Second-order calibration of excitation-emission matrix fluorescence spectra for the determination of N-phenylanthranilic acid derivatives

A spectrofluorimetric method has been developed for the quantitative determination of mefenamic, flufenamic, and meclofenamic acids in urine samples. The method is based on second-order data multivariate calibration (unfolded partial least squares (unfolded-PLS), multi-way PLS (N-PLS), parallel factor analysis (PARAFAC), self-weighted alternating trilinear decomposition (SWATLD), and bilinear least squares (BLLS)). The analytes were extracted from the urine samples in chloroform prior to the determination. The chloroform extraction was optimized for each analyte, studying the agitation time and the extraction pH, and the optimum values were 10 minutes and pH 3.5, respectively. The concentration ranges in chloroform solution of each of the analytes, used to construct the calibration matrix, were selected in the ranges from 0.15 to 0.8 microg mL-1 for flufenamic and meclofenamic acids and from 0.25 to 3.0 microg mL-1 for mefenamic acid. The combination of chloroform extraction and second-order calibration methods, using the excitation-emission matrices (EEMs) of the three analytes as analytical signals, allowed their simultaneous determination in human urine samples, in the range of approximately 80 mg L-1 to 250 mg L-1, with satisfactory results for all the assayed methods. Improved results over unfolded-PLS and N-PLS were found with PARAFAC, SWATLD, and BLLS, methods that exploit the second-order advantage.     

Determination of spectrometer-detector parameters from calibration spectra and the use of the parameters in spectrometer calibrations

The grating equation is used to generate quadratic calibration equations for multichannel detectors with perpendicular and tilted focal planes. The quadratic coefficients are not independent and contain terms that are used to solve for spectrometer-detector parameters. The parameters can be calculated from a quadratic fit at one spectrometer position, but more accurate values can be obtained from quadratic fits at two spectrometer positions. The calculations show that the detector focal plane is tilted by about two degrees. Once values for the spectrometer-detector parameters are obtained from calibrations using at least three lines at one or two spectrometer positions, only one calibration line at any spectrometer position is required to obtain accuracies on the order of 0.1 cm(-1) over a several thousand wavenumber range. The main cause of spectrometer drift is a change in the diffraction angle and/or the spectrometer included angle. This drift is almost totally compensated by the one-line calibration, which adjusts the diffraction angle. A neon pen lamp is used to generate the calibration spectra. Using standard air wavelengths compared to true wavelengths can produce calibration errors of 0.1 to 0.6 cm(-1); the magnitude depends on local conditions and how the laser wavelength is treated.     

Multiple-fluorophore-specie detection with a tapered Fabry-Perot fluorescence spectrometer

A novel fluorescence spectrometer and method for the simultaneous detection of multiple-fluorophore species in a no-moving-parts, instantaneous manner is described. In the reported embodiment of the instrument, a tapered Fabry-Perot filter is used to spatially encode the fluorescence spectrum from a multiple-dye-containing test sample. Using a pseudoinverse reconstruction algorithm, we spectrally decode the particle concentration for each dye specie in the test sample. Experimental results are reported along with a theoretical treatment of the method.     

Mitigation of Rayleigh and Raman spectral interferences in multiway calibration of excitation-emission matrix fluorescence spectra

A weighted parallel factor analysis (W-PARAFAC) model is applied to excitation-emission matrix (EEM) fluorescence spectra of carbamate pesticides to aid with calibration in the presence of Raman scattering. Traditional PARAFAC inefficiently models the Raman scattering, resulting in prediction and calibration errors when a significant background is present. Four different weighting strategies were investigated and compared with subtraction of the appropriate sample background. Using a binary weighting strategy produced superior results, compared with a continuous distribution of weights. Further choice of weighting strategies, which are optimized to include either maximum analyte signal or to exclude a maximum amount of background scattering, is dependent on the degree of overlap and relative signal intensity.     

A simple method for linearizing nonlinear spectra for calibration

The development and acceptance of spectral calibration methods has been an important success story for the field of chemometrics. This paper contains a new study of a very old calibration method (K-matrix calibration, parallel calibration, or generalized inverse prediction) and partial least squares (PLS), the mainstay of modern chemometrics. We show that with some modest amount of modification, the old method of calibration is comparable, in terms of prediction, to PLS for spectroscopy involving nonlinear spectral responses.     

