Syntheses, crystal structures and Raman spectra of Ba(BF4)(PF6), Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4); the first examples of metal salts containing simultaneously tetrahedral BF4 and octahedral AF6 anions

In the system BaF₂/BF₃/PF₅/anhydrous hydrogen fluoride (aHF) a compound Ba(BF₄)(PF₆) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF₄)(PF₆) crystallizes in a hexagonal space group with a=10.2251(4) Å, c=6.1535(4) Å, V=557.17(5) Å³ at 200 K, and Z=3. Both crystallographically independent Ba atoms possess coordination polyhedra in the shape of tri-capped trigonal prisms, which include F atoms from BF₄⁻ and PF₆⁻ anions. In the analogous system with AsF₅ instead of PF₅ the compound Ba(BF₄)(AsF₆) was isolated and characterized. It crystallizes in an orthorhombic Pnma space group with a=10.415(2) Å, b=6.325(3) Å, c=11.8297(17) Å, V=779.3(4) Å³ at 200 K, and Z=4. The coordination around Ba atom is in the shape of slightly distorted tri-capped trigonal prism which includes five F atoms from AsF₆⁻ and four F atoms from BF₄⁻ anions. When the system BaF₂/BF₃/AsF₅/aHF is made basic with an extra addition of BaF₂, the compound Ba₂(BF₄)₂(AsF₆)(H₃F₄) was obtained. It crystallizes in a hexagonal P6₃/mmc space group with a=6.8709(9) Å, c=17.327(8) Å, V=708.4(4) Å³ at 200 K, and Z=2. The barium environment in the shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BF₄⁻, three AsF₆⁻ and three H₃F₄⁻ anions. All F atoms, except the central atom in H₃F₄ moiety, act as μ₂-bridges yielding a complex 3-D structural network.     

Determination of arsenate in natural pH seawater using a manganese-coated gold microwire electrode

Direct electrochemical determination of arsenate (As^V) in neutral pH waters is considered impossible due to electro-inactivity of As^V. As^III on the other hand is readily plated as As⁰ on a gold electrode and quantified by anodic stripping voltammetry (ASV). We found that the reduction of As^V to As^III was mediated by elemental Mn on the electrode surface in a novel redox couple in which 2 electrons are exchanged causing the Mn to be oxidised to Mn^II. Advantage is taken of this redox couple to enable for the first time the electrochemical determination of As^V in natural waters of neutral pH including seawater by ASV using a manganese-coated gold microwire electrode. Thereto Mn is added to excess (∼1 μM Mn) to the water leading to a Mn coating during the deposition of As on the electrode at a deposition potential of −1.3 V. Deposition of As⁰ from dissolved As^V caused elemental Mn to be re-oxidised to Mn^II in a 1:1 molar ratio providing evidence for the reaction mechanism. The deposited As^V is subsequently quantified using an ASV scan. As^III interferes and should be quantified separately at a more positive deposition potential of −0.9 V. Combined inorganic As is quantified after oxidation of As^III to As^V using hypochlorite. The microwire electrode was vibrated during the deposition step to improve the sensitivity. The detection limit was 0.2 nM As^V using a deposition time of 180 s.     

Speciation of arsenic in ground water samples: A comparative study of CE-UV, HG-AAS and LC-ICP-MS

The performance of capillary electrophoresis-ultraviolet detector (CE-UV), hydride generation-atomic absorption spectrometry (HG-AAS) and liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS) have been compared for the speciation of arsenic (As) in groundwater samples. Two inorganic As species, arsenite (As^III), arsenate (As^V) and one organo species dimethyl arsenic acid (DMA) were mainly considered for this study as these are known to be predominant in water. Under optimal analytical conditions, limits of detection (LD) ranging from 0.10 (As^III, AsT) to 0.19 (DMA) μg/l for HG-AAS, 100 (As^III, DMA) to 500 (As^V) μg/l for CE-UV and 0.1 (DMA, MMA) to 0.2 (As^III, As^V) μg/l for LC-ICP-MS, allowed the determination of the above three species present in these samples. Results obtained by all the three methods are well correlated (r² = 0.996*** for total As) with the precision of <5% R.S.D. except CE-UV. The effect of interfering ions (e.g. Fe²⁺, Fe³⁺, SO₄²⁻ and Cl⁻) commonly found in ground water on separation and estimation of As species were studied and corrected for. Spike recovery was tested and found to be 80-110% at 0.5 μg/l As standard except CE-UV where only 50% of the analyte was recovered. Comparison of these results shows that LC-ICP-MS is the best choice for routine analysis of As species in ground water samples.     

