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Cathodic Adsorptive Stripping Voltammetry for Estimation of the Forest Area Pollution with Nickel and Cobalt
Abstract
Necessary conditions were established for simultaneous nickel and cobalt determination in environmental samples, such as
oak wood and soil, based on cathodic adsorptive stripping voltammetry. Ni(II) and Co(II), complexed with dimethylglyoxime,
were determined using a hanging mercury drop electrode. Optimum conditions were found to be: accumulation time 90 s, accumulation
potential −0.80 V vs. SCE, supporting electrolyte 0.2 mol dm−3 ammonia-ammonium chloride buffer (pH = 9.4) + 0.05 mol dm−3 NaNO2 and dimethylglyoxime 2 × 10−4 mol dm−3. A linear current-concentration relationship was observed up to 7.51×10 −7 mol dm−3 for Ni(II) and 7.0 × 10−7 mol dm−3 for Co(II). Excess amounts of zinc(II) interfering with cobalt peaks were masked by complexation with EDTA. Wood and soils
were mineralized by applying a microwave digestion system, using the mixtures H2O2 + HNO3 or HNO3 + HF, respectively. The developed procedure was tested by analysing international reference materials (BCR 62 Olive Leaves
and GBW 08302 Tibet Soil). The developed procedure was used to determine pollution of oak stand with nickel and cobalt in
different regions of Poland.
... The activation potential for electrochemical growth of metal nanocrystals in 0.1 M HCl. References (43)(44)(45)(46)(47) ...
We develop a solution-based nanoscale patterning technique for site-specific deposition and dissolution of metallic nanocrystals. Nanocrystals are grown at desired locations by electron beam–induced reduction of metal ions in solution, with the ions supplied by dissolution of a nearby electrode via an applied potential. The nanocrystals can be “erased” by choice of beam conditions and regrown repeatably. We demonstrate these processes via in situ transmission electron microscopy using Au as the model material and extend to other metals. We anticipate that this approach can be used to deposit multicomponent alloys and core-shell nanostructures with nanoscale spatial and compositional resolutions for a variety of possible applications.
... In many previous studies electroanalytical methods [4], atomic absorption spectrometry [5], and chroma tography [6] have been used for the determination of these metals. For various matrices, inductively coupled plasma mass spectrometry analysis (ICP MS) [7] is a method of choice for the determination of the heavy metals at trace levels because of such advantages as ability to simultaneous multi element deterction, high sensitivity and ease of coupling with other analytical techniques. ...
A new dispersive liquid�liquid microextraction (DLLME) method for preconcentration of trace quantities of Fe(II) and Cu(II) followed by their spectrophotometric determination has been developed. For the extraction, an appropriate mixture of ethanol (the disperser solvent) and carbon tetrachloride (the extrac� tion solvent) was injected rapidly into the water sample containing Fe(II) and Cu(II) after formation of com�plexes with diethyldithiocarbamate. Mean centering (MC) of ratio spectra has been used for simultaneous determination of Fe(II) and Cu(II). Linear range of the method is 1.0–100 ng/mL for Fe(II) and 0.3–100 ng/mL for Cu(II), the detection limit is 0.53 ng/mL and 0.14 ng/mL Cu(II), resp. The interference effect of some anions and cations is reported. The method was applied to the determination of Fe(II) and Cu(II) in well water samples.
... Równie dobre wyniki odnotowano dla ludzkich płynów ustrojowych (moczu i krwi), próbek glebowych oraz różnych materiałów syntetycznych. Opydo [2001] zaproponowała analizę zawartości Co(II) jednocześnie z Ni(II) w drewnie i próbkach glebowych po mineralizacji mikrofalowej w H 2 O 2 + HNO 3 lub HNO 3 + HF, przy użyciu metody katodowej adsorpcyjnej woltamperometrii w obecności oksymów: DMG (dimetyloglioksymu) i nioksymu. Są to kompleksujące związki organiczne często stosowane w analizie chemicznej do wykrywania szeregu metali; DMG stosowany jest jako tzw. ...
