Photoionisation

Consider a hytoophobic sensitizer such as tetramethylbenzidine or phenothiazine incorporated into an anionic micelle. After excitation these molecules will eject electrons via a tunnelling mechanism from the lipid into the aqueous phase where formation of 

Using this principle, light induced charge separation has been achieved for a number of donor/acceptor pairs. Noteworthy are the examples where pyrene served as an electron acceptor and dimethyl aniline as a donor as well as the photoinduced reduction of 

Apparently, a large fraction of chl a escapes from geminite recombination with DQ inside the aggregate. This must be due to the efficient ejection of DQ from the micellar into the aqueous phase as was suggested above in our model considerations. Once in the aqueous phase DQ cannot return into its native micelle since it is electrostatically rejected from the micellar surface. Hence, it will undergo disproportionation into durohydroquinone and DQ. The cation radical chl-a is slowly reconverted into chlorophyll-a as indicated by the bleaching results. 

Oscilloscope Traces Obtained in the 69 nm Laser Photolysis of Chlorophyll-a (3 X 10 5m) in HALS (O.IM) Micelles. From the top traces (l) and (2) decay of the chlorophyll-a triplets in the absence of additivesJ traces (3) and chlorophyll cation radical decay in the presence of 3X10 m duroquinone trace (5) chlorophyll cation decay in the pre-scence of 3X10 DQ and 8X10Pycocyanine. 

The effect of pycocyanine (PC ) observed supports the suggested mechanism. PC is present in the aqueous phase and is reduced by DQ. The neutral PC produced can enter the micelle and reduce in turn chl-a . Thus, the fraction of chl-a initially removed from the sphere of observation is replenished rapidly via this sequence of redox reactions. Hence, no long-tem bleaching of chl-a is expected to occur as indeed is observed. Thus the lifetime of intermediates produced by the photoredox event could be prolonged by several orders of magnitude through en loyment of suitable micellar systems instead of 

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Ionisation detectors. An important characteristic of the common carrier gases is that they behave as perfect insulators at normal temperatures and pressures. The increased conductivity due to the presence of a few charged molecules in the effluent from the column thus provides the high sensitivity which is a feature of the ionisation based detectors. Ionisation detectors in current use include the flame ionisation detector (FID), thermionic ionisation detector (TID), photoionisation detector (PID) and electron capture detector (ECD) each, of course, employing a different method to generate an ion current. The two most widely used ionisation detectors are, however, the FID and ECD and these are described below. 

CE Photoionisation (PI) Ion-cyclotron resonance (ICR) Continuous dynode multiplier... 

Fast atom bombardment (FAB) Plasma desorption (PD) Liquid secondary-ion mass spectrometry (LSIMS) Thermospray (TSP)/plasmaspray (PSP) Electrohydrodynamic ionisation (EHI) Multiphoton ionisation (MPI) Atmospheric pressure chemical ionisation (APCI) Electrospray ionisation (ESI) Ion spray (ISP) Matrix-assisted laser desorption/ionisation (MALDI) Atmospheric pressure photoionisation (APPI) Triple quadrupole (QQQ) Four sector (EBEB) Hybrid (EBQQ) Hybrid (EB-ToF, Q-ToF) Tandem ToF-ToF Photomultiplier... 

APPI and corona discharge-APCI methods were compared [164], A review of photoionisation and photodissociation methods in MS has appeared [165]. 

An ion mobility spectrometer consists of a sample-introduction device a drift tube where ionisation and separation of ions takes place and a detector. Ionisation sources of choice include radioactive sources (e.g. a 63Ni foil), photoionisation methods, corona-spray ionisation, flame ionisation and corona discharge. The most common detection method used to measure the... 

NPD Nitrogen phosphorous detector or PDPI Photodissociation-photoionisation... 

OTT Open-tubular trapping PI-ToF Photoionisation time-of-flight... 

Photoionisation Removing an electron from an atom or molecule due to interaction with a high-energy photon. 

Below the photoionisation threshold a core electron in a free molecule can be excited into empty anti-bonding molecular orbitals (m.o. s) as well as into Rydberg states. These transitions are observable as sharp features directly below the corresponding absorption edge (carbon K, oxygen K etc.). Above the... 

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