Determination of Proteins at Nanogram Levels Using the Resonance Light Scattering Technique with a Novel PVAK Nanoparticle

A novel functionalized polyvinyl alcohol keto-derivative nanoparticle (PVAK) has been prepared in a one-step method using oxidation and degradation under ultrasonic irradiation. The nanoparticle is water-soluble, chemically stable, non-toxic and biocompatible. The surface of the nanoparticle is covered with abundant hydroxyl, carbonyl and carboxyl. At pH 3.0, the interactions of PVAK with different proteins can result in obviously enhanced RLS signals at 380nm. Under optimal conditions, the calibration graphs are linear over the range of 0.024.0µgmL^–1 for human serum albumin (HSA), 0.023.5µgmL^–1 for bovine serum albumin (BSA), and 0.053.5µgmL^–1 for human -globulin (-G), respectively. Detection limits were 6.4ngmL^–1 for HSA, 9.2ngmL^–1 for BSA, and 12.5ngmL^–1 for -G, respectively. The method was employed for the determination of total proteins in human serum with satisfactory results.     

Indirect Determination of Sulfide by Cold Vapor Atomic Absorption Spectrometry

A method for the determination of sulfide based on its interference with the determination of Hg by cold vapor atomic absorption spectrometry is described. The decrease in mercury absorbance at 253.7nm is proportional to the concentration of sulfide over the range of 10–320ngmL^–1. The limit of detection was found to be 7ngmL^–1 and the relative standard deviation (R.S.D.) for the determination of different concentrations of sulfide was in the range of 1.8–2.2%. This method was applied to the determination of sulfide in whole human blood after gas-phase separation.     

Determination of Trace Proteins by Rayleigh Light Scattering Technique with Indophenol Blue

The interaction of indophenol blue (IPB) with proteins in aqueous solution has been studied by optical absorption and Rayleigh light scattering (RLS) spectroscopy. At pH 3.8, the weak RLS of IPB is enhanced by proteins. Based on this phenomenon, a novel method for the determination of proteins at nanogram levels using the RLS technique is developed. The method is simple, practical and sensitive. The linear range is 0.25–20.9µgmL^–1 for BSA, and 0.25–17.6µgmL^–1 for HSA. The detection limits (S/N=3) are 23ngmL^–1 for BSA and 22ngmL^–1 for HAS. The results for the determination of proteins in human serum samples are very close to those obtained by an established clinical method. There is very little interference from amino acids, metal ions or other coexisting compounds.     

Determination of Heavy Metal Ions in Chinese Herbal Medicine by Microwave Digestion and RP-HPLC with UV-Vis Detection

A new method for the simultaneous determination of heavy metal ions in Chinese herbal medicine by microwave digestion and reversed-phase high-performance liquid chromatography (RP-HPLC) has been developed. The Chinese herbal medicine samples were digested by microwave digestion. Lead, cadmium, mercury, nickel, copper, zinc, and tin ions in the digested samples were pre-column derivatized with tetra-(4-chlorophenyl)-porphyrin (T₄-CPP) to form the colored chelates which were then enriched by solid phase extraction with C₁₈ cartridge and eluted from the cartridge with tetrahydrofuran (THF). The chelates were separated on a Waters Xterra RP₁₈ column by gradient elution with methanol (containing 0.05molL^–1 pyrrolidine-acetic acid buffer salt, pH=10.0) and THF (containing 0.05molL^–1 pyrrolidine-acetic acid buffer salt, pH=10.0) as mobile phase at a flow rate of 0.5mLmin^–1 and detected with a photodiode array detector in the range of 350–600nm. In the original samples the detection limits of lead, cadmium, mercury, nickel, copper, zinc and tin are 4ngL^–1, 3ngL^–1, 6ngL^–1, 5ngL^–1, 2ngL^–1, 6ngL^–1, and 4ngL^–1, respectively. This method was applied to the determination of lead, cadmium, mercury, nickel, copper, zinc and tin in Chinese herbal medicine samples with good results.     

Application of Functionalized Ag Nanoparticles for the Determination of Proteins at Nanogram Levels Using the Resonance Light Scattering Method

A novel method for the determination of proteins in aqueous solutions has been developed based on the enhancement of resonance light scattering (RLS) of Ag nanoparticles in the presence of proteins. Factors including acidity of the media, concentration of Ag hydrosol, reaction time, temperature, and interference of non-protein substances were investigated. Under the optimal conditions, with the enhanced RLS signals at 452nm, the linear ranges of calibration curves were 0–0.8µgmL^–1 for bovine serum albumin (BSA), 0–1.2µgmL^–1 for human serum albumin (HSA), and 0–2.5µgmL^–1 for human -IgG (-IgG), respectively. The detection limits were 1.3ngmL^–1 for BSA, 10ngmL^–1 for HAS, and 5.7ngmL^–1 for -IgG.This method has been applied to the analysis of synthetic samples and real human serum samples, and the results were in good agreement with those reported by the hospital, indicating that the method presented here is not only sensitive and simple, but also reliable and suitable for practical applications.     

