Mass flow measurement spectrometer

Apparatus. Preliminary experiments were carried out in a modified Kiselev-type cell [21 ] with a grating spectrometer, PERKIN ELMER model 325. Precise measurements of diffusivities were conducted by means of a fast Fourier Transform IR (FTIR) spectrometer, PERKIN ELMER model 1800 inserted in a complex set-up equipped with UHV, gas dosing and mass flow control systems. Details of the cell and experimental devices will be described elsewhere [22]. 

Another important issue is that a mass spectrum of the collected sample confirms that no decomposition, either during the storage procedure or during measurement in the NMR spectrometer, has occurred. Most fraction collectors have built-in software, which can detect and collect peaks. Due to the special conditions of stop-flow measurements, it is preferable that the fraction collector should also be controlled by the central software. This also means that the measured NMR spectra and the collected fractions are easier to correlate. 

R 18] [A 1] Each module is equipped with a heater (H3-H8) and a fluidic cooling (C03-C06). Temperature sensors integrated in the modules deliver the sensor signals for the heater control. Fluidic data such as flow and pressure are measured integrally outside the micro structured devices by laboratory-made flow sensors manufactured by silicon machining. The micro structured pressure sensor can tolerate up to 10 bar at 200 °C with a small dead volume of only 0.5 pi. The micro structured mass flow sensor relies on the Coriolis principle and is positioned behind the pumps in Figure 4.59 (FIC). For more detailed information about the product quality it was recommended to use optical flow cells inline with the chemical process combined with an NIR analytic or a Raman spectrometer. 

The flow reactor used in the activity studies is described elsewhere [7]. Briefly it consists of a vertical quartz tube in which the sample is supported on a sintered quartz filter. Gases are introduced via mass flow controllers and the temperature is measured after the catalyst bed. Reactants and products are analysed using a quadrupole mass spectrometer and a photo acoustic FTIR gas analyser. 

The catalysts were reduced in flowing H2, or oxidised in air, at 400 C for 3 hours, prior to the activity measurements. The measurements were performed in an atmospheric flow apparatus. The gases used were 4 vol% NO/He, 4 vol% CO/He and 4 vol% 02/He (Hoekloos). The flow rate could be adjusted with mass flow controllers to a maximum of 40 ml/min. The CO/O2 and CO/NO ratios were varied from oxidising to reducing. Product and reactant analysis occurred by means of a mass spectrometer. The conversion of O2 or NO was plotted against the temperature at reducing or stoichiometric gas mixtures, while the conversion of CO was used at oxidising gas mixtures. The temperature was raised with 3°C/min to 400°C. 

Figure 5.38 Electrospray ionization peak areas measured as a function of flow rate for a solution of diltiazem injected (no HPLC column) into a flow of 50 50 acetonitrile water with 1 % acetic acid. A true mass flow dependent detector is predicted (Equation [4.5], Appendix 4.1) to yield peak areas independent of flow rate but this is clearly not observed in (a). A concentration dependent detector should give peak areas proportional to flow rate , and this is observed in (b) at lower flow rates but the peak area response falls below the extrapolated prediction as flow rate increases. Thus in this flow rate range the ESI mass spectrometer did not behave in accord with either of these idealized models.

The reactor outlet was directly connected to a quadrupole mass spectrometer (Balzers QMS 200) and to a UV-analyzer (ABB LIMAS 1IHW) in parallel. NH3, NO, NO2, N2O, O2, and He were dosed from bottled calibrated gas mixtures by mass flow controllers, while water vapor was added by means of a saturator. The catalyst temperature was measured by a K-type thermocouple directly immersed in the catalytic bed. 

Acoustic leak detection - active Acoustic leak detection - passive Differential flow measurement Hydrogen - electrochemical cell Hydrogen - katharometer Hydrogen - mass-spectrometer Oxygen - electrochemical cell Pressure Plugging meter... 

Another specific concentration detector is the infrared (IR) flow-through spectrometer. This detector monitors a specific absorbing group in the solute or polymer. Like the UV detector, the IR detector is relatively insensitive to fluctuations around a set temperature and is therefore particularly suitable for temperatures far above ambient conditions. Indeed, one of the uses for IR detection is in the molar-mass measurement of polyolefins at temperatures exceeding 140°C. Infrared detection is also useful in measuring polymer stoichiometry as a function of molar mass (by monitoring specific functional groups in a copolymer [4]). The detector, however, is solvent-limited in terms... 

In many applications in mass spectrometry (MS), the sample to be analyzed is present as a solution in a solvent, such as methanol or acetonitrile, or an aqueous one, as with body fluids. The solution may be an effluent from a liquid chromatography (LC) column. In any case, a solution flows into the front end of a mass spectrometer, but before it can provide a mass spectrum, the bulk of the solvent must be removed without losing the sample (solute). If the solvent is not removed, then its vaporization as it enters the ion source would produce a large increase in pressure and stop the spectrometer from working. At the same time that the solvent is removed, the dissolved sample must be retained so that its mass spectrum can be measured. There are several means of effecting this differentiation between carrier solvent and the solute of interest, and thermospray is just one of them. Plasmaspray is a variant of thermospray in which the basic method of solvent removal is the same, but the number of ions obtained is enhanced (see below). 

By passing a continuous flow of solvent (admixed with a matrix material) from an LC column to a target area on the end of a probe tip and then bombarding the target with fast atoms or ions, secondary positive or negative ions are ejected from the surface of the liquid. These ions are then extracted into the analyzer of a mass spectrometer for measurement of a mass spectrum. As mixture components emerge from the LC column, their mass spectra are obtained. 

An ion beam causes secondary electrons to be ejected from a metal surface. These secondaries can be measured as an electric current directly through a Faraday cup or indirectly after amplification, as with an electron multiplier or a scintillation device. These ion collectors are located at a fixed point in a mass spectrometer, and all ions are focused on that point — hence the name, point ion collector. In all cases, the resultant flow of an electric current is used to drive some form of recorder or is passed to an information storage device (data system). 

If samples are introduced continuously, then the measurement of isotope ratios can also be continuous as long as sample is flowing into the flame, and several m/z ratios can be examined with almost any kind of mass spectrometer,... 

An important parameter when considering GC resolution of the sample components is the carrier gas linear velocity (flow rate, F), which can be determined by injecting 5-50 /A of argon or butane and measuring the time from injection to detection by the mass spectrometer. An optimum linear velocity using helium as a carrier gas is approximately 30 cm/sec and... 

Eisele and Tanner (146) have devised a similar scheme for the measurement of [HO ] via the chemical conversion of HO to H2 S04 by the addition of S02 to a flowing reactor followed by chemical ionization of gas-phase sulfuric acid to H S04 . The H 04 ion is uniquely identified and quantified in the flowing gas sample by a mass spectrometer. This technique is capable of sensitive, realtime measurement of [HO ], and although relatively new, appears to be perhaps the best overall technique devised to date. 

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