Positrons have been used for material analysis not only because of their novel characteristics, such as an ability to detect open-volume type defects in materials, but also because interactions with solids differ from those of electrons in such processes as scattering and diffraction. Monoenergetic positron beams and microbeams were developed in the 1980s, and positron experiments have made progress in material analyses. In this article we review the fundamental technique of microbeam fabrication, especially using a magnetically-guided positron beam, its extension to various analytical methods, and expectations for future research.
A novel method for preparing samples for use in MALDI-TOFMS (matrix-assisted laser desorption ionization time-of-flight mass spectrometry) is described. Seven hydrolysis products derived from nitrogen mustards and CHCA (α-cyano-4-hydroxycinnamic acid) were selected as model compounds and the matrix, respectively. A capillary atomizer was used for evaporative and spray deposition of the sample/matrix solution, leading to the formation of a freestanding film that coated and accumulated on the MALDI substrate (i.e., sample plate). Compared to the traditional method for MALDI, which involves the production of dried droplets, the surface roughness was reduced, resulting in the accumulation of the sample-doped matrix on the sample plate. This resulted in an increase in the limit of detection of 1 − 2 orders of magnitude. In order to compare the structures of the sample-doped matrices obtained by the traditional dried droplet method versus the spray deposition method (developed in this study), the matrices were examined by SEM (scanning electron microscopy). The design of the capillary atomizer and details of the experimental conditions are reported. The application of this method to the above seven degradation products was successful, suggesting that it has great potential for use as a routine monitoring tool.
Ethylene glycol oligomers were visualized by indirect conductimetric detection based on dilution of the mobile phase due to the analytes. A high electrical conductivity background was maintained by the addition of 5 mM sodium nitrate in the mobile phase, and the analytes were visualized by decreases in the background when they eluted. A capacitively coupled contactless conductivity detector was convenient to monitor effluents from the microcolumn with minimum extra-column band broadening. The signals as negative peaks were linear to the concentration of the analytes, and a concentration detection limit of 0.025% was achieved for tetraethylene glycol at S/N=3, corresponding to the mass detection limit of 38 ng for 0.15 μl injection. The logarithm of the retention factor of ethylene glycol oligomers was linear to the degree of polymerization (DP) as well as to the acetonitrile composition in the mobile phase. These situations allowed us to estimate the DP of eluted ethylene glycol oligomers by using a few oligomers with known DP. The dynamic reserve, defined as the ratio of the background to its noise level achieved under the present conditions, was 2.3 × 105 which was much larger than that achieved by UV absorption detection. The present method was applied to profile ethylene glycol oligomers contained in commercially available PEG reagents.
A simple and sensitive reversed-phase liquid chromatographic method, based on the precolumn derivatization with 9-fluorenylmethyl chloroformate, was developed for the determination of myriocin. The derivatization reaction was performed in organic solvents of pyridine and tetrahydrofuran at 40°C. Several factors influencing the derivative yield were investigated and optimized. The formed derivative was stable for more than 24 h at room temperature. The detection wavelength was 262 nm. The system offered the following analytical parameters: the limit of detection was 0.045 μg ml−1, the linear correlation coefficient was 0.9963 and the linear range response was from 2.0 to 500.0 μg ml−1. The precision of the method was <2.0%. As a preliminary application, the method has been successfully applied to the determination of myriocin in natural and cultured Cordyceps cicadae.
A microemulsion electrokinetic chromatography (MEEKC) method has been developed for the determination of four nitrofuran antibiotics (furazolidone (FZD), furaltadone (FTD), nitrofurazone (NFZ) and nitrofurantoin (NFT)) in turbot fish. The effect of buffer the pH, the concentration of SDS and the concentrations of octane and butan-1-ol were studied systematically. With the optimized experimental conditions (octane, 0.82% (w/w); SDS, 3.48% (w/w); butan-1-ol, 6.48% (w/w); and 10 mM sodium tetraborate buffer (pH 9.70), with 30 kV as the applied voltage) all four analytes were baseline-separated within 8 min. Regression equations revealed a good linear relationship between the peak area of each compound and its concentration. The correlation coefficients of the four analytes were from 0.9945 to 0.9999. The relative standard deviations of the migration times and the peak areas were <1.84 and 5.16% (intra-day). The obtained recovery ranged between 97 and 104%. Moreover, the method was successfully validated and applied to the determination of nitrofuran antibiotics in contaminated fish.
