University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Classification: Chemometrics -> Statistics

Citations 6

"Multivariate Sensor System For The Automatic Control Of Wastewater Streams"
Chem. Tech. 1994 Volume 46, Issue 1 Pages 77-86
Adler, B.;Brueckner, G.;Winterstein, M.

Abstract: Principles and operation of a sensor array for common water and wastewater analysis is described, together with fuzzy control of its operation such as pattern recognition for particular conditions of the water composition and the recognition of changes in the sensor performance. Field experiments were performed by a sensor array for conductivity, pH, and turbidity and a memory-programmable control for data acquisition. Stages of hard clustering by a main-component analysis (Henrion et al., 1986) and fuzzy clustering or alternatively, a neuronal network were used for data evaluation. The results indicated the successful recognition of 1% and 0.05% deviations of nonionic and anionic tensides, respectively. (SFS)
Conductivity pH Turbidity Waste Environmental Electrochemical analysis Sensor

"Review Of The Exponentially Modified Gaussian (EMG) Function Since 1983"
J. Chromatogr. Sci. 1991 Volume 29, Issue 6 Pages 258-266
Jeansonne, M.S.;Foley, J.P.

Abstract: A review with 127 references. Of the exponentially modified Gaussian (EMG) function as model for real chromatography peaks. This review covers the following areas: (1) equations derived from the EMG model, (2) studies of inherent errors in the quantitation of chromatography peaks via use of the EMG model, (3) chromatography applications since 1983, and (4) applications to flow injection anal.
HPLC Fluorescence Mass spectrometry

"Automated Polarographic And Photometric System For Serial Analysis"
Mod. Trends Anal. Chem. 1984 Volume 204, Issue 1 Pages 167-187
K. Tóth,Zs. Fehér, Gy. Horvai, G. Nagy, Zs. Niegreisz, E. Pungor

Abstract: An automated system with polarographic or spectrophotometric detection was developed for the serial anal. of pharmaceutical samples. As models for testing the analyzer, four preparations, Prodectin, Eunoctin, Seduxen and Verospiron containing pyridinol carbamate [1882-26-4], nitrazepam [146-22-5], diazepam [439-14-5] and spironolactone [52-01-7], respectively, were used. All 4 compounds had useful UV absorption and, with the exception of spironolactone, were also polarographically active at the Hg electrode. In polarographic determination, the problems associated with deaeration were overcome by using N bubbling. A peristaltic pump was designed for feeding N continuously, which after a sufficient time, eliminated oxygen completely. The spectrophotometric device differed from the polarographic one in that a flow-through detector preceded the peristaltic pump. A sampling rate of 120/h was achieved with the flow-cell. The methods are reproducible, sensitive and accurate. The relative standard deviation for polarographic and spectrochemical analysis were 1.13-1.35% and 0.14%, respectively. (SFS)
Pyridinolcarbamate Nitrazepam Diazepam Spironolactone Pharmaceutical Spectrophotometry Polarography

"Direct Determination Of Copper In Urine Using A Sol–gel Optical Sensor Coupled To A Multicommutated Flow System"
Anal. Bioanal. Chem. 2004 Volume 380, Issue 1 Pages 108-114
Paula C. A. Jerónimo, Alberto N. Araújo, M. Conceição B. S. M. Montenegro, Celio Pasquini, Ivo M. Raimundo Jr

Abstract: In this work, a multicommutated flow system incorporating a sol-gel optical sensor is proposed for direct spectrophotometric determination of Cu(II) in urine. The optical sensor was developed by physical entrapment of 4-(2-pyridylazo)resorcinol (PAR) in sol-gel thin films by means of a base-catalyzed process. The immobilized PAR formed a red 2:1 complex with Cu(II) with maximum absorbance at 500 nm. Optical transduction was based on a dual-color light-emitting diode (LED) (green/red) light source and a photodiode detector. The sensor had optimum response and good selectivity towards Cu(II) at pH 7.0 and its regeneration was accomplished with picolinic acid. Linear response was obtained for Cu(II) concentrations between 5.0 and 80.0 µg L-1, with a detection limit of 3.0 µg L-1 and sampling frequency of 14 samples h-1. Interference from foreign ions was studied at a 10:1 (w/w) ion:Cu(II) ratio. Results obtained from analysis of urine samples were in very good agreement with those obtained by inductively coupled plasma mass spectrometry (ICP-MS); there was no significant differences at a confidence level of 95%.
Copper Copper(II) Urine Sensor

"Determination Of Copper In Powdered Chocolate Samples By Slurry-sampling Flame Atomic-absorption Spectrometry"
Anal. Bioanal. Chem. 2005 Volume 382, Issue 4 Pages 1099-1102
Walter N. L. dos Santos, Erik G. P. da Silva, Marcelo S. Fernandes, Rennan G. O. Araujo, Antônio C. S. Costa, M. G. R. Vale, S&eagrave;rgio L. C. Ferreira

Abstract: Chocolate is a complex sample with a high content of organic compounds and its analysis generally involves digestion procedures that might include the risk of losses and/or contamination. The determination of copper in chocolate is important because copper compounds are extensively used as fungicides in the farming of cocoa. In this paper, a slurry-sampling flame atomic-absorption spectrometric method is proposed for determination of copper in powdered chocolate samples. Optimization was carried out using univariate methodology involving the variables nature and concentration of the acid solution for slurry preparation, sonication time, and sample mass. The recommended conditions include a sample mass of 0.2 g, 2.0 mol L-1 hydrochloric acid solution, and a sonication time of 15 min. The calibration curve was prepared using aqueous copper standards in 2.0 mol L-1 hydrochloric acid. This method allowed determination of copper in chocolate with a detection limit of 0.4 µg g-1 and precision, expressed as relative standard deviation (RSD), of 2.5% (n=10) for a copper content of approximately 30 µg g-1, using a chocolate mass of 0.2 g. The accuracy was confirmed by analyzing the certified reference materials NIST SRM 1568a rice flour and NIES CRM 10-b rice flour. The proposed method was used for determination of copper in three powdered chocolate samples, the copper content of which varied between 26.6 and 31.5 µg g-1. The results showed no significant differences with those obtained after complete digestion, using a t-test for comparison.
Copper Food Spectrophotometry

"Use Of Multivariate Curve Resolution For Determination Of Chromium In Tanning Samples Using Sequential Injection Analysis"
Anal. Bioanal. Chem. 2005 Volume 382, Issue 2 Pages 328-334
V. Gómez, M. P. Callao

Abstract: We report a method for determining total chromium in tanning samples using sequential injection analysis (SIA) with a diode-array spectrophotometric detector. With a suitable analytical sequence CrO42- is converted to Cr2O72- inside the tubes of the SIA system, after total oxidation of chromium(III). A data matrix is obtained and analyzed by several chemometric techniques based on multivariate analysis: principal components analysis, simple-to-use interactive self-modelling mixture analysis, and multivariate curve resolution-alternating least-squares. We studied several samples from different stages of a tanning process. Two of these samples were easily oxidized but the others needed more extreme conditions. The analytical sequence prepared, which was based on obtaining a pH gradient and used H2SO4 as reagent, is valid and independent of the level of oxidation needed for the sample. We established a calibration model and evaluated the figures of merit. In some samples we found interferents. With this method the amounts of chromium in each sample were quantified and the results were statistically similar to those obtained by use of the reference method, atomic absorption spectrometry.
Chromium, total Chromium(III) Spectrophotometry