Effect of Cu(II), Cd(II) and Zn(II) on Pb(II) biosorption by algae Gelidium-derived materials

Biosorption of Pb(II), Cu(II), Cd(II) and Zn(II) from binary metal solutions onto the algae Gelidium sesquipedale, an algal industrial waste and a waste-based composite material was investigated at pH 5.3, in a batch system. Binary Pb(II)/Cu(II), Pb(II)/Cd(II) and Pb(II)/Zn(II) solutions have been tested. For the same equilibrium concentrations of both metal ions (1 mmol l(-1)), approximately 66, 85 and 86% of the total uptake capacity of the biosorbents is taken by lead ions in the systems Pb(II)/Cu(II), Pb(II)/Cd(II) and Pb(II)/Zn(II), respectively. Two-metal results were fitted to a discrete and a continuous model, showing the inhibition of the primary metal biosorption by the co-cation. The model parameters suggest that Cd(II) and Zn(II) have the same decreasing effect on the Pb(II) uptake capacity. The uptake of Pb(II) was highly sensitive to the presence of Cu(II). From the discrete model it was possible to obtain the Langmuir affinity constant for Pb(II) biosorption. The presence of the co-cations decreases the apparent affinity of Pb(II). The experimental results were successfully fitted by the continuous model, at different pH values, for each biosorbent. The following sequence for the equilibrium affinity constants was found: Pb>Cu>Cd approximately Zn.     

Imaging of metal ion dissolution and electrodeposition by anodic stripping voltammetry-scanning electrochemical microscopy

We have developed a new imaging method for scanning electrochemical microscopy (SECM) employing fast-scan anodic stripping voltammetry (ASV) to provide sensitive and selective imaging of multiple chemical species at interfaces immersed in solution. A rapid cyclic voltammetry scan (100 V/s) is used along with a short preconcentration time (300-750 ms) to allow images to be acquired in a normal SECM time frame. A Hg-Pt film electrode is developed having an equivalent Hg thickness of 40 nm that has good sensitivity at short preconcentration times and also retains thin-film behavior with high-speed voltammetric stripping. Fast-scan anodic stripping currents are shown to be linear for 1-100 microM of Pb (2+) and Cd (2+) solutions using a preconcentration time of 300 ms. SECM images showing the presence of Pb (2+) and Cd (2+) at concentrations as low as 1 microM are presented. In addition, a single ASV-SECM image is shown to produce unique concentration maps indicating Cd (2+) and Pb (2+), generated in situ from a corroding sample, while simultaneously detecting the depletion of O 2 at this sample. The transient voltammetric response at the film electrode is simulated and shows good agreement with the experimental behavior. We discuss the behavior of images and concentration profiles obtained with different imaging conditions and show that mass-transport limitations in the tip-substrate gap can induce dissolution. ASV-SECM can thus be used to detect and study induced dissolution not only at bulk metal surfaces but also on underpotential deposition layers, in this case Cd and Pb on Pt. In addition, we discuss how surface diffusion phenomena may relate to the observed ASV-SECM behavior.     

Preconcentration and Voltammetric Determination of Mercury(II) at a Chemically Modified Glassy Carbon Electrode

In this work, the organic compound 2-mercaptobenzimidazole was covalently bound on the surface of a glassy carbon rod, via silanization, yielding a material capable of selectively complexing Hg(2+) ions. This material was applied as an electrode for voltammetric determination of mercury(II) following its nonelectrolytic preconcentration. After exchanging the medium, the voltammetric measurements were carried out by anodic stripping in the differential pulse mode (pulse amplitude, 50 mV; scan rate, 1.25 mV s(-)(1)) using 10(-)(2) mol L(-)(1) NaSCN solution as supporting electrolyte. An anodic stripping peak was obtained at 0.06 V (vs SCE) by scanning the potential from -0.3 to +0.3 V. After a 5 min preconcentration period in a pH 4.0 Hg(2+) solution, this electrode shows increasing voltammetric response in the range 0.1-2.2 μg mL(-)(1), with a relative standard deviation of 5% and a practical detection limit of 0.1 μg mL(-)(1) (5.0 × 10(-)(7) mol dm(-)(3)). Compared with the conventional stripping approach, this chemically modified glassy carbon electrode procedure presented good discrimination against interference from Cu(II) in up to 10-fold molar excess.     