Niniejsza monografia to jednocześnie koniec pewnego etapu badań i otwarcie kolejnych. Niestety to także kres jednej generacji badaczy, ale i początek następnej. Henryk Greinert (1934-2009); profesor, założyciel i pierwszy kierownik Zakładu Ochrony i Rekultywacji Gruntów Instytutu Inżynierii Środowiska Uniwersytetu Zielonogórskiego, prowadził badania zasobności w kobalt gleb naturalnej genezy już od lat 60. XX w. Ich kamieniami milowymi były prace „Kształtowanie się zawartości i rozmieszczenia kobaltu w ważniejszych glebach Pomorza Zachodniego na tle niektórych ich właściwości” (1966) oraz „Zagadnienie kobaltu w glebach murszowych” (1972). Prace Profesora nie poszły w zapomnienie – ich kontynuacją jest ta monografia, która w swoich zamiarach połączyć miała dokonania dwóch generacji poszukiwaczy nauki. Pod koniec roku 2008 profesor Henryk Greinert zainicjował ideę napisania niniejszej monografii. Niestety nie dane Mu było jej zrealizować. Monografia ta jest więc w pewnym sensie wypełnieniem Jego woli, zbiorem części pracy naukowej Profesora Henryka Greinerta, na nowo zinterpretowanej, rozbudowanej o współczesną wiedzę literaturową i wyniki nowych badań prowadzonych przez zespół Zakładu Ochrony i Rekultywacji Gruntów Uniwersytetu Zielonogórskiego pod kierownictwem profesora Andrzeja Greinerta – autora niniejszej monografii.
W monografii opisano problem występowania kobaltu w środowisku przyrodniczym oraz poddanym presji człowieka. Poddano także dyskusji funkcje kobaltu w przyrodzie. Problematyka kobaltu poruszana jest w literaturze w różnym kontekście – najczęściej w znaczeniu gospodarczym jako interesującego dodatku do różnych stopów. W naukach przyrodniczych opisywany jest zazwyczaj w bezpośrednim związku z uprawą roli i roślin uprawnych przeznaczonych do spożycia przez zwierzęta hodowlane. Minęły 74 lata od czasu, gdy w 1935 roku udowodniono niezbędność kobaltu dla życia owiec, wypasanych na niektórych pastwiskach Australii i Nowej Zelandii. W międzyczasie wykazano, że kobalt jako mikroelement jest potrzebny każdemu organizmowi zwierzęcemu, a także człowiekowi. Efekty badań nad przyczynami anemii złośliwej u ludzi przyczyniły się w znacznym stopniu do rozwiązania problemu niedoboru kobaltu w hodowli zwierząt. Znaleziono lek przeciw anemii złośliwej – witaminę B12, kobalaminę. Poznano szczególną rolę mikroflory glebowej oraz mikroorganizmów zamieszkujących w przewodzie pokarmowym zwierząt przeżuwających w produkcji tej witaminy. Mimo że obecność kobaltu stwierdzono w różnych enzymach, do dzisiaj nie ma pewności, czy spełnia on w nich rolę specyficzną. Nie udowodniono też niezbędności kobaltu dla życia roślin, chociaż wiadomo, że jest on niezbędny dla mikroorganizmów symbiotycznych, współżyjących z roślinami. Stosunkowo rzadko oznaczany jest ten pierwiastek w glebach nie będących w kręgu zainteresowań uprawowców i hodowców zwierząt, jak gleby urbanoziemne, industrioziemne oraz grunty bezglebowe. Nauczyliśmy się różnicować metale ciężkie na te bardziej i mniej groźne dla środowiska przyrodniczego, w tym zdrowia i życia ludzi. Od czasu do czasu przekonujemy się jednak jak bardzo jesteśmy w błędzie postępując według utartych schematów. Kobalt potrafi występować w stężeniach uznawanych przez świat nauki za szkodliwe dla organizmów. Potrafi też w specyficznych warunkach tworzyć izotopy odznaczające się promieniotwórczością. Po kilku spektakularnych awariach i katastrofach elektrowni atomowych na świecie w drugiej połowie XX i na początku XXI wieku, z większą pokorą patrzymy na ten aspekt wpływu m.in. kobaltu na nasze życie. Pojawiają się nowe zagadnienia do naukowego rozstrzygnięcia – w czym objawia się szkodliwość kobaltu wobec organizmów? Jak temu zjawisku zaradzić? W końcu, jak oczyścić wody i gleby z nadmiaru kobaltu lub z jego niepożądanych izotopów? To miejsca, gdzie chemia spotyka zagadnienia ochrony, inżynierii i kształtowania środowiska, w tym rekultywacji terenów zaburzonych przez działalność człowieka.
