric heteropoly acid formed by phosphate and ammonium molybdate in acidic conditions generated chemiluminescence emission via the oxidation of luminol. The detection limit (3× standard deviation of blank) was 0.03 μg P l⁻¹ (1.0 nM), with a sample throughput of 180 h⁻¹. The calibration graph was linear over the range 0.032–3.26 μg P l⁻¹ (r²=0.9880) with relative standard deviations (n=4) in the range 1.2–4.7%. Interfering cations (Ca(II), Mg(II), Ni(II), Zn(II), Cu(II), Co(II), Fe(II) and Fe(III)) were removed by passing the sample through an in-line iminodiacetate chelating column. Silicate interference (at 5 mg Si l⁻¹) was effectively masked by the addition of tartaric acid and other common anions (Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻ and NO₂⁻) did not interfere at their maximum admissible concentrations in freshwaters. The method was applied to freshwater samples and the results (26.1±1.1–62.0±0.4 μg P l⁻¹) were not significantly different (P=0.05) from results obtained using a segmented flow analyser method with spectrophotometric detection (24.4±4.45–84.0±16.0 μg P l⁻¹).     

Persulphate quenching of the excited state of ruthenium(II) tris-bipyridyl dication: thermal reactions

The rate constant for the reaction between the sulphate radical (SO₄^√−) and the ruthenium (II) tris-bipyridyl dication (Ru(bipy)₃²⁺) is (3.3±0.2)×10⁹ mol⁻¹ dm³ s⁻¹ in 1 mol dm⁻³ H₂SO₄ and (4.9±0.5)×10⁹ mol⁻¹ dm³ s⁻¹ in 0.1 mol dm⁻³, pH 4.7 acetate buffer. The SO₄^√−radical produced by the electron transfer quenching of Ru(bipy)₃^2+* by S₂O₈²⁻ reacts rapidly with both acetate buffer and chloride ions. These side reactions result in a reduction in the overall quantum yield of Ru(bipy)₃³⁺ production and reduced reaction selectivity when Ru(bipy)₃^2+* is quenched by persulphate.     

Low-temperature heat capacity and standard molar enthalpy of formation of the complex Zn(Thr)SO4·H2O (s)

Low-temperature heat capacities of the complex Zn(Thr)SO₄·H₂O (s) have been precisely measured with a small sample adiabatic calorimeter over the temperature range from 78 to 373 K. The initial dehydration temperature of the complex (T_d=325.50 K) has been obtained by analysis of the heat-capacity curve. The experimental values of molar heat capacities have been fitted to a polynomial equation by least square method. The standard molar enthalpy of formation of the complex has been determined from the enthalpies of dissolution (Δ_dH_m^Θ) of [ZnSO₄·7H₂O (s) +Thr (s)] and Zn(Thr)SO₄·H₂O (s) in 100 ml of 2 mol dm⁻³ HCl solvent as: Δ_fH_{m,Zn(Thr)SO4·H2O}^Θ=−2111.7±3.4 kJ mol⁻¹. These experiments were made by using an isoperibol solution calorimeter at 298.15 K.     

Photodegradation of a textile dye catalyzed by sol–gel derived nanocrystalline TiO2 via ultrasonic irradiation

Nanocrstalline pure anatase titania were prepared by sol–gel process at room temperature followed by ultrasonication (Ti–US). The photocatalytic activity of Ti–US has been evaluated by the degradation of textile dye, Methylene Blue in presence and absence of common inorganic salts (NO₃⁻, C₂O₄²⁻, SO₄²⁻, citrate). It was observed that, in presence of anions, the degradation of the dye increases significantly. The influence of the presence of H₂O₂ on the degradation rate was studied. The dependence of photodegradation of the dye rates on various parameters such as dye concentration, photocatalyst concentration and pH were also investigated. The photodegradation rate follows first order kinetics. H₂O₂ and UV light have a negligible effect in absence of Ti–US catalyst. The relative photonic efficiency of the system is reported using phenol as a standard organic compound.     