Solderability, IMC evolution, and shear behavior of low-Ag Sn0.7Ag0.5Cu-BiNi/Cu solder joint

The solderability, intermetallic compounds (IMC) evolution, and shear behavior of the low-Ag Sn0.7Ag0.5Cu-3.5Bi-0.05Ni (SAC0705-BiNi)/Cu solder joint was investigated by comparing with Sn0.7Ag0.5Cu (SAC0705)/Cu and Sn3.0Ag0.5Cu (SAC305)/Cu solder joints. Experimental results demonstrated that the melting temperature of Sn0.7Ag0.5Cu-BiNi solder alloy was lower than that of SAC0705 and SAC305 solder. But the melting range of Sn0.7Ag0.5Cu-BiNi was wider. Compared with the other two kinds of alloys, SAC0705-BiNi showed the best wettability. SAC0705/Cu, SAC0705-BiNi/Cu, and SAC305 solder joints appeared similar IMC morphologies and grain size at the beginning of soldering, but evolved to different appearance as the soldering process proceeded. The growth rate of the IMC grains in SAC0705-BiNi/Cu solder joint was the lowest because of the refinement of Ni. SAC0705-BiNi/Cu solder joint showed the highest shear strength before and after being aged, mainly due to the enhancement of solid solution strengthening and dispersion strengthening of Bi and Ni in the bulk solder, as well as the refinement of Ni at the soldering interface.     

Anodic stripping voltammetry enhancement by redox magnetohydrodynamics

The effect of an external magnetic field on linear scan anodic stripping voltammetry (ASV) in solutions of 10(-6)-10(-7) M concentrations of lead, cadmium, and copper at mercury films on glassy carbon electrodes has been investigated. A high concentration of Hg(2+) was added to the analyte solution to induce a large cathodic current during the deposition step. Therefore, a large Lorentz force from the net flux of charge through the magnetic field resulted in convection due to magnetohydrodynamics. The faster delivery of analytes to the mercury film electrode during deposition caused an increase in the anodic stripping peaks. The effect of varying Hg(2+) concentrations (0-60 mM) and magnetic field strengths (0-1.77 T) on the enhancement of the stripping peaks was investigated. Enhancements as large as 129% for peak currents and 167% for peak areas were observed. An enhancement of approximately 100% was observed when 60 mM Fe(3+) replaced high concentrations of Hg(2+). This method of convection exhibits promise for small-volume ASV analysis with possible improved limits of detection and decreased preconcentration times.     

Factors influencing redox magnetohydrodynamic-induced convection for enhancement of stripping analysis

Factors affecting the use of redox magnetohydrodynamics (MHD) to enhance the stripping analysis response to heavy metals have been investigated. The analytes were Pb2+, Cd2+, Cu2+, and Tl+ at concentrations ranging from 5 nM to 2 microM. Co-deposition of analytes with Hg2+ (to form a thin Hg film electrode) occurs along with reduction of a high concentration of Fe3+. The Fe3+ provides the high cathodic current necessary to produce a significant Lorentz force, and therefore enhanced convection and larger stripping signals and sensitivities, when the analysis is performed in the presence of an external magnetic field. The effects of varying Fe3+ concentration (1-100 mM), working electrode size (10 microm-3 mm), and magnetic field strengths (0-1.77 T) generated with electromagnets and NdFeB permanent magnets were investigated. Using 100 mM Fe3+ as the MHD-generating redox species at a 3-mm working electrode and in a magnetic field of 1.77 T, peak areas from linear sweep voltammetry were increased by as much as 159 +/- 5%, compared to the signal obtained in the absence of a magnetic field. Experimental detection limits as low as 5 nM were achieved with only a 1-min preconcentration time. A field strength as low as 0.12 T offers some signal enhancement with 100 mM Fe3+. While linear scan anodic stripping voltammetry was used primarily to obtain the signals after the deposition step, potentiometric stripping analysis was also investigated. Redox MHD is an attractive alternative convection method for applications involving sample volumes too small for mechanical stirring or for in-field applications using portable devices that cannot be complicated by the instrumentation required for mechanical stirring.     

