A combined technique with laser irradiation is suggested to control spark discharge for analytical use, having a unique feature that firing points of the spark discharge can be fixed by laser irradiation. Because the spark discharge easily initiates at particular surface sites, such as non-metallic inclusions, called selective discharge, the concentration of some elements sometimes deviates from their average one in spark discharge optical emission spectrometry. Therefore, stabilization of firing points on a sample surface could improve the analytical precision.
A disposable, screen-printed electrode based on the immobilization of catalase or tyrosinase was developed to construct biosensors for the amperometric determination of azide. The determination principles for azide by these two methods are based on inhibiting the enzymatic consumption of an electrode-detectable substance (hydrogen peroxide or catechol) on an enzyme-immobilized electrode. Both of these methods show a sensitive detection range and a short measuring time.
Temperature-dependent phase-vanishing processes between perfluorohexane (FC-72) and n-heptane (C7H16, volume ratio of 1:1 and phase-vanishing temperature > 41°C), were studied in a glass microchannel-microheater chip under solution-flow conditions. Without applying a voltage to the heater at 21°C, the two liquids in the microchannel were separated into two streams at a solution flow rate (v) of 0.975 cm/s, while the phase boundary between FC-72 and C7H16 vanished in the downstream side of the heater at V = 4.5 V. Then, we conducted Raman intensity imaging during the phase vanishing processes in the microchannel by monitoring the band at 756 (FC-72) or 1456 cm-1 (C7H16). At V = 4.5 V and v = 0.975 cm/s, although no phase boundary between the two liquids in the microchannel was observed, the relevant Raman intensity images indicated the inhomogeneous nature of the solution, and distribution of C7H16 to the FC-72 phase along with solution flow was observed.
An inverted microscope was combined with a compact dye laser with a pulse width of < 190 ps and an intensified charge-coupled device (ICCD) camera with a minimum gate width of 200 ps. The resulting fluorescence lifetime imaging microscope, which has a temporal resolution of 340 ps, was used to measure the fluorescence lifetime of polymer microspherers. The results indicated a fluorescence lifetime of 0.9 ns. The present analytical instrument was also employed in an evaluation of biological cells after labeling them with SYTO 13, a fluorescent dye.
Total reflection X-ray fluorescence spectrometry (TXRF) has been applied for trace elemental analysis of small glass fragments. A small glass sample (a fragment with weight less than 0.5 mg) was decomposed by 100 µg of HF/HNO3 acid; the material was condensed to 10 µl and was dried on a Si wafer. Since the size of the dried residue on the Si wafer was less than 1 cm in diameter, an incident X-ray beam with about 1 cm in width could effectively excite elemental components in such a small glass fragment. The precision of the present technique was checked by analyzing the glass fragments (< 0.5 mg) from NIST SRM612; the relative standard deviations (RSD) of less than 8.1% were achieved for elemental ratios that were normalized by Sr. Fragments (< 0.5 mg) obtained from 23 figured sheet glasses were used as samples for estimating the utility of this technique to forensic discrimination. Comparison of five elemental ratios of Ti/Sr, Mn/Sr, Zn/Sr, Rb/Sr, and Pb/Sr calculated from X-ray fluorescence spectra was effective in distinguishing glass fragments that could not be differentiated by their refractive indexes (RI).
In a diluted H2SO4 solution, Hg(II) reacts with halide anions X- (including Cl-, Br- and I-) to form anionic complexes [HgX4]2- that can further react with berberine to form ion-association complexes of [Ber]2[HgX4]. As a result, the absorption spectra change, their maximum absorption wavelengths are at 230 nm for [Ber]2[HgCl4], 278 nm for [Ber]2[HgBr4] and 300 nm for [Ber]2[HgI4]. However, among the three complexes, only [Ber]2[HgI4] can lead to distinctly enhanced resonance Rayleigh scattering (RRS), and a new RRS spectrum appears. The maximum RRS wavelength is located at 397 nm, and the RRS intensity is proportional to the concentration of berberine in the range of 0 - 2.5 µg mL-1. The optimum conditions, the influence factors for the reaction and the effects of coexisting substances have been investigated. A new, simple and fast RRS method for the determination of berberine based on the ion-association reaction of [HgI4]2- with Ber+ was developed. The method has high sensitivity and good selectivity; the detection limit for berberine (3 σ/K) is 7.22 ng mL-1. The method can be applied to the determination of berberine in some Chinese patent drug and the extracts of Coptis Chinensis. Furthermore, the mechanism of the reaction and the reasons for RRS enhancement have been discussed.
