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排序方式: 共有269条查询结果,搜索用时 15 毫秒
21.
A novel microchip heated nebulizer for atmospheric pressure chemical ionization mass spectrometry is presented. Anisotropic wet etching is used to fabricate the flow channels, inlet, and nozzle on a silicon wafer. An integrated heater of aluminum is sputtered on a glass wafer. The two wafers are jointed by anodic bonding, creating a two-dimensional version of an APCI source with a sample channel in the middle and gas channels symmetrically on both sides. The ionization is initiated with an external corona-discharge needle positioned 2 mm in front of the microchip heated nebulizer. The microchip APCI source provides flow rates down to 50 nL/min, stable long-term analysis with chip lifetime of weeks, good quantitative repeatability (RSD < 10%) and linearity (r(2) > 0.995) with linear dynamic rage of at least 4 orders of magnitude, and cost-efficient manufacturing. The limit of detection (LOD) for acridine measured with microchip APCI at flow rate of 6.2 muL/min was 5 nM, corresponding to a mass flow of 0.52 fmol/s. The LOD with commercial macro-APCI at a flow rate of 1 mL/min for acridine was the same, 5 nM, corresponding to a significantly worse mass flow sensitivity (83 fmol/s) than measured with microchip APCI. The advantages of microchip APCI makes it a very attractive new microfluidic detector. 相似文献
22.
Tapio Salo 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1961,115(1):54-56
Zusammenfassung Zum Nachweis von Isopropanol bei gleichzeitiger Anwesenheit von Methanol, Äthanol und Wasser wurde eine gaschromatographische Methode entwickelt. Die für diesen Zweck günstige Gesamtlänge der Kolonne beträgt 2,84 m, wovon der 2,24 m lange Anfangsteil mit Paraffinphase und der 0,6 m lange Schlußteil mit Polyäthylenglykolphase gefüllt ist. Als empfehlenswerte Temperatur für die Chromatographierung wird 47° C angegeben, wobei die Retentionszeiten für Methanol 12,1 min, für Äthanol 20,0 min, für Isopropanol 25,0 min und für Wasser 36 min betragen. Die Methode eignet sich ebenfalls gut zur quantitativen Bestimmung kleiner Äthanolmengen (1–3 Gew.-%) in Isopropanol. 相似文献
23.
24.
Hakala KS Laitinen L Kaukonen AM Hirvonen J Kostiainen R Kotiaho T 《Analytical chemistry》2003,75(21):5969-5977
Good reliability of Caco-2 permeability studies requires competent sampling and analytical methods to ensure the comparability of day-to-day experiments. In this work, two n-in-one LC/MS/MS methods based on two different ionization techniques were developed and validated for a group of reference compounds; eight of them are recommended by the Food and Drug Administration (FDA) for the evaluation of oral drug permeability. The performance of a new ionization technique, atmospheric pressure photoionization (APPI), as an interface for quantitative LC/MS analysis was evaluated in comparison to the electrospray ionization (ESI). Generally, the validation parameters, including sensitivity, accuracy, and repeatability, were comparable for the APPI and ESI methods. The main difference was that the linear quantitative range of APPI was 3-4 orders of magnitude (r(2) >/= 0.998) whereas in ESI it was typically 2-3 orders of magnitude (r(2) >/= 0.990). By the APPI and ESI methods, the simultaneous analysis of nine highly heterogeneous compounds was achieved within 5.5-7 min, which leads to significant savings in time and cost of the analyses. The successful validation data indicate the usefulness of both the methods for the rapid and sensitive (LOD values typically =5 nM) testing of drug transport across the Caco-2 monolayers, and after case-specific modification, the methods enable the permeability screening of new drug candidates. The applicability and reliability of both methods was demonstrated with a real batch of Caco-2 samples, each providing similar values of apparent permeability (P(app)). In addition, the individual permeabilities of the compounds in the cocktail experiments correlated closely to the ones obtained from single-compound experiments. 相似文献
25.
