Agilent Two Sources are Better Than One-More Choices for Sample Ionization with ESI APCI Application Note
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1. e Compound 1 an extended aromatic ring system with an amine molecular formula not provided MW 451 e Compound 2 an aliphatic amide with an amine aliphatic benzyl ether chain having the molecular formula C33H44N2S204 MW 596 1 e Both compounds were provided as solids and were dissolved in HPLC grade reagents to give a 1 0 pg mL 1 ppm concentration solution for direct infusion into the mass spectrometer e Syringe Pump Conditions Flow Rate 10 L min 10 ppm for ESI 20 L min 20 ppm for APCI Solvent Composition 50 50 Methanol 0 1 Formic acid LC MS Application Note 6 MS Parameters Application Note Number 6 September 2003 ESI API Drying Gas API Nebulizing Gas Scan Time SIM Width Needle Shield Capillary Detector MS Parameters 21 psi at 225 C 51 psi 0 25 sec 0 7 5000V 600V 50V 1500V APCl API Drying Gas API Nebulizing Gas API Auxiliary Gas Corona Discharge Needle Shield Capillary Detector 1 of 2 15 psi at 150 C 60 psi 17 psi at 350 C 5 pA 5000V 600V 50V 1500V www varianine com Results and Discussion The ESI molecular ion scan for Compound 1 is shown in Figure 1 The protonated molecular ion M H is observed at m z 452 1 as expected Conversely when Compound 1 is infused into the APCI source Figure 1 a very weak molecular ion is observed at the expected m z 452 1 when compared to the ESI conditions Negative ionization yielded2. NOTICE Varian Inc was acquired by Agilent Technologies in May 2010 This document is provided as a courtesy but is no longer kept current and thus will contain historical references to Varian For more information go to www agilent com chem tt Agilent Technologies Two Sources are Better Than One More Choices for Sample lonization with ESI and APCI J Beck and C Schmidt Varian Inc Introduction Two compounds were submitted for molecular weight deter mination using the 1200L LC MS Electrospray lonization ESI is generally the ionization method of choice for compounds analyzed with LC MS systems ESI works well for a wide variety of analytes However there are instances where particular analytes do not ionize well with ESI In these cases a second ionization method Atmospheric Pressure Chemical lonization APCI may often give the needed sensitivity While both positive ESI and APCI can result in a charged analyte the process of ionization is very different With ESI protonation of the analyte occurs in liquid phase With APCI a protonated solvent molecule donates a proton to the analyte in the gas phase In general APCI is better suited for ionization of non polar volatile low molecular weight molecules while ESI is better suited for more polar non volatile molecules Instrumentation e Varian 1200L LC MS equipped with ESI and APCI sources e Harvard Apparatus Pump 11 Syringe Pump Materials and Reagents
3. lity to ionize different analytes greatly increases These data represent typical results For further information contact your local Varian Sales Office LC MS Application Note 6 2 of 2 www varianinc com
4. no molecular ion in either APCI or ESI mode Molecular lon Spectra Compound 1 452 1 451 1 ESI Nf j Ilaj I 440 i 450 460 T 470 mz A APCI 439 1 452 1 437 0 451 1 J sN L I i l I A A i 1 y N AN h l ii Jw Fa L J kna aio 420 430 ao 450 460 470 m z Figure 1 ESI produces excellent molecular ion signal for Compound 1 while APCI does not As the molecular formula was not provided for the molecule the cluster of ions associated with the molecule cannot be assigned for example the presence of isotopes within the structure The ESI molecular ion scan for Compound 2 is shown in Figure 2 At the expected m z ratio for the protonated molecule 597 1 no signal is observed However when switching the ionization source from the ESI to APCI a distinct molecular ion peak is observed at m z 597 1 in Figure 2 Molecular lon Spectra Compound 2 ESI 580 590 600 l 610 m z APCI 580 590 600 610 m z Figure 2 APCI produces excellent molecular ion signal for Compound 2 while ESI does not Conclusion A wide variety of analytes can be routinely analyzed using the Varian 1200L LC MS system However one ionization source may not provide the information for the analyte of interest based on its characteristics and various mobile phase conditions By having access to both ionization methods ESI as well as APCI the abi
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Agilent Two Sources are Better Than One More Choices for Sample Ionization with ESI APCI Application