Assessing the detectability of antioxidants in two‐dimensional high‐performance liquid chromatography

This paper explores the analytical figures of merit of two‐dimensional high‐performance liquid chromatography for the separation of antioxidant standards. The cumulative two‐dimensional high‐performance liquid chromatography peak area was calculated for 11 antioxidants by two different methods—the areas reported by the control software and by fitting the data with a Gaussian model; these methods were evaluated for precision and sensitivity. Both methods demonstrated excellent precision in regards to retention time in the second dimension (%RSD below 1.16%) and cumulative second dimension peak area (%RSD below 3.73% from the instrument software and 5.87% for the Gaussian method). Combining areas reported by the high‐performance liquid chromatographic control software displayed superior limits of detection, in the order of 1 × 10^?6 M, almost an order of magnitude lower than the Gaussian method for some analytes. The introduction of the countergradient eliminated the strong solvent mismatch between dimensions, leading to a much improved peak shape and better detection limits for quantification.     

Hydrogen ADPs with Cu Kα data? Invariom and Hirshfeld atom modelling of fluconazole

For the structure of fluconazole [systematic name: 2‐(2,4‐difluorophenyl)‐1,3‐bis(1H‐1,2,4‐triazol‐1‐yl)propan‐2‐ol] monohydrate, C₁₃H₁₂F₂N₆O·H₂O, a case study on different model refinements is reported, based on single‐crystal X‐ray diffraction data measured at 100 K with Cu Kα radiation to a resolution of sin θ/λ of 0.6 Å⁻¹. The structure, anisotropic displacement parameters (ADPs) and figures of merit from the independent atom model are compared to `invariom' and `Hirshfeld atom' refinements. Changing from a spherical to an aspherical atom model lowers the figures of merit and improves both the accuracy and the precision of the geometrical parameters. Differences between results from the two aspherical‐atom refinements are small. However, a refinement of ADPs for H atoms is only possible with the Hirshfeld atom density model. It gives meaningful results even at a resolution of 0.6 Å⁻¹, but requires good low‐order data.     

Invariom‐model refinement of l‐valinol

The structure of l ‐valinol [(S)‐(+)‐2‐amino‐3‐methyl­butan‐1‐ol or hydroxy­lated l ‐valine], C₅H₁₃NO, has been determined at 100 K by single‐crystal X‐ray diffraction. The independent atom model geometry, Flack parameter and figures of merit are compared with results from an invariom structure refinement. The latter provides H‐atom positions free of independent atom model bias and therefore yields a more accurate hydrogen‐bond pattern, and the geometry from invariom refinement shows an improved agreement with results from a quantum chemical geometry optimization.     

Room-temperature fluorescence spectrometry of some pharmaceutical compounds

Room-temperature fluorescence of 66 pharmaceutical drugs are presented using a mixture of ethanol/water as solvent. The analytical figures of merit for the fluorescent species are reported with limits of detection ranging between 1 and 30 ng/ml for most of them and with average blank standard deviation of 7.6%. The spectral band half-widths are also reported.     

Evaluation and characterization of a commercial zeeman-modulated tungsten-strip electrothermal atomic absorption spectrometer

The operating parameters and the quantitative of an AAZ-2 Zeeman-modulated tungsten-strip atomic absorption spectrometer are reported. The figures of merit for Ag, Au, Cd, Co, Cu, Fe, Mn, Ni, Pb, Tl, and Zn are reported. Detection limits obtained with the AAZ-2 were comparable to those obtained with other metal atomizers reported in the literature. A maximum heating rate of 12 K ms^?1 was measured for the tungsten-strip atomizer.     

Simultaneous or scanning data acquisition? A theoretical comparison relevant to inductively coupled plasma sector-field mass spectrometers

The benefits of simultaneous multichannel detection over single-channel scanning detection are well established in analytical chemistry. Multichannel detection increases duty cycle, which leads to enhanced sensitivity, detection limits, and reduced analysis time. Also, multichannel detection used with either isotope-ratio or internal-standard techniques provides a mechanism to reduce the effect of multiplicative or flicker noise prevalent in plasma sources. An additional benefit of simultaneous detection is superior analysis of short-lived transient signals. Presented here is a theoretical comparison between simultaneous/continuous multichannel acquisition and single-channel scanning acquisition. To conduct this comparison, reported sensitivity, single-channel precision, and background values for commercial inductively coupled plasma sector-field mass spectrometers (ICP-SFMS) are used to generate theoretical figures of merit for both acquisition methods. Among the figures of merit that will be considered are detection limits, precision, and analysis time, particularly for multi-element or multi-isotope analysis.     

