Method design and validation for the determination of uranium levels in human urine using high-resolution alpha spectrometry

Quantification of uranium in human urine is a valuable technique for assessing occupational and public exposure to uranium. A reliable method has been developed and validated in the ARPANSA Radiochemistry Laboratory by means of standard radiochemical separation and purification techniques and measurement using high-resolution alpha spectrometry. This method can be used to evaluate the levels of naturally occurring ²³⁴U, ²³⁵U and ²³⁸U in urine. Method design and validation is the process of defining an analytical requirement, and then confirming that the method under consideration has performance capabilities consistent with what the application requires. The method was designed to measure levels down to 2 mBq/day of total uranium, corresponding to approximately 1/100th of the annual committed effective dose of 20 mSv. Validation tests were developed to assess selectivity, accuracy, recovery and quantification of uncertainty. The radiochemical recovery of this method was measured using ²³²U tracer. The typical minimum detectable concentration for total uranium for 24-h urine samples is approximately 0.6 mBq/day or 0.019 μg/day.

Chemistry, spectroscopy and analytical applications of certain chemiluminescent reactions

Chemiluminescence, the production of light from a chemical reaction, has found widespread use in analytical chemistry. Both tris (2, 2’-bipyridyl) ruthenium (II) and acidic potassium permanganate are chemiluminescence reagents that have been employed for the determination of a diverse range of analytes. This thesis encompasses some fundamental investigations into the chemistry and spectroscopy of these chemiluminescence reactions as well as extending the scope of their analytical applications. Specifically, a simple and robust capillary electrophoresis chemiluminescence detection system for the determination of codeine, O6-methylcodeine and thebaine is described, based upon the reaction of these analytes with chemically generated tris(2,2'-bipyridyl)ruthenium(III) prepared in sulfuric acid (0.05 M). The reagent solution was contained in a glass detection cell, which also held both the capillary and the cathode. The resultant chemiluminescence was monitored directly using a photomultiplier tube mounted flush against the base of the detection cell. The methodology, which incorporated a field amplification sample introduction procedure, realised detection limits (3a baseline noise) of 5 x 10~8 M for both codeine and O6-methylcodeine and 1 x 10~7 M for thebaine. The relative standard deviations of the migration times and the peak areas for the three analytes ranged from 2.2 % up to 2.5 % and 1.9 % up to 4.6 % respectively. Following minor instrumental modifications, morphine, oripavine and pseudomorphine were determined based upon their reaction with acidic potassium permanganate in the presence of sodium polyphosphate. To ensure no migration of the permanganate anion occurred, the anode was placed at the detector end whilst the electroosmotic flow was reversed by the addition of hexadimethrine bromide (0.001% m/v) to the electrolyte. The three analytes were separated counter to the electroosmotic flow via their interaction with a-cyclodextrin. The methodology realised detection limits (3 x S/N) of 2.5 x 10~7 M for both morphine and oripavine and 5 x 10~7 M for pseudomorphine. The relative standard deviations of the migration times and the peak heights for the three analytes ranged from 0.6 % up to 0.8 % and 1.5% up to 2.1 % respectively. Further improvements were made by incorporating a co-axial sheath flow detection cell. The methodology was validated by comparing the results realised using this technique with those obtained by high performance liquid chromatography (HPLC), for the determination of both morphine and oripavine in seven industrial process liquors. A complimentary capillary electrophoresis procedure with UV-absorption detection was also developed and applied to the determination of morphine, codeine, oripavine and thebaine in nine process liquors. The results were compared with those achieved using a standard HPLC method. Although over eighty papers have appeared in the literature on the analytical applications of acidic potassium permanganate chemiluminescence, little effort has been directed towards identifying the origin of the luminescence. It was found that chemiluminescence was generated during the manganese(III), manganese(IV) and manganese(VII) oxidations of sodium borohydride, sodium dithionite, sodium sulfite and hydrazine sulfate in acidic aqueous solution. From the corrected chemiluminescence spectra, the wavelengths of maximum emission were 689 ± 5 nm and 734 ± 5 nm when the reactions were performed in sodium hexametaphosphate and sodium dihydrogenorthophosphate or orthophosphoric acid environments respectively. The corrected phosphorescence spectrum of manganese(II) sulfate in a solution of sodium hexametaphosphate at 77 K, exhibited two peaks with maxima at 688 nm and 730 nm. The chemical and spectroscopic evidence presented strongly supported the postulation that the emission was an example of solution phase chemically induced phosphorescence of manganese(II). Thereby confirming earlier predictions that the chemiluminescence from acidic potassium permanganate reactions originated from an excited manganese(II) species. Additionally, these findings have had direct analytical application in that manganese(IV) was evaluated as a new reagent for chemiluminescence detection. The oxidations of twenty five organic and inorganic species, with solublised manganese(IV), were found to elicit analytically useful chemiluminescence with detection limits (3 x S/N) for Mn(II), Fe(II), morphine and codeine of 5 x 10-8 M, 2.5 x 10-7 M, 7.5 x 10-8 M and 5 x 10-8M, respectively. The corrected emission spectra from four different analytes gave wavelengths of maximum emission in the range from 733 nm up to 740 nm indicating that these chemiluminescence reactions also shared a common emitting species, excited manganese(II). Whilst several analytical problems were addressed in this thesis and answers to certain questions regarding the fundamentals of acidic potassium permanganate chemiluminescence were proposed, there are several areas that would benefit from further research. These are outlined in the final chapter of this thesis.

