Nina Jensen

Electrostatic spraying: a novel technique for preparation of polymer coatings on electrodes.

A liquid flow emerging from a tip or a thin tube under the influence of a strong electric field will, due to charging of the dielectric liquid, break up into small droplets. Thus, if a polymer material is dissolved in the liquid, this electrodeposition technique can be utilized for producing polymer coatings on electrodes. The method was applied for in situ formation of ultrathin (∼3000 Å) cellulose acetate (CA) phase inversion membranes on glassy carbon electrodes. The purpose of the membrane was to protect the electrode surface from fouling by macromolecular species. The spraying liquid consisted of CA, acetone, and aqueous magnesium perchlorate as pore former, and the spraying voltage was 14 kV. Profilometric measurements showed that the thickness of the spray-cast membranes was much more uniform than that of similar membranes formed by solvent casting. By using cadmium and lead as test analytes and differential pulse anodic stripping voltammetry as detection method, it was found that the membranes prepared by spray casting offered better protection against interference from poly(ethylene glycol) (PEG) 6000 than those prepared by solvent casting. Also, the interference from PEG 2000 was significantly reduced. Experimental details of the electrostatic spraying technique are given.

Suppression of surfactant interferences in anodic stripping voltammetry by sodium dodecyl sulfate

Abstract It was investigated whether interferences from surfactants in anodic stripping voltammetry (ASV) could be remedied by the anionic surfactant sodium dodecyl sulfate (SDS) which causes little or no interference in itself. Cadmium and lead were used as test analytes, and measurements were performed in acetate buffer as well as in 0.1 M HNO3. One hundred parts per million of the interfering surfactant was added. SDS eliminated severe interference from the non-ionic surfactants Triton© X-100 and dodecyl octaethylene glycol ether as well as from the polymer polyethylene glycol 6000 and from the cationic surfactant cetyl trimethyl ammonium bromide. SDS could not remedy the extraordinarily severe interference from the cationic surfactant cetyl pyridinium chloride. Two anionic surfactants were also tested as interferents but they had little detrimental effect on the ASV signals. The effect of SDS was explained by the formation of mixed micelles which scavenge the interferent in the bulk solution and by competitive displacement of the interferent at the electrode surface.

Signal stability of Nafion-coated thin mercury film electrodes for stripping voltammetry

The signal stability of the Nafion-coated thin mercury film electrode (NCTMFE) was studied by using cadmium and lead as test analytes and differential pulse anodic stripping voltammetry as detection method. In particular, the effect of the casting solvent and the curing procedure employed in the preparation of the polymer film was examined. Best results were obtained with N,N-dimethylacetamide as casting solvent and a two-step curing procedure in which the polymer was evaporated to dryness at 55 degrees and cured at 105 degrees with a hot-air gun. Mercury plating was performed ex situ. An NCTMFE prepared in this manner has a better signal stability than ex situ-plated as well as in situ-plated conventional mercury film electrodes.

Use of sodium dodecyl sulfate as an antifouling and homogenizing agent in the direct determination of heavy metals by anodic stripping voltammetry

The effectiveness of the anionic surfactant sodium dodecyl sulfate (SDS) for suppressing adsorption interferences in anodic stripping voltammetry (ASV) was investigated. The samples included fruit juices, wine, beer, milk powder and waste water, and the analytes were cadmium, lead and copper. In most of the samples, the ASV signals were severely depressed or even absent due to electrode fouling, but addition of SDS in concentrations up to 10 g L(-1) proved effective in restoring the ASV response. By using SDS as an interference suppressor, the content of lead and copper in a milk powder reference material was determined, and the results were in agreement with the certified values. In this determination, which could not have been performed without SDS, the surfactant also served as a homogenizing agent, preventing separation of the sample components. The effect of SDS was explained by the interaction of the surfactant with the electrode surface and with the constituents of the sample matrix.

Regulation of cell proliferation and cell density by the inorganic phosphate transporter PiT1

AbstactBackgroundThe inorganic phosphate (Pi) transporter, PiT1 (SLC20A1), is ubiquitously expressed in mammalian cells. It has previously been shown that down-regulation of PiT1 severely impaired the proliferation of two transformed human cells lines, HepG2 and HeLa, and the tumorigenicity of HeLa cells in nude mice. Moreover, PiT1 knock-out mice do not survive past E12.5 and from E10.5, the embryos were found to be growth-retarded and showed reduced proliferation of liver cells. Isolated mouse embryonic fibroblasts with knocked out as well as reduced PiT1 expression levels also exhibited impaired proliferation. Together these results suggest that a certain level of PiT1 is important for proliferation. We have here investigated the role of PiT1 in regulation of cell proliferation using two strictly density-inhibited cells lines, the murine MC3T3-E1 and NIH3T3 cells.ResultsWe found that knock-down of PiT1 in MC3T3-E1 cells led to impaired proliferation supporting that at least a certain level of PiT1 is important for wildtype level of proliferation. We, however, also observed that MC3T3-E1 and NIH3T3 cells themselves regulate their endogenous PiT1 mRNA levels with lower levels in general correlating with decreased proliferation/increased cell density. Moreover, over-expression of human PiT1 led to increased proliferation of both MC3T3-E1 and NIH3T3 cultures and resulted in higher cell densities in cultures of these two strictly density-inhibited cell lines. In addition, when we transformed NIH3T3 cells by cultivation in fetal bovine serum, cells over-expressing human PiT1 formed more colonies in soft agar than control cells.ConclusionsWe conclude that not only is a certain level of PiT1 necessary for normal cell division as suggested by previously published studies, rather the cellular PiT1 level is involved in regulating cell proliferation and cell density and an increased PiT1 expression can indeed make NIH3T3 cells more sensitive to transformation. We have thus provided the first evidence for that expression of the type III Pi transporter, PiT1, above the endogenous level can drive cell proliferation and overrule cell density constraints, and the results bridge previous observations showing that a certain PiT1 level is important for regulating normal embryonic growth/development and for tumorigenicity of HeLa cells.