Simultaneous determination of mercury and arsenic by anodic stripping voltammetry

An electrochemical method for the simultaneous determinations of Hg^II concentration and total As^III and As^V concentration has been developed. The method does not require the additional preliminary step of the chemical reduction of As^V to As^III, or oxidation of As^III to As^V before stripping analysis takes place. Also, the method for the simultaneous determination of Hg^II concentration and As^III concentration is described. Measurements were performed in 0.1 M HCl using a gold-plated graphite electrode as sensor. Detection limits for both methods are below 0.4 ppb. Relative standard deviation did not exceed 15%. The possible interference by other trace metals was investigated. Analyses of natural water and industrial solutions were made using proposed methods and AAS. The t-test demonstrates that there was no significant difference between the results obtained with these methods. Proposed methods decrease the time of analysis because concentrations of the Hg^II and arsenic ions were measured simultaneously. Also, the removal of the additional step of chemical reduction of As^V to As^III or oxidation of As^III to As^V decreases analysis time, and also reduces the chance of contamination due to the use of additional reagents.     

Simultaneous capillary electrophoretic determination of Sc(III) and Y(III) based on the complex-formation with a lacunary Keggin-type [PW11O39] complex

Trace amounts of Sc(III) and Y(III) can react with [PW₁₁O₃₉]⁷⁻ to form the ternary Keggin-type complexes: [P(Sc^IIIW₁₁)O₄₀]⁶⁻ and [P(Y^IIIW₁₁)O₄₀]⁶⁻ having high molar absorptivities in the UV region. Since the rate of the complex-formation was very rapid and the kinetically stable ternary anions migrated in the capillary with different electrophoretic mobilities, the complex-formation reaction was applied to the simultaneous CE determination of Sc(III) and Y(III) with direct UV detection at 250 nm. For both Sc(III) and Y(III), the pre-column method provided linear calibration curves in the range of 2 × 10⁻⁷ to 1 × 10⁻⁵ M; the respective detection limits were 1 × 10⁻⁷ M (the signal-to-noise ratio = 3). The proposed method was successfully applied to the determination of Sc(III) and Y(III) in river water.     

Simultaneous capillary electrophoretic determination of Sb(III) and Bi(III) based on the complex-formation with a W(VI)-P(V) reagent

A capillary electrophoretic method was developed for the simultaneous determination of Sb(III) and Bi(III). A 1.0 mM W(VI)-0.10 mM P(V) complexing reagent readily reacted with a mixture of trace amounts of Sb(III) and Bi(III) to form the corresponding ternary Keggin-type complexes; [P(Sb^IIIW₁₁)O₄₀]⁶⁻ and [P(Bi^IIIW₁₁)O₄₀]⁶⁻ in 0.01 M malonate buffer (pH 2.4). Since the peaks due to the migrations of the ternary complex anions were well separated in the electropherogram, the pre-column complex-formation reaction was applied to the simultaneous CE determination of Sb(III) and Bi(III) with direct UV detection at 255 nm. The calibration curves were linear in the range of 2×10⁻⁷-5×10⁻⁵ M; a detection limit of 1×10⁻⁷ M was achieved for Sb(III) or Bi(III) (the signal-to-noise ratio=3).     

Simple and selective determination of arsenite and arsenate by electrospray ionization mass spectrometry

Arsenic pollution of public water supplies has been reported in various regions of the world. Recently, some cancer patients are treated with arsenite (As^III); most Japanese people consume seafoods containing large amounts of negligibly toxic arsenic compounds. Some of these arsenic species are metabolized, but some remain intact. For the determination of toxic As^III, a simple, rapid and sensitive method has been developed using electrospray ionization mass spectrometry (ESI-MS). As^III was reacted with a chelating agent, pyrrolidinedithiocarbamate (PDC, C₄H₈NCSS^-) and tripyrrolidinedithiocarbamate-arsine, As(PDC)₃, extracted with methyl isobutyl ketone (MIBK). A 1 μL aliquot of MIBK layer was directly injected into ESI-MS instrument without chromatographic separation, and was detected within 1 min. Arsenate (As^V) was reduced to As^III with thiosulfate, and then the total inorganic As was quantified as As^III. This method was validated for the analysis of urine samples. The limit of detection of As was 0.22 μg L⁻¹ using 10 μL of sample solution, and it is far below the permissible limit of As in drinking water, 10 μg L⁻¹, recommended by the WHO. Results were obtained in < 10 min with a linear calibration range of 1-100 μg L⁻¹. Several organic arsenic compounds in urine did not interfere with As^III detection, and the inorganic As in the reference materials SRM 2670a and 1643e were quantified after the reduction of As^V to As^III.     

