The use of impregnated filters to collect traces of gases in the atmosphere : Part ii. collection of sulfur dioxide on membrane filters

HA and AA Millipore filters impregnated with 5% potassium bicarbonate and dried were found to be suitable for sampling concentrations of sulfur dioxide in air. The impregnation technique and filter loadings are described; flow rates are relatively unaffected by impregnation. The apparatus and procedures used for preparation and sampling known concentrations of sulfur dioxide in air are described. Comparisons of actual and theoretical concentrations in the 0.1 to 10 p.p.m. range showed that the concentrations prepared must be assayed.The collection efficiency of impregnated filters was evaluated for sodium tetrachloromercurate-(II) (less than 10% which is in contrast with the 100% efficiency found with TCM as a scrubbing solution) and potassium bicarbonate (greater than 95%). The capacity of the filters was such that sampling a 10 p.p.m. sample for at least 1 h is possible.     

Preparation of immobilized glucose oxidase membrane by the plasma polymerization technique

Glucose oxidase was immobilized on a Millipore (MP) filter by coating with plasma-polymerized propargyl alcohol. The resulting immobilized enzyme membrane was used as a glucose sensor. The properties as a glucose electrode system were evaluated by amperometric response with either the steady-state method or the reaction rate method. The response was proportional to concentrations of the glucose solution up to 2 mM and the sensitivity was dependent on the amount of GOD impregnated into the MP filter.     

Application of an improved method for measurements of gaseous nitric acid in the nonurban atmosphere

Summary A modified filter technique to separate particles and gaseous HNO₃ is described, which is based on the use of filters of the Millipore FPLG type in combination with a virtual impactor. It enables routine measurements of gaseous HNO₃ in the atmosphere at background levels. Some results of measurements both in the marine background and over rural and semi-rural continental regions are presented.     

Non-destructive multi-element photonactivation analysis of environmental materials

A non-destructive method of photon-activation analysis with 30-MeV bremsstrahlung followed by high-resolution gamma-spectrometry has been developed for multi-element determination in ambient air and in air-pollution emissions. The sample materials were the NBS standard reference material. Fly Ash. and atmospheric particulates collected on a Millipore filter. Simultaneous irradiation of the sample with synthetic multi-element standards containing 33 elements has shown that the technique can determine up to 21 elements in a single sample. The method is simple and gives reproducible results.     

Determination of trace metals in water using x-ray fluorescence spectrometry

A simple, rapid and accurate method for water analysis is proposed. The analytical procedure for the determination of Fe, Mn, Zn, Cu, Cd, As, Pb and Se in water in concentrations as low as a few ppM involves precipitation with a carrier of the metals by diethyldithiocarbamate (DDTC) or 1-(2-pyridylazo)-2-naphthol (PAN) and filitration through a Millipore filter. The precipitates collected on the filter disc are examined by X-ray fluorescence analysis. PAN is excellent for the determination of several metal ions at the ppM level, and DDTC can be used with tartrate as a masking agent if water samples contain large amounts of iron(III).     

Brain gangliosides: an improved simple method for their extraction and identification

Total ganglioside extracts prepared from brain tissue were concentrated either by dialysis against Carbowax or by employing Millipore filter cones. Thin-layer chromatography was then carried out using silica gel plates. After location of the various fractions quantitation was effected by direct densitometry. The methods that have been adopted are rapid and suitable for the study of brain gangliosides in post mortem and biopsy material in a clinical chemistry laboratory.     

Sample collection,filtration and preservation protocols for the determination of 'total dissolved' mercury in waters