Speciation of heavy metals by modified BCR sequential extraction procedure in different depths of sediments from Sungai Buloh, Selangor, Malaysia

The sequential extraction procedure proposed by the European Standard, Measurements and Testing (SM&T) program, formerly the Community Bureau of Reference (BCR), was applied for partitioning of heavy metals (HMs) in river sediments collected along the course of Sungai Buloh and the Straits of Malacca in Selangor, Malaysia. Eight elements (V, Pb, Cd, Cr, Co, Ni, Cu and Zn) from seven stations (S1-S7) and at different depths were analyzed using the modified BCR Sequential Extraction Procedure (SEP) in combination with ICP-MS to obtain the metal distribution patterns in this region. The results showed that heavy metal contaminations at S2 and S3 was more severe than at other sampling sites, especially for Zn, Cu, Ni and Pb. Nevertheless, the element concentrations from top to bottom layers decreased predominantly. The samples from the Straits of Malacca (S4-S7) the highest contamination factors obtained were for Co, Zn and Pb while the lowest were found for V and Cr, similar to Sungai Buloh sediments. The sediments showed a low risk for V, Cr, Cu and Pb with RAC values of less than 10%, but medium risk for Co, Zn (except S3), Cd at S1 and S2 and Ni at S1, S3 and S5. Zn at S3 and Cd at S3-S7 showed high risk to our sediment samples. There is not any element of very high risk conditions in the selected samples.     

Antimony film electrode for electrochemical stripping analysis

In this work, an antimony film electrode (SbFE) is reported for the first time as a possible alternative for electrochemical stripping analysis of trace heavy metals. The SbFE was prepared in situ on a glassy carbon substrate electrode and employed in combination with either anodic stripping voltammetry or stripping chronopotentiometry in nondeaerated solutions of 0.01 M hydrochloric acid (pH 2). Several key operational parameters influencing the electroanalytical response of SbFE were examined and optimized, such as deposition potential, deposition time, and composition of the measurement solution. The SbFE exhibited well-defined and separated stripping signals for both model metal ions, Cd(II) and Pb(II), surrounded with low background contribution and a relatively large negative potential range. The electrode revealed good linear behavior in the examined concentration range from 20 to 140 microg L-1 for both test metal ions, with a limit of detection (3sigma) of 0.7 microg L-1 for Cd(II) and 0.9 microg L-1 for Pb(II) obtained after a 120 s deposition step, and good reproducibility, with a relative standard deviation (RSD) of +/-3.6% for Cd(II) and +/-6.2% for Pb(II) (60 microg L-1, n = 12). When comparing the SbFE with the commonly used mercury film electrode and recently introduced bismuth film electrode, the newly proposed electrode offers a remarkable performance in more acidic solutions (pH < or = 2), which can be advantageous in electrochemical analysis of trace heavy metals, hence contributing to the wider applicability of electrochemical stripping techniques in connection with "mercury-free" electrodes.     