Determination of Iron(III), Cobalt(II) and Chromium(III) in Various Water Samples by Flame Atomic Absorption Spectrometry After Preconcentration by Means of Saccharomyces Carlsbergensis Immobilized on Amberlite XAD-4

A method for the determination of Fe(III), Co(II) and Cr(III) by flame atomic absorption spectrophotometry (FAAS) after preconcentrating on a column containing S. carlsbergensis immobilized on Amberlite XAD-4 has been developed. The optimum values of pH, amount of adsorbent, elution solution and flow rate of the sample solution were determined for the quantitative recovery of the analytes. The effect of interfering ions on the recovery of the analytes was also investigated. Under the optimum conditions, recoveries of Fe(III), Co(II) and Cr(III) by S. carlsbergensis immobilized on Amberlite XAD-4 were 99±2, 100±2 and 98±2% at 95% confidence level, respectively. The limit of detections for Fe(III), Co(II) and Cr(III) were 2.8, 3.9 and 7.4ngmL^–1, respectively. The proposed method was applied to the determination of the analytes in various water samples. The validity of the method was checked with spiked water samples. Fe(III), Co(II) and Cr(III) was determined with a relative error of less than 5%.     

Determination of Volatile Sulfur Compounds in Beverage and Coffee Samples by Purge-and-Trap On-Line Coupling with a Gas Chromatography-Flame Photometric Detector

A sensitive and fast analytical method using purge-and-trap on-line coupling with gas chromatography was developed for the determination of trace volatile sulfur compounds including dimethyl sulfide (DMS), ethyl-methyl sulfide (EMS), and dimethyl disulfide (DMDS) in beverage and coffee samples. The analytes were purged for 12min from the sample by high purity nitrogen at a flow rate of 35KPa and preconcentrated in the cooled fused-silica capillary trap at –75°C. The NaCl content in the samples was maintained at 10%. The volatile sulfur compounds were separated with an Agilent-6890 gas chromatograph by a suitable temperature program and detected by means of a flame photometric detector (FPD). The detection limits were 80ngL^–1 for DMS, 80ngL^–1 for EMS, and 100ngL^–1 for DMDS, respectively. This method was successfully applied to the determination of volatile sulfur compounds in different beverage and coffee samples.     

Electrochemical Determination of 4-Nitrophenol Using a Single-Wall Carbon Nanotube Film-Coated Glassy Carbon Electrode

A single-wall carbon nanotubes (SWNT) film coated glassy carbon electrode (GCE) was fabricated for the direct determination of 4-nitrophenol (4-NP). The electrochemical behaviors of 4-NP at the SWNT-film coated GCE were examined. In 0.1M phosphate buffer with a pH of 5.0, 4-NP yields a very sensitive and well-defined reduction peak at the SWNT-modified GCE. It is found that the SWNT film exhibits obvious electrocatalytic activity towards the reduction of 4-NP since it not only increases the reduction peak current but also lowers the reduction overpotential. Based on this, an electrochemical method was proposed for the direct determination of 4-NP. The reduction peak current varies linearly with the concentration of 4-NP ranging from 1×10^–8 to 5×10^–6M, and the detection limit is 2.5×10^–9M after 3min of open-circuit accumulation. The relative standard deviation at 2×10^–7M 4-NP was about 6% (n=10), suggesting excellent reproducibility. This new method was successfully employed to determine 4-NP in several lake water samples.     

Determination of Caffeine Using a Simple Graphite Pencil Electrode with Square-Wave Anodic Stripping Voltammetry

A simple commercial graphite pencil electrode (GPE) was utilized for monitoring caffeine using the square-wave anodic stripping voltammetry (SWASV) method. This method was applied to determine the caffeine levels in several tea samples, which yielded a relative error of 1% in the concentrations. Caffeine was deposited at 0.0V (vs. Ag/AgCl), then reduced at +1.40V to strip it on the GPE. Optimal experimental conditions for the analysis were found to be as follows: pH value of 9 for the medium; deposition potential of 0.0V; deposition time of 120s; SW frequency of 25Hz; SW amplitude of 45mV, and step potential of 6mV. Given these optimum conditions, a linear range was observed within the concentration of 0500mgL^–1. At caffeine concentrations of 50.0, 250.0, and 500.0mgL^–1, the relative standard deviations in measured concentrations (n=12) were 0.19, 0.09, and 0.11%, respectively. The detection limit was found to be 9.2mgL^–1, which is comparable with the result obtained using a carbon paste electrode, equivalent to 8.2mgL^–1.     