Maximum likelihood estimation for rician distributed data in analytical q-ball imaging

Analytical q-ball imaging is widely used for reconstruction of orientation distribution function (ODF) using diffusion weighted MRI data. Estimating the spherical harmonic coefficients is a critical step in this method. Least squares (LS) is widely used for this purpose assuming the noise to be additive Gaussian. However, Rician noise is considered as a more appropriate model to describe noise in MR signal. Therefore, the current estimation techniques are valid only for high SNRs with Gaussian distribution approximating the Rician distribution. The aim of this study is to present an estimation approach considering the actual distribution of the data to provide reliable results particularly for the case of low SNR values. Maximum likelihood (ML) is investigated as a more effective estimation method. However, no closed form estimator is presented as the estimator becomes nonlinear for the noise assumption of the Rician distribution. Consequently, the results of LS estimator is used as an initial guess and the more refined answer is achieved using iterative numerical methods. According to the results, the ODFs reconstructed from low SNR data are in close agreement with ODFs reconstructed from high SNRs when Rician distribution is considered. Also, the error between the estimated and actual fiber orientations was compared using ML and LS estimator. In low SNRs, ML estimator achieves less error compared to the LS estimator.

A new solution method for homogenization of effective properties of electromagnetic honeycombs

In this paper, an analytical model and its new numerical solution using the homogenization method are developed to determine the effective electromagnetic characteristics of honeycombs. Based on the proposed solution method, the electromagnetic properties are obtained by employing the multi-scale homogenization theory and periodical electric (magnetic) potential boundary conditions. Further, the effect of geometry of honeycomb's unit cell on effective electromagnetic properties is investigated with the use of the proposed method. The numerical results are compared with analytic results using the Smith-Scarpa's semi-empirical formula.

Identification of nonlinear fMRI models using Auxiliary Particle Filter and kernel smoothing method

Hemodynamic models have a high potential in application to understanding the functional differences of the brain. However, full system identification with respect to model fitting to actual functional magnetic resonance imaging (fMRI) data is practically difficult and is still an active area of research. We present a simulation based Bayesian approach for nonlinear model based analysis of the fMRI data. The idea is to do a joint state and parameter estimation within a general filtering framework. One advantage of using Bayesian methods is that they provide a complete description of the posterior distribution, not just a single point estimate. We use an Auxiliary Particle Filter adjoined with a kernel smoothing approach to address this joint estimation problem.

Development of microfluidic-based analytical methodology for studying the effects of chemotherapy agents on cancer tissue

Whilst a multitude of techniques have been employed to study the biology of tumour tissue and its response to chemotherapeutic reagents, most current methodologies do not capture the sophistication of the in vivo environment. Microfluidics however offers the ability to maintain and interrogate primary tissue samples in an environment with biomimetic flow characteristics. In this study head and neck squamous cell carcinoma (HNSCC) tumour biopsies have been used to investigate the performance of a microfluidic device for generating clinically-useful information. The response of fresh and cryogenically-frozen primary HNSCC or metastatic lymph node samples to chemotherapy drugs (cisplatin, 5-flurouracil or docetaxel), alone and in combination, were monitored for both proliferation (water-soluble tetrazolium salt metabolism) and cell death biomarker release (lactate dehydrogenase, LDH) “off-chip”. The frozen tissue showed no significant difference in terms of either proliferation or LDH release in comparison with the matched fresh samples. Administration of all drugs caused cell death, in a dose-response manner, with the combination showing the greatest amount of cytotoxicity particularly at days 8 and 9; correlating well with published clinical data. The system described here offers an innovative method for studying the tumour microenvironment in vitro and, through incorporation of relevant analytical modules, provides the basis of a pre-clinical device that can be used to define personalised treatment regimens.

