On the signal response of various pesticides in electrospray and atmospheric pressure chemical ionization depending on the flow-rate of eluent applied in liquid chromatography–tandem mass spectrometry

Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization

“…These analytes formed mainly radical cations in DA-APCI, but protonated molecules in APCI. The result is in agreement with previous reports using APCI, which have shown signal decrease at high flow rates, especially for lower polarity compounds [38,39]. The flow rate dependence in APCI could be explained by the growth of solvent cluster size, which reduces proton transfer between protonated solvent clusters and analytes with low PA. Also, an increased amount of solvent impurities in the source may lead to competition for protons between analytes and the impurities, and decrease the ionization efficiency of the analytes.…”

Chemical Analysis of Pesticides Using GC/MS, GC/MS/MS, and LC/MS/MS

“…The design and operational parameters of individual API ion sources can also lead to varying results between the sensitivity of ESI versus APCI and consequently should be evaluated for the system under use and expected flow rate conditions. Table 3 shows that flow rate conditions for the separation are an important consideration as ESI is generally most sensitive at lower flow rates typically near 0.2 mL/min and consequently it may be desire to utilize smaller particle size (2-3µm) LC/MS columns however the reduction in sample loading capacity should also be consider (Asperger et al, 2001;Titato et al,2007). If using higher flow rate conditions for the separation on columns (5µm, 150 to 250 mm X 4.6 mm) then the flow is generally split prior to MS (Banerjee et al, 2009;Crescenzi et al, 1995;Di Corcia et al, 2000).…”

“…If using higher flow rate conditions for the separation on columns (5µm, 150 to 250 mm X 4.6 mm) then the flow is generally split prior to MS (Banerjee et al, 2009;Crescenzi et al, 1995;Di Corcia et al, 2000). APCI is most often operated under high flow rates 1-2 mL/min (Table 3) and optimal flow varies with chemical class (Asperger et al, 2001;Titato et al, 2007). OPs are distinctly different and require lower flow rates for optimal sensitivity with APCI (Asperger et al, 2001;Jansson et al, 2004;Titato et al, 2004).…”

“…APCI is most often operated under high flow rates 1-2 mL/min (Table 3) and optimal flow varies with chemical class (Asperger et al, 2001;Titato et al, 2007). OPs are distinctly different and require lower flow rates for optimal sensitivity with APCI (Asperger et al, 2001;Jansson et al, 2004;Titato et al, 2004). Even if sensitivity is better with the more popular ESI methods there may be preference to use APCI for some chemical classes (OPs, chloracetanildes, pyrethroids, phenoxyacid herbicides, carbamates) to take advantage of other factors which include the following: (1) APCI is generally less prone to sodium adduct formation that ESI; (2) APCI can be less prone to matrix impacts as compared to ESI (Souverian et al, 2004); and (3) in some cases the SRM transition can differ from ESI so that co-eluting peaks can be isolated with MS/MS thereby reducing chromatographic resolution needs (see Table 3).…”

“…However these chloro and nitrophenols have also been analyzed successfully by APCI (Silgoner et al, 1997). OP degradation products including 3,5,6-trichloro-2-pyridinol, diethyl phosphate, 2-isopropyl-6-methyl-4-pyrimidinol, malathion monocarboxylic acid, and OPoxons (Raina and Sun, 2008) as well as OP sulfones and sulfoxides (Jansson et al, 2004;Chung andChang, 2010, Hiemstra et al, 2007;Economou et al, 2009) are more sensitive with LC-ESI + /MS/MS and some OPs observe a drastic loss in sensitivity with an APCI source at high flow rates (Asperger et al, 2001). Degradation products of triazines and phenylureas have been done by LC-APCI + /MS/MS but for triazines lower MDLs can be achieved with GC-EI/MS/MS (Dagnac et al, 2005;Goncalves et al, 2006).…”