Do dzisiaj nie uzgodniono wyceny zasobności gleb w kobalt. Liczby graniczne używane podczas wyceny zasobności gleb w mikroelementy nie uwzględniają kobaltu. W ślad za tym nie uznaje się za konieczne umieszczanie analiz tego pierwiastka w programach badań, w tym wykonywanych w ramach monitoringu środowiska.
Kobalt to bez wątpienia ciekawy obiekt badań – konieczny dla życia z jednej strony i potencjalnie szkodliwy z drugiej, dawno odkryty i w wielu aspektach nieznany, interesujący i odsuwany na drugi plan.
... The distribution of Co, with the exception of accumulator peaks, is quite homogeneous in the long-term plot (Figure 4). Cobalt availability when associated to Ni (its mass fraction in leaves were below the detection limit of 4 mg/kg) is related to the metallurgic industry (Opydo, 2001). The distinct behaviour of Co was associated to the presence of Garcinia gardneriana species, whose mass fractions were high for Co and Zn. ...
The atmosphere may act as an important source of chemical elements for the Atlantic Forest, one of the hottest world biodiversity hotspots. However, chemical responses for chemical element availability are not expected to be equal for each plant species. In this sense, the present work encompasses a baseline study for biomonitoring purposes based on the identification of different strategies of native tree species in accumulating chemical elements. Instrumental neutron activation analysis was employed for chemical characterisation of leaf and soil compartments. Results indicated a low level of pollution because the major part of the studied species has shown chemical mass fractions within the expected range in leaf compartment. By estimating leaf–soil bioaccumulation factor, some species were found to accumulate the nutrients Co, Na, Se and Zn, some trace elements Br, Ba, Cs, Hg, Rb, Sc and Sr and the lanthanides Ce, La and Sm despite the environmental variability.
... In some cases, the metal has a carcinogenic effect [1]. The development of metallurgy has resulted in a steady increase of cobalt in the environment [2]. ...
The complexation of Co(II) with 4-(2-pyridylazo)resorcinol (PAR) was studied by spectroscopy and voltammetry. In addition,
an adsorptive stripping voltammetric method was developed for the determination of ultra trace levels of Co(II) using a hanging
mercury drop electrode. The method is based on accumulation of Co(II) on a mercury electrode using PAR as the complexing agent.
The effects of instrumental and chemical parameters on the sensitivity of the method were investigated. The detection limit
of the method is 0.003ng/mL. Most foreign species do not interfere with the determination. The high sensitivity and selectivity
of this method were demonstrated by determination of cobalt in blood and water samples.
... So, it is very important and necessary to develop reliable, fast and sensitive methods for the determination of heavy metals in environmental and biological samples, too. Several techniques such as neutron activation analysis (NAA) [2], energy dispersive X-ray fluorescence (XRF) spectrometry [3,4], inductively coupled plasma-atomic emission spectrometry (ICP-AES) [5,6], atomic absorption spectrometry using either flame (FAAS) [7][8][9][10] or electrothermal atomization (ETAAS) [11][12][13][14], chromatography [15][16][17][18][19][20][21][22][23][24], electroanalytical techniques [25][26][27], UV-Vis spectrophotometry [1,[28][29][30][31][32][33][34][35][36][37] have been used for the multielement analysis in different matrices. In recent years, flow systems with voltammetric [38] or spectrophotometric [39] detection systems have also been developed. ...
A simple, sensitive and rapid derivative spectrophotometric method using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) has been developed for simultaneous determination of Co(II), Ni(II) and Fe(II) which have very similar chemical behavior and appear together in many real samples. The complexes of all these metal ions with 5-Br-PADAP were formed immediately at pH 7.0 ammonium acetate buffered solution and were stable for at least 24h. Second derivative spectra were selected for evaluation, because working wavelength determination was more precise and spectral overlap was less than in the ordinary and first derivative spectra. Three wavelengths at which the complexes exhibit extremum (2)D values for Co(II), Ni(II) and Fe(II) were selected as analytical wavelengths, i.e., 640, 600 and 740nm, respectively. Calibration curves drawn with zero-to-peak values at mentioned wavelengths were linear between 80 and 2000ngml(-1) for each metal ion. Concentrations of Co(II) and Ni(II) were calculated from the total (2)D values and the sum of the linear equations for these three cations at 640 and 600nm, after Fe(II) assay by making use of the (2)D value at 740nm. Limits of detection (LOD) for Co(II), Ni(II) and Fe(II) were 2.7, 13.9 and 3.0ngml(-1), respectively. The method has been applied to tool steel and heater resistance wire samples successfully.