Removal and recovery of heavy metals from aqueous solution using Ulmus carpinifolia and Fraxinus excelsior tree leaves

Ulmus carpinifolia and Fraxinus excelsior tree leaves, which are in great supply in Iran, were evaluated for removal of Pb(II), Cd(II) and Cu(II) from aqueous solution. Maximum biosorption capacities for U. carpinifolia and F. excelsior were measured as 201.1, 172.0 mg/g for Pb(II), 80.0, 67.2 mg/g for Cd(II) and 69.5, 33.1 mg/g for Cu(II), respectively. For both sorbents the most effective pH range was found to be 2-5 for Pb(II), 3-5 for Cd(II) and 4-5 for Cu(II). Metal ion biosorption increased as the ratio of metal solution to the biomass quantity decreased. Conversely, biosorption/g biosorbent decreased as the quantity of biomass increased. The biosorption of metal ions increased as the initial metal concentration increased. Biosorption capacities of metal ions were in the following order: Pb(II)>Cd(II)>Cu(II). The equilibrium data for Pb(II) and Cu(II) best fit the Langmuir adsorption isotherm model. Kinetic studies showed that the biosorption rates could be described by a second-order expression. Both the sorbents could be regenerated using 0.2 M HCl during repeated biosorption-desorption cycles with no loss in the efficiency of the Cu(II) removal observed. Biosorption of Pb(II), Cd(II) and Cu(II) was investigated in the presence of Na, K, Mg and Ca ions. The results from these studies show a novel way of using U. carpinifolia and F. excelsior tree leaves to remove Pb(II), Cd(II) and Cu(II) from metal-polluted waters.     

Evaluation of the metal uptake of several algae strains in a multicomponent matrix utilizing inductively coupled plasma emission spectrometry

Three freshwater heat-killed, lyophilized blue-green algae strains have been characterized as to their ability to accumulate heavy metals with a focus on the utilization of these algae as an analytical preconcentration technique. This study examines the metal uptake in several multicomponent mixtures by using inductively coupled plasma optical emission spectrometry (ICP-OES). Six milligrams of a pure strain of algae was added to 20-mL aliquots of buffered (pH 5.5-6.5) multielement solutions containing 0.1, 0.5, 1.0, 2.0, and 4.0 mg/L of K, Mg, Ca, Fe, Sr, Co, Cu, Mn, Ni, V, Zn, As, Cd, Mo, Pb, and Se. All three algae strains exhibit relatively high adsorption affinities for Fe, Pb, and Cu, with uptake between 70 and 98% at the 4 ppm concentration level. Biosorption occurs for essentially every element with the relative affinities decreasing in the order Pb greater than Fe greater than Cu greater than Cd greater than Zn greater than Mn greater than Mo greater than Sr greater than Ni greater than V greater than Se greater than As greater than Co for Chlorella pyrenoidosa at the 4 mg/L concentration level. Although some minor differences were seen, the other algae strains (Stichococcus bacillaris and Chlamydomonas reinharti) displayed similar adsorption behavior over the concentration range studied, indicating similar cell wall binding sites. Langmuirian isotherms exhibited a minimum of two slopes over the concentration range of 0.1-4.0 mg/L, indicating the probable existence of at least two adsorption mechanisms.     

Electrodialytic extraction of Cd and Cu from sediment from Sisimiut Harbour, Greenland

A previous study showed that the sediment of Sisimiut Harbour, Greenland is polluted with Cu and Cd to an extent where toxicological effects must be expected. This study was aimed at evaluating the possibility for removing Cu and Cd from this sediment by an electrodialytic method and also to evaluate the removal rate of the two heavy metals. The sediment was suspended in distilled water during application of current. Both heavy metals were removed successfully. The Cu concentration was reduced from 97 to 16mg/kg and the Cd concentration was reduced from 0.55 to 0.03mg/kg after 28 days with an applied current density of 1.2mAcm(-2). However, it was seen that the removal rate decreased considerably after 3 days with an applied current density of 0.5mAcm(-2) and the major part of the two heavy metals was removed during the first 3 days (the Cu concentration was reduced with 74% and the Cd concentration with 80%). Thus a large reduction in concentrations can be obtained relatively fast. During the process of electrodialytic treatment the sediment suspension is acidified and reaches pH 2 after about 3 days (with 0.5mAcm(-2)), where it stabilizes. A comparison with chemical extraction in HNO(3) at about the same pH showed that 50-70% more Cu and 11% more Cd was removed during the electrodialytic treatment.     