Flame Atomic Absorption Spectrometric Determination of Gold and Palladium Using Microcolumn On-line Preconcentration and Separation

A microcolumn on-line preconcentration and separation system was developed for the flame atomic absorption spectrometric (FAAS) determination of trace levels of gold and palladium. The analytes were selectively adsorbed onto the microcolumn packed with 2-mercaptothiazole immobilized silica gel (MBTSG) in an acidity range of 0.1 to 6.0M HCl at a sampling flow rate of 4.0mLmin^–1. The analytes adsorbed could be desorbed by a thiourea solution with a flow rate of 2.0mLmin^–1. Most of the common coexisting metal ions at a concentration of 25.0mgmL^–1 and anions at a concentration of 50.0mgmL^–1 did not interfere with the preconcentration and determination of Au and Pd. The limits of detection (LOD), defined as three times the standard deviation of the blank (3), of Au and Pd are 10ngmL^–1 and 26ngmL^–1, respectively, with a preconcentration time of 60s. The relative standard deviation (RSD) is about 2.0% for 0.20µgmL^–1 Au and 0.30µgmL^–1 Pd. With a sample loading time of 30min, 6.7ngmL^–1 Au and 10ngmL^–1 Pd can be preconcentrated quantitatively. A geological sample, an anode slime and a secondary nickel alloy were successfully determined with the proposed method, and the results obtained showed good agreement with the certified values.Received December 23, 2002; accepted May 14, 2003 Published online August 8, 2003     

Photoluminescence of osmocene and decamethylosmocene

Osmocene (and decamethylosmocene) is characterized by a lowest-energy ligand field triplet which occurs at _max=372nm (374nm) in absorption and 567nm (572nm) in emission. This orange–yellow phosphorescence is rather intense at 77K but is also visible at r.t.     

Determination of Nucleic Acids Based on their Resonance Light Scattering Enhancement Effect on Metalloporphyrin Derivatives

A new method for the determination of nucleic acids at nanogram per mL level is proposed based on the enhanced resonance light scattering (RLS) signal resulting from the interaction of metalloporphyrins with nucleic acids. Under optimum conditions, the weak RLS signal of metalloporphyrin is enhanced by nucleic acids, and the enhanced RLS intensity is proportional to the concentration of nucleic acids. The detection limits of calf thymus DNA were 3.5ngmL^–1, 2.9ngmL^–1 and 1.0ngmL^–1 for three metalloporphyrins, respectively. Synthetic samples were determined with satisfactory results.     

Development of an FI-ICP Method for On-Line Preconcentration and Determination of Platinum

This paper presents a new simple and rapid procedure for the preconcentration and determination of platinum. It is based on the adsorption of the metal ion and preconcentration on a micro-column (3cm×3mm) placed in the injection valve of a flow injection (FI) manifold and packed with 1,5-bis[(2-pyridyl)-3-sulphophenyl-methylene]thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex 1X8-200). The metal was eluted from the column using a solution of 2M HNO₃. Various parameters and chemical variables affecting the preconcentration and determination of this metal by ICP-AES were evaluated. Five variables (sample flow rate, eluent flow rate, nebulizer flow rate, buffer concentration and mixing coil length) were considered as factors in the optimisation process. Interactions between analytical factors, and their optimal levels were investigated using two level factorial and central matrix designs. The optimum conditions established were applied to the determination of platinum by flow injection inductively coupled plasma atomic emission spectrometry (FI-ICP-AES). The method has a linear calibration range of 25 to at least 200ngmL^–1 with a detection limit of 7.4ngmL^–1 (S/N=3) and a throughput of 10 samples h^–1 using 5min. preconcentration time. The precision of the method (RSD) was 3.06% ngmL^–1 at the 50ngmL^–1 level of Pt(IV) and 2.93% at the 150ngmL^–1 level. The accuracy of the method was examined by determining the analyte content in spiked waters and by analysing an automobile catalyst standard reference material. The results show good agreement with the certified value and sufficiently high recoveries.     