NMR measurements coupled with pattern-recognition analysis offer a powerful mixture-analysis tool for latent-feature extraction and sample classification. As fundamental applications of this analysis for mixtures, the 1H spectra of 176 kinds of green, black, oolong and other tea infusions were acquired by a 500 MHz NMR spectrometer. Each spectrum pattern was analyzed by a multivariate statistical pattern-recognition method where Principal Component Analysis (PCA) was used in combination with Soft Independent Modeling of Class Analogy (SIMCA). SIMCA effectively selected variables that contribute to tea categorization. The final PCA resulted in clear classification reflecting the fermentation and processing of each tea, and revealed marker variables that include catechin and theanine peaks.
The channel flow double electrode (CFDE) was used for the evaluation of the oxygen reduction activities in alkaline solution of rare-earth oxide-supported silver catalysts. The CFDE cell was modified for the experiment using the powder catalyst as a working electrode. In the present experiment, the silver electrode was supported with CeO2 in order to improve the performance of the oxygen reduction. The detecting electrode current for HO2- emitted from the working electrode was recorded simultaneously with the measurement of the i-E curve of each working electrode. Moreover, the average number of charge transfers n was calculated from the working and detecting electrode currents. The value of n for the oxygen reduction was approximately 4 for silver electrode supported with rare-earth oxide, compared with the n value of pure silver that was smaller than 4. On the basis of these results, the mechanisms of oxygen reduction on these electrodes and role of the rare-earth oxide in alkaline solution were discussed.
A novel method for prevention of the oxidation of Sb(III) during sample pretreatment, preconcentration of Sb(III) and Sb(V) with nanometer size titanium dioxide (rutile) and speciation analysis of antimony, has been developed. Antimony(III) could be selectively determined by flow injection-hydride generation-atomic absorption spectrometry, coexisting with Sb(V). Trace Sb(III) and Sb(V) were all adsorbed onto 50 mg TiO2 from 500 ml solution at pH 3.0 within 15 min, then eluted by 10 ml of 5 mol/l HCl solution. One eluent was directly used for the analysis of Sb(III); to the other eluent was added 0.5 g KI and 0.2 g thiourea to reduce Sb(V) to Sb(III), then the mixture was used for the determination of total antimony. The antimony(V) content is the mathematical difference of the two concentrations. Detection limits (based on 3σ of the blank determinations, n = 11) of 0.05 ng/ml for Sb(III) and 0.06 ng/ml for Sb(V), were obtained.
The combination of an enzyme-based biosensor and alkaline hydrolysis was developed for the measurement of poly(3-hydroxybutyrate) (PHB). The principle of the determination is based on that the alkaline condition converts PHB to produce its monomer, 3-hydroxybutyrate (3-HB), which generates a detectable current signal by an amperometric biosensor through coupled two-enzyme reactions on an electrode. This method takes less than 40 min, and results in a linear detection range of 0.5 - 110 mg L-1 PHB with a detection limit of 0.3 mg L-1 by the saturated production of 3-HB; it can also take less than 15 min and result in a linear detection range of 1.0 - 160 mg L-1 PHB with a detection limit of 0.5 mg L-1 by a part production of 3-HB. The method also shows simple operation and high reproducibility.