A dual selection/recognition effect is described for cobalt (II)ions (Co ²⁺ ). It is based on bovine serum albumin-metal-Co ²⁺ coordination (BSA-Co ²⁺ )and the use of a molecularly imprinted polymer (MIP). An electrochemiluminescence (ECL)switch sensor was designed for detecting nanomolar levels of Co ²⁺ . The BSA-Co ²⁺ coordination complex was chosen as a template to prepare a MIP modified switch sensor. The coordination reaction between BSA and Co ²⁺ provides the first step in recognition, and MIP provides the second step for Co ²⁺ . This leads to a strong improvement in selectivity of the sensor. A multi-walled carbon nanotube/Cu nanoparticles/carbon quantum dots nanocomposite (MWCNT/Cu/C-dots)acts as an ECL device, and the BSA-Co ²⁺ complex quenches the ECL signal. Therefore, the elution and resorption of BSA-Co ²⁺ can be used as a switch to control ECL. Additionally, a method was established to detect Co ²⁺ , with the detection limit as low as 3.07 × 10 ⁻¹⁰ mol/L. The method was applied to the analysis of spiked environmental water, soil samples, and agricultural products. The recovery rates of the method were in the range of 87.5–111.3%.
AbstractA selective and sensitive derivative method has been proposed for the simultaneous determination of trace amounts of Co(II) and Ni(II) with morpholinedithiocarbamate (MDTC) in the presence of sodium lauryl sulphate (SLS). The molar absorption coefficients of the 1:2 complex of Co(II) and Ni(II) at 326 nm and 322 nm are 2.248 × 104 and 2.505 × 104 L mol−1 cm−1 for zero order. The analytical sensitivity for the second derivative of Co(II) and Ni(II) complexes are 0.0044 μg mL−1 and 0.0060 μg mL−1. The developed derivative procedure, using the zero‐crossing technique, has been successfully applied for the analysis of Co(II) and Ni(II) simultaneously in different alloy samples.
A first-derivative spectrophotometry method for the simultaneous determination of Co (II) and Ni (II) with Alizarin Red S in presence of Triton X-100 is described. Measurements were made at the zero-crossing wavelengths at 549.0 nm for Co (II) and 546.0 nm for Ni (II). The linearity is obtained in the range of 0.291- 4.676 μg/ml of Ni (II) and 0.293- 4.124 μg/ml of Co (II) in the presence of each other by using first derivative spectrophotometric method. The possible interfering effects of various ions were studied. The validity of the method was examined by using synthetic mixtures of Co (II) and Ni (II). The developed derivative procedure, using the zero crossing technique, has been successfully applied for the simultaneous analysis of Co (II) and Ni (II) in spiked water samples.
IntroductionSoil Solution Sampling, Storage and FiltrationParticle Size FractionationLiquid–Liquid ExtractionIon-Exchange Resins and Solid-Phase ExtractionDerivatization Techniques to Create Volatile SpeciesChromatographic Separation of Trace Element SpeciesCapillary ElectrophoresisDiffusive Gradients in Thin FilmsIon-Selective ElectrodesDonnan Membrane TechniqueVoltammetric TechniquesMicroelectrodes and MicrosensorsModels for Predicting Metal Speciation in Soil SolutionConclusions
References
In this work, a simple, rapid, selective, sensitive and economical method has been developed for the simultaneous separation and preconcentration of trace amounts of copper, nickel, cadmium, and zinc in aqueous medium using XAD-4 resins that were modified with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) as an analytical reagent. The sorption is quantitative in the pH range 7.0-9.5, whereas quantitative desorption occurs instantaneously with 2 M HCl and selected trace elements have been determined using flame atomic absorption spectrometry. The linearity is maintained between 0.04-4.0 mg L-1 for copper, 0.1-4.0 mg L-1 for nickel, 0.02-1.3 mg L-1 for cadmium and 0.01-1.4 mg L-1 for zinc. The detection limits were 12 μg L-1 for Cu(II), 30 μg L-1 for Ni(II), 6 μg L-1 for Cd(II), and 4 μg L-1 for Zn(II) in the final solution. Various parameters such as the effect of pH, flow rate, breakthrough volume and interference of a large number of anions and cations have been studied and the proposed method was used for determination of these metal ions in water and standard samples. In order to compare the proposed method, the actual water samples were analyzed by direct FAAS (using standard addition method). Determination of these metal ions in standard samples confirmed that the proposed method has good accuracy.
