@article {1528,
	title = {Atmospheric pressure photoionization for ionization of both polar and nonpolar compounds in reversed-phase LC/MS},
	journal = {Analytical Chemistry},
	volume = {78},
	number = {23},
	year = {2006},
	note = {ISI Document Delivery No.: 110TZTimes Cited: 12Cited Reference Count: 9Robb, Damon B. Blades, Michael W.},
	month = {Dec},
	pages = {8162-8164},
	type = {Article},
	abstract = {Atmospheric pressure photoionization can provide high ionization efficiency simultaneously to both polar and nonpolar compounds delivered in reversed-phase solvent. The method to achieve this utilizes toluene as a dopant and simply requires that the solvent flow be limited so that reactions between toluene photoions and the organic component of the solvent are not driven to completion. Under these conditions, toluene photoions remain in the source for ionizing nonpolar compounds via charge exchange ( electron transfer), while protonated solvent ions are available for proton-transfer reactions with polar molecules. The reagent ion mixture is then suitable for ionizing a wide range of both polar and nonpolar compounds. The critical effect of solvent flow rate is demonstrated here with results for a test analyte, 9-methylanthracene, which may be ionized by either charge exchange or proton transfer. For a solvent of 50: 50 methanol/ water (v/v), lowering the flow from 200 to 50 mu L min(-1) results in a 10 x increase in charge exchange ionization efficiency-further flow reductions provide even greater enhancements. This method is compatible with sample delivery by direct infusion and micro- and narrow-bore LC, as well as conventional LC using a flow splitter.},
	keywords = {DOPANT, MASS-SPECTROMETRY, SOLVENT FLOW},
	isbn = {0003-2700},
	url = {<Go to ISI>://000242405300042},
	author = {Robb, D. B. and Blades, M. W.}
}
@article {1529,
	title = {Factors affecting primary ionization in dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC/MS},
	journal = {Journal of the American Society for Mass Spectrometry},
	volume = {17},
	number = {2},
	year = {2006},
	note = {ISI Document Delivery No.: 012ZFTimes Cited: 25Cited Reference Count: 20},
	month = {Feb},
	pages = {130-138},
	type = {Article},
	abstract = {The sensitivity of dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC/MS is generally reduced at higher solvent flow rates. Theory suggests that quenching of excited-state precursors to the dopant ions, via collisions with vaporized solvent molecules, may be one mechanism responsible for this trend. To ascertain if the primary rate of ionization is affected by quenching, experiments were performed utilizing an ionization detector to determine the primary ion current generated by irradiating vaporized mixtures of toluene dopant and methanol solvent. The results indicate that no loss of primary ion current occurs as the solvent flow is increased, provided the dopant-to-solvent ratio is held constant. Additional primary ion current can always be generated by increasing the dopant flow rate and/or the lamp power. Thus, quenching of excited-state precursors to the dopant ions, leading to a reduction in the primary rate of ionization, is not the mechanism responsible for the observed loss of sensitivity at higher liquid solvent flow rates.},
	keywords = {DETECTOR, LIQUID-CHROMATOGRAPHY, MASS-SPECTROMETRY, PERFORMANCE, PLASMA, SOLVENT FLOW},
	isbn = {1044-0305},
	url = {<Go to ISI>://000235378700003},
	author = {Robb, D. B. and Blades, M. W.}
}
