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101.
A reversed-phase PB LC-MS method was used for the determination and unequivocal identification of vitamin K(1) in some vegetable samples. The method was also applied to the identification of other constituents in the food analyzed. LC-MS experiments were carried out in both EI and negative-ion CI modes. Preliminary sensitivity studies on vitamin K(1) showed a detection limit of 2 ng (signal-to-noise ratio=3) in negative-ion operation and in single-ion monitoring at m/z 450. Quantitative results obtained with LC-MS for the extracts of four vegetables were compared with those of LC-UV analyses performed at 247 nm. 相似文献
102.
Pressurized sample preparation devices (High Pressure Asher, Pressurized Microwave Digestion system, compared with a PTFE decomposition vessel) were used to dissolve certified metal alloy samples (steel, copper) for ICP analysis. Based on the results of the analysis it was established that both up-to-date devices can be advantageously applied to quickly and quantitatively dissolve metal alloy samples. To dissolve the samples, two different kinds of acid mixtures (A: nitric and hydrochloric acid; B: nitric and hydrochloric and sulphuric and phosphoric acid) were used. The sample preparation is simpler and less time-consuming than the earlier commonly used methods, sample loss and degree of contamination are also reduced. Steel samples containing tungsten, titanium and niobium (less than 0.5%) can only be analyzed using a mixture of the four acids. By dissolving steel samples in the nitric and hydrochloric acid mixture, the concentration of their most common elements (Cr, Ni, Mn, V, Cu) as well as their S and P content can be determined. Copper alloy samples can be dissolved quickly by the pressurized microwave decomposition device using hydrochloric acid and diluted (1:1) nitric acid. 相似文献
103.
A new computer programme for the computation of formation constants of complex species in solution is presented. The programme can be applied to all kinds of potentiometric titration data, including multi-reactant and multi-electrode systems. A statistical analysis is made of the results in order to assess their validity, and to assist in hypothesis testing. 相似文献
104.
Kramer DM Kaufman L Rothschild P Hale J Wummer J Hake KK 《IEEE transactions on medical imaging》1991,10(3):382-386
Three-dimensional Fourier transform (3-DFT) magnetic resonance imaging (MRI) offers advantages in terms of signal-to-noise (S/N) per unit of time for the case where a large number of slices is desired. This advantage is enhanced when the relaxation time, T(1 ), is short. Because time limitations in 3-DFT imaging force the use of short time intervals, TR, between excitations of a slice, lesion contrast is often undesirable at mid-and high-field strength even when the S/N is good. At low fields, where T(1) values are short, high S/N and contrast can both be achieved with 3-DFT MR images. The conceptual and analytical aspects of low-field 3-DFT MRI are presented and demonstrated at 640 G. 相似文献
105.
Quantization improvement in MRI using dual quantizers 总被引:1,自引:0,他引:1
The quantization of magnetic resonance imaging (MRI) data can cause information loss due to quantizer/data mismatch. The authors address a method for improved quantization as well as techniques for measuring the improvement in such methods. A dual quantizer scheme is described and simulated which is fast and more accurately quantizes MRI data than conventional methods. The approach is to use two quantizers, one for the high-level data and one for the low-level data. This adaptive, dual quantization scheme is simple and provides significant improvements in image quality, especially for three-dimensional (3-D) acquisition. Results are given which show how well the low frequencies are represented and indicate the increased fidelity of the high-frequency components. These results show a significant improvement in signal-to-noise ratio as well as in detection tasks for both noiseless data and data which include varying amounts of system noise. 相似文献
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Kwiat P Weinfurter H Herzog T Zeilinger A Kasevich MA 《Physical review letters》1995,74(24):4763-4766
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