Ca(AsF3)(AsF6)2: the first alkaline earth metal cation coordinated to AsF3

Ca(AsF₃)(AsF₆)₂ was prepared by the reaction of CaF₂ with excess AsF₅ in AsF₃ solvent. The compound crystallizes in an orthorhombic crystal system, space group Pnma, with a =1034.9(4) pm, b = 1001.7(4) pm and c = 1088.4(4) pm, V = 1.1283(8) nm³ and Z = 4. Calcium is coordinated to eight fluorine atoms, with six fluorine atoms located at the corners of a regular trigonal prism originating from six AsF₆ units. Two rectangular faces of the trigonal prism are capped by fluorine atoms from two fluorine bridged AsF₃ molecules. For the first time, AsF₃ is shown to serve as a bridging ligand to two metal cations, with bridging distances of F(AsF₃)-Ca = 241.1 and 243.2 pm. It was found, again for the first time, that the bridging As-F distances are shorter (172.4 and 173.1 pm) than the terminal As-F distance (184.5 pm). The Raman spectrum shows vibrational modes that are readily assigned to AsF₃ and AsF₆⁻.     

Potentiometric flow injection determination of manganese(II) by using a hexacyanoferrate(III)-hexacyanoferrate(II) potential buffer

A highly sensitive potentiometric flow injection analysis method for the determination of manganese(II), utilizing a redox reaction with hexacyanoferrate(III) in near neutral media containing ammonium citrate is described. The analytical method is based on the detection of the change in potential of a flow-through type redox electrode detector, resulting from the composition change of an [Fe(CN)₆]³⁻-[Fe(CN)₆]⁴⁻ potential buffer solution. A linear relationship between the potential change (peak height) and the concentration of manganese(II) was found. Manganese(II) in a wide concentration range from 10⁻⁴ to 10⁻⁷ M could be determined by appropriately altering the concentration of the potential buffer from 10⁻³ to 10⁻⁵ M. The lower detection limit of manganese(II) was determined to be 1×10⁻⁷ M. The sampling rate and relative standard deviation were 20 h⁻¹ and 1.9% (n=8) for 6×10⁻⁶ M manganese(II), respectively. The proposed method was successfully applied to the determination of manganese(II) in actual soil samples obtained from tea fields. Analytical results obtained by the proposed method were in good agreement with those obtained by an atomic absorption spectrophotometric method.     

X-ray Crystal Structure of (CNSSS)2(M)2 (M = AsF6 −, SbF6 −, Sb2F11 −)

The crystal structures of (CNSSS)₂(AsF₆)₂, (CNSSS)₂(SbF6)₂, and two phases of (CNSSS)₂(Sb₂F₁₁)₂ have been determined. The AsF₆ ^?, SbF₆ ^?, and α-Sb₂F₁₁ ^? salts crystallize as reddish-brown plates whereas the β-Sb₂F₁₁ ^? salt crystallizes as green rods. The dication ^ß+SSSNCCNSSS^+ß (1²⁺) is the same in all four structures and consists of two 7π rings linked by a sp²-sp² C-C bond (1.462 Å in 1 (AsF₆)₂). The packing in the four structures is similar with stacks of dications along the a-axis and alternating sheets of dications and anions lying in the bc-plane. The differences in the dication-dication contacts is reflected in the variable temperature magnetic data.     