Magnetic Proximity Effects in V/Fe Superconductor/Ferromagnet Single Bilayer Revealed by Waveguide-Enhanced Polarized Neutron Reflectometry

Polarized neutron reflectometry is used to study the magnetic proximity effect in a superconductor/ferromagnet (SC/FM) system of composition Cu(32 nm)/ V(40 nm)/Fe(1 nm)/MgO. In contrast to previous studies, here a single SC/FM bilayer, is studied and multilayer artefacts are excluded. The necessary signal enhancement is achieved by waveguide resonance, i.e., preparing the V(40 nm)/Fe(1 nm) SC/FM bilayer sandwiched by the highly reflective MgO substrate and Cu top layer, respectively. A new magnetic state of the system was observed at temperatures below 0.7T _C manifested in a systematic change in the height and width of the waveguide resonance peak. Upon increasing the temperature from 0.7T _C to T _C, a gradual decay of this state is observed, accompanied by a 5% growth of the diffuse scattering. This behavior can be explained in a natural way by the polarization of the superconducting electrons upon the SC transition, i.e., an appearance of additional induced magnetization within the SC, due to the proximity of the FM layer.     

Feasibility of pressurization to speed up enzymatic hydrolysis of biological materials for multielement determinations

The feasibility of pressurized solvents (liquids at a high pressure and/or high temperature without the subcritical point being reached) has been newly investigated to accelerate enzymatic hydrolysis processes of mussel tissue for multielement determinations. The target elements (Al, As, Cd, Co, Cu, Fe, Hg, Li, Mn, Pb, Se, Sr, V, and Zn) were released from dried mussel tissue by action of two proteases (pepsin and pancreatin), and they have been evaluated by inductively coupled plasma optical emission spectrometry (ICP-OES). Variables inherent to the enzymatic activity (pH, ionic strength, temperature, and enzyme mass) and factors affecting pressurization (static time, pressure, and number of cycles) were simultaneously studied by applying a Plackett-Burman design (PBD) as the screening method. Results showed that pH, ionic strength, and temperature were the most statistically significant factors (confidence interval of 95%) under pressurized conditions for pepsin, while pH and ionic strength affected pancreatin activity. This means that metal extraction is mostly attributed to enzymatic activity. The static time (enzymatic hydrolysis time) was found statistically nonsignificant for most of the elements, meaning that the hydrolysis procedure can be finished within a 2-15 min range. For pepsin, optimized conditions (pH 1.0, temperature 40 degrees C, pressure 1500 psi, static time 2 min, and number of cycles 3) gave quantitative extractions for As, Cd, Co, Cu, Hg, Li, Mn, Pb, Se, Sr, V, and Zn. The pepsin mass was 0.05 g, and the solution was Milli-Q water at pH 1.0 (adjusted with hydrochloric acid). For pancreatin, quantitative recoveries were only reached for As, Cd, Cu, Li, Pb, and Sr at room temperature, at a pressure of 1500 psi, for a static time of 2 min and a number of cycles of 3. The extraction solution was a 0.3 M potassium dihydrogen phosphate/potassium hydrogen phosphate buffer at a pH of 7.5 working at room temperature. Around 0.5 g of diatomaceous earth was used as dispersing agent for hydrolyses with either enzyme. Analytical performances, such as limits of detection and quantification and repeatability of the overall procedure, have been established. Finally, accuracy of the methods was assessed by analyzing seafood certified reference materials (GBW-08571, DORM-2, DOLT-3, TORT-2), fatty tissues certified reference materials (BCR 185, NIST 1577b), and fibrous certified reference materials (BCR 62, GBW-08501).     

