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.     

Kinetic Spectrophotometric Determination of Trace Aluminum by Catalytic Activity of Al<Superscript>3+</Superscript> on the Oxidation of Methylene Blue by Hydrogen Peroxide

A novel kinetic spectrophotometry for the determination of trace aluminum is described based on the catalytic activity of Al³⁺ on the redox reaction between methylene blue (MB) and hydrogen peroxide in acetate buffer (pH 3.8). The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of the dye at the maximum absorption wavelength of 670nm. The variables that affected the reaction rate were fully investigated, and the optimum conditions were established. Aluminum can be determined in the range of 0–80ngmL^–1 with a detection limit of 1.0ngmL^–1. The relative standard deviation for 10 replicate determinations of 40ngmL^–1 aluminum is 0.9%. The method was used to determine aluminum in tap water and biological samples and produced satisfactory results.Received December 18, 2002; accepted May 5, 2003 published online August 22, 2003     

The Electrochemical Behavior of p-Aminophenol at a ω-Mercaptopropionic Acid Self-Assembled Gold Electrode

A -mercaptopropionic acid (MPA) self-assembled monolayer modified electrode (MPA/SAM/Au) on a gold electrode has been fabricated. The characterization of the MPA/SAM/Au was investigated using attenuated total reflection-fourier transform infrared (ATR-FTIR) and A.C. impedance. The electrochemical behaviors of p-aminophenol (p-AP) were studied at the MPA/SAM/Au by cyclic voltammetry and semi-derivative voltammetry (SDV) in BR buffer solution. The modified electrode shows excellent electrocatalytic activity for the redox of p-AP and accelerates the electron transfer rate. The diffusion coefficient (D) is 4.55×10^–6cm²s^–1. The oxidative peak current increases linearly with the concentration of p-AP in the range of 4.0×10^–88×10^–6molL^–1 and 1.0×10^–52×10^–4molL^–1 by square wave voltammetry response, respectively. The detection limit (three times the signal blank/slope) is up to 1.2×10^–8molL^–1. The modified electrode is able to eliminate the interference of p-benzenediol, o-benzenediol and o-AP at a 40-, 90- or 70-fold concentration of p-AP, and it has been satisfactorily used for the determination of the real sample.     

Determination of Iron in Tap and Waste Water Using Liquid–Liquid Extraction in a Flow-Injection System

A flow-injection procedure for the determination of iron(III) in water is described. The procedure is based on the formation of an ion pair between the tetraphenylarsonium (Ph₄As⁺) (TPA) or tetrabutylammonium (But₄N⁺) (TBA) cations and the tetrathiocyanatoferrate(III) complex (TTF). This ion pair is extracted with chloroform, and the absorbance of the organic phase is measured at 503nm (for Ph₄As⁺) or 475nm (for But₄N⁺). Iron concentrations higher than 0.9×10^–6molL^–1 (50µgL^–1) can be detected in the first case, with a relative standard deviation of 1.9% (n=12), a linear application rangeof between 1.34 and 54.0×10^–6molL^–1 (75–3015µgL^–1), and a sampling frequency of 30h^–1. For the ion pair with But₄N⁺, the detection limit is 0.52×10^–6molL^–1 (29µgL^–1), with a relative standard deviation of 1.6% and a linear application range between 0.73 and 54.0×10^–6molL^–1. Under the proposed working conditions, only Pd(IV), Cu(II) and Bi(III) interfere. With the application of the merging zones technique, considerable amounts of organic reagent can be saved. The TBA method was applied to the analysis of iron(III) in tap and industrial waste waters.     

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.     

Energy Transfer Electrogenerated Chemiluminescence for the Determination of Sulfite

A simple and novel electrogenerated chemiluminescence (ECL) method for the determination of sulfite has been developed based on the energy transfer ECL process. It was found that a weak ECL signal of sulfite was electrochemically generated on a platinum electrode in neutral aqueous solution. The signal was strongly enhanced by rhodamine B as an energy receptor and further enhanced by the neutral surfactant Tween 80. In 0.10M phosphate buffer solution (pH=7.5) containing 2.0×10^–6gmL^–1 rhodamine B and 0.4% (v/v) Tween 80, the ECL response to the concentration of sulfite at a potential of 0.82V was linear over a range of 1.0×10^–7gmL^–1 to 8.0×10^–6gmL^–1, and the detection limit was 5×10^–8gmL^–1. The relative standard deviation (n=11, 1.0×10^–6gmL^–1) was 3.8%. The proposed method has been successfully applied to the determination of sulfite in pharmaceutical injections and white sugar samples.     

