An in situ study of metal complexation by an immobilized synthetic biopolymer using tapping mode liquid cell atomic force microscopy.

Near-field scanning optical microscopy and tapping mode, liquid cell atomic force microscopy were used to study the conformational changes in simple short-chain silica-immobilized biopolymer, poly(L-cysteine) (PLCys), as the polymer was exposed to reducing, metal-rich, and acidic environments, respectively, to simulate on-line metal preconcentration. In a reducing environment (0.01 M dithiothreitol in pH 7.0 ammonium acetate buffer), the PLCys features resembled islands on the surface of the glass, 36 +/- 7 nm in height and 251 +/- 60 nm in diameter. Upon exposure to metal (Cd2+ buffered at pH 7.0), the PLCys islands broke up into smaller metal binding clusters whose features were lower in height, 22 +/- 5 nm, and diameter, 213 +/- 53 nm. Exposure to 0.01 M HCl used for metal stripping resulted in protonation of the polymer chains and further reduction in the polymer height to 12 +/- 5 nm. These changes in molecular structure have given new insight into the mechanisms involved to achieve strong binding as well as rapid, quantitative release of bound metals to flexible short-chain synthetic biopolymers.

Comparison and evaluation of the synthetic biopolymer poly-L-aspartic acid and the synthetic "plastic" polymer poly-acrylic acid for use in metal ion-exchange systems.

Poly-L-aspartic acid (PLAsp), a biopolymer, and a similar synthetic polymer, poly-acrylic acid (PAA), each consisting of approximately 50 repeating Asp and acrylic acid monomers, respectively, were immobilized onto controlled pore glass (CPG) and evaluated for use as metal ion-exchange materials. Both polymers achieve metal complexation primarily through their repeating carboxylate side groups resulting in a similar binding trend for the metals tested (Ca(2+), Cd(2+), Co(2+), Cu(2+), Mg(2+), Mn(2+), Na(+), Ni(2+), Pb(2+)), with metal binding capacities ranging from <0.1 to 12 micromol metal/g column and <0.1 to 32 micromol metal/g column for PLAsp and PAA respectively. Cu(2+) and Pb(2+) exhibited strong binding to both materials, while the other metals demonstrated only weak or minimal binding. Both columns allowed for quantitative release of bound metals through acid stripping and experienced increased overall metal binding with increasing pH. Both systems also maintained similar structural and chemical stability when continuously exposed to neutral buffered, highly acidic, oxidizing, large molecule rich, and elevated temperature environments. The main differences between the two systems are the material cost and system biodegradability.

Thermophoretic collection and analysis of submicrometer ag particles emitted from a graphite tube-type electrothermal vaporizer.

Using thermophoretic collection with a cooled Cu probe, particles generated in an electrothermal vaporizer (ETV) from a AgNO(3) solution sample have been collected and analyzed using transmission electron microscopy and high-energy electron diffraction (HEED). Ag particles are spherical and, interestingly, have diameters falling into one of four size regimes, <5, 15, 25, and >40 nm. An extremely large number (estimated at >10(8)) of particles with diameters of <100 nm are collected. For an aqueous AgNO(3) solution deposited in the ETV, the HEED pattern of the collected aerosol particles exiting the pulse heated ETV matched body centered cubic Ag((s)), and the large number of diffraction spots suggests that particles are composed of microcrystalline domains. The features of the particles confirm earlier predictions of homonucleation as the primary particle formation mechanism. "Groupings" of apparently disconnected particles were a unique feature seen from the pulse-heated vaporization of the dried sample. This morphology is unique and does not appear like any other clustering or aggregation of particles reported elsewhere. It is not clear what causes this particle grouping, although the absence of these groupings when a 700 °C thermal pretreatment step was introduced suggests that the AgNO(3) decomposition plays a role in their formation. It is suggested that the particles formed from homonucleation are created very near the graphite surface and are cooled quite rapidly to form the solid silver particles. A mechanism is presented to explain the appearance of silver in the gas phase at temperatures below the vaporization temperature for silver metal.

Cadmium, copper and zinc complexes of poly-L-cysteine.

The metal complexes of poly-L-cysteine (PLC) were evaluated for their potential use in trace metal preconcentration and separation. Formation constants (log K) for the Cd2+ and Zn2+ complexes of PLC estimated by spectrophotometric titration were 8.0 +/- 0.8 and 9.5 +/- 0.5, respectively. The PLC sulfhydryl groups were most likely oxidized to disulfides by Cu2+, and binding of Cu+ with the molecule was expected. The moles of metal bound by PLC reflecting its strongest sites relative to a stable competing ligand for Cu2+ and Zn2+ were 1.4 and 0.40 mmol g-1 of PLC, respectively. The presence of Na+ (29 mmol l-1) or Ca2+ (0.5 mmol l-1) had no measurable effect on the amount of Zn-PLC complex formed.

Preconcentration of nickel and cobalt on algae and determination by slurry graphite-furnace atomic-absorption spectrometry.

Unicellular green algae have been utilized to preconcentrate Ni(2+) and Co(2+) ions from sea-water and riverine water samples. Studies have shown that rinsing the algae with 0.12M hydrochloric acid improves the adsorption of nickel and cobalt, and the optimum range of pH of extraction is wide. The maximum extraction efficiencies were 84 and 73% for Ni and Co, respectively, at ng/ml levels. The sea-water matrix and relatively small amounts of many impurities reduce the adsorption efficiency for both nickel and cobalt. The preconcentration is achieved by mixing 6 mg of algae with 50-100 ml of sample, and subsequently isolating the algae by centrifugation. The pellet of algae is then resuspended in 1 ml of 0.08M nitric acid, and analyzed as a slurry by graphite-furnace atomic-absorption spectrometry. The values found for nickel and cobalt in riverine (SLRS-1) and sea-water (CASS-1) standard reference materials are within the limits of certification.

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.

Metal oxide reduction: A low-temperature reaction with graphite in flameless atomic-absorption spectrometry.

The ability of graphite to reduce metal oxides to the free metal is discussed. Differential thermal analysis and X-ray photoelectron spectroscopy are used to investigate the reaction in the case of CuSO(4). The reduction process is shown to occur at temperatures which are low relative to the appearance temperature of Cu. Thew results suggest that the appearance temperature of the element is governed by the vapour pressure of the metal and not by the reduction process.