The objective of the work carried out was to recommend protocols for the collection, filtration (0.45 microm) and preservation of surface water samples for the subsequent determination of total 'dissolved' Hg. Cold vapour (CV) ICP-MS was employed to determine Hg; samples were acidified to a strength of 4 mol l(-1) HCl and 1% NaBH4 was used as the reducing agent in-line. Four types of 125 ml bottles were studied (Teflon, fluorinated ethene propene copolymer, FEP; high density polyethylene, HDPE; polyethylene terephthalate copolyester, PET; polypropylene, PP), together with three cleaning methods (EPA Methods 1631, 1638 and a rinse with reverse osmosis deionised water, 'MilliQ'). The transmission properties of the four materials were also studied to evaluate the potential for contamination from atmospheric Hg0. Results of this bottle study (n = 195), all below the detection limit of 0.5 ng l(-1), indicate that the bottles of choice, from an economic and time-saving perspective, are HDPE and PP, the latter being preferable if the sample is to be stored in a contaminated atmosphere. The bottles would be used on a once-only basis, negating the need for labourious and costly cleaning on repeat use. A simple rinse with MilliQ water would suffice prior to use. Twelve 0.45 microm filter systems (mostly Millipore and Gelman) were studied for (a) their potential Hg contamination properties and (b) their retention of Hg, possibly in colloidal form, during filtration. Ottawa River water, spiked at 50 ng l(-1) Hg, was used as a control sample. Again blank values were all negative, indicating contamination was not a concern but different recoveries of Hg were obtained across the different systems. The optimum systems to use, in that they provided maximum recovery (ca 80%) of Hg, are the Millipore Sterivex capsule and the Millipore Millex disc, both based on the hydrophilic Durapore membrane. The lowest recoveries (23-36%) were found with the Gelman AquaPrep systems and the Millipore HN nylon filter. Four control samples, Ottawa, Rideau and Gatineau Rivers, and a MilliQ blank, were used to study three preservation approaches, in the media: 0.5% BrCl, 2% HCl and 0.04% K2Cr2O7 in 1% HNO3. Mercury was stable for 28 days in a medium of 0.5% BrCl in all four samples but the other two media showed a loss of up to ca 20% Hg over this time frame, the loss being sample and time dependent. This may be a species transformation which is not detected by CV-ICP-MS from an HCl medium but this requires further investigation. Mercury was stable over the 28 days in the spiked blank MilliQ sample for all three preservation media.     

Trace element analysis of waters by X-ray emission spectroscopy

X-ray emission spectroscopy is a rapid, simple and accurate method for multielement trace analysis of water. This is accomplished by trace elements precipitation with a nonspecific chelating agent APDC (ammonium-1-pyrollidine dithiocarbamate) and filtration through a Millipore filter. In that way the uniform targets suitable for X-ray analysis were made and elements in concentrations as low as few ppb could be determined. APDC chelation over broad pH ranges for different elements in seawater is discussed. The best pH range for simultaneous determination of these elements is found. Results of analysis of seawater samples taken near the island Krk in the Adriatic sea are presented.     

Measurement of active pore size distribution of microporous membranes - a new approach

The active pore size distribution of a Millipore MF-VS membrane filter was studied by a new, recently developed, measurement method. The effect of absolute pressure and equilibration time (the amount of time during which the tested sample was allowed to equilibrate with the gas phase under a given set of conditions) on the resultant pore size distribution profiles was investigated. The results indicate that a drastic reduction in time needed to measure the active pore size distribution by this new method is made possible by performing the measurement at subatmospheric pressures in the range 40-80 mmHg. Apparently with equilibration times of not more than 15-20 min correct pore size distribution profiles may be obtained at these lower absolute pressures.     

Determination of total mercury in workroom air by atomic absorption or x-ray fluorescence spectrometry after collection on carbon-loaded paper

The routine determination of total mercury in workroom air of an alkali chloride electrolysis plant equipped with mercury cells, is described. The procedure is based on atomic absorption spectrometry (a.a.s.) (cold vapour technique) or x-ray fluorescence spectrometry (x.r.f.s.) after collection on carbon-loaded paper fixed in a disposable Millipore filter holder. The lowest quantity of mercury that can be determined is 0.2 μg by a.a.s. and 2 μg by x.r.f.s. Samples taken in the plant gave a relative standard deviation of about 2 % for a.a.s. and 3 % for x.r.f.s.     

Synthesis of N-methyl and N-11C-methyl spiperone by phase transfer catalysis in anhydrous solvent

Spiperone, a butyrophenone neuroleptic drug, has been used in binding studies of dopamine receptors. L?ngstr?m et al. developed N-11C-methyl spiperone, and, in cooperate with Wagner et al., made it possible to visualize the distribution of dopamine receptors in the human brain in vivo. In this paper, we independently developed another synthetic method of N-11C-methyl spiperone using the phase transfer catalyst in an anhydrous solvent. Separation of the product is feasible only by passing the reactant solution through a Millipore filter and injecting it onto high pressure liquid chromatography (HPLC). The time required for the synthesis and purification of N-11C-methyl spiperone from 11C-methyl iodide and spiperone was 20 min. Radiochemical yield exceeded 35% against 11C-methyl iodide without correcting decay of the radioactivity.     