Spectral simulation methodology for calibration transfer of near-infrared spectra

A spectrum simulation method is described for use in the development and transfer of multivariate calibration models from near-infrared spectra. By use of previously measured molar absorptivities and solvent displacement factors, synthetic calibration spectra are computed using only background spectra collected with the spectrometer for which a calibration model is desired. The resulting synthetic calibration set is used with partial least squares regression to form the calibration model. This methodology is demonstrated for use in the analysis of physiological levels of glucose (1-30 mM) in an aqueous matrix containing variable levels of alanine, ascorbate, lactate, urea, and triacetin. Experimentally measured data from two different Fourier transform spectrometers with different noise levels and stabilities are used to evaluate the simulation method. With the more stable instrument (A), well-performing calibration models are obtained, producing a standard error of prediction (SEP) of 0.70 mM. With the less stable instrument (B), the calibration based solely on synthetic spectra is less successful, producing an SEP value of 1.58 mM. For cases in which the synthetic spectra do not describe enough spectral variance, an augmentation protocol is evaluated in which the synthetic calibration spectra are augmented with the spectra of a small number of experimentally measured calibration samples. For instruments A and B, respectively, augmentation with measured spectra of nine samples lowers the SEP values to 0.64 and 0.85 mM.     

Design of a fast compton spectrometer for measuring megavoltage bremsstrahlung spectra

Measurements of bremsstrahlung X-ray spectra produced by high energy electron linacs (such as those found in many cancer therapy centers) pose special problems. These machines typically operate at very low duty factors, have very high photon fluences, and produce X-rays of energy too high to be measured accurately with a single detector. A compton pair spectrometer utilizing fast plastic scintillators and nanosecond timing techniques suitable for these measurements is described.     

Portable total reflection X-ray fluorescence spectrometer for nanogram Cr detection limit

A portable total reflection X-ray fluorescence spectrometer is presented. The present spectrometer mainly consists of a 1.5-W X-ray tube, a waveguide type slit, a detector, and a sample carrier (a quartz optical flat), and these components are contained in an attache case-type box. Continuum X-rays emitted from the low-power X-ray tube are used for the excitation of the X-ray fluorescence, and the minimum detection limit for Cr is a few nanograms or the level of 1013 atoms/cm2.     

Extreme-ultraviolet calibration of thin-film Zr filters for the cosmic hot interstellar plasma spectrometer

The design and calibration of thin-film Zr transmission filters for the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) spaceborne astronomical telescope is presented. The transmission of a 1,000-A-thick Zr filter is measured for wavelengths from 45 to 1,304 A as well as its variability with respect to expected space-flight enviromental extremes of temperature, vibration, and atomic O bombardment. For the CHIPS spectral band of 90-260 A, the transmission of the Zr fiter is deemed useful between 90 and 200 A and is stable with respect to expected temperature and vibrational changes. The maximum atomic O bombardment decreases the filter transmission between 90 and 130 A by approximately 20% and does not appreciably affect the rest of the CHIPS bandpass. These results make Zr an acceptable filter candidate for CHIPS.     

用于流动注射氢化物发生原子荧光光谱分析的在线预还原器件

研制一种用于流动注射氢化物发生-原子荧光光谱分析法测定氢化物发生元素的在线预还原器件,该器件由专门设计的程序运行。预还原室可水浴加热以便加快预还原反应减少预还原时间。各个氢化物发生元素的预还原条件需要分别优化。对以砷为例的试验证明,使用该器件在线预还原的校准曲线和离线手工预还原的校准曲线吻合,表明该器件的预还原是完全的。在分析批量试样时,该预还原器件具有方便、减轻制样工作量等优点。该器件可用于和各种同类型的流动注射氢化物发生原子荧光光谱仪联用。     

Predicting response spectra for earthquake signals generated as filtered noise

Generating families of earthquake signals which in mean fulfill a given response spectrum can be done by filtering white noise through a linear filter and multiplying the filtered signal with a time-window function. To design the filters, the response spectrum of the filtered white noise sequences must be predicted. In the past years several methods for doing this have been suggested.In this article, we have modified some of these methods and also proposed a new method. We have compared the methods by doing simulations. It was found that the proposed method was useful for predicting response spectra of signals with slow decaying time-window functions. A further benefit of the proposed method is that it could be used for predicting response spectra with time varying frequency content.     