This study describes an analytical methodology developed for determination of phthalate esters (di-n-butyl, butylbenzyl and di-2-ethylhexyl phthalate) and adipate (di-n-ethylhexyl adipate) by solid-phase microextraction (SPME) and gas chromatography in normal saline solutions and, in bi-distilled water used to reconstitute medicines. An 85-μm-polyacrylate SPME fiber was selected and used in all analyses. The parameters affecting extraction efficiency were simultaneously optimized, firstly by means of a two-level full factorial design including a center point and subsequently through a Doehlert design for two-variables. Satisfactory detection limits in the range of 0.18 to 0.75 μg L−1 and excellent precision, with relative standard deviation values being lower than 15.1% (n = 6), were obtained. Relative sensitivities of between 72.3 and 124.3% were obtained.
A rapid and sensitive assay for the quantification of imperatorin in plasma and tissues has been developed. An analysis was performed by gas chromatography/mass spectrometry in the selected ion-monitoring mode. The main pharmacokinetic parameters obtained were Tmax = 1.23 ± 0.26 h, Cmax = 0.95 ± 0.38 μg/mL, AUC = 3.42 ± 0.52 h μg/mL and Ka = 1.34 ± 0.18 h. The experimental results showed that imperatorin was easily absorbed, but its elimination was slow, from 3 to 12 h after oral administration. The concentrations of imperatorin in rat liver, kidney, lung, and heart were higher than those in other organs. To determine the free fraction in serum, samples were filtered using ultrafiltration membranes with a molecular weight cut-off of 10 kDa, and extracted using liquid-liquid extraction. The protein binding values in rat plasma, spontaneous hypertensive rat plasma, human plasma and human serum albumin were 84 ± 3, 69 ± 7, 81 ± 7 and 75 ± 3%, respectively.
A method was developed for the extraction of valproic acid (VPA) by hollow-fiber coated wire as a lab-made solid-phase microextraction (SPME) fiber and its determination by capillary gas chromatography in human serum and pharmaceutical formulations. In this study, a piece of copper wire coated by polypropylene hollow-fiber membrane was used as a SPME fiber, and its efficiency for the extraction of VPA from the headspace of samples prior to gas chromatographic analysis was evaluated. The optimum conditions of microextraction process were selected, and the limit of detection for VPA was found to be 85 μg L−1 in solution and 1.7 mg L−1 in human serum. A low detection limit, a wide linear dynamic range (0.25 − 100 mg L−1), good repeatability (RSD%<4 in formulations and RSD%<7 in serum samples) and a higher mechanical durability due to its metallic base are some of the most important advantages of the proposed fiber.
Neutron activation analysis with an internal standard correction was applied to the determination of Cr and Co in a ceramics certified reference material (NMIJ CRM 8004-a silicon nitride powder). Cesium was used as an internal standard to compensate for any inhomogeneity of the neutron flux through an irradiation capsule and to improve the repeatability of gamma-ray measurements. It was found that the linearity of the calibration curves of Cr and Co was improved by using an internal standard. The analytical results of Cr and Co in NMIJ CRM 8004-a were in good agreement with those obtained by ICP-OES, ICP-sector field mass spectrometry (ICP-SFMS), and isotope dilution/ICP-SFMS for Cr. The relative expanded uncertainties (k = 2) were 1.9% for Cr and 1.5% for Co. The uncertainties were comparable to those of atomic spectrometric methods.
In acetic acid buffer solution, glucose oxidase (GOD) catalyzed the dissolved oxygen oxidation of glucose to form H2O2. In succession, horseradish peroxidase (HRP) catalyzed the H2O2 oxidizing excess I− to form I3−. The I3− combined with a cationic surfactant (CS) such as tetradecyl dimethyl benzyl ammonium chloride (TDMBA) to produce TDMBA-I3 association particles that exhibited the strongest resonance scattering (RS) peak at 460 nm. The enhanced RS intensity at 460 nm was linear with glucose concentration in the range of 2.0 × 10−8 − 2.0 × 10−6 mol/L, with a detection limit of 8.5 × 10−9 mol/L. The glucose in serum samples were assayed by the enzyme catalytic RS assay and by spectrophotometry. The results of both assays showed a close correlation. This assay has simplicity, sensitivity and good specificity for quantitative determination of glucose.
