Determining detection limits and minimum detectable concentrations for noble gas detectors utilizing beta-gamma coincidence systems

Beta-gamma coincidence counting is one of two acceptable noble gas monitoring measurement modes for Comprehensive Nuclear-Test-Ban-Treaty (CTBT) verification purposes defined in CTBT/PC/II/WG.B/1. Rigorous derivations of detection limits and minimum detectable activity concentrations for - coincidence data are derived in this paper. Different sampling methodologies are modeled to show how the MDC is affected by different sample collection times, spectral collection times, background radon levels, and other factors.     

Estimation of the minimum detectable concentration and optimum instrumental conditions in precision absorption spectrophotometry of substances in the condensed phase

An expression for the signal-to-noise ratio in precision absorption spectrophotometry of molecules in the condensed phase is derived and used to calculate the theoretical minimum detectable sample concentration, C(mt), and to predict the best instrumental condition for measurement. Single-beam and double-beam instruments are considered. The theoretically calculated values of C(mt) for several organic molecules are compared with the practical minimum detectable sample concentrations, C(mp), which are those concentrations giving an absorbance of 0-002. As long as the source of radiation is intense, and the root-mean-square noise-to-signal ratio for incident radiation passing through the blank is known, then the expression for C(mt) is extremely simple and easy to evaluate for any given substance whose molar absorptivity is known. The influence of instrumental parameters on the value of C(mt) is evaluated, and only the monochr omator slitwidth, the number of combined blank and sample signal measurements, and the frequency response bandwidth of the electrometer-readout system have any significant effect on the value of C(mt) (for any given wavelength setting of the monochromator).     

Analysis of siliceous materials and coal by atomic absorption spectrophotometry with fusion for sample decomposition

The oxalic acid-lithium carbonate-lithium tetraborate (1:1:1) fusion agent proposed previously for cement analysis is applied to determine the composition of various siliceous samples including granite, clay, flyash, sand and silica fume. For samples with silica content higher than 70%, the sample size had to be reduced from 0.10 to 0.01 g and a recovery factor was needed in silica determination to account for the precipitation of silica during acid dissolution. Attempt has also been made to determine the major metallic elements in coal by fusion directly without the ashing procedure, and the results obtained were good. Further, the ash content of coal was proposed to be determined by establishing a relation between the ash content and the sum of the concentrations of four major oxides (i.e. the oxides of Si, Al, Fe and Ca), and the proposed method is accurate and is time saving compared with that determined by direct ashing at 800 degrees C.     

Quantitative determination of vitamin b12 by cyan dosage,with infrared absorption spectrophotometry

Microchimica Acta - Vitamin B12 has been determined by measurement of the infrared absorption of the cyano-group band at 2137 cm?1, the samples being pelleted with KBr. The error is within...     

The absorption spectrum of the pyrene excimer obtained by modulation excitation spectrophotometry

A well resolved spectrum has been obtained for the pyrene excimer in deoxygenated cyclohexane using modulation excitation spectrophotometry.     

EDOT‐diketopyrrolopyrrole copolymers for high bulk hole mobility and near infrared absorption

To obtain novel low‐bandgap materials with tailored hole‐transport properties and extended absorption, electron rich 3,4‐ethylenedioxythiophene is introduced as a comonomer in diketopyrrolo[3,4‐c]pyrrole copolymers with different aryl flanking units. The polymers are characterized by absorption and photoluminescence spectroscopy, dynamic scanning calorimetry, cyclic voltammetry, and X‐ray diffraction. The charge transport properties of these new materials are studied carefully using an organic field effect transistor geometry where the charge carriers are transported over a narrow channel at the semiconductor/dielectric interface. These results are compared to bulk charge carrier mobilities using space‐charge limited current (SCLC) measurements, in which the charge carrier is transported through the complete film thickness of several hundred nanometers. Finally, charge carrier mobilities are correlated with the electronic structure of the compounds. We find that in particular the thiophene‐flanked copolymer PDPP[T]₂‐EDOT is a very promising candidate for organic photovoltaics, showing an absorption response in the near infrared region with an optical bandgap of 1.15 eV and a very high bulk hole mobility of 2.9 × 10^?4 cm² V^?1 s^?1 as measured by SCLC. This value is two orders of magnitudes higher than SCLC mobilities reported for other polydiketopyrrolopyrroles and is in the range of the well‐known hole transporting polymer poly(3‐hexylthiophene). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 639–648     

Ensemble wavelet modelling for determination of wheat and gasoline properties by near and middle infrared spectroscopy

The wavelet transform has been shown to be a useful tool for multivariate calibration. However, the choice of wavelet transform settings (wavelet family, length and number of decomposition levels) for a given application is still an open problem. The present paper proposes an alternative approach, which consists of generating an ensemble model by combining individual models obtained with different wavelet transform settings. The advantages of the proposed method are demonstrated in two analytical problems, namely the determination of moisture and protein in wheat by near infrared spectroscopy and the determination of specific mass and three distillation temperatures (T10, T50, T90) in gasoline by middle infrared spectroscopy. In these problems, the results varied considerably among individual models, which underlines the risk associated to an inadequate choice of wavelet transform settings. In contrast, the ensemble model always provided adequate results in terms of prediction error and noise sensitivity. The proposed method can be seen as an advantageous alternative for multivariate calibration in the wavelet domain, as it frees the analyst from the need to choose a particular configuration for the wavelet transform.     