Synthesis and characterization of three new fluorovanadate complexes: N(C2H5)4[VOF4], N(CH3)4[VOF3Cl], N(C4H9)4[VOF3Br] and theoretical calculations of VOF4, VOF3Cl and VOF3Br ions

The reaction of VOF₃ with (C₂H₅)₄NF, (CH₃)₄NCl and (C₄H₉)₄NBr salts in anhydrous CH₃CN produced new complexes with the anion general formula [VOF₃X]⁻ in that (X = F⁻, Cl⁻, Br⁻). These were characterized by elemental analysis, IR, UV/Visible and ¹⁹F NMR spectroscopy. The optimized geometries and frequencies of the stationary point are calculated at the B3LYP/6-311G level of theory. Theoretical results showed that the VX (X = F, Cl, Br) bond length values for the [VOF₃X]⁻ in compounds 1-3 are 1.8247, 2.4031 and 2.5595 Å, respectively. Also, the VF₅ bond length values in [VOF₃X]⁻ are 1.824, 1.812 and 1.802 Å, respectively. These results reveal that the bond order for VX bonds decrease from compounds 1 to 3, while for VF₅ bonds, the bond orders increase. It can be concluded that the decrease of VX bonds lengths and the increase of VF₅ bond lengths in compounds 1-3 result from the increase of the hyperconjugation from compounds 1 to 3. Harmonic vibrational frequencies and infrared intensities for VOF₄⁻, VOF₃Cl⁻ and VOF₃Br⁻ are studied by means of theoretical and experimental methods. The calculated frequencies are in reasonable agreement with the experiment values. These data can be used in models of phosphoryl transfer enzymes because vanadate can often bind to phosphoryl transfer enzymes to form a trigonal-bipyramidal structure at the active site.     

The room temperature preparation of metastable fluorides and potent oxidizers

The low electronegativity of an oxidation state in an anion enables high oxidation states, e.g. Ni^IV, and Ag^III, to be easily attained in liquid anhydrous HF (aHF), made basic with fluoride-ion donors. The oxidation state can be enhanced if elemental fluorine is photo-dissociated. Teflon^® valves and lines, especially transparent and kinetically stable fluorocarbon containers for the aHF solutions, provide for this. Binary fluorides that are of low solubility in aHF, can be displaced by stronger F⁻ acceptors from their high oxidation-state anions. NiF₄, NiF₃, and AgF₃, which can be made in this manner, are thermodynamically unstable with respect to loss of fluorine. The electronegativity of the oxidation state in the binary fluoride is higher than in the anion (hence the metastability) and when a strong F⁻ acceptor converts the binary fluoride into a cationic species, the electronegativity is further enhanced. Thus cationic Ag^III and Ni^IV are superior to KrF⁺, as one-electron oxidizers and are the most potent oxidizers known thus far. They are able to remove the electron from all platinum-metal hexafluoro-anions, MF₆⁻, to liberate the hexafluorides. All of this chemistry can be achieved at or below room temperature.     

Low temperature preparation and uses of potent oxidizers

Because electronegativity of an oxidation state is low in an anion, salts of the high oxidation-state species [AgF₄]⁻ and [NiF₆]²⁻ can be easily made, at 0 °C, in liquid anhydrous HF (aHF) made basic with alkali fluorides. The containers are transparent fluorocarbon, and the F₂ is photo-dissociated. The [NiF₆]²⁻ salts, and the metastable binary fluorides NiF₄ and NiF₃, derived from them, are efficient fluorinating agents for the conversion of hydrido compounds to their fully fluorinated relatives. With F₂ in aHF made acidic with fluoride-ion acceptors (e.g. MF₅, M = As, Sb, Bi) attained oxidation-states are often lower (e.g. Ag^II, Au^II) because of the higher electronegativity in cations. Cationic Ag^III and Ni^IV species (derived from the anions) are sufficiently long-lived, and potent, to generate the most powerfully oxidizing hexafluorides of the second and third transition series (i.e. [MF₆], M = Pt, Ru, Rh). This synthesis is especially valuable for RhF₆, and has provided for the reinvestigation of the interaction of it with O₂. It is proposed that the unexpectedly large unit cell of O₂RhF₆ is a result of the presence of neutral O₂ and neutral RhF₆ as well as O₂⁺ and RhF₆⁻ in the lattice.     

