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Development of analytical methods for the differential diagnosis of exposure to lead

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posted on 01.10.2012, 15:00 by Maha Sadi Tutunji
The modern comprehensive approach in problem solving was adopted in this study to resolve the analytical problems associated with the differential diagnosis of various degrees of exposure to lead. Thorough investigation of all the analytical steps was undertaken starting with the sampling procedure, through the proper choice of the analytical methods for the analysis of indicators of dose and indicators of effect, to the data reduction and evaluation. Reliable, selective and sensitive analytical techniques were developed for the direct analysis of lead, bismuth, antimony and the porphyrin carboxylic acids in body fluids. The sampling step was arbitrarily re-defined on the basis of the lead metabolic model to include two sampling conditions: the non-steady state and the steady state conditions. For diagnostic purposes the results obtained when sampling is done in the non-steady state proved to be more valuable. Analytical results obtained from the steady state condition were also quite revealing. A direct, sensitive, selective and reliable potentiometric stripping analysis method for the trace determination of lead as an indicator of dose in blood,plasma and urine was developed. The various parameters and experimental conditions were investigated. The signals obtained from dearated solutions of the samples using Hg(II) as the oxidant were compared with those obtained from nondearated solutions in which dissolved oxygen acted as the oxidant. The low detection limits of the former method ensured that during the analysis of control specimens in particular, the analyst ',\/ill not be working near the detection limits of the method. Freedom from organic and inorganic interferences coupled with enhancement of the sensitivity due to matrix effects rendered the method particularly useful. By slight modification of the pro- xcedure a wide working range can be attained. Good correlation coefficients bet'ofJeen added and measured Pb(Il) were obtained and method comparison with the thermal ionization stable isotope dilution mass spectrometry and the atomic absorption spectrometry gave a correlation of 0.9999. The adopted PSA in dilute dearated samples of body fluids was adapted for the determination of trace concentrations of Bi(!Il) and Sb(IlI) in body fluids. Slight modifications of the electrolyzing potential using the in situ plating procedure and longer deposition periods were necessary. The results indicated that in subjects highly exposed to lead, high concentrations of Si(lIl) and Sb(III) were detected. An ion pair reversed phase HPLC method coupled with fluorescence detection proved valuable for the analysis of blood and urinary porphyrin carboxylic acids. By optimization of the chromatographic conditions using either the fast RP-C18 Ultrasphere XL-DDS column or the Lichrosorb RP-C2 column and multinear gradient eiution with a mobile phase consisting of methanol/water, both containing 5 mMol/1 tetrabutylammonium phosphate as the counter ion, we were able to detect the earliest biochemical changes that occur in the haem biosynthetic pathway resulting from exposure to lead. The developed method permitted the detection of porphyrins in trace concentrations of 0.2 ng directly in urine samples without tedious sample pretreatment. A wide linear response curve was obtained. The method allows the differential diagnosis of the various diseases that produce derangements in the haem biosynthetic pathway.



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© Maha Sadi Tutunji

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A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.



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