H-point standard addition method, HPSAM, with simultaneous addition of three analytes is proposed for the resolution of ternary mixtures. It is a modification of the previously described H-point standard addition method that permits the resolution of three species from a unique calibration set by making the simultaneous addition of the three analytes. The method calculates the analyte concentration from spectral data at two wavelengths where the two species selected as interferents present the same absorbance relationship. These wavelength pairs are easily found, and can be selected to give the most precise results. Diethyldithiocarbomate (DDC) in a cationic micellar solution of cetyltrimethylammonium bromide (CTAB) was used for determination of Fe(II), Co(II) and Cu(II) at pH 5.50. The results showed that simultaneous determination of Fe(II), Co(II) and Cu(II) could be preformed in the range of 0.0-6.0, 0.0-8.0 and 0.0-12.0mugml(-1), respectively. The proposed method was successfully applied to the simultaneous determination of Fe(II), Co(II) and Cu(II) in several synthetic mixtures containing different concentration of Fe(II), Co(II) and Cu(II).
Evaluation of different solid electrode systems for detection of zinc, lead, cobalt, and nickel in process water from metallurgical nickel industry with use of differential pulse stripping voltammetry has been performed. Zinc was detected by differential pulse anodic stripping voltammetry (DPASV) on a dental amalgam electrode as intermetallic Ni–Zn compound after dilution in ammonium buffer solution. The intermetallic compound was observed at −375 mV, and a linear response was found in the range 0.2–1.2 mg L−1 (r
2=0.98) for 60 s deposition time. Simultaneous detection of nickel and cobalt in the low μg L−1 range was successfully performed by use of adsorptive cathodic stripping voltammetry (AdCSV) of dimethylglyoxime complexes on a silver–bismuth alloy electrode, and a good correlation was found with corresponding AAS results (r
2=0.999 for nickel and 0.965 for cobalt). Analyses of lead in the μg L−1 range in nickel-plating solution were performed with good sensitivity and stability by DPASV, using a working electrode of silver together with a glassy carbon counter electrode in samples diluted 1:3 with distilled water and acidified with H2SO4 to pH 2. A new commercial automatic at-line system was tested, and the results were found to be in agreement with an older mercury drop system. The stability of the solid electrode systems was found to be from one to several days without any maintenance needed.
Diphenycarbazone has been used for the simultaneous determination of cobalt and nickel by partial least square regression method. DPC complexes of cobalt and nickel at pH 7-10 are of pink color, which are soluble in TX-100 micellar media. A partial least square multivariate calibration method for the analysis of binary mixtures of cobalt and nickel was developed. The total relative standard error for applying the PLS method was calculated. The accuracy and reproducibility of the determination method for various known amounts of Co(II) and Ni(II) in their binary mixtures were tested. The effects of diverse ions on the determination of cobalt and nickel to investigate the selectivity of the method were also studied. The proposed method was applied to the synthetic binary mixtures, alloys and pharmaceutical samples.
Estimation of the degree of aluminium absorption by oak stands on the Krotoszyn Plateau and on reference areas is reported in this paper. Soil pH, the content of exchangeable aluminium in soil and the content of aluminium in the xylem and roots of Quercus robur L were determined. The performed studies show a very strong acidification of soils from the investigated areas of the Krotoszyn Plateau; pH vs. 1 M KCl did not exceed 4.0, whereas the content of exchangeable Al in some places was > 50 mg/100 g. The results also showed an elevated content of aluminium in the wood and roots of oaks growing on the Krotoszyn Plateau as compared to oaks in Zawiercie (near a Steel Mill), where the reaction of soil is neutral. The content of Al in the xylem of oaks from the Krotoszyn Plateau was over the range 3.8-9.9 μg/g, in the roots 198-499 μg/g. that in the xylem and roots of oaks in Zawiercie was 1.5 μg/g and 56 μg/g, respectively. Q.
