Amine/phenyl gradient derived base layer as a comprehensive extractive phase for headspace cooled in-tube microextraction of volatile organic compounds in saliva.

A gradient derived base layer extractive phase was synthesized and applied for the determination of volatile organic compounds (VOCs) in saliva samples using the headspace cooled in-tube microextraction (HS-CITME) method. The base layers from three different sols of phenyltriethoxysilane (PTES), octyltrimethoxysilane (OTMS) and methyltrimethoxysilane (MTMS) as nonpolar precursors were individually dip coated on the stainless steel wires (SSW). Then, the hydrolyzed polar precursor aminopropyltriethoxysilane (APTES) reacted with the silanol groups already formed on the surface of SSWs via controlled rate infusion (CRI) method. The presence of polar and non-polar functional groups on the surface of substrate was evaluated by Fourier-transform infrared spectroscopy (FTIR) while the morphology and thickness of the most suitable gradient coating (amine/phenyl) were also investigated by scanning electron microscopy (SEM). Assessment of the gradient extractive phase efficiency was carried out determining a group of VOCs with different polarities coupled with gas chromatography-mass spectrometry (GCMS) and the improved performance of the synthesized base layer coatings was observed. Furthermore, a cooling device was designed and implemented to the extracting system to improve the efficiency by influencing the exothermic nature of process. The data were analyzed by principal component analysis (PCA), and hierarchical cluster analysis (HCA) and the results were interpreted by polarities of analytes. Finally, under the optimized conditions, the limits of detection (LOD) and limits of quantification (LOQ) were 0.15 and 0.50 ng L-1, respectively. The intra-day and inter-day relative standard deviations (RSDs) at 5 and 50 ng L-1 (n = 3) using a single extractive phase were 2-6 and 10-17, respectively. The data associated with RSDs% for three extractive phases were between 16 and 19 %. Eventually, the method was conveniently applied to the extraction of VOCs from saliva samples of smokers and satisfactory relative recoveries (RR%) (95-108 %) were achieved and low quantities of VOCs were detected.

Simultaneous Determination of Preservatives in Dairy Products by HPLC and Chemometric Analysis.

Cheese and yogurt are two kinds of nutritious dairy products that are used worldwide. The major preservatives in dairy products are sodium benzoate, potassium sorbate, and natamycin. The maximum permitted levels for these additives in cheese and yogurt are established according to Iranian national standards. In this study, we developed a method to detect these preservatives in dairy products by reversed phase chromatography with UV detection in 220 nm, simultaneously. This method was performed on C18 column with ammonium acetate buffer (pH = 5) and acetonitrile (73 : 27 v/v) as mobile phase. The method was carried out on 195 samples in 5 kinds of commercial cheeses and yogurts. The results demonstrated insufficient separation where limit of detection (LOD) and limit of quantitation (LOQ) ranged from 0.326 to 0.520 mg/kg and 0.989 to 1.575 mg/kg in benzoate and sorbate, respectively. The correlation coefficient of each calibration curve was mostly higher than 0.997. All samples contained sodium benzoate in various ranges. Natamycin and sorbate were detected in a remarkable amount of samples, while, according to Iranian national standard, only sorbate is permitted to be added in processed cheeses as a preservative. In order to control the quality of dairy products, determination of preservatives is necessary.

Enhanced target factor analysis.

Target testing or target factor analysis, TFA, is a well-established soft analysis method. TFA answers the question whether an independent target test vector measured at the same wavelengths as the collection of spectra in a data matrix can be excluded as the spectrum of one of the components in the system under investigation. Essentially, TFA cannot positively prove that a particular test spectrum is the true spectrum of one of the components, it can, only reject a spectrum. However, TFA will not reject, or in other words TFA will accept, many spectra which cannot be component spectra. Enhanced Target Factor Analysis, ETFA addresses the above problem. Compared with traditional TFA, ETFA results in a significantly narrower range of positive results, i.e. the chance of a false positive test result is dramatically reduced. ETFA is based on feasibility testing as described in Refs. [16-19]. The method has been tested and validated with computer generated and real data sets.