Determination of the Interaction of Arsenic and Human Serum Albumin by Online Microdialysis Coupled to LC with Hydride Generation Atomic Fluorescence Spectroscopy

Study on the stoichiometry and affinity of the arsenicals bound to HSA is an important step toward a better understanding of arsenic toxic effects. After incubation of As^III or As^V with HSA at the physiological conditions (pH 7.43 and 37 °C), the free arsenicals and arsenic-HSA complexes were separated and detected by the combined techniques of microdialysis and liquid chromatography with hydride generation atomic fluorescence spectroscopy (MD–LC–HGAFS). The decrease of As^III peak response rather than As^V indicated that HSA reacted with As^III but not As^V. The binding plots indicated that the binding between HSA and As^III was in Scatchard pattern when the concentration ratios of As^III to HSA were ≤1:1. The strong binding sites (n ₁) were 1.6 and the stability constant (K ₁) was 1.54 × 10⁶ M^?1. When the concentration ratios of As^III to HSA were >1:1, the binding was in Plasvento pattern with the stability constant K ₂ ? 0 and no specific binding of As^III with HSA. On the contrary, As^V did not show binding with HSA. The results showed that As^III reacted with HSA more readily than As^V, which provides a chemical basis for arsenic toxicity.     

Determination of arsenic and antimony in seawater by voltammetric and chronopotentiometric stripping using a vibrated gold microwire electrode

The oxidation potentials of As⁰/As^III and Sb⁰/Sb^III on the gold electrode are very close to each other due to their similar chemistry. Arsenic concentration in seawater is low (10–20 nM), Sb occurring at ∼0.1 time that of As. Methods are shown here for the electroanalytical speciation of inorganic arsenic and inorganic antimony in seawater using a solid gold microwire electrode. Anodic stripping voltammetry (ASV) and chronopotentiometry (ASC) are used at pH ≤ 2 and pH 8, using a vibrating gold microwire electrode. Under vibrations, the diffusion layer size at a 5 μm diameter wire is 0.7 μm. The detection limits for the As^III and Sb^III are below 0.1 nM using 2 min and 10 min deposition times respectively. As^III and Sb^III can be determined in acidic conditions (after addition of hydrazine) or at neutral pH. In the latter case, oxidation of As⁰ to As^III was found to proceed through a transient As^III species. Adsorption of this species on the gold electrode at potentials where Sb^III diffused away is used for selective deposition of As^III. Addition of EDTA removes the interfering effect of manganese when analysing As^III. Imposition of a desorption step for Sb^III analysis is required. Total inorganic arsenic (iAs = As^V + As^III) can be determined without interference from Sb nor mono-methyl arsenious acid (MMA) at 1.6 < pH < 2 using E_dep = −1 V. Total inorganic antimony (iSb = Sb^V + Sb^III) is determined at pH 1 using E_dep = −1.8 V without interference by As.     

Electrochemical behavior of hexafluoroniobate, heptafluorotungstate, and oxotetrafluorovanadate anions in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide room temperature ionic liquid

Electrochemical behavior of hexafluoroniobate (Nb(V)F₆⁻), heptafluorotungstate (W(VI)F₇⁻), and oxotetrafluorovanadate (V(V)OF₄⁻) anions has been investigated in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPyrTFSA) ionic liquid at 298 K by means of cyclic voltammetry and chronoamperometry. Cyclic voltammograms at a Pt electrode showed that Nb(V)F₆⁻ anion is reduced to Nb(IV)F₆²⁻ by a one-electron reversible reaction. Electrochemical reductions of W(VI)F₇⁻ and V(V)OF₄⁻ anions at a Pt electrode are quasi-reversible and irreversible reactions, respectively, according to cyclic voltammetry. The diffusion coefficients of Nb(V)F₆⁻, W(VI)F₇⁻ and V(V)OF₄⁻ determined by chronoamperometry are 1.34 × 10⁻⁷, 7.45 × 10⁻⁸ and 2.49 × 10⁻⁷ cm² s⁻¹, respectively. The Stokes radii of Nb(V)F₆⁻, W(VI)F₇⁻, and V(V)OF₄⁻ in BMPyrTFSA have been calculated to be 0.23, 0.38, and 0.12 nm, from the diffusion coefficients and viscosities obtained.     