Study of interactions of different rubber blends by infrared spectrophotometry using LDPE as matrix material for sample preparation

Use of LDPE as the matrix material in sample preparation for IR analysis of raw rubbers has been established earlier. In this paper different rubber blends have been analysed using the same technique. Interaction of different blend systems has been studied and probable interactions have been proposed.     

Water revealed as molecular mirror when measuring low concentrations of sugar with near infrared light

Near infrared spectroscopy is an overtone spectroscopy regarded as a quick and non-destructive method that provides analytical solutions for components that represent approximately 1% or more of the total mass of the investigated composite samples. Aquaphotomics offers the possibility for disentanglement of information remaining hidden in the spectra when conventional data evaluation methods are used, since this concept utilizes changes of the water structure induced by the measured solute as specific molecular vibrations at water bands. Here, near infrared technique and aquaphotomics are applied for non-destructive identification and quantification of mono- and di-saccharide solutes at 100–0.02 mM concentration that is accepted as unachievable with near infrared spectroscopy. The results presented in this study support the aquaphotomics' water molecular mirror concept that explores spectral changes related to water molecular rearrangements caused by minute changes of the solutes in the aqueous systems. The method provides quick and accurate alternative for classical analytical measurements of saccharides even at millimolar concentration levels.     

Signal and data processing for atomic absorption spectrophotometry

The state-of-the-art of signal and data processing techniques for atomic absorption spectrophotometry is described and discussed. Aspects of optical and atomizer design of greatest importance for providing the best signal to noise S/N ratio and minimum curvature are summarized. In background corrected systems, amplifier gain and time constants must be carefully matched, especially for transient signals. A method is given for calculating the sampling time of peak search systems. Methods of signal averaging are described and the importance of precision calculations is stressed. The correct sequence of readings for calibration is discussed. The causes of curvature are shown for simple and complex curves and methods of correction are compared. Other desirable functions are calculation of sensitivity and detection limit, error warnings and external data output facilities.     

Estimation of leaf transmittance in the near infrared region through reflectance measurements

A method, which allows one to compensate for the incomplete collection of transmitted light (T) by an integrating sphere, has recently been developed, and shown to be reliable provided that the absorptance (A) of the leaf in the NIR region (750-800 nm) can be neglected, allowing one to set R+T=1, where R denotes the reflectance; this implies that proper compensation can only be applied to healthy leaves, which do not absorb in the NIR region. To overcome this limitation, the feasibility of an alternative, requiring neither measurements of T nor an elaborate analysis of radiative transport through a leaf, is explored. Not surprisingly, this simplistic alternative provides results which (in general) do not agree with those found by using the compensation method, but the two approaches converge in the spectral regions where absorptance is low (that is, where R+T> or =0.9). The "T-through-R" method, as described here, thus provides an additional check on the correction factor used in conjunction with the integrating sphere, and extends the applicability of the compensation method to situations where NIR absorptance is not negligible, e.g., in the presence of 'browning' pigments produced upon the oxidation of polyphenols during leaf senescence.     

The absorption spectrum of the first excited singlet state of pyrene obtained by modulation excitation spectrophotometry

The absorption spectrum of the first excited singlet state of pyrene dissolved in polymethylmethacrylate has been obtained over the range 390–500 nm using modulation excitation spectrophotometry. The advantages of this technique as compared to nanosecond laser flash photolysis are discussed.     

Effect of density on the induced near infrared absorption spectrum of solid parahydrogen

The evolution of the induced near infrared absorption spectrum of solid parahydrogen as a function of pressure, at 4.2 K and up to 10 kbar, is given here. A blue frequency shift and a strong intensity enhancement are observed, which depend upon the nature of the line. The continuous presence of an S₁(0) line shows that molecules are not situated at centers of inversion symmetry, and it appears that the crystalline structure remains hexagonal close-packed (hep) in the compressed solid.     

Electronic absorption and fluorescence spectrophotometry of quinacrine

The absorption and fluorescence spectra of quinacrine and its dealkylated derivative, 2-methoxy-6-chloro-9-aminoacridine, were studied as a function of pH and Hammett acidity. The relative stability and high quantum yield of the dication derived from quinacrine make it the most desirable species for fluorimetric determination. This species predominates in the region pH 8-H_o-6. The alkylamino side-chain of quinacrine appears to interfere with excited state protonation and dissociation of the dication. Moreover, in the dication, the steric interaction between the side-chain and the 9-amino group may prevent coplanarity between the 9-amino group and the acridine ring, thereby favoring the aminoacridine over the iminoacridan structure.     

单纯形最优化法在氢化物原子吸收分析中的应用

单纯形法^[1-7]是一种动态寻优方法。它能在交互作用复杂，因素较多的场合使用，对实验有全面优化的效果，克服了单因素优选法无法考虑各因素间的交互影响、 准确性低、工作量大的缺点。它能在实验次数较少的情况下，快速的找出接近最佳分析条件组合，综合优化性能指标较小。     

Developments in light sources and detectors for atomic absorption spectroscopy

In a tribute to the contributions of Sir Alan Walsh to atomic spectroscopy, and in particular to his pioneering efforts in conceiving and developing the technique of atomic absorption spectroscopy, a brief overview is given of some developments in light sources and detection methods that took place during his leadership of the spectroscopy group at the CSIRO Division of Chemical Physics, Melbourne, Australia. The topics covered include hollow-cathode lamps, high-intensity lamps, resonance detectors, selective modulation of resonance lines emitted by hollow-cathode sources and isotopic analysis.