The direct synthesis of dimethyl ether from syngas over hybrid catalysts with sulfate-modified γ-alumina as methanol dehydration components

A series of γ-Al₂O₃ samples modified with various contents of sulfate (0–15 wt.%) and calcined at different temperatures (350–750 °C) were prepared by an impregnation method and physically admixed with CuO–ZnO–Al₂O₃ methanol synthesis catalyst to form hybrid catalysts. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions. The results revealed that the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration increased significantly when the content of sulfate increased to 10 wt.%, resulting in the increase in both DME selectivity and CO conversion. However, when the content of sulfate of SO₄²⁻/γ-Al₂O₃ was further increased to 15 wt.%, the activity for methanol dehydration was increased, and the selectivity for DME decreased slightly as reflected in the increased formation of byproducts like hydrocarbons and CO₂. On the other hand, when the calcination temperature of SO₄²⁻/γ-Al₂O₃ increased from 350 °C to 550 °C, both the CO conversion and the DME selectivity increased gradually, accompanied with the decreased formation of CO₂. Nevertheless, a further increase in calcination temperature to 750 °C remarkably decreased the catalytic activity of SO₄²⁻/γ-Al₂O₃ for methanol dehydration, resulting in the significant decline in both DME selectivity and CO conversion. The hybrid catalyst containing the SO₄²⁻/γ-Al₂O₃ with 10 wt.% sulfate and calcined at 550 °C exhibited the highest selectivity and yield for the synthesis of DME.     

The electrolyte NRTL model and speciation approach as applied to multicomponent aqueous solutions of H2SO4, Fe2(SO4)3, MgSO4 and Al2(SO4)3 at 230–270 °C

This work presents chemical modeling of solubilities of metal sulfates in aqueous solutions of sulfuric acid at high temperatures. Calculations were compared with experimental solubility measurements of hematite (Fe₂O₃) in aqueous ternary and quaternary systems of H₂SO₄, MgSO₄ and Al₂(SO₄)₃ at high temperatures. A hybrid model of ion-association and electrolyte non-random two liquid (ENRTL) theory was employed to fit solubility data in three ternary systems H₂SO₄–MgSO₄–H₂O, H₂SO₄–Al₂(SO₄)₃–H₂O at 235–270 °C and H₂SO₄–Fe₂(SO₄)₃–H₂O at 150–270 °C. Employing the Aspen Plus™ property program, the electrolyte NRTL local composition model was used for calculating activity coefficients of the ions Al³⁺, Mg²⁺ Fe³⁺ and SO₄²⁻, HSO₄⁻, OH⁻, H₃O⁺, respectively, as well as molecular species. The solid phases were hydronium alunite (H₃O)Al₃(SO₄)₂(OH)₆, hematite Fe₂O₃ and magnesium sulfate monohydrate (MgSO₄)·H₂O which were employed as constraint precipitation solids in calculating the metal sulfate solubilities. A correlation for the equilibrium constants of the association reactions of complex species versus temperature was implemented. Based on the maximum-likelihood principle, the binary interaction energy parameters for the ionic species as well as the coefficients for equilibrium constants of the reactions were obtained simultaneously using the solubility data of the ternary systems. Following that, the solubilities of metal sulfates in the quaternary systems H₂SO₄–Fe₂(SO₄)₃–MgSO₄–H₂O, H₂SO₄–Fe₂(SO₄)₃–Al₂(SO₄)₃–H₂O at 250 °C and H₂SO₄–Al₂(SO₄)₃–MgSO₄–H₂O at 230–270 °C were predicted. The calculated results were in excellent agreement with the experimental data.     

Biosensor for phenol based on the direct electron transfer blocking of peroxidase immobilising on silica–titanium

Horseradish peroxidase (HRP) was immobilised on silica gel modified with titanium oxide. This material was employed to prepare modified carbon paste electrode. The direct electron transfer of the hydrogen peroxide reduction by HRP was blocked when immobilised on silica–titanium. This biosensor presented a very sensitive response for phenol (1 μmol l⁻¹) at an applied potential of 0 mV vs SCE. The best condition was achieved in phosphate buffer pH 6.8, ratio of hydrogen peroxide/phenol higher than 0.35. The biosensor showed a linear response range between 10 and 50 μmol l⁻¹ of phenol, adjusted by the equation j=−32.8+16.3 [phenol], for n=5 with a correlation coefficient of 0.9995. The response time of the biosensor was about 3 s.     

