Laser aerosol spectrometer

Note DMS differential mobility spectrometer, SMPS scanning mobility particle sizer, CPC condensation particle counter, TDMPS twin differential mobility particle sizer, DMPS differential mobility particle sizer, OPC optical particle counter, APS aerodynamic particle sizer, MAS mass aerosol spectrometer, LAS-X optical laser aerosol spectrometer, ELPI electrical low pressure impactor... 

All measurements were made using a Particle Measuring Systems Inc, Laser Aerosol Spectrometer Model LAS-X. The LAS-X Is a light scattering Instrument which uses a He-Ne laser. The gas sampling... 

Trimborn et al. (2000) have developed a mobile system for the on-line analysis of single airborne particles and for the characterisation of particle populations in aerosols, using a transportable laser mass spectrometer. A schematic diagram of their setup is shown in Figure 3.12. 

With the new equipment it is claimed that both types of errors are eliminated by using overlapping laser beams, producing one double crested beam profile. Each particle then creates a single, continuous signal that has two crests. Particles with only one crest are phantom particles, or with more than two crests are coincident errors and are logged for concentration calculations, but are not used in building the size distribution. The commercial development of aerosol spectrometers is a very active area of research, and one should check for the latest information with the manufacturers of such instruments. 

For non-volatile sample molecules, other ionisation methods must be used, namely desorption/ionisation (DI) and nebulisation ionisation methods. In DI, the unifying aspect is the rapid addition of energy into a condensed-phase sample, with subsequent generation and release of ions into the mass analyser. In El and Cl, the processes of volatilisation and ionisation are distinct and separable in DI, they are intimately associated. In nebulisation ionisation, such as ESP or TSP, an aerosol spray is used at some stage to separate sample molecules and/or ions from the solvent liquid that carries them into the source of the mass spectrometer. Less volatile but thermally stable compounds can be thermally vaporised in the direct inlet probe (DIP) situated close to the ionising molecular beam. This DIP is standard equipment on most instruments an El spectrum results. Techniques that extend the utility of mass spectrometry to the least volatile and more labile organic molecules include FD, EHD, surface ionisation (SIMS, FAB) and matrix-assisted laser desorption (MALD) as the last... 

Aerosol and cloud spectrometer 0.1- to 3.0- xm particles 0.3- to 20.0- xm particles laser scattering inside a cavity in the free air stream 36... 

The development of aerosol mass spectrometers (AMS), starting with work by Allen and Gould [27] and Sinha et al. [28], which focusses mainly on compounds ionisable at temperatures below 1,300°C such as sulphates and organic matter. Recently Park et al. [29] have developed a laser-induced ionisation method also allowing the detection of some metals and metal oxides. AMS without particle size separation are now small enough in size and power consumption to be used in longterm monitoring networks [30]. 

Specially shaped cells are required for special uses. One case in point is the cell depicted in Fig. 9.4C, which was designed to correct the variation of aerosol density in LA-ICP-MS and was a laboratory-made laser light-scattering cell for insertion into the aerosol transport tube between the laser ablation system and the torch. In this way, the temporal variation of signals from the laser light-scattering cell was correlated with that of the ion signals from the mass spectrometer [28]. 

Figure A. 11 Schematic diagram of the system components for particEe analysis by mass spectrometry, (a) Interface with external aerosol. Panicles ate introduced from the exterior through an aerosol beam with associated skimmers into (b) volatilizing and Ionizing region. The arrival of each panicle at the detector location is sensed by a laser that energizes a more powerful laser which focuses on the incoming particle to generate tons that pass to the (c) mass spectrometer, which may be of various types including quadrupole or time-of-flight. (From Sinha el al. 1983.)...

Ice particle measurements in the expansion experiment with 40% OC soot aerosol markedly differ from the 16% OC sample. Note that the optical particle spectrometer hardly detects any ice particles. Additionally, extinction signatures of ice are barely visible in the infrared spectra and diere is only a weak intensity increase of the back-scattered laser light in course of the expansion. The number concentration of ice crystals is less than 10 cm, thus < 1% of the seed aerosol particles act as deposition ice nuclei. In contrast to the 16% OC experiment, no precise critical ice saturation ratio can be specified for the 40% OC soot sample. RHi continues to increase to 190% because very little water vapour is lost on the small surface area of the scarce ice crystals. In summary, die comparison of the two expansion experiments provides first evidence that a higher fraction of organic carbon notably suppresses the ice nucleation potential of flame soot particles. 

The prepared sample must then be introduced into the MS. Liquid samples, usually weakly acidified solutions, can be converted into an aerosol by aspiration into the ICP/MS carrier gas in a mixing tube and inserted as a vapor. Alternatively, the prepared solutions can be applied to a TIMS filament and dried (see Section 17.5.1). The filament is subsequently inserted into the mass spectrometer. Direct volatilization from a furnace is an alternative for some elements. Ablation of a solid surface by a laser followed by direct injection of the aerosol is discussed in Section 17.7.2. 

In an aerosol SEC/MALDI experiment, the effluent from the SEC column was combined with a matrix solution and sprayed directly into a MALDI-TOF spectrometer. Ions were formed by irradiation of the aerosol particles with a pulsed UV laser. The ions were separated in a two-stage TOE apparatus, and averaged mass spectra were stored throughout the SEC/MALDI experiment. The matter of coupling MALDI with SEC has been recently reviewed, and it was concluded that off-line SEC/MALDI is routine today, whereas considerable work is still necessary in order to make on-line SEC/ MALDI a viable alternative to the off-line method. ... 

A pulsed sample introduction (PSI) interface and laser-induced multiphoton ionization have been also used to couple LC with TOF instruments [56]. The interface consists of a heated capillary for aerosol generation and a high-temperature pulsed nozzle for sample vaporization. The LC effluent enters the heated capillary at a flow rate between 0.5 and 1.6 mLmin A solenoid allows the sample vapor to enter the mass spectrometer in a pulse form. 

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