Suppression of protein interferences in anodic stripping voltammetry by sodium dodecyl sulphate

The anionic surfactant sodium dodecyl sulphate (SDS) can effect desorption of proteins from surfaces, and this mechanism has been exploited for suppressing adsorption interferences in anodic stripping voltammetry (ASV). Using cadmium and lead as test analytes, and albumin and lysozyme as model interferents, it was found that ASV signals strongly depressed by proteins regain their initial magnitude (prior to protein addition) when SDS is added in a concentration above a threshold value. Also, SDS protected against protein interference when the surfactant was added prior to the protein. SDS in itself caused little or no interference.

Phase-inversion cellulose acetate membranes for suppression of protein interferences in anodic stripping voltammetry

The phase-inversion (PI) method was used to cast permselective cellulose acetate membranes on glassy carbon electrodes with the aim of suppressing protein interferences in anodic stripping voltammetry (ASV). By using cadmium and lead as test analytes and differential pulse ASV as detection method, it was found that the modification of the electrode greatly reduces the interference from albumin. Cellulose acetate membranes prepared by the PI method give better protection against protein interference and have more reproducible permeability characteristics than membranes of comparable thickness prepared by the base hydrolysis method. An optimization study of the PI coating procedure was undertaken.

Effect of the Pretreatment of Recast Nafion Membraneson Their Rejection of the Albumin Interferencein Anodic Stripping Voltammetry

The title subject was examined using cadmium and lead as test analytes and differential pulse anodic stripping voltammetry as detection method. Ultrathin (ca. 0.3 µm) Nafion coatings were deposited on glassy carbon by electrostatic spray deposition. This technique proved far superior to evaporative casting with respect to the uniformity of the polymer layer. Overall, it was found that the pretreatment of the Nafion coating had a major effect on the extent of the albumin interference. Swelling of the Nafion coating in nitric acid and lithium hydroxide significantly reduced albumin interference, whereas treatment with sodium hydroxide and cesium hydroxide did not have an effect. Heat treatment (140 °C) of Nafion in the H+ form worsened the albumin interference, and the same trend was seen for the Na+ and Cs+ forms but not for the Li+ form. These results show that the degree of albumin interference is determined not only by the permeability of the coating but also by adsorption onto the outer surface of the membrane. The experimental results are explained in terms of the conformational changes of Nafion induced by the pretreatments.

Annotation paper Interference by volatile nitrogen oxides in the determination of mercury by flow injection cold vapor atomic absorption spectrometry.

The determination of mercury by the title method with sodium tetrahydroborate as reducing agent can be interfered with by volatile nitrogen oxides which inhibit the reduction of mercury by scavenging the reducing agent. The nitrogen oxides are formed as reduction products of nitric acid during sample decomposition. The interference effect was encountered in the determination of mercury in sewage sludge digests, and the main symptom was poor reproducibility of the shape of the mercury peak. The area of the mercury peak is more resistant to the interference than the peak height. The nitrogen oxide interference did not cause any systematic error in the mercury determination when calibration was done by standard addition. The interference can be easily remedied by purging the sample with argon.

Primary Brain Calcification Causal PiT2 Transport-Knockout Variants can Exert Dominant Negative Effects on Wild-Type PiT2 Transport Function in Mammalian Cells

Primary brain calcification (PBC) is a neurodegenerative disorder characterized by calcium-phosphate deposits in the basal ganglia and often also other areas of the brain. The prevalent clinical manifestations are cognitive impairment, neuropsychiatric symptoms, and movement disorders. In recent years, monoallelic variants in SLC20A2, which encodes the type III sodium-dependent inorganic phosphate (Pi) transporter 2 (PiT2), have been linked to the familial form of PBC in 40–50% of the families reported worldwide as well as to sporadic cases of PBC. Further insight into the disease mechanism is, however, needed. Based on co-expression studies of wild-type and variant PiT2 in Xenopus laevis oocytes, the molecular disease mechanism associated with SLC20A2 missense variants has formerly been suggested to be haploinsufficiency. We have here used mammalian cells isolated from a Slc20a2−/− mouse and co-expression of human wild-type and variant PiT2. Two of the variants studied have both been reported twice in unrelated PBC cases: PiT2D28N in two sporadic cases and PiT2E575K in a familial and a sporadic case. We find that in mammalian cells, the analyzed SLC20A2 missense variants can exert their effect in a dominant negative manner resulting in decreased wild-type PiT2 Pi transport. Thus, compared to monoallelic lack of functional PiT2 protein expression, which reasonably points towards haploinsufficiency, certain SLC20A2 missense variants may be more detrimental for cellular Pi uptake and potentially contribute to an earlier disease onset and/or a more severe phenotype as observed for Slc20a2−/− mice compared to Slc20a2+/− mice.