A method for the determination of ofloxacin (OFL) has been developed, based on the enhancement of resonance light scattering (RLS) of OFL in the presence of alizarin violet 3B (AV3B). Under the experimental conditions, the RLS intensity of AV3B was greatly enhanced by adding OFL. At pH 5.09, the enhancement of the RLS intensity at 439.5 nm was proportional to the concentration of OFL in the range 0.10 − 2.50 μg/ml. The detection limit (3σ) was 0.013 μg/ml. At pH 6.90, the enhancement of the RLS intensity at 405.0 nm was proportional to the concentration of OFL in the range 0.05 − 3.00 μg/ml. The detection limit (3σ) was 0.021 μg/ml. The proposed method with high sensitivity, selectivity and reproducibility was satisfactorily applied to the determination of OFL in human serum.
This paper describes a green analytical procedure for the determination of bumetanide using diffuse reflectance spectroscopy. The proposed method is based on reflectance measurements of a violet compound produced from a spot test reaction between bumetanide and p-dimethylaminocinnamaldehyde (p-DAC) in an acid medium, using filter paper as a solid support. The best conditions for the reaction have been found by experimental design methodologies. All reflectance measurements were carried out at 525 nm, and the linear range was from 1.37 × 10−4 to 1.37 × 10−3 mol L−1, with a correlation coefficient of 0.998. The detection limit was estimated to be 3.98 × 10−5 mol L−1. Five commercial medicines containing bumetanide were analyzed by the proposed method. No interferences were observed from the common excipients present in pharmaceutical formulations. The results were favorably compared with those obtained by the United States Pharmacopoeia procedure at 95% confidence level.
The applicability of 2-hydroxybenzaldehyde benzoylhydrazone (2-HBBH) for determining Cd(II), Cu(II), Pb(II) and Bi(III) ions by adsorptive cathodic stripping voltammetry was studied. The sensitivity of metal reduction peak currents was highly enhanced with the addition of 2-HBBH to metallic solutions, showing the adsorptive characteristics of the complexes. Variable factors affecting the response (mainly: the influences of pH, supporting electrolyte and deposition potential on selectivity and sensitivity) were investigated. Limits of detection suitable for trace analysis were obtained: 0.28 μg L−1 for Cd(II) at pH 10; 0.026 μg L−1 for Pb(II) at pH 9; 0.285 μg L−1 for Bi(III) at pH 8 and 0.051 μg L−1 for Cu(II) at pH 9.5. Simultaneous determinations of two groups of elements, consisting of Cd(II)-Pb(II)-Cu(II) and Cd(II)-Pb(II)-Bi(III), at pH 9.5 and 9, respectively, were described with good resolution and sensitivities. Metals were quantified at concentrations in the range from 0.5 to 14 μg L−1. The RSD at a concentration level of 5 μg L−1 of metal was 4.28% for Cd(II), 2.99% for Pb(II), 4.82% for Bi(III) and 1.35% for Cu(II). The method was applied to the simultaneous determination of metals in certified reference water (TMDA-62) and in synthetic water samples with satisfactory results.
A poly(vinyl chloride) matrix membrane sensor for the selective determination of thiocyanate has been developed based on the use of copper(II)-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex (Cu-PADAP) as a novel charged carrier, and o-nitrophenyloctyl ether (o-NPOE) as a solvent mediator. The sensor displays a significantly enhanced response towards SCN− ions over the concentration range 7.0 × 10−6 to 1.0 × 10−2 mol L−1 with a detection limit of 5.6 × 10−6 mol L−1 and a calibration slope of −57.5 ± 0.5 mV decade−1. The sensor exhibits a long life-span, long-term stability, high reproducibility, and a fast response time. The selectivity coefficients of some anions were calculated using the separate solutions method, and found to be in the following order: SCN− > ClO4− > I− > Sal− > NO2− > Br− > NO3− = CH3COO− > Cl− > SO42− = PO43−. The effects of the pH and ionic membrane additives (e.g. tridodecylmethylammonium chloride, TDMAC and potassium tetrakis[bis(3,5-trifluoromethyl)phenyl] borate, KTFPB) were examined. The sensor was used for the determination of SCN− ions in saliva and urine samples collected from some smoker and non-smoker donors. The developed sensor was also applied to determine the cyanide content in electroplating waste water samples after its conversion into thiocyanate. The application of the sensor to monitor the potentiometric titration of Ag+ and Hg2+ using SCN− resulted in sharp inflection breaks at the equivalent points. The data obtained using the proposed sensor correlate very well with results collected using the standard methods of thiocyanate, cyanide and metal analysis.
