Indirect atomic absorption spectrometric determination of mixtures of chloride and iodide by precipitation in an unsegmented flow system

Chloride and iodide are injected into a carrier silver nitrate and the precipitates formed are retained on a stainless-steel filter, so that total chloride and iodide can be determined by the decrease in the atomic absorption signal for silver. The silver chloride precipitate is subsequently dissolved with ammonia and chloride only is determined. Iodide is determined by difference. Mixtures of these anions at μg ml^?1 levels can be determined for chloride/iodide ratios from 7.5:1 to 1:60, with a sampling frequency of ca. 10 h^?1. Applications to the determination of chloride in foodstuffs and wines are described. Up to 10 samples per hour can be handled and 50–100 samples can be run before the filter must be cleaned.     

Röntgenfluorimetrische Bestimmung von Sulfidspuren im ppb-Bereich in wäßrigen Lösungen nach Austauschreaktion an dünnen Silberhalogenidschichten

Sulphide concentrations in the ppm and ppb range can be determined by X-ray fluorescence spectrometry in aqueous solutions with a volume up to 3 l. The solution to be analysed is passed through a thin layer of a silver halide precipitate whereby the sulphide ions are held back as silver sulphide. The membrane filter with the silver halide deposit is directly used for measuring the X-ray intensity from sulphur. The experimental conditions used include: 2?=23.20°, KAP, X-ray tube with a chromium anode, 50 kV, 40 mA, and a throughflow proportional counter. Interferences of numerous accompanying components were investigated as well as the stability of solutions with very low sulphide concentrations. These solutions can be stabilized sufficiently with ascorbic acid at pH 12, but in the case of natural water only in presence of zinc ions. The method is applicable to sulphide amounts greater than 0.1 μg. The variation coefficient for sulphide amounts of ≈ 10 μg was found to be 2.3%.     

A simple indirect automatic method to determine total iodine in milk products by flame atomic absorption spectrometry

A simple, precise and accurate automatic method for the determination of total iodine in milk products by indirect atomic absorption spectrometry is proposed. Iodide in solutions resulting from alkaline ashing of samples is precipitated with silver ion in a precipitation-dissolution flow manifold, which allows performing on-line the retention of the silver iodide precipitate formed on a filter, its wash with diluted ammonia and its dissolution with a diluted thiosulfate solution. Dissolved silver is also determined on-line by flame atomic absorption, and the achieved amount of this metal is proportional to that of iodine in the sample. The proposed method is very selective, avoids interferences from anions present in the samples, which can be also precipitated with silver, because these silver compounds are dissolved with ammonia at the washing step. This method allows the determination of iodine in the range 0.011-0.35 μg mL⁻¹ with a relative standard deviation between 1.3 and 6.8% at a rate of ca. 17 samples h⁻¹.     

The adsorption behavior of p-hydroxybenzoic acid on a silver-coated filter paper by surface enhanced Raman scattering

On dried filter paper coated with silver nanoparticles, surface-enhanced Raman scattering (SERS) spectra of p-hydroxybenzoic acid (PHBA) were studied, and high-quality SERS spectra were obtained, indicating that the silver-coated filter paper is a highly SERS-active substrate. The analysis showed that the adsorption behavior of PHBA molecules on silver nanoparticles coated on filter paper was different from that in silver aqueous colloids. On the filter paper, it was found that the SERS spectra of PHBA changed with the proportion of PHBA molecules and silver nanoparticles, indicating that the adsorption behavior of PHBA molecules changed with the proportion. The probable reasons are given.     

Determination of nanogram amounts of sulphide by release of radioactive iodide

Two variants of a technique for determination of ng-amounts of sulphide ions in liquid samples are presented. They are based on the replacement of radioactively labelled iodide from silver iodide by sulphide. In the first variant, suitable for small sample volumes, the labelled silver iodide is fixed on a filter paper disc which is then shaken with the solution to be analysed until equilibrium is attained. In the second variant, suitable for sample volumes up to 300 ml, the sample solution is passed through a filter paper disc carrying labelled silver iodide or through a labelled silver iodide precipitate. The amount of sulphide is determined from the activity of the released radioiodide by comparison with standards which have been processed in the same way. The method is applicable to sulphide amounts greater than 5 ng and concentrations greater than 0.2 ppM. The interference by many common accompanying anions and cations has been investigated.     