Specific adsorption of halogen anions on hydrous γ-Al2O3

The paper reports results of a study on the specific adsorption of F⁻, Cl⁻, Br⁻, I⁻, ClO₃⁻, BrO₃⁻, IO₃⁻ and IO₄⁻ on hydrous γ-Al₂O₃. The isotherms of the anion adsorption and the adsorption dependencies on pH and the ionic strength of the solution have been determined under the equilibrium conditions. According to the degree of affinity to γ-Al₂O₃, the anions can be ordered as: I⁻3⁻−−3⁻3⁻4⁻−. It has been established that the sorption of IO₄⁻ and F⁻ involves the formation of surface complexes in the inner co-ordination sphere, whereas that of Cl⁻, Br⁻, I⁻, ClO₃⁻, BrO₃⁻ and IO₃⁻ takes place through formation of ion pair complexes in the outer co-ordination sphere. In the dynamic system, the exchange isoplanes and elution curves have been determined for selected anions on columns filled with Al₂O₃. It has been shown that γ-Al₂O₃ can be used for isolation and concentration of IO₃⁻ from natural waters in order to decrease the limit of the ions determination to 2 μg l⁻¹. Using differential pulse voltammetry (DPV), after isolation and concentration on γ-Al₂O₃, the content of iodates has been determined in mineral, marine and tap water doped with these ions.     

Manipulation of separation selectivity of inorganic anions in electrostatic ion chromatography by the use of mixed cationic–zwitterionic micelles as the column coating solution

This paper describes an electrostatic ion chromatographic system in which the separation selectivity for inorganic anions, especially for sulfate and phosphate, could be manipulated by altering the molar ratio of the zwitterionic and cationic surfactants in the column coating solution used to prepare the stationary phase. The zwitterionic surfactant used for this study was 3-(N,N-dimethyltetradecylammonio)propanesulfonate (Zwittergent-3-14) and the cationic surfactant was tetradecyltrimethylammonium (TTA). Using a reversed-phase C₁₈ column (250×4.6 mm I.D.) coated with 10/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the stationary phase and either NaHCO₃ or Na₂CO₃ aqueous solution as the eluent, together with suppressed conductivity detection, baseline separation of seven model inorganic anions was obtained. The elution order for those anions was found to be F⁻4²⁻−4²⁻2⁻−3⁻. Under the same conditions but using 1/10 (mM/mM) of TTA/Zwittergent-3-14 mixed micelles as the column coating solution, the elution order for these model ions was F⁻4²⁻4²⁻−2⁻−3⁻. The early elution of phosphate and sulfate is a unique attribute of this system. Detection limits for F⁻, HPO₄²⁻, Cl⁻, SO₄²⁻, NO₂⁻, Br⁻ and NO₃⁻ (S/N=3, sample injection volume 100 μl) were 0.11, 0.12, 0.12, 0.18, 0.49, 0.49, 0.52 μM, respectively.     

Solvent extraction of arsenic from acid medium using zinc hexamethylenedithiocarbamate as an extractant

Using zinc hexamethylenedithiocarbamate (Zn(HMDC)₂) and flame atomic absorption spectrometry (FAAS) and/or flow injection hydride generation atomic absorption spectrometry (FI-HGAAS), solvent extraction of As(III) from HCl and H₂SO₄ media into 2,6-dimethyl-4-heptanone (diisobutyl ketone, DIBK) was examined. Arsenic(III) was quantitatively extracted with 2.41×10⁻³ mol l⁻¹ Zn(HMDC)₂ from about 0.004 (pH 2.4) to 4 mol l⁻¹ HCl and H₂SO₄ aqueous solutions. The logarithmic conditional extraction constant of As(HMDC)₃ in the HCl–DIBK system was determined to be 8.3±0.7, by the measurement of the distribution ratios of Zn(II) and As(III). The effectiveness of the proposed extraction method was ascertained in the determination of As in geochemical standard reference materials supplied by the Geological Survey of Japan. Furthermore, the analysis of arsenic in procedural blanks was 0.083±0.003 μg l⁻¹.     