Ultramicroband array electrode. 1. Analysis of mercury in contaminated soils and flue gas exposed samples using a gold-plated iridium portable system by anodic stripping voltammetry

The applicability of a gold-plated iridium Nano-Band array ultramicroelectrode (6 microm by 0.2 microm, 64-microm interspacing, 100 electrode bands) in the analysis of mercury using a portable system is demonstrated by anodic stripping voltammetry in real-life samples. Optimized measurement parameters, 0.1 M HCl electrolyte, plating potential of 0 mV, and staircase scan mode were identified. The dynamic linear range is 10-180 ppb at 5-s deposition time with 1.5 microC of gold plated. The experimental detection limit for Hg2+ in 0.1 M HCl was 0.5 ppb at a deposition time of 4 min and a scan rate of 10 V/s. Real-life samples, such as flue gas exposed samples from flue gas simulators could be analyzed within 5 min using the method of standard additions. We identified a field-portable extraction procedure for soil samples using 1:1 concentrated HNO3/30% H2O2 mixture, compatible with ASV and the iridium electrode. The detection limit for soils is 1 ppm. The results obtained using ASV are in good agreement with reference values using cold vapor atomic absorption for the sample matrixes studied here. To our knowledge, this is the first mercury application using a reusable iridium array ultramicroelectrode. The portable potentiostat is less than 500 g, and together with the portable digestion method, makes the Nano-Band Explorer system field applicable.     

Nanostructured electrochemical sensors based on functionalized nanoporous silica for voltammetric analysis of lead, mercury, and copper

We have successfully developed electrochemical sensors based on functionalized nanostructured materials for voltammetric analysis of toxic metal ions. Glycinylurea self-assembled monolayers on mesoporous silica (Gly-UR SAMMS) were incorporated in carbon paste electrodes for the detection of toxic metal ions such as lead, copper, and mercury based on adsorptive stripping voltammetry (AdSV). The electrochemical sensor yields a linear response at a low ppb level of Pb2+ (i.e., 2.5-50 ppb) after a 2-min preconcentration period, with reproducible measurements (%RSD = 3.5, N = 6) and an excellent detection limit (1 ppb). By exploiting the interfacial functionality of Gly-UR SAMMS, the sensor is selective for the target species, does not require the use of a mercury film, and can be easily regenerated in dilute acid solution. The rigid, open, parallel pore structure, combined with suitable interfacial chemistry of SAMMS, also results in fast analysis times (2-3 min). The nanostructured SAMMS materials enable the development of miniature sensing devices that are compact and low cost, have low energy consumption, and are easily integrated into field-deployable units.     

Reliability evaluation of nano-bi/silver paste sensor electrode for detecting trace metals

The reliability of sensor characteristics for a nano-bismuth (Bi)/silver (Ag) paste electrode has been investigated by comparison with Hg/Bi film electrodes in terms of accuracy and precision. Using Ag paste instead of carbon paste as a conducting layer, the sensitivity and detection limit of the sensor electrode were more enhanced due to a lower electrical conductivity of Ag. For the evaluation of detecting ability, the Zn, Cd, and Pb ion concentrations of the prepared standard solutions were experimentally measured on Hg film, Bi film, and nano-Bi electrodes using anodic stripping voltammetry. A nano-Bi electrode can detect Zn, Cd, and Pb ions at 0.1 ppb with higher precision and accuracy compared with Hg film and Bi film electrodes. From the trace analyses of Zn, Cd, and Pb ions in commercial drinking water and river water using a nano-Bi electrode and inductively coupled plasma (ICP) technique, it was concluded that the nano-Bi electrode exhibited excellent sensing characteristics with high reliability, and could detect even traces of Zn, Cd, and Pb ions that were not detected by the ICP method.     

Low Blank Preconcentration Technique for the Determination of Lead, Copper, and Cadmium in Small-Volume Seawater Samples by Isotope Dilution ICPMS

A simple low-blank method is described for the analysis of Pb, Cu, and Cd in seawater using Mg(OH)(2) coprecipitation and isotope dilution inductively coupled plasma mass spectrometry (ICPMS). Here, 20-40 μL of 9 M aqueous NH(3) is mixed into a 1.3 mL seawater sample spiked with enriched isotopes of Pb, Cu, and Cd. After centrifugation, the supernatant is discarded and the Mg(OH)(2) precipitate dissolved in 100 μL of 5% HNO(3) for ICPMS analysis. This method is simple, accurate, and precise, with detection limits of Pb = 1.3 pM, Cu = 39 pM, and Cd = 5.0 pM and blanks of Pb = 0.62 pM, Cu = 27 pM, and Cd = 6.0 pM. The method is demonstrated by oceanographically consistent profiles of these trace metals at an ocean station in the eastern North Atlantic.     

