Multivariate optimization on flow-injection electrochemical hydride generation atomic absorption spectrometry of cadmium.

A novel electrochemical hydride generation (ECHG) system working in flow-injection (FI) mode was developed for determination of cadmium coupled to an electrically heated quartz tube atomizer (QTA) by atomic absorption spectrometry (AAS). A Plackett-Burman experimental design for screening has been used to evaluate the influence of several variables on the analytical response. Then, the significant parameters such as the concentration of NaCl in catholyte, applied electrolytic current and flow rate of carrier gas have been simultaneously optimized using a central composite design (CCD). Under the optimized conditions, the detection limit (3σ(b), n=9) was found to be 0.51 ng mL(-1) Cd and the relative standard deviation (RSD) for nine replicate analyses of 20 ng mL(-1) Cd was 6.5%. The calibration curve was linear in the range of 2-50 ng mL(-1) of Cd. The potential interferences from various ions were also evaluated. The analysis of a reference material showed good agreement with the certified value. The proposed method was successfully applied to the determination of Cd in tap water sample.

Electrochemical hydride generation of thallium.

An electrochemical hydride generation (ECHG) technique was developed to improve the determination of thallium by atomic spectrometry. The technique is based on the catholyte variation system for production of thallium hydride. Using Pb-Sn alloy as cathode, a transient peak shaped signal was achieved and its height, the maximum absorbance value, was taken as an analytical parameter. Parameters that might affect the hydride generation efficiency were investigated and the analytical performance of the method under the optimized experimental conditions was assessed. The linear range was 1-250 ng mL(-1) for thallium and the relative standard deviation of the method was 4.2% (RSD, n=7). The LOD for thallium was found to be 0.8 ng mL(-1), showing a significant improvement relative to conventional chemical hydride generation techniques. The proposed method was applied to the determination of thallium in unalloyed zinc standard reference material. This method offers high sensitivity, simplicity, rapidness, freeness from reagent and low acid consumption.

Mechanistic aspects of electrochemical hydride generation for cadmium.

The mechanistic aspects of a novel methodology for the electrochemical hydride generation (EcHG) of cadmium, entitled as the catholyte variation, have been studied. The hydrogen overvoltage of different cathode materials was determined in dilute electrolyte. The lead-tin alloy used as the cathode material for the EcHG of Cd had the highest hydrogen overpotential. In this technique, both electrolyte medium and cathode surface would change during electrolysis. The catholyte variation EcHG coupled with a flame heated quartz tube atomizer (QTA) atomic absorption spectrometer (AAS) produced peak-shaped transient signal of Cd. The analytical signal was significantly enhanced at neutralization time. The simultaneous production of lead and tin hydrides as well as the hydrogen at that time may speed up the desorption of cadmium species from the surface of the cathode. Also the high hydrogen overvoltage and the neutral medium aided the formation and separation of cadmium hydride molecules. The generated CdH2 vapour was kinetically stable.

Electrochemical hydride generation atomic absorption spectrometry for determination of cadmium.

An electrolytic hydride generation system for determination of another hydride forming element, cadmium, by catholyte variation electrochemical hydride generation (EcHG) atomic absorption spectrometry is described. A laboratory-made electrolytic cell with lead-tin alloy as cathode material is designed as electrolytic generator of molecular hydride. The influences of several parameters on the analytical signal have been evaluated using a Plackett-Burman experimental design. The significant parameters such as cathode surface area, electrolytic current, carrier gas flow rate and catholyte concentration have been optimized using univariate method. The analytical figures of merit of procedure developed were determined. The calibration curve was linear up to 20ngml-1of cadmium. The concentration detection limit (3σ, n=8) of 0.2ngml-1 and repeatability (relative standard deviation, n=7) of 3.1% were achieved at 10.0ngml-1. It was shown that interferences from major constituents at high concentrations were significant. The accuracy of method was verified using a real sample (spiked tap water) by standard addition calibration technique. Recovery of 104% was achieved for Cd in the spiked tap water sample.