Development of a dispersive liquid–liquid microextraction method using a lighter‐than‐water ionic liquid for the analysis of polycyclic aromatic hydrocarbons in water

A dispersive liquid–liquid microextraction method using a lighter‐than‐water phosphonium‐based ionic liquid for the extraction of 16 polycyclic aromatic hydrocarbons from water samples has been developed. The extracted compounds were analyzed by liquid chromatography coupled to fluorescence/diode array detectors. The effects of several experimental parameters on the extraction efficiency, such as type and volume of ionic liquid and disperser solvent, type and concentration of salt in the aqueous phase and extraction time, were investigated and optimized. Three phosphonium‐based ionic liquids were assayed, obtaining larger extraction efficiencies when trihexyl‐(tetradecyl)phosphonium bromide was used. The optimized methodology requires a few microliters of a lighter‐than‐water phosphonium‐based ionic liquid, which allows an easy separation of the extraction solvent phase. The obtained limits of detection were between 0.02 and 0.56 μg/L, enrichment factors between 109 and 228, recoveries between 60 and 108%, trueness between 0.4 and 9.9% and reproducibility values between 3 and 12% were obtained. These figures of merit combined with the simplicity, rapidity and low cost of the analytical methodology indicate that this is a viable and convenient alternative to the methods reported in the literature. The developed method was used to analyze polycyclic aromatic hydrocarbons in river water samples.     

直接法中偏离因子的探讨

直接法中品质因子普遍存在着物理意义不够明确的缺点。通过改变R_k表达式中平均此例常数K的定义,得到R_H。从而克服了R_k和R_α受系统误差干扰及R_k分辨率不高的缺点,且有一定的物理意义。实验结果表明,R_H具有直接法中偏离因子的作用。预计它在判定推导出位相准确性方面会比直接法目前使用的其它判据好。     

Figures of merit for an ICP-echelle spectrometer system

Figures of merit of an ICP-echelle Spectrometer System are presented for 55 elements. The analytical importance of each figure of merit is discussed. The analytical results obtained with the ICP-echelle system compare well with previously published figures for ICP studies.     

EMG模型参数间的联系

通过色谱拖尾峰EMG数学模型的计算机数值计算, 建立了拖尾峰特征参数之间的三类不同性质的线性关系, 佐证并修正了一些经验公式, 提出了计算模型参数与保留时间之间线性关系的新方法。     

A heuristic and parallel simulated annealing algorithm for variable selection in near‐infrared spectroscopy analysis

A new heuristic and parallel simulated annealing algorithm was proposed for variable selection in near‐infrared spectroscopy analysis. The algorithm employs a parallel mechanism to enhance the search efficiency, a heuristic mechanism to generate high‐quality candidate solutions, and the concept of Metropolis criterion to estimate accuracy of the candidate solutions. Several near‐infrared datasets have been evaluated under the proposed new algorithm, with partial least squares leading to improved analytical figures of merit upon wavelength selection. Improved robust and predictive regression models were obtained by the new algorithm. The method could also be helpful in other chemometric activities such as classification or quantitative structure‐activity relationship problems.     

BSA optimization and dosimetric assessment for an electron linac based BNCT of deep‐seated brain tumors

A study was conducted to investigate a photoneutron spectrum based on a 25 MeV electron linac for treatment of deep-seated brain tumors in the context of boron neutron capture therapy (BNCT). Based on a series of Mont Carlo N-Particle simulations, tungsten and uranium with optimized geometry were selected as the most appropriate converters for (e,γ) and (γ,n) reactions, respectively. The final optimized photoneutron source yield was 5.78 × 10¹³ n/s/mA, which is a high value for these kinds of sources. A beam shaping assembly (BSA) for the proposed neutron source containing optimal moderators, filter, reflector, and collimator was simulated. Results showed that using this BSA enables us to meet International atomic energy agency recommended figures of merit at the BSA beam port. Also, the calculated in-phantom figures of merit and dose evaluation results via a simulated head phantom confirmed that the designed neutron source and its related BSA configuration can potentially treat deep-seated brain tumors in BNCT framework. In the present study, some in-phantom figures of merit such as advantage depth, advantage depth dose rate, advantage ratio, and treatment time are 7.6 cm, 0.7 Gy/min, 4.2, and 17.8 min, respectively.     

The Analysis of Chlorinated Phenol Solutions by Capillary Electrophoresis Coupled with Direct and Indirect Amperometric Detection Using a Boron‐Doped Diamond Microelectrode

Analysis of aqueous solutions containing chlorinated phenol pollutants was accomplished by capillary electrophoresis with direct and indirect amperometric detection using a boron‐doped diamond microelectrode. The microelectrode was prepared by (i) coating a thin film of boron‐doped polycrystalline diamond on a sharpened platinum wire (76‐μm diameter) and (ii) sealing the coated wire in a polypropylene pipet tip. The diamond microelectrode, used in end‐column detection, exhibited a low and stable background current with low peak‐to‐peak noise and good electrochemical activity for the pollutants without any conventional pretreatment. The electrode performance was evaluated in terms of the linear dynamic range, sensitivity, limit of quantitation, and response precision for the detection of several priority pollutants (2‐chlorophenol, 3‐chlorophenol, 4‐chlorophenol, 2,4‐dichlorophenol, 2,4,6‐trichlorophenol, and pentachlorophenol). The diamond microelectrode gave good detection figures of merit for these contaminants in the direct amperometric mode with no evidence of any electrode fouling. As an example, the concentration limit of quantitation for 2‐chlorophenol was 100 nM or 13 ppb (S/N=3) and the relative standard deviation of the peak height for 9 injections was 4.7±0.5% (est. 1.1 nL inj.). The separation efficiency was greater than 100 000 plates/m for all seven solutes. The microelectrode was also employed for the indirect detection of the chlorinated phenols. In this approach, which is useful for detecting electroinactive solutes, ferrocene carboxylic acid was added to the run buffer as the electrophore. Good detection figures of merit were also achieved for the separation and detection of 2‐chlorophenol, 3‐chlorophenol, and 2,4‐dichlorophenol in this mode, although the linear dynamic range was not as wide and the limit of quantitation was not as low as in direct amperometry. For example, the concentration limit of quantitation for these pollutants was in the mid micromolar range (1–10 ppm) with excellent response reproducibility of 3.2±0.8%, or less.     