Silver nanoparticle-treated filter paper as a highly sensitive surface-enhanced Raman scattering (SERS) substrate for detection of tyrosine in aqueous solution

Highly sensitive SERS substrates based on deposition of silver nanoparticles on commercially available filter paper were prepared in this work, and used to overcome problems found in analyses of aqueous samples. To prepare silver nanoparticle- (AgNP) doped filter substrates, a silver mirror reaction was used. The procedures for substrate preparation were systematically optimized. Pretreatment of filter paper, reaction time, temperature, and concentration of reagents for silver mirror reactions were studied. The morphologies of the resulting substrates were characterized by field-emission scanning electron microscopy (FE-SEM) and correlated with the SERS signals by probing with p-nitrothiophenol (pNTP). Filter papers with different pretreatments were found to have different sizes and distributions of AgNPs. The best performance was found when filter paper was pre-treated with ammonia solution before growth of AgNPs. Based on the SEM images, the resulting AgNPs had roughly spherical shape with a high degree of uniformity. The silver-coated filter paper substrates provide much higher SERS signals compared to glass substrates and the reproducibility was improved significantly. Based on statistical analyses, the relative standard deviations for substrate-to-substrate and spot-to-spot were both were less than 8% and the enhancement factors for the substrates were, in general, higher than 107. The SERS substrates were used to selectively detect tyrosine in aqueous solution. Results indicate that filter-based SERS substrates are highly suited to detection of tyrosine. Compared to glass-based SERS substrates, 50 times more SERS signal was observed in detection of tyrosine. The linear range can be up to 100 μM with a detection limit of 625 nM (SN(-1)=3).     

Preparation of silver nanoparticles with controlled particle size

Silver colloids show different colors due to light absorption and scattering in the visible region based on plasmon resonance. The resonance wavelength depends on particle size and shape. Here we report chemical reduction methods for preparation of silver nanoparticles exhibiting multicolor in aqueous solutions. Depending on chemical conditions the obtained nanoparticles are different regarding size and morphology.In order to investigate the relationship between size, stability and color of silver colloids we obtained silver nanoparticles in aqueous solutions using different reducing agents. The effect of polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) on stabilization of obtained silver colloids was investigated. We have also studied the effect of silver precursor and its concentration on the formation of stable silver colloids.UV-VIS spectrum for silver colloids contains a strong plasmon band near 410 nm, which confirms silver ions reduction to Ag° in the aqueous phase. The formation of metal silver was also confirmed by powder X-ray diffraction (XRD) analysis. The diameter size of silver nanoparticles was in the range from 5 nm to 100 nm     

Differential preconcentration of arsenic(III) and arsenic(V) with thionalide loaded on silica gel

2-Mercapto-N-2-naphtylacetamide (thionalide) on silica gel is used for differential preconcentration of μg l^?1 levels of arsenic(III) and arsenic(V) from aqueous solution. In batch experiments, arsenic(III) was quantitatively retained on the gel from solutions of pH 6.5–8.5, but arsenic(V) and organic arsenic compounds were not retained. The chelating capacity of the gel was 5.6 μmol g^?1 As(III) at pH 7.0. Arsenic retained on teh column was completely eluted with 25 ml of 0.01 M sodium borate in 0.01 M sodium hydroxide containing 10 mg l^?1 iodine (pH 10). The arsenic was determined by silver diethyldithiocarbamate spectrophotometry. Arsenic(V) was subsequently determined after reduction to arsenic(III) with sulphite and iodide. Arsenic(III) and arsenic(V) in sea water are shown to be < 0.12 and 1.6 μg l^?1, respectively.     