Effect of cathodic electrolyte on the performance of electrochemical hydride generation from graphite cathode.

The classic silver diethyldithiocarbamate (SDDC) spectrophotometric procedure for arsenic determination has been used for investigation of the effect of cathodic electrolyte on the performance of electrochemical hydride generation (HG) from graphite cathode. The results of this study show that the presence of a soft metal ion such as Cd(II), Sn(II) and/or Zn(II) in the acidic cathodic electrolyte can increase effectively the efficiency of electrochemical hydride generation and decrease the effect of interferences. The possible mechanisms of these effects have been discussed in detail. The parameters related to the electrochemical hydride generation were investigated. Also the characteristic data of the electrochemical hydride generation and common hydride generation by NaBH(4) were compared. Under optimised conditions, the system is selective to As(III) and total inorganic analyses can be performed after a pre-reduction stage prior to electrochemical hydride generation. This will allow the differential determination of inorganic arsenic species. The method is appropriate to the determination of 4-40mug of each arsenic species.

Determination of mercury(II) ion by electrochemical cold vapor generation atomic absorption spectrometry.

A technique for determination of mercury is described; it is based on electrolytic reduction of Hg(II) ion on a graphite cathode, the trapping of mercury vapor and its volatilization into a quartz tube aligned in the optical path of an atomic absorption spectrometer. The electrochemical cell consisted of a graphite cathode and an anode operating with constant direct current for the production of mercury atoms. A pre-activated graphite rod was used as the cathode material. The optimum conditions for electrochemical generation of mercury cold vapor (the electrolysis time and current, the flow rate, the type of electrode and electrolyte) were investigated. The characteristic electrochemical data with chemical cold vapor using NaBH4-acid were compared. The presence of cadmium(II), arsenic(III), antimony(III), selenium(IV), bismuth(III), silver(I), lead(II), lithium(I), sodium(I) and potassium(I) showed interference effects which were eliminated by suitable separation techniques. The calibration curve is linear over the range of 5-90 ng ml(-1) mercury(II). The detection limit is 2 ng ml(-1) of Hg(II) and the RSD is 2.5% (n = 10) for 40 ng ml(-1). The accuracy and recovery of the method were investigated by analyzing spiked tap water and river water.

Inhibition of PDK-1 activity causes a reduction in cell proliferation and survival.

3-Phosphoinositide-dependent kinase-1 (PDK-1) was identified by its ability to phosphorylate and activate protein kinase B (PKB) in vitro [1,2] and can phosphorylate and activate additional protein kinases in the AGC family in vitro [3-6]. Its role in vivo has, however, only begun to be addressed. We used antisense oligonucleotides directed against PDK-1 expression to explore the role of PDK-1 in human glioblastoma cells (U87-MG), which express a mutant PTEN allele. Reduction in PDK-1 levels resulted in inhibition of PKB activity, and a reduction in phosphorylation on Thr308 and Ser473 of PKB. p70 S6 kinase (p70(S6K)) activity was also reduced. Cell proliferation was dramatically inhibited following treatment with PDK-1 antisense oligonucleotides, due to a combination of decreased cell doubling and an increase in apoptosis. This is in contrast to direct inhibition of phosphoinositide 3-OH kinase (PI 3-kinase), which results in G1 arrest with no effect on apoptosis. This study confirms both PKB and p70(S6K) as in vivo substrates for PDK-1. The effect of acute PDK-1 loss on cell proliferation and survival suggests the involvement of PI 3-kinase dependent and independent signaling events, and implicates PDK-1 as a potential therapeutic target for human neoplasms.

Genetic heterogeneity in ductal carcinoma of the breast.