Ion chromatography of organic-rich natural waters from peatlands: I. Cl, NO2, Br, NO3, HPO4, SO4 and oxalate

Organic-rich natural waters from peat bogs in continental (Switzerland) and maritime (Shetland Islands, Scotland) areas were analysed for Cl⁻, NO₂⁻, Br⁻, NO₃⁻, HPO₄²⁻, SO₄²⁻ and oxalate using ion chromatography. These anions can be determined simultaneously in the surface and pore water samples from the continental bogs using a 250-μl injection loop. Using this loop, the detection limits were ca. 5 ng/g for the monovalent anions and SO₄²⁻ and 10 ng/g for HPO₄²⁻ and oxalate. An organics-removal cartridge (Dionex OnGuard P) was used to remove humic materials. These cartridges did not significantly affect the measured concentrations of anions in blind standards. Analyses of deionized water treated with these cartridges are not significantly different from those for untreated deionized water. For the maritime bogs, the relatively high concentrations of Cl⁻ (more than 100μ/g in many samples) and SO₄²⁻ (up to 50 μg/g) require two separate determinations for complete analyses. A 10-μl injection loop was used to determine Cl⁻, Br⁻ and SO₄²⁻. A 250-μl injection loop was used to measure NO₂⁻, NO₃⁻, HPO ₄²⁻ and oxalate. In each instance a Dionex OnGuard P cartridge was used to remove humic materials. In addition, a chloride-removal cartridge (Dionex OnGuard AG) was used to remove Cl⁻ when the larger injection loop was used. This cartridge has no significant effect on the measurement of HPO_4-²⁻ at concentrations of 20 ng/g. In each of the bog water chromatograms there were usually a number of unknown peaks. These are probably due mainly to organic anions.     

Studies on elution conditions for the determination of anions by supressed ion-interaction chromatography using a graphitized carbon column

A new method has been developed for ion-interaction chromatography with suppressed conductivity detection and a new graphitized carbon packing, which is sintered from carbonic material at a high temperature. Combinations of various eluting agents, tetrabutylammonium hydroxide (TBA) and acetonitrile have been investigated to optimize the separation of eight common anions (F⁻, Cl⁻, NO₂⁻, Br⁻, NO₃⁻, SO₄²⁻, HPO₄²⁻ and I⁻). Calibration curves were linear from 0.5 to 10 μg/ml for F⁻, from 1.0 to 20 μg/ml for Cl⁻, NO₂⁻ and NO₃⁻, from 2.5 to 50 μg/ml for Br⁻ and SO₄²⁻ and from 5.0 to 100 μg/ml for HPO₄²⁻ and I⁻ with a correlation coefficient (r) of 0.999 or better. The relative standard deviations (R.S.D.s) of peak areas were between 0.2 and 0.9% for 10 repeated measurements. The application of this newly developed method was demonstrated by the determination of chloride, bromide and sulfate in pharmaceutical compounds using the direct injection method. The analytical results were within ±2% (relative) of the theoretical value, and thus in good agreement with the theoretical value for each sample.     

Self-assembling gold nanoparticles on thiol-functionalized poly(styrene-co-acrylic acid) nanospheres for fabrication of a mediatorless biosensor

A novel strategy to construct a sensitive mediatorless sensor of H₂O₂ was described. At first, a cleaned gold electrode was immersed in thiol-functionalized poly(styrene-co-acrylic acid) (St-co-AA) nanosphere latex prepared by emulsifier-free emulsion polymerization St with AA and function with dithioglycol to assemble the nanospheres, then gold nanoparticles were chemisorbed onto the thiol groups and formed monolayers on the surface of poly(St-co-AA) nanospheres. Finally, horseradish peroxidase (HRP) was immobilized on the surface of the gold nanoparticles. The sensor displayed an excellent electrocatalytical response to reduction of H₂O₂ without the aid of an electron mediator. The biosensor showed a linear range of 8.0 μmol L⁻¹–7.0 mmol L⁻¹ with a detection limit of 4.0 μmol L⁻¹. The biosensor retained more than 97.8% of its original activity after 60 days’ storage. Moreover, the studied biosensor exhibited good current reproducibility and good fabrication reproducibility.     

Field investigation of major and minor ions along Summit (Central Greenland) ice cores by ion chromatography

As a part of the European EUROCORE and GRIP (Greenland Ice Core Project) operations aimed at recovering deep ice cores at Summit (Central Greenland), we have for the first time successfully performed ion chromatography measurements in the field and investigated in detail the soluble impurities, including Na⁺, NH⁺₄, K⁺, Mg²⁺, Ca²⁺, F⁻, CH₃COO⁻, CH₂ OHCOO⁻, HCOO⁻, CH₃SO₃⁻, Cl⁻, NO⁻₂, SO₄²⁻ and C₂O₄²⁻, trapped in ice deposited over some 200 000 years in Greenland.     