Determination of Attogram Quantities of Silver via Quenching of the Solid Substrate Room-Temperature Phosphorescence of Rhodamine B Based on the Catalysis of its Oxidation by Potassium Persulfate

A new method of SS-RTP for the determination of trace silver has been established. This method is based on the fact that Ag⁺, when activated by ,-bipyridyl (bipy) in a media of HAc–NaAc (pH=4.9), can catalyze the reaction of Rhodamine B (RhoB) oxidized by K₂S₂O₈, thus causing the Solid Substrate Room-Temperature Phosphorescence (SS-RTP) of RhoB to be quenched. The activating efficiency of bipy is 6.7 times higher than that of o-phenanthroline (phen). The reduction of the phosphorescence intensity (I_p) of RhoB is directly proportional to the concentration of Ag⁺ ions in the range of 1.6016.0agspot^–1 (0.40µLspot^–1). The regression equation of the working curve can be expressed as I_p=18.78+5.100m_Ag+ (agspot^–1) (r=0.9994, n=6), the detection limit is 0.28agspot^–1. This rapid, accurate and sensitive method has been successfully applied to the determination of trace silver in tea and human hair samples, and the results agree well with the Atomic Absorption Spectroscopy (AAS) method. The mechanism of the catalyzing reaction is also discussed.     

Determination of Nucleic Acids Based on Shifting the Association Equilibrium between a Heptamethine Cyanine Dye and Poly-Lysine

A near-infrared (near-IR) fluorescence recovery method for the determination of nucleic acids is presented. This method employs a two-reagent system composed of anionic heptamethines cyanine (HMC) and polycationic poly-lysine. The fluorescence of HMC, with maximum excitation and emission wavelengths at 778 and 804nm, respectively, was quenched by poly-lysine in proper concentration, but recovered by adding nucleic acids. Under optimal conditions, the recovered fluorescence was proportional to the concentration of nucleic acids. The calibration graphs are linear over the range of 5–300ngmL^–1 for herring sperm DNA (FS DNA), 2–100ngmL^–1 for calf thymus DNA (CT DNA) and 5–500ngmL^–1 for snake ovum RNA (SO RNA). The corresponding detection limits are 1.49ngmL^–1 for FS DNA, 0.7ngmL^–1 for CT DNA and 1.61ngmL^–1 for SO RNA, respectively. Four synthetic and three real nucleic acid samples were determined with satisfactory results.     

Au-Induced Faceting of Si(5 5 12)

The growth of Au on the stable, high-index Si(5512) surface has been studied using scanning tunneling microscopy (STM). At very low coverages and moderate annealing temperatures (0.1ML, 400–500°C), Au appears to decorate the underlying Si rows and form an array of rows that maintains the underlying (5512) periodicity of 5.4nm. For higher annealing temperatures and coverages, however, Au causes faceting to a number of nearby planes. The two primary facets formed at lower (0.15ML) and higher (0.5–2ML) coverages are the (337) and (225) planes, which are tilted 0.7° down [towards (111)] and 1.1° up from (5512), respectively. Both orientations are in fact subunits of the (5512) unit cell, so their presence is not surprising. In addition to these facets, two types of sawtooth morphologies composed of planes oriented further from (5512) are found at very high annealing temperatures (800–900°C). These include (113)+(7715) planes at very low coverage (0.05ml) and (113)+(5511) planes at higher coverage (1ML), where (113) is tilted up by 5.3° and (7715) and (5511) are tilted down by 2.9° and 2.2°, respectively. Au adsorption on Si(5512) therefore results in the formation of five possible facet planes: (113), (225), (337), (5511), and (7715).     

Magnetic Separation Immunoassay for Digoxin in Plasma with Flow Injection Fluorescence Detection