This paper introduces a generalized design method for polynomial-based interpolation filters. These filters can be implemented
by using a modified Farrow structure, where the fixed finite impulse response (FIR) sub-filters possess either symmetrical
or anti-symmetrical impulse responses. In the proposed approach, the piecewise polynomial impulse response of the interpolation
filter is optimized directly in the frequency domain using either the minimax or least mean square criterion subject to the
given time domain constraints. The length of the impulse response and the degree of the approximating polynomial in polynomial
intervals can be arbitrarily selected. The optimization in the frequency domain makes the proposed design scheme more suitable
for various digital signal processing applications and enables one to synthesize interpolation filters for arbitrary desired
and weighting functions. Most importantly, the interpolation filters can be optimized in a manner similar to that of conventional
linear-phase FIR filters. 相似文献
26.
Rönnholm Mats R. Hernández Carucci José R. Arve Kalle Eränen Kari Salmi Tapio 《Topics in Catalysis》2007,42(1-4):195-198
A silver/alumina catalyst was tested for its NO
x
reduction activity during oxygen-rich conditions and during variation in the input parameters (nitric oxide, octane and oxygen).
The experimental data using the microreactor was investigated by means of artificial neural networks (ANN). 相似文献
27.
Heidi Markus Päivi Mäki-Arvela Narendra Kumar Natalya V. Kul’kova Patrik Eklund Rainer Sjöholm Bjarne Holmbom Tapio Salmi Dmitry Yu. Murzin 《Catalysis Letters》2005,103(1-2):125-131
The natural lignan hydroxymatairesinol was hydrogenolysed to a potential anticarcinogenic substance matairesinol over different carbon-supported palladium catalysts. The reaction was conducted in 2-propanol at 70 °C under hydrogen flow in a stirred glass reactor. The catalysts were characterised by N2-physisorption, CO pulse chemisorption and pH measurement of aqueous catalyst slurries. The most active catalyst (Degussa-Hüls) gave yields of matairesinol over 90% in 4 h. It was concluded that the acidity of the catalyst had a profound influence on the reaction rate. 相似文献
28.
Tapio Pulli 《Microelectronics Reliability》1985,25(6):1067-1071
The reliabilities of a three-state device and redundant structures of two such devices are considered, and it is shown that although the two failure modes were equally probable there may be advantages in using redundancy of two devices in series or parallel. It is also shown that the optimal redundant structure of two devices is not solely dependent on the failure mode distribution of the device. 相似文献
29.
Tiina Sikanen Thomas Zwinger Santeri Tuomikoski Sami Franssila Reijo Lehtiniemi Carl-Magnus Fager Tapio Kotiaho Antti Pursula 《Microfluidics and nanofluidics》2008,5(4):479-491
This work presents experimental [infrared (IR) thermography] and computational (finite element model) results of temperature
distributions of an electrokinetic separation chip. Thermal characteristics of both the electrolyte solution and the polymer
chip (SU-8) are taken into account in modeling temperature distributions during electrokinetic flow. Multiphysics and multiscale
simulation couples electrostatics, heat transfer, and fluid dynamics. The accompanying IR thermography is a non-contact method,
which can measure fractional temperature differences with sub-second time resolution. Any structures or temperature marker
molecules interfering with the experiment are not needed. Nominal spot size in the IR measurements is 30 μm with a field of
view of several millimeters enabling both local and chip-scale temperature monitoring simultaneously. As a result, we present
a computer model for electrokinetic chips, which enables simulation of fractional temperature changes during electrophoresis
under real operating conditions. The accuracy of the model is within ±1°C when the deviation in electrochemical processes
is taken into account. The simulation results also suggest that the temperature on the chip surface qualitatively reflects
the temperature inside the microchannel with an average offset of 1–2°C. 相似文献
30.
Esa Toukoniitty Johan Wärnå Dmitry Yu. Murzin Tapio Salmi 《Chemical engineering science》2010,65(3):1076-1087
Transient techniques are frequently used for catalytic gas-phase processes, but the application of transient techniques on catalytic three-phase systems is very scarce. Transient kinetic experiments provide valuable additional information about the behaviour of complex organic reaction systems, which was illustrated here with continuous enantioselective three-phase hydrogenation of ethyl benzoylformate over supported Pt catalyst particles in a fixed bed. The catalyst stability and the details of the adsorption–desorption behaviour of the reaction participants were revealed by transient experiments. Quantitative modelling of the data was based on kinetic experiments and characterisation of the reactor flow pattern by an inert tracer. Both liquid-phase species and adsorbed surface species were included in the modelling. The model predicted correctly the dynamic behaviour of the complex organic system under transient conditions. The approach is generally applicable to complex organic systems undergoing catalytic transformations. 相似文献