Membrane inlet system

An extensive and detailed coverage of the MS of expls in general has been documented (Ref 163). Volatile constituents of Comp A-3, Comp B, pressed TNT and cast TNT were surveyed with a residual gas analyzer MS (Ref 40). The mass spectra of all possible TNT (except for 3,4,5-TNT) and DNT isomers in the vapor phase were obtained as a function of ionizing voltage (Refs 65 84). The use of membrane inlet systems for the separation of TNT vapor in trace vapor detection is described and an analysis of the membrane inlet system for quadrupole mass spectroscopy is presented (Refs 95 113). Estimations of the vapor pressure of TNT were made mass spectrometrically in the range of 50—... 

An important problem with membrane inlet systems is quantification because the membrane behavior is more or less unpredictable [138, 352] however, the membrane inlet can be even more rapid [56,57]. 

One of the instruments obtained by ERDA will be evaluated at ORNL to assess its potential as a monitor for hazardous by-products from alternative energy sources. Investigations to determine the desirability of a membrane inlet system for concentrating organic vapors are planned. The feasibility of using a portable gas chromatograph with the portable mass spectrometer, when a complex mixture analysis is required, is also being studied. 

AMETEK s ProMaxion process mass spectrometer can monitor up to 32 components. Automated sample switching at the multiport allows unattended analysis of process and calibration gases. Different calibration and analysis methods can be assigned to each sample port. A membrane inlet system is incorporated for ambient gas sampling. The available mass range is 1-200 amu. The detection range is 10 ppm to 100 % with a Faraday cup detector lower LODs are possible with an electron multiplier. 

The method has shown to deliver good results for the fingerprinting of biodiesel fuel [34] and perfumes [33], for the analysis of fabric softeners and surfactants [35], coupling to membrane inlet systems (MIMS-DeSSI) [4], and to analyze components separated on TLC plates [36]. However, the method appears to exhibit low inter-system compatibility in some laboratories high voltages were needed to obtain a signal. 

An alternative approach is the use of a membrane inlet system. Polymer membranes have been used, for several decades, for the selective introduction of molecules into the ion source region of a mass spectrometer. The membrane acts as a semi-permeable barrier and by selecting a hydrophobic material, typically a silicone polymer, an inlet can be constructed which allows organic compounds to diffuse through the membrane and into the inlet of a mass spectrometer while acting as a barrier to water. This idea has been combined with PTR-MS to detect various compounds in water [7]. A water pump is used... 

Kristensen GH, Klausen MM, Hansen VA, Lauritsen FR (2010) On-line monitoring of the dynamics of trihalomethane concentrations in a warm public swimming pool using an unsupervised membrane inlet mass spectrometry system with off-site real-time surveillance. Rapid Commun Mass Spectrom 24(l) 30-34... 

The air temperature of the intermediate cell is assumed to be equal to 15 °C. This intermediate cell is dehumidified by the membrane contactor system placed at the evaporator inlet. The dehumidified air is driven to an air curtain at the top of the door separating the intermediate cell from storage cell. The heat load of the system and the air circulation ratio are assumed to be constant. The temperature of CaCl2 solution at the inlet of the membrane contactor is assumed to be equal to the indoor IC air temperature. The following parameters have been measured ... 

The principles, sampling systems, control of the measuring device and application of MS for bioprocesses have been summarized by Heinzle [157,158] and Heinzle and Reuss [162]. Samples are introduced into a vacuum (< 10 5 bar) via a capillary (heated, stainless steel or fused silica, 0.3 x 1000 mm or longer) or a direct membrane inlet, for example, silicon or Teflon [72,412]. Electron impact ionization with high energy (approx. 70 eV) causes (undesired) extensive fragmentation but is commonly applied. Mass separation can be obtained either by quadrupole or magnetic instruments and the detection should be performed by (fast and sensitive) secondary electron multipliers rather than (slower and less sensitive) Faraday cups (Fig. 21). 

To drive the volatile products directly from the electrode surface via a suitable inlet system into the vacuum chamber of the mass spectrometer, a plain gas-permeable membrane (e.g. PTFE or polyethylene) on which the electrode material is deposited by sputtering or vacuum evaporation is usually used. Alternatively, the material can be deposited onto a metal gauze that is fixed close to the gas-permeable membrane. DBMS cell constructions such as that shown in Big. 12.39 have been described that allow the use of massive electrodes, which are more easily available. 

The MS-200 has a membrane inlet concentrator which allows a wide range of gases to be identified and measured from the low parts per billion range up to percentage levels. No operator maintenance or specialist knowledge is required for the vacuum system. The system also uses El ionisation and a TOP mass analyser. The mass range is up to 1000 amu and sensitivity is <5ppb (for benzene). 

Tarkiainen, V., Kotiaho, T., Mattila, I. et al. (2005) On-line monitoring of continuous beer fermentation process using automatic membrane inlet mass spectrometric system. Talanta, 65... 

Figure 8.21. Two interface techniques used for DTA-MS by Aspina et ai. (79). Interface ( ) is continuous inlet system with bypass (b) membrane separator. 

C. Lanzerstorfer, H. Puxbaum, The palladium/silver membrane focusing injector-a new inlet system for thermal desorption capillary gas chromatography, Fresenius J. Anal. Chem. 1991, 339(4). 223-225. 

Membrane systems can also be integrated into traditional units. The design of a hybrid membrane separation system is determined by several considerations, such as membrane permeance and selectivity, CO2 concentration of the inlet gas and the target required, the gas value (per ca. 30 N m, the price of gas in 2007 was 6- 7 in the United States, whereas in Nigeria, which is far from being well-developed gas market, it may be as low as 0.50 if the gas can be used at all), and the location of the plant (on an offshore platform, the weight, footprint, and simplicity of operation are critical onshore, the total cost is more significant). ... 

The simplest form of RO/NF system contrail entails the adjustment of only two variables membrane inlet pressure and reject-flow rate, as shown in Figure 2.20. These functions affect the quantity and quality of RO permeate and indirectly potential for membrane... 

A programmable logic controller (PLC)-based membrane system utilises remote input/ output (I/O) functionality. The PLC communicates with various remote I/O control enclosures in the membrane plant, and performs all sequencing and inter-locking functions. In a fuUy automated system, independent (non-PLC) controllers such as PID (proportional plus integral plus derivative) or other tuning allow the operator to modulate control valves, e.g. feed water temperature, membrane inlet pressure and... 

RO control systems provide safety features for operating high-pressure RO feed water pumps. Pressures at pump inlet and discharge, membrane inlet, product output and reject... 

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