The performance of a newly synthesized carbosilane dendrimer bearing four triethylene glycol ether (TEG) units, Si(CH2CH2CH2Si(Me)2CH2CH2CH2(OCH2CH2)3Me)4 (1), as ionophores in ion-selective electrodes has been investigated. Optimization of the plasticized polyvinyl chloride membrane composition has produced electrodes that exhibit a Nernstian response for potassium ions. The best general characteristics exhibited by the electrodes were found when the membrane composition ratio of DPE:1:NaTPB:PVC 60:3:2:35 (wt%) was used. The response of the electrode was linear with a Nernstian slope of 58.3 mV/decade over the K+ ion concentration range of 1.9 × 10-7 to 1.0 × 10-1 M with a detection limit of 3.1 × 10-7 M. The response time to achieve a 95% steady potential for the K+ concentration ranging from 1.0 × 10-1 to 1.0 × 10-8 M was less than 10 s, and it was found that the electrode is suitable for use within a pH range of 5.5 - 8.5. The selectivity coefficients (log KPotK+,Mn+), which were determined by the fixed interference method, showed good selectivity for K+ against most of the interfering cations. The influence of this selective ion-binding behavior using electrospray ionization time-of-flight (ESI-TOF) mass spectrometric studies is discussed.
A new PVC membrane ion selective electrode which is highly selective towards Ni(II) ions was constructed using a Schiff base containing a binaphthyl moiety as the ionophore. The sensor exhibited a good Nernstian response for nickel ions over the concentration range 1.0 × 10-1 - 5.0 × 10-6 M with a lower limit of detection of 1.3 × 10-6 M. It has a fast response time and can be used for a period of 4 months with a good reproducibility. The sensor is suitable for use in aqueous solutions in a wide pH range of 3.6 - 7.4 and works satisfactorily in the presence of 25% (v/v) methanol or ethanol. The sensor shows high selectivity to nickel ions over a wide variety of cations. It has been successfully used as an indicator electrode in the potentiometric titration of nickel ions against EDTA and also for the direct determination of nickel content in real samples: effluent samples, chocolates and hydrogenated oils.
We have developed a highly La(III)-selective PVC membrane electrode based on a hexaaza macrocycle, 8,16-dimethyl-6,14-diphenyl-2,3,4:10,11,12-dipyridine-1,3,5,9,11,13-hexaazacyclohexadeca-3,5,8,11,13,16-hexaene [Bzo2Me2Pyo2(16)-hexaeneN6] (I) as membrane carrier, dibutylbutyl phosphonate (DBBP) as solvent mediator and sodium tetraphenylborate (NaTPB) as lipophilic additive. The best performance was given by the membrane of macrocycle I having a composition 10:260:5:120 (I:DBBP:NaTPB:PVC). The electrode exhibits a Nernstian response to La(III) ion in the concentration range 1.0 × 10-1 - 7.94 × 10-7 M with a slope of 19.8 ± 0.2 mV/decade of concentration and a detection limit of 5.62 × 10-7 M. The response time of the sensor is 12 s and it can be used over a period of 4 months with good reproducibility. The electrode works well over a pH range of 2.5 - 10.0 and in partially non-aqueous medium with up to 30% organic content. The sensor was also used as an indicator electrode in potentiometric titration of La(III) ions with EDTA and for determining La(III) concentration in real samples.
In this paper, a new PVC-based liquid-membrane anion-selective electrode based on a copper(II) of N,N′-bis(salicylidene)-1,2-bis(p-aminophenoxy)ethane tetradentate complex (Cu(II)BBAP) is described, which displays a preferential potentiometric response to iodide ion at pH 2.0 and an anti-Hofmeister selectivity sequence: I- > SCN- > ClO4- > NO2- > H2PO4- > NO3- > SO42- > Br- > Cl-. The electrode exhibits a near-Nernstian potential linear range of 8.2 × 10-7 - 1.0 × 10-1 M with a detection limit of 5.3 × 10-7 M and a slope of -58.8 mV per decade. The A.C. impedance technique and the UV/Vis spectroscopy technique were used to analyze the response mechanism. The electrode could be applied to determine iodide in medicine analysis, and the obtained results were fairly satisfactory.
