Classification of Urinary Calculi using Feed-Forward Neural Networks

Recent studies have shown that more than 80% of the analysed samples of urinary calculi in our  laboratory were mainly composed of four types of calculi, consisting of the following substances: (1) whewellite and weddellite, (2) whewellite, weddellite and uric acid, (3) whewellite, weddellite and struvite and (4) whewellite, weddellite and carbonate apatite. In this work the results of classification of these types of calculi (using their infrared spectra in the region 1450–450 cm–1) by feed-forward neural networks are presented. Genetic algorithms were used for optimization of neural networks and for selection of the spectral regions most suitable for classification purposes. The generalization abilities of the neural networks were controlled by an early stopping procedure. The best network architecture and the most suitable spectral regions were chosen using twentyfold cross-validation. The cross-validation error for the real samples varies from 5.3% to 5.9% misclassifications, which makes the proposed method a promising tool for the identification of these types of calculi.KEY WORDS:Urinary calculi, infrared spectroscopy, classification, neural networks, variable selection, genetic algorithms

HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY METHOD FOR DETERMINATION OF PRESERVATIVES IN BEVERAGES

Benzoic and sorbic acids, and their sodium, potassium and calcium salts are widely used as preservatives in acidic foods and beverages. They inhibit the growth of molds and yeasts, and are also effective against wide range of bacteria which explains the benefit of their usage. The health effects have led to limitation on the concentrations that can be used in food and beverages. Because of that, the analytical determination of these preservatives is important for consumer interest and protection. Therefore, a new reversed-phased HPLC method for a fast, simple, accurate and precise determination of potassium sorbate and sodium benzoate in different beverages is developed. In this purpose, a HPLC system equipped with UV diode array detection is employed. Separation and determination of investigated preservatives are performed using Purospher® STAR RP-18 (30 mm x 4 mm; 3 μm) analytical column. Methanol/phosphate buffer (pH = 3.70) (20/80, V/V) is used as a mobile phase, with flow rate of 1 mL/min, constant column temperature of 25°C and UV detection at 225 nm and 255 nm. Successful separation conditions are obtained using an isocratic elution within 6 min. Accuracy, precision, limit of detection, limit of quantification, and linearity range are evaluated. The separation factor value of 1.128 showed that this method can be successfully used for simultaneousdetermination of benzoates and sorbates. The obtained data indicated that the concentration of investigated preservatives found in the analyzed beverages available on the local Macedonian markets is in accordance with Macedonian maximum levels for food safety

Solid-phase steam-assisted synthesis of hydroxyapatite nanorods and nanoparticles

10.1007/s10853-010-4691-1Journal of Materials Science45226059-6067JMTS