Aging and wear resistant characterization of al-5Mg-X(Si, Cu, Ti)/SiCp composites produced by pressureless infiltration method

The effects of SiC particle size and alloy elements such as Si, Cu and Ti on the response to aging treatment and wear resistance in Al-5Mg-X(Si,Cu,Ti)/SiCp composites fabricated by pressureless infiltration method have been investigated by hardness tester, scanning electron microscope (SEM), X-ray diffractometer (XRD), differential scanning calorimetry (DSC) and wear tester. The Al-5Mg-0.3Si-0.1Cu-0.1Ti/SiC_P composites had better wear resistance property among Al-5Mg-X(Si,Cu)/SiC_P composites. The wear resistance property of all the composites was enhanced after aging at 170°C for 8 hrs due to precipitates of '(Mg₂Si) phase. The wear resistance property of the composite as-fabricated with 50 m size of SiC particle is superior to that of the composite as-fabricated with 100 m SiC size of particle. In Al-5%Mg alloy aged at 170°C for 8 hrs, the frictional seizure appeared more than abrading speed of 1.90 m/s, but in Al-5Mg-(Si,Cu,Ti)/SiC_P composites aged at 170°C for 8 hrs, the frictional seizure was not found at abrading speed ranging from 0.5 m/s to 4.3 m/s.     

Determination of cadmium rich corner of Cd–Cu–Zn,Cd–Cu–Mg,and Cd–Cu–Pb phase diagrams

Abstract

The liquidus temperatures along the monovariant trough running from the Cd–Cu–Cd₃ eutectic in each of the systems Cd–Cu–Zn, Cd–Cu–Mg, and Cd–Cu–Pb were determined using thermal and microstructural analyses. The solidus temperatures in the Cd–Cu–Mg system were also determined using thermal analysis. Alloys of monovariant composition in the Cd–Cu–Zn and Cd–Cu–Mg systems were found to have higher liquidus temperatures than the binary eutectic, indicating that the monovariant trough in these systems slopes down towards the binary eutectic. In the Cd–Cu–Pb system the liquidus temperatures along the monovariant were found to be lower than that of the binary eutectic. For the Cd–Cu–Zn system the present results are at variance with an earlier investigation.

MST/579     

Rapid diagnostic barcode system for codetection of multiple protein markers

An ultrasensitive immunodiagnostic readout method based on an electrochemical analysis is presented. Different inorganic quantum dot (QD) nanocrystals (ZnS, CdS, and PbS) are tagged to antibodies for the on-site voltammetric stripping measurements of multiple antigen targets. The multiprotein electrical sensing capability is coupled to the amplification feature of anodic stripping voltammetric transduction and with an efficient magnetic removal (to minimize nonspecific adsorption and cross-reactivity effects). Sandwich-immunoassay formats were performed using model proteins (/spl beta//sub 2/-microglobulin, myoglobin, and human serum albumin). These encoding QD tracers with distinct redox potential yield highly sensitive and selective stripping peaks at -1.11 V (Zn), -0.67 V (Cd), and -0.52 V (Pb) at the mercury-film screen printed carbon electrode (versus Ag/AgCl reference). The position and size of these peaks reflect the identity and risk level of the corresponding antigen marker. The favorable signal-to-noise characteristics of the response for the initial 25-ng/mL mixture indicate a detection limit of ca. 10 ng/mL far below the early warning range and allow a reliable determination of very low protein concentrations. Such analog peaks of the QDs were converted to simple and rapid barcode signals. The digital readout system can code 215 electrically tuned barcodes to mark different protein analytes and to be useful for a wireless communication system.