A systematic study on the electrochemical behavior of diosmin in Britton-Robinson buffer (pH 2.0 - 10.0) at a glassy carbon electrode (GCE) was made. The oxidation process of the drug was found to be quasi-reversible with an adsorption-controlled step. The adsorption stripping response was evaluated with respect to various experimental conditions, such as the pH of the supporting electrolyte, the accumulation potential and the accumulation time. The observed anodic peak current at +0.73 V vs. Ag/AgCl reference electrode increased linearly over two orders of magnitude from 5.0 × 10-8 M to 9.0 × 10-6 M. A limit of detection down to 3.5 × 10-8 M of diosmin at the GCE was achieved with a mean recovery of 97 ± 2.1%. Based on the electrochemical data, an open-circuit accumulation step in a stirred sample solution of BR at pH 3.0 was developed. The proposed method was successfully applied to the determination of the drug in pharmaceutical formulations. The results compared favorably with the data obtained via spectrophotometric and HPLC methods.
Ephedrine-imprinted polymeric microspheres have been prepared in an aqueous system by multi-step swelling and suspension polymerization, using methacrylic acid (MAA) as a functional monomer, and ethylene glycol dimethacrylate (EGDMA) as a cross-linker. Scanning electron microscopy (SEM) was used as a means to identify the structure features of the obtained polymers. Further, we examined the recognition mechanism of the polymers and the influences of some chromatographic conditions, such as the mobile-phase composition, flow-rate, column temperature and sample amount on the retentivity and selectivity for (-)-ephedrine and (+)-ephedrine. The results reveal that stable macroporous polymer beads with good size monodispersity were obtained, the average size of which was 3 - 5 µm. Baseline chiral separation of the template isomers was achieved on a short column (50 mm × 4.6 mm i.d.) when the prepared polymer beads were used as a stationary phase, while the non-imprinted polymers (NIPs) did not show such ability. The optimized chromatographic condition was as follows: acetonitrile-acetic acid (99.8/0.2, v/v) as the mobile phase; sample amount, 40 - 80 µg; flow rate, 1.0 ml min-1; and column temperature, room temperature, respectively. It is assumed that two classes of binding sites exist in the porous polymers, one being hydrophilic binding sites, the other being hydrophobic binding sites.
A simple and ultrasensitive method, which was based on cold vapor generation (CVG) coupled to atomic fluorescence spectrometry (AFS), was proposed for speciation analysis of inorganic mercury (Hg2+) and methylmercury (MeHg) in water samples. In the presence of UV irradiation, all the mercury (MeHg + Hg2+) in a sample solution can be reduced to Hg0 by SnCl2; without UV irradiation, only Hg2+ species can be determined. So the concentration of MeHg can be obtained from the difference of the total mercury and Hg2+ concentration; thus, speciation analysis of Hg2+ and MeHg was simply achieved without chromatographic separation. Under the optimized experimental conditions, the limits of detection were 0.01 ng mL-1 for both Hg2+ and MeHg. The sensitivity and limit of detection were not dependent on the mercury species, and a simple Hg2+ aqueous standard series can be used for the determination of both Hg2+ and MeHg.
An ultra-sensitive colorimetric method to quantitate hundreds of polynucleotide molecules by gold nanoparticles with silver enhancement has been developed. The hybridization products from the target polynucleotides with biotin-labeled probes and gold nanoparticle-functioned oligonucleotides were immobilized to microplates via avidin-biotin system, and the absorbance signals of gold nanoparticles were amplified by silver enhance solution. This sandwich colorimetric assay can detect as few as 600 molecules for single-strand oligonucleotides and as few as 6000 molecules for double-strand polynucleotides in a 50 µL reaction system.
Trace impurities in high-purity cadmium were determined by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). To overcome some potentially problematic spectral interference, measurements were acquired in both medium and high-resolution modes. The matrix effects due to the presence of excess HCl and cadmium were evaluated. The optimum conditions for the determination were tested in this experiment and discussed. The detection limits ranged from 0.01 to 0.27 µg g-1, depending on the elements. The results for the determination of 22 trace elements in high-purity cadmium are presented.
Inductively coupled plasma-mass spectrometry (ICP-MS) incorporated with an on-line preconcentration system was used to determine trace amounts of ten metals including Ni, Cu, Zn, Rh, Ag, Cd, In, Au, Tl, and Pb in aqueous solutions and seawater. These metals, which formed the complexes, were retained in a sorbent microcolumn, followed by elution with methanol through a desolvation unit, which was capable of removing 83% of methanol. The limits of detection for these elements were determined simultaneously to be in the range from 3 to 20 ng/L.