Hierarchical,Titania‐Coated,Carbon Nanofibrous Material Derived from a Natural Cellulosic Substance

Hierarchical, titania‐coated, nanofibrous, carbon hybrid materials were fabricated by employing natural cellulosic substances (commercial filter paper) as a scaffold and carbon precursor. Ultrathin titania films were firstly deposited by means of a surface sol–gel process to coat each nanofiber in the filter paper, and successive calcination treatment under nitrogen atmosphere yielded the titania–carbon composite possessing the hierarchical morphologies and structures of the initial paper. The ultrathin titania coating hindered the coalescence effect of the carbon species that formed during the carbonization process of cellulose, and the original cellulose nanofibers were converted into porous carbon nanofibers (diameters from tens to hundreds of nanometers, with 3–6 nm pores) that were coated with uniform anatase titania thin films (thickness ≈12 nm, composed of anatase nanocrystals with sizes of ≈4.5 nm). This titania‐coated, nanofibrous, carbon material possesses a specific surface area of 404 m² g^?1, which is two orders of magnitude higher than the titania–cellulose hybrid prepared by atomic layer deposition of titania on the cellulose fibers of filter paper. The photocatalytic activity of the titania–carbon composite was evaluated by the improved photodegradation efficiency of different dyes in aqueous solutions under high‐pressure, fluorescent mercury‐lamp irradiation, as well as the effective photoreduction performance of silver cations to silver nanoparticles with ultraviolet irradiation.     

Metal nanoparticle-enhanced room temperature phosphorescence of diiodofluorescein on the filter paper substrate

<正>Metal-enhanced room temperature phosphorescence of diiodofluorescein was first observed on filter paper surface.The phosphorescence intensity is 2.5-fold brighter from diiodofluorescein on silver nanoparticles-deposited filter paper as compared with an identical control sample without silver nanoparticles.Furthermore,enhanced absorption was also observed for the same system.Our findings suggest that both singlet and triplet states can couple to surface plasmons and enhance phosphorescence quantum yields at room temperature,as well as to increase the excitation rate of lumophores at room temperature.     

Surface enhancement effect on the diffuse reflectance infrared Fourier transform spectra of compounds having a pyridine ring

A surface enhancement effect was examined for the diffuse reflectance infrared spectra of structurally related compounds having a pyridine ring when a silver colloidal solution was used as the medium which induced the effect. Filter paper, which was considered to provide a favorable state of aggregation of the silver colloidal particles, was used for the preparation of the samples to be measured. It was proved experimentally that when the molecules were dissolved in the silver colloidal solution and the resulting solution was applied dropwise to filter paper, the spectra measured for the filter paper sample exhibited a surface-enhanced infrared absorption (SEIRA) effect for some samples, but not for other samples. It was speculated that the existence of an electron-donating functional group in the molecule was necessary for the realization of SEIRA in the diffuse reflectance infrared spectra. This speculation was confirmed by experiments involving other types of molecules: l-phenylalanine, m-aminophenol and p-chloroaniline.     

Electrolytic investigations : Electrolytic determination of silver after a silver chloride precipitation

A procedure is described for determining silver electrolytically after first precipitating the silver as silver chloride. The silver chloride is filtered through a filter paper, and the filter paper and precipitate are treated with a mixture of perchloric, sulfuric, and nitric acids. The solution is then evaporated to fumes of sulfuric acid, and the silver determined electrolytically by the cyanide method.     

Reduction of chloride matrix effect using silver oxide as a precipitating reagent for the determination of trace anions in chloride-rich samples via ion chromatography