The content of heavy metals - Zn, Cd, Pb and Cu - in oak wood of Quercus robur L. and in the soil was investigated. The studies were carried out in five areas: on the Krotoszyn Plateau, in two areas of the Copper Basin, in the area of Zawiercie and in the control area in Kórnik. The results showed an elevated content of copper in the wood of oaks from the Krotoszyn Plateau as compared with oaks from the other investigated areas. The copper content in the examined oaks was 0.6 µg/g in Kórnik, 1.1 µg/g in Zawiercie, 3.9-15.8 µg/g in the Copper Basin, whereas in the oaks of the Krotoszyn Plateau it amounted to 7.0-26.5 µg/g. It was also noticed that there is a correlation between the copper content in the wood and sanitary condition of the trees. The content of other toxic metals in the oak stands of the Krotoszyn Plateau was on the level of non-polluted areas ranging between 0.08-0.21 µg/g for Cd, 0.12-0.45 µg/g for Pb and 9.1-14.7 µg/g for Zn.
Aluminum toxicity can be an Important growth limiting factors occurring on acid soils where crop yields may be Increased if Al availability is reduced. A combination of liming to reduce plow layer Al plus the selection of plant species or cultivars within species that tolerate high subsoil Al are potential solution. Aluminum toxicity, Al tolerance mechanisms, physiological and biochemical effects of Al on plant growth, plant species tolerance to Al toxicity and methodology for Al screening are discussed.
A fast, sensitive method to determine Co (II) in unpurged ocean seawater is presented. The method combines high scan speed staircase voltammetry (HSACSV) and nitrite catalytic effect to enhance Co(II)-dimethylglyoxime reduction currents. The catalytic effect was magnified using high speed adsorptive cathodic stripping voltammetry and peak currents of ca. 0.1 μA were obtained for pM cobalt samples using 30-s deposition times. The effect of buffer, pH, nitrite concentration and scan speed on cobalt sensitivity was studied. Capacitance currents developed at high scan speeds were filtered by background subtraction. The same procedure was successfully applied to remove oxygen interference in unpurged solutions. Blank voltammograms were obtained in different ways yielding similar results without variation in peak reproducibility or accuracy. Nickel and zinc interferences were removed using a cleaning potential before the scan at −1.03 V. Ratios over 10 000 fold were eliminated using more negative cleaning potential steps. Nickel can also be measured by this method. Total analysis time of unpurged seawater (pM levels of cobalt) was decreased to reagents addition time, 30-s adsorption period and 10-s quiescence time. A detection limit of 5.9 pM Co was achieved in seawater. Short analysis time, sensitivity and portable hardware recommend this method for aboard determinations of cobalt. An oceanic profile of cobalt was measured at the Central East Atlantic Ocean.
The adsorption of the Ni(II) dimethylglyoxime complex, Ni(DMGH)2, on mercury was studied as a function of time by voltammetric and differential capacitance methods in ammonia and borate buffers. The influence of the adsorption potential and the complex concentration was also studied.The adsorption equilibrium shows a reversible behaviour. The experimental data conform to the Frumkin adsorption isotherm. The standard electrochemical Gibbs energy of adsorption and the interaction parameter obtained from the fit indicate the presence of attractive forces between adsorbed molecules and a standard electrochemical Gibbs energy of adsorption comparable with those of pentanol and hexanol.The experimental rate of adsorption, at short times, is independent of time. It is also linearly dependent on the complex concentration and exponentially dependent on the adsorption potential. The experimental rate law can be explained with a model considering the adsorption kinetics as being controlled by the adsorption of the complex.
The application of square wave voltammetry (SWV) for the routine determination of six elements has been examined and optimized. Square wave voltammetry is more sensitive for the determination of Zn, Ni and Co in comparison with differential pulse anodic stripping voltammetry (DPASV). For Cd and Pb, no significant improvement in sensitivity was observed. At Cu concentrations < 1 μg 1−1, only DPASV can lead to satisfactory results. The great advantage of SWV is the shortening of the determination time for Zn, Cd, Pb and Cu, which is only half the time needed by DPASV and similar to the time needed for the determination of one element by ET AAS.