Adsorptive Catalytic Voltammetry of Physcion in the Presence of Dissolved Oxygen at a Carbon Paste Electrode

A novel electroanalytical method for the determination of physcion is described for the first time. Physcion yields an adsorption catalytic voltammetric peak at –0.74V (vs. SCE) in 0.4molL^–1 NH₄Cl–NH₃·H₂O buffer solution (pH 10.5) at a carbon paste electrode (CPE). The experimental results indicated that physcion is efficiently accumulated at a CPE by adsorption. In the subsequent potential scan, physcion was reduced to a homologous anthrahydroquinone compound. The compound was then immediately oxidized to physcion by the dissolved oxygen in the solution, and then physcion was again reduced at the CPE. As a result, a cyclic catalytic reaction was established. The second-order derivative peak current is proportional to the physcion concentration in the ranges of 2.0×10^–104.0×10^–9molL^–1 (accumulation 90s) and 4.0×10^–92.0×10^–8molL^–1 (accumulation 60s). The limit of detection is 8×10^–11molL^–1 (S/N=3) for a 120s accumulation time. The method was applied to the direct determination of physcion in the medicinal plant polygonum multiflorum Thumb with satisfactory results.     

Voltammetric Determination of Bismuth in Water and Nickel Metal Samples with a Sodium Montmorillonite (SWy-2) Modified Carbon Paste Electrode

A simple and reliable electrochemical method for the determination of bismuth in water and nickel metal samples using a sodium montmorillonite (SWy-2) modified carbon paste electrode was described. Due to its strong cation-exchange ability and adsorptive characteristics, SWy-2 significantly enhances the sensitivity of determination for Bi³⁺. Bi³⁺ is firstly preconcentrated and then reduced on the modified electrode surface at –0.50V. After that, reduced bismuth is stripped from the electrode surface during the positive potential sweep of –0.50V to 0.20V, and a well-defined stripping peak at –0.12V appears. The stripping peak current is proportional to the concentration of Bi³⁺ from 4×10^–9molL^–1 to 1×10^–6molL^–1. The detection limit (signal-to-noise=3) is 1×10^–10molL^–1 after 5min. accumulation. The proposed method was successfully applied to the determination of bismuth in water and nickel metal 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.     

Polarographic Determination of Lovastatin in the Presence of H2O2 in Pharmaceuticals, Human Urine and Serum

The polarographic reduction and catalytic behavior of lovastatin are studied by polarography and cyclic voltammetry. The reduction wave of lovastatin appears at ca. –1.49V (vs. SCE) in 0.16molL^–1 Na₂B₄O₇–KH₂PO₄ (pH=7.4) supporting electrolyte containing 20% ethanol. It is ascribed to a 2e^–, 2H⁺ addition to the carbonyl group on lactone ring. If H₂O₂ is present, the reduction wave is catalyzed to produce a polarographic catalytic wave. Based on the catalytic wave, a novel method for the determination of lovastatin is proposed. A rectilinear calibration curve of the catalytic wave was obtained for lovastatin concentration in the range 1.5×10^–8 to 1.0×10^–6molL^–1. The peak current of the catalytic wave is ca. 12 times higher than that of the corresponding reduction wave. The detection limit is 8.0×10^–9molL^–1. The proposed method is simpler, faster and more sensitive than the known methods for lovastatin analysis, and can be applied to the direct determination of lovastatin in pharmaceuticals, urine and serum without preliminary separation.     