Synthesis, structure and magnetism of a S-shaped multi-iron substituted arsenotungstate containing a trivacant Keggin [B-α-AsW9O34] and a hexavacant Keggin [α-AsW6O26] fragments

A S-shaped multi-iron substituted arsenotungstate [enH₂]₂[(α-H₂As^VW₆O₂₆)Fe₃(H₂O)(B-α-H₄As^VW₉O₃₄)]₂[Fe]₂·8H₂O (1) (en=ethylenediamine) has been prepared by reaction of K₁₄[As₂^IIIW₁₉O₆₇(H₂O)]·nH₂O with Fe₂(SO₄)₃·xH₂O under hydrothermal conditions and structurally characterized by elemental analyses, IR spectra, UV spectra, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction. The skeleton of 1 consists of two asymmetric sandwich-type subunits [(α-H₂As^VW₆O₂₆)Fe₃(H₂O)(B-α-H₄As^VW₉O₃₄)]⁵⁻ linked by a di-Fe^III cluster. Moreover, magnetic susceptibility measurements demonstrate that 1 indicates the antiferromagnetic coupling interactions within Fe^III centers with the best-fitting set of parameters of J₁=−7.07 cm⁻¹, J₂=−0.45 cm⁻¹ and g=2.05, which are generated by the addition of the expressions of the molar susceptibilities of two tri-Fe^III clusters and one di-Fe^III cluster derived from for spin pairs coupled through the isotropic exchange interactions.     

Multielemental speciation of As, Se, Sb and Te by HPLC-ICP-MS

An anion exchange HPLC-ICP-MS procedure allowing the simultaneous multielemental speciation analysis of arsenic, selenium, antimony and tellurium has been developed. Four arsenic species (As^III, As^V, monomethylarsonic acid and dimethylarsinic acid), two selenium species (Se^IV and Se^VI) may be determined in a single run as well as one antimony (Sb^V) and one tellurium species (Te^VI). Alternatively Sb and/or Te may be used as internal standards for As and Se speciation studies. Optimisation of ICP-MS conditions led to satisfactory relative (0.01 (Sb^V) to 1.8 (Se^VI) ng ml⁻¹) and absolute detection limits (1–180 pg). Reproducibility ranged from 3.1 to 5.6% and the linearity was verified in the 0–200 ng ml⁻¹ range.     

Determination of the Interaction of Arsenic and Human Serum Albumin by Online Microdialysis Coupled to LC with Hydride Generation Atomic Fluorescence Spectroscopy

Study on the stoichiometry and affinity of the arsenicals bound to HSA is an important step toward a better understanding of arsenic toxic effects. After incubation of As^III or As^V with HSA at the physiological conditions (pH 7.43 and 37 °C), the free arsenicals and arsenic-HSA complexes were separated and detected by the combined techniques of microdialysis and liquid chromatography with hydride generation atomic fluorescence spectroscopy (MD–LC–HGAFS). The decrease of As^III peak response rather than As^V indicated that HSA reacted with As^III but not As^V. The binding plots indicated that the binding between HSA and As^III was in Scatchard pattern when the concentration ratios of As^III to HSA were ≤1:1. The strong binding sites (n ₁) were 1.6 and the stability constant (K ₁) was 1.54 × 10⁶ M⁻¹. When the concentration ratios of As^III to HSA were >1:1, the binding was in Plasvento pattern with the stability constant K ₂ ≅ 0 and no specific binding of As^III with HSA. On the contrary, As^V did not show binding with HSA. The results showed that As^III reacted with HSA more readily than As^V, which provides a chemical basis for arsenic toxicity.

     

Disposable biosensor based on cathodic electrochemiluminescence of tris(2,2-bipyridine)ruthenium(II) for uric acid determination

A new method for uric acid (UA) determination based on the quenching of the cathodic ECL of the tris(2,2-bipyridine)ruthenium(II)–uricase system is described. The biosensor is based on a double-layer design containing first tris(2,2-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) electrochemically immobilized on graphite screen-printed cells and uricase in chitosan as a second layer. The uric acid biosensing is based on the ECL quenching produced by uric acid over the cathodic ECL caused by immobilized Ru(bpy)₃²⁺ in the presence of uricase. The use of a −1.1 V pulse for 1 s with a dwelling time of 10 s makes it possible to estimate the initial enzymatic rate, which is used as the analytical signal. The Stern–Volmer type calibration function shows a dynamic range from 1.0 × 10⁻⁵ to 1.0 × 10⁻³ M with a limit of detection of 3.1 × 10⁻⁶ M and an accuracy of 13.6% (1.0 × 10⁻⁴ M, n = 5) as relative standard deviation. Satisfactory results were obtained for urine samples, creating an affordable alternative for uric acid determination.