The electrochemical behaviour of Ni(II) on the mercury electrode in the presence of dimethylglyoxime was investigated in weakly alkaline media by different techniques. The occurrence of the voltammetric peak could be ascribed to the reduction of nickel from its adsorbed state as the bis(dimethylglyoximato)nickel(II) complex. The position of the peak is pH dependent and the peak height is proportional to the surface concentration of Ni(DMG)2. Adsorption equilibria could be expressed at low coverages by simple Langmuir type isotherms. The kinetic parameters for the totally irreversible charge transfer process suggest that the rate determining step is the transfer of the second electron to the absorbed intermediate.
An assessment of the voltammetric method based on chelate adsorption at the hanging mercury drop electrode is described for the simultaneous determination of nickel and cobalt in biological materials. The interfacial accumulation of the elements as metal dimethylglyoximates during the adsorption step, and the use of differential-pulse voltammetry during the reduction step, provide substantial gains in the sensitivity of their voltammetric responses. The decomposition of the sample material by direct dry ashing provides a blank-free approach for the accurate determination of the elements. Application of the method to the available certified biological reference materials for cobalt and nickel was successful. The limits of detection obtained under the conditions of this study were 0.01 μg g-1 and 0.02 μg g-1 for cobalt and nickel, respectively, in bovine liver.
Mercury film microelectrodes were used to determine iron in osteoblast-like cell culture medium by performing adsorptive cathodic stripping voltammetry in the presence of catechol. The optimized analytical conditions are a catechol concentration of 5.00 × 10−4 mol L−1, pH 8.0 and a collection potential of −1.80 V which eliminates the copper interference. The reoxidation period was limited to the time between switching to −0.10 V and scanning up to the metal peak (ca. −0.40 V). The limit of detection obtained for a 30 s collection time was 1.93 × 10−8 mol L−1 iron. The results achieved by this procedure and using the square-wave voltammetry technique are accurate and precise. Biological assays were performed to evaluate the mineralization process.
Recently, the highly specific and sensitive technique of adsorption voltammetry has been developed for ultra-trace metal determination. the method involves adsorption of a ligand at an electrode, accumulation of the metal as an adsorbed complex and reduction of the adsorbed metal complex. In this work, the differential pulse adsorption voltammetric method for the determination of cobalt and nickel has been examined to determine whether adsorption voltammetric methods are likely to provide equivalent data to the widely used methods based on anodic stripping voltammetry when applied to speciation studies in natural water systems. Importantly, in contrast to anodic stripping methods for the determination of copper, lead and cadmium in natural waters, data for cobalt and nickel are essentially independent of the presence or absence of ultra-violet irradiation pretreatment methods aimed at removing dissolved organic material. It is therefore suggested that dimethylgloxime, the organic reagent used in the adsorption voltammetric method for determination of cobalt and nickel, enables the detection not only of labile nickel and cobalt complexes of the kind determined in anodic stripping voltammetry but also of the majority of organically bound cobalt and nickel complexes. That is, the high stability constants and specificity of dimethylglyoxime towards cobalt and nickel enables essentially total metal concentrations to be determined. From this result, it is suggested that all speciation studies on natural water systems undertaken via adsorption voltammetric methods will need to be assessed critically to establish whether total metal or specific forms of the metal are being determined. That is, because anodic stripping and adsorption voltammetric methods are based on fundamentally different principles they need not necessarily provide equivalent data in the area of trace metal analysis.
A method was developed to determine low levels of cobalt in whole blood, serum and plasma. Samples of blood (0.2 ml) were mineralized at 160 degrees C in the presence of concentrated nitric acid. Residual organic matter was destroyed by digestion using ultraviolet irradiation after dilution with water. The cobalt concentration was determined by catalytic cathodic stripping voltammetry (CSV) preceded by adsorptive collection of cobalt complexed with diphenylglyoxime (DPG). The optimized analytical conditions for the CSV analysis included a DPG concentration of 0.5 mumol l-1, 0.05 mol l-1 ammonium chloride buffer (pH 9.3), 0.15 mol l-1 nitrite, a deposition potential of -0.75 V, an adsorption time of 30-120 s and a negative potential scan using the differential-pulse modulation. The limit of detection was 40 pg of cobalt in 0.2 ml of blood, which was limited by the blank level of cobalt in the reagents after purification.