Carbon nanotube (CNT) gel, which is composed of a mixture of single-wall CNT, an ionic liquid, and a thermostable D-proline dehydrogenase (D-Pro DH) immobilized electrode was utilized for the determination of D-amino acids (DAAs) in food samples. When a critical comparison with CNT, Ketjen Black (KB), and carbon powder (CP) was also carried out, the CNT/D-Pro DH immobilized electrode showed the highest sensitivity and the lowest detection limit of D-proline. In addition, the CNT/D-Pro DH immobilized electrode was applied to detection of DAAs in rice wine and vinegar samples. The concentrations of DAAs in rice wine and vinegar samples were 0.0210 ± 0.0001 and 0.55 ± 0.05 mmol L−1, respectively.
The optimum conditions of the mobile phase for HPLC with electrochemical detection (HPLC-ECD) were selected from among solvents of different grades with the standard deviation (SD) of area measurements based on FUMI (function of mutual information) theory as a criterion. In HPLC-ECD for determining baicalin and baicalein using a phosphoric acid-methanol-water mixture (0.5:60:40, v/v/v) as a mobile phase, the effects of three grades of phosphoric acid, of five grades of methanol, and of seven grades of water on the measurement precision were examined. The mixture, if characterized by the minimum SD of measurements, was selected as the optimal mobile phase. This selection method saves considerable amounts of chemicals and experimental time, and would be a useful exploration technique for the routine check and troubleshooting of HPLC-ECD.
A new chiral liquid-chromatographic method was developed for the enantiomeric separation of ofloxacin with a fluorescence detector. The enantiomers of ofloxacin were baseline resolved on a Chiralcel OD-H (250 mm × 4.6 mm, 5 μm) column using a mobile-phase system containing hexane-ethanol-methanol-acetic acid-diethylamine (70/20/10/0.45/0.05, v/v/v/v/v). The presence of diethylamine in the mobile phase has played an important role in enhancing the chromatographic efficiency and resolution between enantiomers.
In this paper a simple protocol is described for estimating of solid-phase extraction (SPE) elution volumes of steroids based on retention data generated from micro-planar chromatography. Particularly, the retention of selected steroids, including estrogens and progestagens, was studied on wettable with water octadecylsilica HPTLC plates and mobile phases composed of methanol:water mixtures ranging from 20 to 100% (v/v). It was found that TLC retention data can be linearized by plotting RM values of steroids against a reciprocal form of the organic modifier molar fraction (1/Xs). Using such a mathematical approach, the retention parameter of steroids investigated could be easily back-calculated for a wide range of mobile-phase compositions, using few initial experimental data points. The hold-up time of SPE cartridges filled with 0.5 g of C-18 adsorbent was determined experimentally, and appropriate retention factor values (kSPE) for components of interest studied were calculated. Using an appropriate slope and intercept coefficients of the linear-regression equation formed as log kSPE = aRM + b, the steroids SPE elution volumes were predicted beyond the experimental data range that was available for a solid-phase extraction experiment, particularly for mobile phases that contained a high level of water.
A simple column electrode, S-CE, with a glassy carbon fibers working electrode stuffed into a Teflon tube was developed. The current-potential curves for the reductions of [Fe(CN)6]3− and Fe3+ observed at the S-CE were analyzed based on a theory for those at an ordinary column electrode. A quantitative electrolysis was performed at the S-CE rapidly within 20 s. An accurate and precise coulometric determination could be attained at the S-CE even with a fairly dilute solution. For example, coulometric reductions of 5 × 10−5 and 5 × 10−6 M Fe3+ were attained with efficiencies (n = 5) of 99.7 ± 0.2 and 101.9 ± 1.1%, respectively.