Genetic heterogeneity in breast cancer has been observed both by cytogenetic and loss of heterozygosity (LOH) analyses; however, the frequency with which genetically heterogeneous clones arise is unknown. In this study, a panel of 115 breast carcinomas was analyzed to determine the extent of clonal divergence in tumor foci at progressive stages of tumor evolution. Intraductal, infiltrating, and metastatic tumor components were microdissected from each tumor and tested for LOH at 20 microsatellite markers on seven chromosomal arms. Of these cases, 24 (21%) demonstrated genetically divergent clones during tumor progression. Clonal divergence, inferred from discordant LOH patterns, was observed most commonly between intraductal and infiltrating tumor (18 cases), but was also demonstrated between infiltrating and metastatic tumor (11 cases). Discordant LOH was observed with markers on one chromosomal arm in 16 cases, on two in 7 cases, and on four in 1 case, and was observed most commonly with markers on 17p, 17q, and 16q. More detailed microdissection of four cases provided evidence for a specific chronology of genetic alterations occurring during the progression of each tumor. The results indicate that the different tumor components observed microscopically in breast cancer specimens often represent genetically divergent clones.

Evaluation of electrochemical hydride generation for spectrophotometric determination of As(III) by silver diethyldithiocarbamate.

A batch electrochemical hydride generation system was developed for the spectrophotometric determination of inorganic As(III) by silver diethyldithiocarbamate. This method is based on electrochemical reduction of As to Arsine (AsH(3)) in acidic media and on the subsequent reaction of AsH(3) with silver diethyldithiocarbamate to give an absorbing complex at 525 nm. The electrochemical generator consisted of a cathode cell separated from the anode cell by a porous glass frit and was operated with a constant direct current. A pre-activated graphite rod was used as cathode material for the production of AsH(3). The parameters related to the electrochemical hydride generation were investigated. Under optimized conditions, only As(III) can be converted to AsH(3) and a pre-reducing stage is required for total inorganic As analysis. The characteristic data of the electrochemical hydride generation and common hydride generation by NaBH(4) were compared. Also, the effects of interferences and their elimination were investigated. An absolute detection limit of 0.5 mug (3s(b)) and a concentration detection limit of 0.05 mug/ml were obtained using a 10 ml sample volume. The relative standard deviation for five replicate analysis of 30 mug As(III) was 1.2%. The accuracy and recovery of the method were demonstrated by analysing spiked artificial sea water and tap water.

Loss of heterozygosity on chromosome 11p15 during histological progression in microdissected ductal carcinoma of the breast.

Microdissection of histologically identifiable components from formalin-fixed, paraffin-embedded tissue sections allows molecular genetic analyses to be correlated directly with pathological findings. In this study, we have characterized loss of heterozygosity (LOH) at chromosome 11p15 at different stages of progression in microdissected tumor components from 115 ductal carcinomas of the breast. Microdissected foci of intraductal, infiltrating, and metastatic tumors were analyzed to determine the stage of progression at which LOH at 11p15 occurs. LOH was detected in 43 (37%) of 115 cases. Foci of intraductal carcinoma could be microdissected from 85 cases, of which 30 (35%) showed LOH at some stage of progression. LOH was detected in the intraductal component in 26 of these 30 cases. Interstitial deletions were characterized by using a panel of 10 highly polymorphic markers. The smallest region of overlap (SRO) for LOH at 11p15 was bounded by the markers D11S4046 and D11S1758. LOH at 11p15.5 showed no correlation with estrogen receptor status, the presence of positive lymph nodes, tumor size, histological grade, or long-term survival. We conclude that 11p15 LOH usually occurs early in breast cancer development but less frequently does not develop until the infiltrating or metastatic stages of tumor progression.

The preconcentration of mercury and methylmercury on dithizone-coated polystyrene beads.

The preconcentration of "inorganic" and methyl mercury cations from aqueous solution is described. The procedure involves collection of mercury on dithizone-coated macroreticular resin beads prior to analysis by cold-vapour atomic absorption spectroscopy. The beads are readily prepared before use and give rise to quantitative selective recovery of "inorganic" and methyl mercury from fresh and saline water samples.