Clusters Formed in Heavy Ionic Liquids as Potential DMA Standards
CHANAKYA BAGYA RAMESH, Luis-Javier Perez-Lorenzo, Yang Wang, Michel Attoui,
University of Miami Abstract Number: 592
Working Group: Instrumentation and Methods
AbstractHeavy ionic liquids developed at The Air Force Research Laboratory are of interest in electrical propulsion, and are being evaluated at Yale for the distribution of mass/charge and the stability of their clusters produced upon electrospraying. In this study, we have evaluated the potential of these clusters to be used as mobility standards, in functions such as the evaluation of differential mobility analyzers (DMAs). We have investigated two room temperature molten salts, referred to as IL-A ([A
+A
-], with A
+=C
17H
16F
17N
2S
+; A
-=C
2F
6NO
4S
2-) and IL-C ([C
++A
-], with C
++=C
18H
32N
4+2). The ionic liquids were diluted in methanol and electrosprayed into a parallel plate DMA for classification, after which they were introduced into a time-of-flight mass spectrometer (MS) covering the m/z range of up to 5000 Da. IL-A has a monovalent cation (A
+) while IL-C has a divalent cation (C
++). Both ILs share the same monovalent anion. Within the mass range considered, we see that IL-C forms several singly charged clusters in the form [C
++(C
-)
2]
n(C
++C
-) with 0≤n≤5. For IL-C the most abundant signal corresponds to n=0 at m/z=548.18 Da with mobility 1.05 cm
2/Vs and FWHM of 4.5%. For the same mass range, IL-A forms clusters in the form [A
+(A
-)]
n(A
+) with 0≤n≤4. The most abundant signal corresponds to n=0 at m/z=603.07 Da with mobility 1.16 cm
2/Vs and FWHM of 10.6%. Upon increasing the sheath flow, we see peak width for cations from both ILA and ILC reduce from 10.6% to 7.9% and 22.4% to 18.8% respectively. At the same time, peak widths for largest clusters did not change significantly and remained at 2.7% and 2.1% for IL-A and IL-C. Suggesting that the widths are intrinsically a range of mobilities. These are comparable to width of least mobile peak corresponding to the salt tetradodecyl ammonium bromide.