Search results for "spectrum"
showing 10 items of 2043 documents
Rapid and sensitive ultra-high-pressure liquid chromatography-quadrupole time-of-flight mass spectrometry for the quantification of amitraz and ident…
2008
Liquid chromatography under high pressure in combination with quadrupole time-of-flight mass spectrometry (QqTOF-MS and MS/MS) has been used to detect amitraz degradation products in pears, to characterize their structures, and to evaluate their occurrences in samples of different origins. Using the proposed approach, the parent pesticide and four degradation products were identified. To this end, pear samples were extracted with ethyl acetate and anhydrous sodium sulphate. Amitraz was found to be rapidly decomposed into four related compounds, of which N-(2,4-dimethylphenyl)formamidine (DMPF) was the most abundant and persistent. N,N'-bisdimethylphenylformamidine (BDMPF), 2,4-dimethylforma…
Identification of unknown pesticides in fruits using ultra-performance liquid chromatography–quadrupole time-of-flight mass spectrometry
2007
Abstract Ultra-high-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UPLC-QqTOF-MS) is an emerging technique offering more rapid and efficient separation, as well as the possibility to obtain accurate mass measurement and tandem mass spectrometry (MS/MS). This paper deals with the use of UPLC-QqTOF-MS to identify the pesticide residues present in complex pear extracts. Carbendazim, imazalil, and ethoxyquin were successfully identified because of the accurate mass determination of their protonated molecule and their major fragments in the product ion mass spectra. A few plastic and latex additives were also found, most of them probably coming from the packaging …
First-order derivative resolution of overlapped PAH peaks with common mass spectra in gas chromatography–mass spectrometry
2007
Abstract First-order derivative of 15 points smoothed chromatograms of mixtures of benzo( b )fluoranthene (BbF) and benzo( k )fluoranthene (BkF) for the m / z 252 ion obtained using two microscans has been proposed as a simple alternative to the resolution of overlapped chromatographic peaks of these two compounds which have identical mass spectra. The procedure provides limits of detection of 12 and 29 ng g −1 for BbF and BkF, respectively and offers the possibility to use the 250 and 248 ions to confirm the identity of these analytes.
Effect of particle size distribution in laser-induced breakdown spectroscopy analysis of mesoporous V–SiO2 catalysts
2011
In this paper, the effect of particle size on Laser-Induced Breakdown Spectroscopy (LIBS) analysis of mesoporous V–SiO2 catalyst samples was investigated. The measurements were realized on three LIBS devices with different parameters. Concentrations of V in samples used for LIBS experiments previously determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) varied from 1.2 to 4.7 w/w%. Granulometry of silica samples was modified by two grinding methods (conventional vibration mill and cryogenic mill) and three sets of samples with different particle size distributions were obtained. Ground samples were then deposited in the form of a thin layer on the adhesive tape a…
On-line gel permeation chromatography–attenuated total reflectance–Fourier transform infrared determination of lecithin and soybean oil in dietary su…
2007
Gel permeation chromatography (GPC) with attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometry detection has been proposed for the simultaneous determination of lecithin and soybean oil in dietary supplements. The method involves the extraction of analytes with dichloromethane in an ultrasound water bath and the injection of 2 ml of centrifuged and filtered extracts into the system integrated by two Envirogel GPC columns (19 mm x150 mm, 19 mm x 300 mm) coupled on-line. Dichloromethane was used as mobile phase. A method has been developed to select the most appropriated wavenumber to be used for the determination of each considered compound from the calculation of a…
Towards noncontact skin melanoma selection by multispectral imaging analysis
2011
A clinical trial comprising 334 pigmented and vascular lesions has been performed in three Riga clinics by means of multispectral imaging analysis. The imaging system Nuance 2.4 (CRi) and self-developed software for mapping of the main skin chromophores were used. Spe- cific features were observed and analyzed for malignant skin melanomas: notably higher absorbance (especially as the difference of optical density relative to the healthy skin), uneven chromophore distribution over the lesion area, and the possibility to select the "melanoma areas" in the correla- tion graphs of chromophores. The obtained results indicate clinical potential of this technology for noncontact selec- tion of mel…
New imaging techniques and opportunities in endoscopy.
2011
Gastrointestinal endoscopy is undergoing major improvements, which are driven by new available technologies and substantial refinements of optical features. In this Review, we summarize available and evolving imaging technologies that could influence the clinical algorithm of endoscopic diagnosis. Detection, characterization and confirmation are essential steps required for proper endoscopic diagnosis. Optical and nonoptical methods can help to improve each step; these improvements are likely to increase the detection rate of neoplasias and reduce unnecessary endoscopic treatments. Furthermore, functional and molecular imaging are emerging as new diagnostic tools that could provide an oppor…
Contact and contactless diffuse reflectance spectroscopy: potential for recovery monitoring of vascular lesions after intense pulsed light treatment.
2011
Optical fiber contact probe diffuse reflectance spectroscopy and remote multispectral imaging methods in the spectral range of 400 to 1100 nm were used for skin vascular malformation assessment and recovery tracing after treatment by intense pulsed light. The results confirmed that oxy-hemoglobin relative changes and the optical density difference between lesion and healthy skin in the spectral region 500 to 600 nm may be successfully used for objective appraisal of the therapy effect. Color redness parameter a* = 2 is suggested as a diagnostic border to distinguish healthy skin and vascular lesions, and as the indicator of phototreatment efficiency. Valuable diagnostic information on large…
Synthesis of 8-aminomorphans with high KOR affinity
2021
2-Azabicyclo[3.3.1]nonanes (morphans) with a (3,4-dichlorophenyl)acetyl group at 2-position and a pyrrolidino moiety at 8-position were designed as conformationally restricted analogs of piperidine-based KOR agonists. The synthesis started with 4-oxopiperidine-2-carboxylic acid comprising 13 reaction steps. At first the ketone 10 was transformed into diester 7 bearing a propionate side chain. Dieckmann condensation of diester 7 to afford bicyclic enolester 14 and subsequent Krapcho deethoxycarbonylation represent the key steps of the synthesis. The enantiomeric pyrrolidines (1S,5R,8R)-5a and (1R,5S,8S)-5a were separated by chiral HPLC. The eutomer (1S,5R,8R)-5a showed high KOR affinity (K-i…
Femtosecond laser induced breakdown spectroscopy of air–methane mixtures
2013
Abstract Femtosecond laser pulses are used in order to induce dielectric breakdown in gaseous mixtures, namely in some reactive air–methane mixtures. The light emitted from the laser induced plasma was analyzed while the main emission features are identified and assigned. From the analysis of the emission spectra, a linear relationship was found to hold between the intensity of some spectral features and methane content. Finally, the use of femtosecond laser induced breakdown as a tool for the in situ determination of the composition of gaseous mixtures (e.g., equivalence ratio) is also discussed.