Voltammetric Behavior of Dopamine at ct-DNA Modified Carbon Fiber Microelectrode

A sub-micrometer thin-layer DNA modified carbon fiber microcylinder electrode was prepared by electrodeposition of ct-DNA at 1.5V (vs. Ag/AgCl). The voltammetric behavior of dopamine (3-hydroxytyramine) was investigated at the modified electrode. It was found that the modified electrode exhibits a highly electrocatalytic activity toward dopamine oxidation. Differential pulse voltammetry was used for determination of dopamine in pH 7.4 phosphate buffer solution. A linear response of the peak current versus the concentration was found in the range of 4×10^–6 to 10^–4molL^–1 at 10^–4molL^–1 AA (ascorbic acid) coexistence (R=0.9959) and the range of 6×10^–5 to 10^–3molL^–1 at 10^–3molL^–1 AA (R=0.9960). The presence of a high concentration of ascorbic acid did not interfere with the determination. The proposed method exhibited good recovery and reproducibility. This method can be applied to the detection of DA in real samples.     

Electrochemical Behavior of Epinephrine at a Penicillamine Self-Assembled Gold Electrode,and its Analytical Application

The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The self-assembled electrode shows obvious electrocatalytic activity for the oxidation of epinephrine (EP). In phosphate buffer (pH 7.73), a sensitive oxidation peak was observed at 0.190V with the PCA modified Au electrode. The peak current is proportional to the concentration of EP in the range of 2.0×10^–56.0×10^–4molL^–1 and 5.0×10^–6 2.0×10^–4molL^–1 for cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with the detection limits of 1.8×10^–7 and 1.3×10^–7molL^–1, respectively. The possible reaction mechanism is also discussed. The PCA self-assembled monolayer modified gold electrode is highly stable and can be applied to the determination of EP in practical injection samples. Application is simple, rapid and produces accurate results.     

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     

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 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.     

Electrochemical Determination of Cinnamtannin B1 with a Pyrolytic Graphite Electrode

Cinnamtannin B1 (trimeric proanthocyanidin), which is identified and isolated from the effective fraction of the root of Lindera aggregata (Sims) Kosterm, is one kind of condensed tannin used as an effective antipyrotic and antitumor agent. Its electrochemical response can be obtained at a pyrolytic graphite electrode. Consequently, an easily performed and sensitive method for the determination of cinnamtannin B1 is developed. The detection limit is estimated to be 1.0×10^–7M with the linear determination range of 2.0×10^–7M to 1.8×10^–6M. Five replicate analyses of 1.0×10^–6M cinnamtannin B1 yields an RSD value of 2.1%. Since the working electrode does not need to be modified with any other species, it is very stable, repeatable and easily treated, and this method therefore potentially useful in real sample analysis.     

Application of Lanthanide-Sensitised Chemiluminescence to the Determination of Levofloxacin, Moxifloxacin and Trovafloxacin in Tablets

A flow injection method including chemiluminescence detection has been developed and applied to the determination of fluoroquinolones levofloxacin, moxifloxacin and trovafloxacin in tablets. The proposed method is based on the luminescent properties of the system Ce(IV)–sulphite–fluoroquinolone and the addition of a trivalent lanthanide ion as emission-sensitizer. The optimum conditions for chemiluminescence emission were investigated for each fluoroquinolone. The best results were achieved when employing Eu(III) as lanthanide cation for levofloxacin and moxifloxacin, and Tb(III) for trovafloxacin. These fluoroquinolones were determined over the concentration range of 0.5–3.5µgmL^–1, 0.2–3.0µgmL^–1 and 0.008–0.400µgmL^–1, with detection limits of 0.100, 0.035 and 0.008µgmL^–1, respectively. The relative standard deviations were in the range of 1.0–2.5% for all three cases. The method was applied to the determination of three fluoroquinolones in their respective pharmaceutical preparations and compared with an independent UV-spectrophotometric method. The results were satisfactory.     

Flow Injection Determination of Lomefloxacin Based on Photochemically Sensitized Chemiluminescence

A photochemical chemiluminescence (CL) method for the determination of lomefloxacin (LFX) is proposed. LFX undergoes a photochemical reaction when irradiated with ultraviolet light, and a complex is formed when the photoproduct reacts with terbium(III), which can greatly enhance the CL of the Ce⁴⁺–Na₂SO₃ system. Under optimum experimental conditions, the linear range is between 9.0×10^–10 and 1.0×10^–5M, and the detection limit is 2.2×10^–10M. The relative standard deviation for the determination of 5.0×10^–8M LFX was 3.0% (n=11). The method has been successfully applied to the determination of LFX in dosage form, serum samples and urine samples. The recoveries were 97.9–102.3% for serum and urine samples. The possible mechanism is presented.     

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.     

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.