Design and optimization of the calibration procedure for a miniaturized Fourier transform spectrometer

This paper presents a Fourier transform infrared (FT-IR) spectrometer calibration procedure based on an unusual source made from a spectrally selective surface. An alternative solution to the usual calibrators has been developed to cope with the tight mass budget of an instrument devoted to Mars surface exploration. The designed system has proved effective, in terms of achievable radiometric accuracy, despite the drawbacks due to the significant reflectivity of the sources. The proposed procedure is a standard "two-source" approach in which both cold and hot sources are thermally controlled surfaces, similar to an optical solar reflector, associated to a filament lamp. Such a system allows the required signal to be achieved in the 2-25 l m instrument wavelength range. Source optimization was performed using, as a cost function, the computed radiometric uncertainty, while the required absolute accuracy of the instrument was imposed as the optimization constraint.     

Integrated similarity indices for component recognition in mixtures with three-dimensional fluorescence spectra

Component recognition is a very important issue in the analysis of mixed three-dimensional fluorescence spectra and it can be realized by calculating the similarity index between the reference spectra and the computed spectra from the trilinear decomposition of the three-dimensional data arrays. However, the most popular similarity index available in the literature for processing three-dimensional fluorescence spectra takes advantage of only part of the information from the trilinear decomposition. It works well when there are clear differences between the component spectra, but it may fail when the spectra are severely overlapped. In order to overcome the shortcomings and to adapt to the rapid development of online monitoring, we propose a type of integrated similarity index (ISI) that is particularly superior for component recognition in mixtures with severely overlapped spectra. The ISI makes full use of as much information of the three-dimensional fluorescence spectra as possible, namely, of both the waveform and the characteristic peak wavelength, as well as both the emission spectra and the excitation spectra. With the ISI, the recognition process can be accomplished automatically and more accurately in extreme cases than the traditionally defined similarity indices that are based on only one specific feature. The feasibility of the ISI is demonstrated by experiments with mixtures of phenol, cresol, and thymol.     

Development of a total reflection X-ray fluorescence spectrometer for ultra-trace element analysis

A simple and fairly inexpensive total reflection X-ray fluorescence (TXRF) spectrometer has been designed, constructed and realized. The spectrometer is capable of ultra-trace multielement analysis as well as performs surface characterization of thin films. The TXRF setup comprises of an X-ray generator, a slit-collimator arrangement, a monochromator/cutoff-stage, a sample reflector stage and an X-ray detection system. The glancing angle of incidence on the two reflectors is implemented using a sine-bar mechanism that enables precise angle adjustments. An energy dispersive detector and a GM counter are employed for measuring respectively the fluorescence intensities and the direct X-ray beam intensity. A Cu-target X-ray generator with its line focus window is used as an excitation source. The spectrometer is quite portable with its compact design and use of a peltier cooled solid state detector for energy dispersive detection. Alignment and characterization of the TXRF system has been performed and the minimum detection limits for various elements have been determined to be in the range of 100 pg to 5 ng even at low X-ray generator powers of 30 kV, 5 mA. The capability of the TXRF system developed for thin film characterization is also demonstrated.     

A least squares procedure for calculating the calibration constants of a portable gamma-ray spectrometer

In this study, a least squares procedure for calculating the calibration constants of a portable gamma-ray spectrometer using the general inverse matrix method is presented. The procedure weights the model equations fitting to the calibration data, taking into account the variances in the counting rates and in the radioactive standard concentrations. The application of the described procedure is illustrated by calibrating twice the same gamma-ray spectrometer, with two independent data sets collected approximately 18 months apart in the same calibration facility.     

荧光法测定医用维生素B_2片剂中维生素B_2的含量

研究了荧光分光光度计测定医用维生素B2片剂中维生素B2的含量。其荧光的激发波长为Ex;457 nm,发射波长为Em:528 nm。回收率为96.8%-100.0%,变易系数为2.03%。