A new method was developed for the determination of trace anions in chloride-rich samples via ion chromatography by reducing the concentration of chloride ions using silver oxide as a precipitating reagent. In this method the sample pretreatment was started with the addition of silver oxide powder followed by 8 min of stirring and 2 min of centrifugation at a speed of 1500 rpm. The supernatant was diluted with a 1:10 ratio using deionized water and filtered with a 0.22 microm NC filter. All the samples were analyzed in a Dionex ICS-2500 system with an ED50 electrochemical detector in conductivity mode. On the basis of Dionex IonPac AG18 (50 mm x 2 mm) and AS18 (250 mm x 2 mm) columns, 25 AL sample filtrate was eluted isocratically with a mobile phase of 32 mmol/L NaOH at a flow rate of 0.25 mL/ min and each eluted analyte was detected after postcolumn suppression via a Dionex anion suppressor ULTRA II (2 mm). With this method most of the common anions at mg/kg level in chloride-rich samples can be accurately quantified. By controlling the equivalent weight ratio of silver oxide to chloride in sample solutions and the time of pretreatment, the free silver and chloride ions in the sample solution are optimized such that most coexisting common anions can be determined simultaneously.     

Comparison of the adsorption orientation for 2-mercaptobenzothiazole and 2-mercaptobenzoxazole by SERS spectroscopy

In this study, the adsorption orientation for 2-mercaptobenzothiazole (MBT) and 2-mercaptobenzoxazole (MBO) on to silver mirror and silver sol substrates have been studied by surface enhanced Raman scattering (SERS). The MBT and MBO were chemisorbed on both silver mirror and silver sol after deprotonation with a tilted orientation to the silver surfaces. The surface enhanced properties of MBT and MBO showed that the substrate of silver mirror was superior to the sliver sol. The SERS spectra of MBT and MBO revealed that both of the MBT and MBO were adsorbed on silver surfaces strongly by a common sulfur molecule and a sulfur atom from MBT and an oxygen atom from MBO. Therefore, the adsorption orientation of MBT and MBO was little tilted perpendicularly to the silver surfaces. The adsorption geometry did not undergo any significant changes in acidic and basic solutions. It showed that the adsorption orientation for MBT and MBO were stable in the both solutions.     

Electrochemical synthesis, characterization and some properties of a polymer derived from thioflavin S

Polymeric films derived from thioflavin S were electrosynthesized on mild steel and silver electrodes in sulfuric acid and lithium perchlorate-containing aqueous solutions. The introduction of thioflavin S in an acidic solution protected the surface of steel from corrosion. The electrochemical behavior of the steel coated with a layer of poly(thioflavin) was examined by electrochemical impedance spectroscopy. The films exhibited a capacitive behavior and were semi-conductive in nature. Infra red reflectance measurements of the polymer films at the steel surface showed that the polymer structure retained the aromatic structure of the benzene and thiazole rings with the distinction of a nitrogen quinone vibrational band. Surface morphology of the polymer film was examined with scanning electron microscopy. The films are yellow, compact and dense when electrochemically formed onto steel surfaces when compared to a blue rather porous when formed onto silver electrode. The mechanism of electropolymerization of thioflavin is given and found similar to that of aniline with the possibility of metal chelation with the sulfur and/or nitrogen in the thiazole ring.     

Size of elementary clusters and process period in silver nanoparticle formation

The time dependence of small-angle X-ray scattering (SAXS) curves for silver nanoparticle formation was followed in situ at a time resolution of 0.18 ms, which is 3 orders of magnitude higher than that used in previous reports (ca. 100 ms). The starting materials were silver nitrate solutions that were reacted with reducing solutions containing trisodium citrate. The SAXS analyses showed that silver nanoparticles were formed in three distinct periods from a peak diameter of ca. 0.7 nm (corresponding to the size of a Ag(13) cluster) during the nucleation and the early growth period. The Ag(13) clusters are most likely elementary clusters that agglomerate to form silver nanoparticles.     