Kinetic–catalytic–spectrophotometric determination of low concentrations of molybdenum in white wines

The paper describes the determination of the molybdenum content in white wines based on its catalytical action on the kalium iodide oxidation by hydrogen peroxide in acid medium.

The optimum reaction conditions (the catalyst, KI and H₂O₂ concentrations, the pH value, the order of the reagent additions, the temperature) have been found by studying the effect of the reaction variables.

The influence of some metallic ions (Ca²⁺, Mg²⁺, Zn²⁺, Cd²⁺, Fe²⁺ and Fe³⁺) and complexing anions (F⁻, C₂O²⁻₄, EDTA⁴⁻) on the catalyzed reaction rate was elucidated.

The molybdenum concentration was estimated by the tangent, fixed-time and fixed-absorbance method. The obtained average values for molybdenum content in white wines are within the 1.77×10⁻⁷–1.83×10⁻⁷ mol l⁻¹ range.     

Green synthesis of methyl trifluoropyruvate catalyzed by solid acids

Solid acids – NiSO₄/Al₂O₃, Fe₂(SO₄)₃/Al₂O₃ and TiO₂/SO₄²⁻ – appeared to be effective catalysts for the acid catalyzed synthesis of methyl ester of trifluoropyruvic acid. They are active at 150–180 °C.     

Decolorization and mineralization of textile dyes at solution bulk by heterogeneous nanophotocatalysis using immobilized nanoparticles of titanium dioxide

Nanophotocatalysis using nanostructured semiconductors constitute one of the emerging technologies for destructive oxidation of organics such as dyes. This paper deals with the decolorization and mineralization of reactive dyes by heterogeneous nanophotocatalysis using an immobilized TiO₂ nanoparticle photocatalytic reactor. A simple and effective method was used to immobilization of titanium dioxide nanoparticles. Reactive Orange 107 (RO 107, sulphatoethylsulphonyl reactive dye) and Reactive Red 152 (RR 152, monochlorotriazine reactive dye) were used as model compounds. UV–vis and ion chromatography (IC) analyses were employed to obtain the details of the photocatalytic degradation of the selected dyes. The effects of operational parameters such as H₂O₂, dye concentration, anions (NO₃⁻, Cl⁻, SO₄²⁻, HCO₃⁻ and CO₃²⁻) and pH were investigated. Formate, acetate and oxalate anions were detected as dominant aliphatic intermediates where, they were further oxidized slowly to CO₂. Nitrate, sulfate and chloride anions were detected as the photocatalytic mineralization of RO 107 and RR 152. Kinetics analysis indicates that the photocatalytic decolorization rates can usually be approximated zero-order model for RO 107 and first-order model for RR 152 dyes. Results show that the photocatalytic process occurred at solution bulk and the employment of optimal operational parameters may lead to complete decolorization and mineralization of dye solutions.     

Voltammetric determination of glucose based on reduction of copper(II)–glucose complex at lanthanum hydroxide nanowire modified carbon paste electrodes

A novel voltammetric method for the determination of β-d-glucose (GO) is proposed based on the reduction of Cu(II) ion in Cu(II)(NH₃)₄²⁺–GO complex at lanthanum(III) hydroxide nanowires (LNWs) modified carbon paste electrode (LNWs/CPE). In 0.1 mol L⁻¹ NH₃·H₂O–NH₄Cl (pH 9.8) buffer containing 5.0 × 10⁻⁵ mol L⁻¹ Cu(II) ion, the sensitive reduction peak of Cu(II)(NH₃)₄²⁺–GO complex was observed at −0.17 V (versus, SCE), which was mainly ascribed to both the increase of efficient electrode surface and the selective coordination of La(III) in LNW to GO. The increment of peak current obtained by deducting the reduction peak current of the Cu(II) ion from that of the Cu(II)(NH₃)₄²⁺–GO complex was rectilinear with GO concentration in the range of 8.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol L⁻¹, with a detection limit of 3.5 × 10⁻⁷ mol L⁻¹. A 500-fold of sucrose and amylam, 100-fold of ascorbic acid, 120-fold of uric acid as well as gluconic acid did not interfere with 1.0 × 10⁻⁵ mol L⁻¹ GO determination.