Extraction of hyaluronic acid (HA) from rooster comb and characterization using flow field-flow fractionation (FlFFF) coupled with multiangle light scattering (MALS)

Hyaluronic acid (HA) was extracted in a relatively large scale from rooster comb using a method similar to that reported previously. The extraction method was modified to simplify and to reduce time and cost in order to accommodate a large-scale extraction. Five hundred grams of frozen rooster combs yielded about 500?mg of dried HA. Extracted HA was characterized using asymmetrical flow field-flow fractionation (AsFlFFF) coupled online to a multiangle light scattering detector and a refractive index detector to determine the molecular size, molecular weight (MW) distribution, and molecular conformation of HA. For characterization of HA, AsFlFFF was operated by a simplified two-step procedure, instead of the conventional three-step procedure, where the first two steps (sample loading and focusing) were combined into one to avoid the adsorption of viscous HA onto the channel membrane. The simplified two-step AsFlFFF yielded reasonably good separations of HA molecules based on their MWs. The weight average MW (M(w) ) and the average root-mean-square (RMS) radius of HA extracted from rooster comb were 1.20×10(6) and 94.7?nm, respectively. When the sample solution was filtered through a 0.45?μm disposable syringe filter, they were reduced down to 3.8×10(5) and 50.1?nm, respectively.     

In situ 3D characterization of membrane fouling by yeast suspensions using two-photon femtosecond near infrared non-linear optical imaging

In situ non-invasive 3D characterization of membrane fouling was achieved using femtosecond near infrared non-linear optical imaging together with a novel crossflow filtration module. Washed fluorophore-labelled yeast suspensions were filtered through Millipore 0.22 μm mixed cellulose ester membranes and the fouling layer was imaged at different times throughout the experiment.

Based on the 3D femtosecond images, it has been possible to identify fine structural features of the cake and to measure the thickness of the filter cake formed on the microfiltration (MF) membranes. Our findings reveal that low concentration feeds result in the initial formation of a patchy monolayer of cells leading to a multilayered cake, whilst at higher concentrations a multilayer cake forms rapidly. For patchy cakes, the technique offers greater resolution than that which is achievable with the direct observation through membrane technique. Deposited cell aggregates and broken fragments of cells can clearly be imaged. For thick cakes, it has been possible to image up to depths 45 μm below the cake surface in the present work.     

Transcellular transport of low density lipoprotein through cultured newborn rat skin epidermal cell monolayer

Epidermal cells from newborn rat skin were cultured on type IV collagen-coated Millipore filter, and the transport of low density lipoprotein (LDL) labeled with Rhodamine B isothiocyanate (RB-LDL) through the cultured cell layer was examined. The transport of RB-LDL was dependent on temperature and biological energy. The transport was low at 17 degrees C, but above 20 degrees C, it became high with increase in temperature up to 37 degrees C. The transport was markedly inhibited by the energy inhibitors 2-deoxyglucose and NaN3. Furthermore, the transport was saturable at the RB-LDL concentration of about 300 micrograms/ml and the activation energy of the transport was determined as 104.6 kJ/mol. No degradation product of LDL (apoprotein B) was observed during LDL transport through the cultured cell layer. The transport of RB-LDL through skin epidermal cells in culture is suggested to be mediated by transcytotic vesicles, but not by endocytosis and exocytosis via the lysosomal system, nor through cellular junctions.     

Some comments on the applicability of gas permeation methods to characterize porous membranes based on improved experimental accuracy and data handling

The measurement of the gas permeability coefficient as a function of the mean pressure across a membrane can be used to determine a mean pore radius of the membrane. This method has been applied by several authors to characterize microporous and asymmetric ultrafiltration or hyperfiltration membranes. This paper shows how the data acquisition and handling are improved. Experiments are performed on microporous Millipore membranes with a nominal pore radius of 50 nm and on ultrafiltration merebranes of poly(2,6-dimethyl-1,4-phenyleneoxide) with an expectedly sharp pore-size distribution around 2 nm. For the Millipore membrane an unexpected dependence of the calculated pore radius on the type of gas used in the experiment has been found. Measurements on the ultrafiltration membranes indicate that the viscous flow contribution to the permeability coefficient cannot be determined with sufficient accuracy. It is concluded that application of the gas permeation method has some limitations which were not previously recognized.     