Immunoassay (IA) is a sensitive and selective approach for low level quantitation of drugs. Magnetic separation immunoassays use magnetic beads to facilitate the separation of bound labeled antigens from free antigens in solution. Digoxin was chosen for this study because low level analysis (ngmL^–1) in biological samples isrequired, antibodies to digoxin were commercially available and derivatization procedures for fluorescence labeling were well established. A competitive immunoassay format was used in this study. Streptavidin coated magnetic beads were attached to biotinylated anti-digoxin antibodies for the separation. The inhibition curve for off-line magnetic separation immunoassay of digoxin in spiked plasma was characterized and the dynamic range of the curve was 0.25–2.5ngmL^–1. A power fit weighted by the inverse of concentration was found to provide the best fit to the data (r=0.9934). The percent RSDs for the two controls, 0.8 and 2.2ngmL^–1, were 9.95% and 20.62% (n=6) and the percent errors were 11.75% and 22.63% (n=6), respectively. The limit of detection (LOD) in plasma is 0.14ngmL^–1. The dynamic range of the inhibition curve for on-line magnetic separation immunoassay of digoxin was 0.5–15ngmL^–1 of digoxin. A quadratic fit was found to provide the best fit to the data (r=0.9937). The percent RSDs for the two controls, 4.0 and 12ngmL^–1, were 14.1% and 10.7% (n=6) and the percent errors were 5.8% and 3.3% (n=6) from the spiked value, respectively. The LOD was estimated to be 0.44ngmL^–1 (determined as two times the standard deviation of the blank, n=6). The on-line method has the advantages of being relatively easy to automate in the continuous flow mode and is adaptable for use in conjunction with HPLC separations.     

Application of L-Cysteine-Capped ZnS Nanoparticles in the Determination of Nucleic Acids Using the Resonance Light Scattering Method

Nanometer-sized L-cysteine-capped ZnS particles were synthesized by a colloidal aqueous method. The functionalized nanoparticles are water-soluble and suitable for biological applications. In Tris-HCl buffer solution, nucleic acids combine with cysteine-capped nano-ZnS particles by intermolecular forces to form larger nanoparticles. There are two resonance light scattering peaks at 304.5nm and 373.8nm, respectively. The enhanced RLS is related to the concentration of nucleic acids in the range of 0.04 to 1.2µgmL^–1 for calf thymus DNA and 0.2 to 1.0µgmL^–1 for fish sperm DNA. The detection limits (3) are 19ngmL^–1 for calf thymus DNA and 23ngmL^–1 for fish sperm DNA, respectively. Four synthetic samples were analyzed satisfactorily.     

Determination of Total Selenium Content in Cereals and Bakery Products by Flow Injection Hydride Generation Graphite Furnace Atomic Absorption Spectrometry Applying in-situ Trapping on Iridium-Treated Graphite Platforms

A flow injection hydride generation graphite furnace atomic absorption spectrometric (FI-HG-GFAAS) method was applied to the determination of Se in Se-doped and undoped cereals and bakery products. For the purpose of doping, the soils used for the cultivation of the cereals were dosed with Se-doped foliar fertilizers. The samples were dissolved in a mixture of HNO₃ and H₂O₂ solutions using microwave-assisted digestion. The decomposition of H₂Se generated from the sample solutions and the trapping of elemental Se were performed at a temperature of 300°C on an Ir-pretreated integrated graphite platform of a transversally heated graphite atomizer (THGA). For release of the trapped Se within a fairly short atomization time (5s), an atomization temperature of 2200°C was observed to be optimal. The overall efficiency of hydride generation, transport and trapping was 86%.The upper limit of the linear dynamic range of calibration was 10µgL^–1, which corresponds to 0.5µgg^–1 for solid samples. Recovery of the samples spiked with Se^VI solutions was found to be 93±6% on average. The relative standard deviation of the determinations was less than 8%. The limit of detection was found to be 0.06µgL^–1, corresponding to 3ngg^–1 for solid samples. The accuracy of the method was verified with the use of IAEA-155 (whey powder) certified reference material. End-capped THGA tubes resulted in an extension of the linear calibration range compared to that of standard THGAs.The Se content in bakery products made of undoped cereals ranged from 7.7 to 68ngg^–1 (wet weight) in 18 samples, whereas the Se content of the corresponding cereals was found to be below 100ngg^–1 (wet weight). The Se level of cereals grown on soils treated with Se-doped fertilizers ranged from 128 to 1046ngg^–1 (wet weight), and it depended linearly on the Se concentration of the corresponding foliar fertilizer.     

Determination of Na,K, Rb and Cs Distribution in Human Brain Using Neutron Activation Analysis

This study aims to investigate the distribution of Na, K, Rb and Cs in human brains (5 individuals, 12 brain parts, mean age: 75 years). Distribution of the trace metals between lipid fraction and brain tissue was investigated in solvent extraction experiments. Determinations were carried out by instrumental neutron activation analysis. The present results show a rather non-homogeneous distribution for Na and a relatively uniform distribution for K, Rb and Cs. The mean concentrations found are 7440µgNag^–1 dry weight, 12800µgKg^–1, 14µgRbg^–1 and 50ngCsg^–1. A highly significant positive correlation was found between Rb and Cs. Solvent extraction experiments showed that 19% of Rb and 26% of Cs of the total content is located in lipid fraction.