Fig. 4. Histogram of the number of charges lost at each ion emission event for individual ions generated from a 20 mM NaCl solution. The observed frequency shifts are exclusively to higher values, indicating that only positively charged ions are emitted. The charge loss distribution is fit by a Gaussian curve (red dotted line) centered at 1.1e with standard error of 0.07e. The Gaussian fit indicates equal probabilities for a measurement above and below ∼1e, meaning that the width of the distribution is primarily a consequence of measurement uncertainty rather than losses of multiple charges.