An analytical approach to predict web-warping and longitudinal strain in flexible roll formed sections of variable width

To reduce weight and improve passenger safety there is an increased need in the automotive industry to use Ultra High Strength Steel (UHSS) for structural and crash components. However, the application of UHSS is restricted by their limited formability and the difficulty of forming them in conventional stamping. An alternative method of manufacturing structural auto body parts from UHSS is the flexible roll forming process, which allows the manufacture of metal sheet with high strength and limited ductility into complex and weight-optimized components. One major problem in the flexible roll forming of UHSS is the web-warping defect, which is the deviation in height of the web area over the length of the profile. It has been shown that web-warping is strongly dependant to the permanent longitudinal strain formed in the flange of the part. Flexible roll forming is a continuous process with many roll stands, which makes numerical analysis extremely time intensive and computationally expensive. An analytical model of web-warping is therefore critical to improve design efficiency during the early process design stage before FEA is applied. This paper establishes for the first time an analytical model for the prediction of web-warping for the flexible roll forming of a section with variable width. The model is based on evaluating longitudinal edge strain in the flange of the part. This information is then used in combination with a simple geometrical model to investigate the relationship between web-warping and longitudinal strain with respect to process parameters.

Analytical modeling of partially shaded photovoltaic systems

As of today, the considerable influence of select environmental variables, especially irradiance intensity, must still be accounted for whenever discussing the performance of a solar system. Therefore, an extensive, dependable modeling method is required in investigating the most suitable Maximum Power Point Tracking (MPPT) method under different conditions. Following these requirements, MATLAB-programmed modeling and simulation of photovoltaic systems is presented here, by focusing on the effects of partial shading on the output of the photovoltaic (PV) systems. End results prove the reliability of the proposed model in replicating the aforementioned output characteristics in the prescribed setting. The proposed model is chosen because it can, conveniently, simulate the behavior of different ranges of PV systems from a single PV module through the multidimensional PV structure.

Ultra-wideline 14N solid-state NMR as a method for differentiating polymorphs: glycine as a case study

Nitrogen-14 solid-state NMR (SSNMR) is utilized to differentiate three polymorphic forms and a hydrochloride (HCl) salt of the amino acid glycine. Frequency-swept Wideband, Uniform Rate, Smooth Truncated (WURST) pulses were used in conjunction with Carr-Purcell Meiboom-Gill refocusing, in the form of the WURST-CPMG pulse sequence, for all spectral acquisitions. The ¹⁴N quadrupolar interaction is shown to be very sensitive to variations in the local electric field gradients (EFGs) about the ¹⁴N nucleus; hence, differentiation of the samples is accomplished through determination of the quadrupolar parameters CQ and ηQ, which are obtained from analytical simulations of the ¹⁴N SSNMR powder patterns of stationary samples (i.e., static NMR spectra). Additionally, differentiation of the polymorphs is also possible via the measurement of ¹⁴N effective transverse relaxation time constants, T^eff2(¹⁴N). Plane-wave density functional theory (DFT) calculations, which exploit the periodicity of crystal lattices, are utilized to confirm the experimentally determined quadrupolar parameters as well as to determine the orientation of the ¹⁴N EFG tensors in the molecular frames. Several signal-enhancement techniques are also discussed to help improve the sensitivity of the ¹⁴N SSNMR acquisition method, including the use of selective deuteration, the application of the BRoadband Adiabatic INversion Cross-Polarization (BRAIN-CP) technique, and the use of variable-temperature (VT) experiments. Finally, we examine several cases where ¹⁴N VT experiments employing Carr-Purcell-Meiboom-Gill (CPMG) refocusing are used to approximate the rotational energy barriers for RNH3⁺ groups.