Surface-enhanced Raman scattering of single-walled carbon nanotubes on silver-coated and gold-coated filter paper

Surface-enhanced Raman scattering (SERS) spectra of single-walled carbon nanotubes (SWCNTs) on metal-coated filter paper are reported for the first time. Experimental results show that the metal-coated filter paper is very effective and active. The SERS spectrum not only shows that all Raman bands of SWCNTs in normal Raman scattering have been generally enhanced, but also shows many new bands, which characterize the structure of SWCNTs and the interaction between SWCNTs and silver/gold nanoparticles, arising from symmetry lowering and selection rule relaxing of SWCNTs induced by the silver/gold surface. In our case, it is difficult to separate the contributions of the electromagnetic and chemical mechanisms to the great enhancement of the Raman signal. The analysis shows that the SERS spectra of SWCNTs on the metal-coated filter paper provide convenience for probing the sample molecules with fine structures related to defects of SWCNTs, the diameter of SWCNTs, and the SERS mechanism of SWCNTs deposited on metal-coated filter paper. Moreover, this can be used as a probe technique for monitoring the synthesis quality of SWCNTs with significant higher sensitivity than other methods, which has promise of being a new technique for monitoring synthesis quality of SWCNTs.     

Preconcentration of silver(I), gold(III) and palladium(II) in sea water with p-dimethylaminobenzylidenerhodanine supported on silica gel

A water-insoluble chelating material, p-dimethylaminobenzylidenerhodanine on silica gel (DMABR—SG) is described for preconcentration of trace amounts of silver(I), gold(III) and palladium(II) from water samples. Radioactive tracers (^110mAg and ¹⁹⁵Au) were used to study the behavior of silver and gold; palladium was monitored spectrophotometrically as its 1-(2-pyridylazo)naphthol complex in chloroform. In batch experiments, silver was quantitatively retained on the DMABR—SG at acidities ranging from 1.7 M to pH 5, and gold from 3 M to pH 5; equilibrium was achieved within 1 min for both elements. From sea water, silver ion was completely retained at pH 1.0–6.5 and gold ion at pH 1.0–3.5. In the case of palladium, shaking for about 20 min was required for quantitative retention at pH 1.0–5.0 for aqueous solution and at pH 1.0–7.0 for sea water. The chelating capacity of the DMABR—SG was 23 μmol Ag, 11 μmol Au and 11 μmol Pd per g. Quantitative recovery of silver and gold on DMABR—SG columns from sea water was achieved at higher flow rates (1–2 l h^-1 and 2–3 l h^-1, respectively) than with other chelating resins, e.g., Chelex 100, palladium required slower flow rate (150 ml h^-1). Silver retained on the DMABR—SG column was completely eluted with 20 ml of 2.5% sodium thiosulfate solution but palladium remained on the column. Silver, gold and palladium were quantitatively eluted with 20 ml of 0.1% thiourea in 0.1 M hydrochloric acid.     

The retention of iodine fission products on iodide precipitates

A fast and selective method has been developed for the separation of the iodine fission products in the primary cooling water of nuclear reactors. The parameters of the selective retention were studied on silver, thallium(I) and mercury(II) iodide. Retention experiments were performed on adequately thick layers of “free” precipitates and on precipitates fixed in filter paper. The latter method substantially increases the retention capacity. The papers with fixed precipitate are easy to handle. The filter paper with silver iodide precipitate was found to be the most satisfactory for the selective retention of fission iodine from reactor water.     

An optimal method of DNA silver staining in polyacrylamide gels

A silver staining technique has widely been used to detect DNA fragments with high sensitivity on polyacrylamide gels. The conventional procedure of the silver staining is tedious, which takes about 40-60 min and needs five or six kinds of chemicals and four kinds of solutions. Although our previous improved method reduced several steps, it still needed six kinds of chemicals. The objective of this study was to improve further the existing procedures and develop an optimal method for DNA silver staining on polyacrylamide gels. The novel procedure could be completed with only four chemicals and two solutions within 20 min. The steps of ethanol, acetic acid, and nitric acid precession before silver impregnation have been eliminated and the minimal AgNO3 dose has been used in this up-to-date method. The polyacrylamide gel of the DNA silver staining displayed a golden yellow and transparent background with high sensitivity. The minimum 0.44 and 3.5 ng of DNA amount could be detected in denaturing and nondenaturing polyacrylamide gel, respectively. This result indicated that our optimal method can save time and cost, and still keep a high sensitivity for DNA staining in polyacrylamide gels.