Simultaneous determination of traces of iron, cobalt, nickel, copper, mercury and lead in water by energy-dispersive x-ray fluorescence spectrometry after preconcentration as their piperazino-1,4-bis(dithiocarbamate) complexes

A bidentate chelating agent has been proposed to preconcentrate seven metal ions dissolved in an aqueous sample for their simultaneous determination using energy-dispersive x-ray fluorescence spectrometry. The metal ions are precipitated as their polymeric piperazino-1,4-bis(dithiocarbamate) chelates, which are then collected by vacuum filtration on a Millipore membrane filter for direct examination by x-ray fluorescence analysis. Iron, cobalt, nickel, copper and zinc are determined by means of their K x-rays and mercury and lead by means of their L x-rays. A detection limit in the μg1⁻¹ range can be achieved for all metals tested in 250-ml water samples with a counting time of 600 s. Effective precipitation of all metals occurs at pH 6–7. The recoveries of eight analyses of the metals in a multielement standard using the proposed method ranged from 97 to 105% and the precision ranged from 2.3 to 3.1%. High concentrations of calcium and magnesium do not interfere with the method. The method is simple, sensitive and accurate, and has been used for the simultaneous determination of the seven metals under study in environmental samples and synthetic mixtures.     

Oxidation of glucose to gluconic acid by glucose oxidase in a membrane bioreactor

Glucose oxidase (GO) (EC 1.1.3.4) was used as catalyst for oxidizing glucose into gluconic acid utilizing a 10-mL Bioengineering Enzyme Membrane Reactor® or a 400-mL Millipore Stirred Ultrafiltration Cell (MSUC) coupled with a Millipore UF membrane (cutoff of 100 kDa) and operated for 12 h under an agitation of 100 rpm, pH 5.5, and 30°C. The effect of feeding rate (0.10, 0.15, or 0.20 min^?1), glucose (2.5 or 5.0 mM), and GO (1.0 or 2.0 mg/mL) concentrations on the catalysis were studied. A yield of about 75% was attained when the MSUC filled with 1.0 mg/mL of GO was fed with 2.5 mM glucose solution at a rate of 0.15 min^?1.     

Distribution and determination of Pb, Cd, Bi and Cu in the sea brine system: solution--colloidal particles--biota

The distribution of Pb, Cd, Bi, and Cu in Black Sea brine system (solution--colloidal particles--biota) produced in Burgas and Pomorie salterns is studied. The established distribution of the title elements among the brine components is as follows: Pb--25% in the salt solution, 30%--in colloidal particles, 45%--in biota (Halobacterium salinarium and microalgae Dunaliela salina); Cu--30% in the salt solution, 22%--in colloidal particles, 48%--in biota. Cd and Bi are not detected in biota. They are uniformly distributed (50%: 50%) between the salt solution and colloidal particles. Two procedures for analysis are developed. The first one is designed for determination of the total content of the studied metals in brine. It involves elimination of the biota interference by addition of ethanol, extraction and pre-concentration of the metals with NaDDC into CCl4 followed by FAAS determination. The second procedure intends determination of the elements in the separate components of the brine. It involves separation of the colloidal particles through centrifugation, separation of the studied elements from the resulting solution as dithiocarbamate complexes on a Millipore filter, dissolution of the retained metal species and subsequent FAAS analysis.     

碳纳米管对羟基磷灰石基复合材料力学性能的影响

将力学性能优良的碳纳米管(CNTs)与羟基磷灰石(HA)生物陶瓷相复合,发展CNTs/HA复合材料来应用于骨组织修复领域,有望解决HA生物陶瓷力学性能的不足。通过3种不同的制备方法,即通过表面活性剂将CNTs分散在HA基体中、通过酸碱中和反应将CNTs与HA共沉淀以及通过体外浸泡在CNTs上矿化生长HA等方法来获得CNTs/HA复合材料。深入研究CNTs的表面结构和分散状态对CNTs/HA复合材料力学性能的影响。结果表明,CNTs的添加改变了HA的脆性,导致复合材料抗压力学性能得到提高。但是,由于复合材料制备方法的不同,导致CNTs在HA基体中的分散状态、表面结构的完整性以及与HA的界面结合情况不同,导致其抗压力学性能不同。其中,通过表面活性剂将CNTs分散在HA基体中而获得复合材料的抗压力学性能表现最好,而CNTs与HA通过共沉淀法所获得复合材料的抗压力学性能表现最差。