Sector field mass spectrometers in ICP-MS

A new generation of sector field mass spectrometers, with improved analytical figures of merit at even lower prices, is commercially available, giving a strong impetus to the development of inductively coupled plasma mass spectrometry (ICP-MS) sector field instrument applications in the analytical community. It is the aim of this paper to give an overview of these instruments, to introduce some basic concepts, to discuss their peculiarities and performance, and to present some selected examples of analytical applications to demonstrate the `state of the art'.     

Electrocatalytic Oxidation of Estrogenic Phenolic Compounds at a Nickel‐Modified Glassy Carbon Electrode

This paper demonstrates for the first time, successful electrocatalytic oxidation of electroactive estrogenic phenolic compounds (EPCs) at a nickel‐modified glassy carbon electrode (Ni‐GCE). The electrode was evaluated in terms of electrocatalytic activity, sensitivity, linear dynamic range, limit of detection, and response stability. In comparison to bare glassy carbon electrode, current amplification was observed for EPCs at Ni‐GCE, for example, for a 40 µM estrone at Ni‐GCE was amplified by a factor of 1224. The Ni‐GCE gave good figures of merit with no evidence of electrode fouling. As an example, the limit of detection (S/N=3) for 17β‐estradiol was 100 nM and the response precision (n=5) was 3.4 %.     

An evaluation of the analytical performance of collinear multi-pulse laser induced breakdown spectroscopy

A detailed study of the relevant analytical figures of merit for time- and spatially integrated multi-pulse laser induced breakdown spectroscopy (MP-LIBS) was performed. Laser bursts containing up to 6, ns-range duration collinear pulses, separated by 20–40 μs interpulse gaps were used in the experiments, and the effect of the number of pulses within the burst on the analytical parameters was investigated. Signal enhancement, repeatability, matrix effects, background signals, sensitivity, linear dynamic range and limits of detection were studied for 20 lines of 11 elements in different solid matrices. It was established that all analytical figures of merit significantly improved with respect to those of single- or double-pulse LIBS as a result of the use of multiple laser pulses. For example, six-pulse limits of detection values were found to be with a factor of 4.2–16.7 lower than for double-pulses and calibration plots were found to be linear up to several tens of percents concentrations in some alloys.     

A simple micro‐extraction plate assay for automated LC‐MS/MS analysis of human serum 25‐hydroxyvitamin D levels

This short application note describes a simple and automated assay for determination of 25‐hydroxyvitamin D (25(OH)D) levels in very small volumes of human serum. It utilizes commercial 96‐well micro‐extraction plates with commercial 25(OH)D isotope calibration and quality control kits. Separation was achieved using a pentafluorophenyl liquid chromatography column followed by multiple reaction monitoring‐based quantification on an electrospray triple quadrupole mass spectrometer. Emphasis was placed on providing a simple assay that can be rapidly established in non‐specialized laboratories within days, without the need for laborious and time consuming sample preparation steps, advanced calibration or data acquisition routines. The analytical figures of merit obtained from this assay compared well to established assays. To demonstrate the applicability, the assay was applied to analysis of serum samples from patients with chronic liver diseases and compared to results from a routine clinical immunoassay. Copyright © 2015 John Wiley & Sons, Ltd.     

Room-temperature phosphorimetry of polyaromatic hydrocarbons with organized media and paper substrate: A comparative study

Room-temperature phosphorescence of some polyaromatic hydrocarbons as model compounds with stabilization by use of a microemulsion of a non-polar solvent, has been examined. Some advantage in the preparation of the solutions is achieved. A comparative study of room-temperature phosphorimetry in microemulsion and micellar media, on paper substrates and at low temperature has also been made. The spectral characteristics and analytical figures of merit are given.     

Analysis of some organochlorine pesticides in seafood samples by solid-phase extraction—Gas chromatography

Summary The use of the solid-phase extraction technique for the rapid sample preparation of organochlorine pesticides is described. Samples were simultaneously extracted, cleaned, and fractionated by the solid-phase extraction method and a further separation and determination of extracted fractions was carried out by gas chromatography with either an electron capture or a Hall electrolytic conductivity detector. The percent recovery of the extracted seven pesticides was compared to that of the conventional liquid-liquid extraction method. The analytical figures of merit., chromatograms, and statistic data are reported. The application of this method was demonstrated by a real fish sample determination with mass spectra for confirmation of Kepone detection.