Supplementary Figure S1.
Current-voltage diagram of dark, glow and arc discharges; adapted from [2].
Supplementary Figure S2.
ECI conditions of Oxaliplatin (C8H14N2O4Pt; MR = 397.30; 1 pmol injection; 500
fmol/μL) gave no radical cation under ECI conditions, but only a protonated (and
sodiated) species under ECI and ESI conditions. The isotopic pattern measured for
Oxaliplatin is identical to the one calculated for [M+H]+ and [M+Na]+.
Supplementary Figure S3.
Comparison of the spectra for Reserpine (II; (C33H40N2O9C12H10Fe1; MR = 608.69 Da; 1
pmol; 500 fmol/μL) under ESI (A) and ECI (B) conditions. Under ESI and ECI
conditions, an [M+H]+ ion was observed. No electrochemical oxidation was observed as
the ionization potential of reserpine is higher than that of Fe/Fe•+.
This is in contrast to electrochemical oxidations inherent to ESI, which depend on the
electrolysis of water (ionization potential 12.6 eV), which can oxidize many organic
compounds.
Supplementary Figure S4.
Electrospray Ionization using thermal discharge conditons.
The setup is essentially the same as shown in Fig. 2A with the exception that the capillary
is at very short distance to the orifice (less than 0.5 cm). This creates thermal arcs under
high current, low voltage conditions. When oxygen is used as a nebulizing gas, radical
OH• ions are formed in a plasma and react with the analyte to form multiple oxygenated
species.
Supplementary Figure S 5. (A) ECI chromatogram of 250 zmol of ferroceneiodoacetamide (IV, C12H12I1N1O1Fe1; MR = 368.98 Da) on column. The ferrocene-based
label was stable under standard gradient RP HPLC conditions. One peak eluted at 8.76
min with an m/z = 368.9 Da. At least a 10:1 signal to noise ratio at 5000 resolution under
full scan conditions was observed for 100 zeptomol injected on column. (B) Blank
injection showing background at 368.9 Da. (C) The concentration was linear in the range
from 100 zeptomol to 10 attomol. Concentrations used were 50, 125, 500, 5000 zmol/μL.
Individual injections are shown as , the mean is shown as . The inset shows an
expansion of the injections at lower concentrations.
Supplementary Table 1: Current measurements under ESI and ECI conditions.
HV @
capillary
tip
Desolvation
gas temp. in
ºC
N2 flow
Current
between R
and tip
Current @
grounded
liquid
junction
Measured
Ion
Intensity
for 100
fmol
injection
of E-Fc (I)
Solvent
system
2 KV
(ESI)
250
300L
0.1 μA
< 10 picoA
<1 ct
5 KV
(ECI)
500
500L
19 μA
< 10 picoA
>1000 cts
H2O: ACN
1:1 0.2%
FA
H2O: ACN
1:1 0.2%
FA
1. Current between the 33 MOhm resistor and the capillary tip. At 2 KV (ESI
conditions) a 0.1 μA current was measured representing a dark discharge. At 5KV (CD
initiated ECI conditions) the current was increased to 19 μA between the resistor and the
tip (“downstream” as suggested by Ochran8).
2. There was no measurable upstream current in ESI and ECI conditions. This was
measured using a liquid junction connection with a PEEK Tee connector and a gold wire
at the 1 m point of the PEEK tubing, just in front of the LC pump. The picoammeter was
attached to the gold wire and measured current flow from the junction to ground. To
eliminate any possible further leakage current additional PEEK tubing (1m) with PEEK
fittings was added between the liquid junction and the LC pump. Due to background
signals of the pumps and fans, 10 picoA was the lowest measurable current. No upstream
ground current was observed under any conditions.
Supplementary Table 2: Samples analyzed in this study.
Compound
E-FC (I)
Reserpine (II)
Fc-GSH (III)
Fc-IAA (IV)
Oxaliplatin (V)
Conc.
250
fmol/uL
2500
fmol/uL
500
fmol/uL
500
fmol/uL
50
pmol/uL
From 50
zmol/uL
to 5
amol/uL
500
fmol/uL
ECI
500 fmol
ESI
500 fmol
APCI
5 pmol
1 pmol
1 pmol
1 pmol
1 pmol
100 pmol
100 zmol 10 amol
1 pmol
1 pmol
Injection volume
2 uL; direct
injection
2 uL; direct
injection
2 uL; direct
injection
2 uL; direct
injection
2 uL; direct
injection
2 uL; LC
2 uL; direct
injection