X. Xu et al.
[
9–13]
using CSI-MS.
MS can provide molecularly specific, highly
yellow precipitation was collected by filtration, washed by ethanol
three times and dried in an oven. Finally, re-crystallization of the
[
14–18]
sensitive, high-throughput approach to chemical analysis.
According to the advantage of MS and the low thermal decom-
position effect of CSI, a sample approach, CSI-MS, was installed
and used in this study. With simple operation, high analysis
speed and the ability to obtain structural information, it has been
used to precisely detect the solution structure and self-assembly
behavior of salicylaldehyde azine (SAA). This technology will not
damage the integrity of the molecules; therefore, it can provide
the molecular structure of aggregation in solution. Compared
with traditional techniques, the feasibility of the present
approach to detect multilayer films has been confirmed. Thus, this
new MS technique has potential significance for a wide variety of
structural investigations in the natural sciences.
2
product was accomplished by DMSO/H O. Single crystals suitable
for X-ray diffraction of SAA are obtained by evaporating the
absolute ethanol solutions at room temperature. Crystallographic
parameters and refinement details are listed in Table S1
(Supporting Information).
Setup of CSI-MS
CSI-MS analysis was performed using a LCT Premier XE time of
flight mass spectrometer (Waters, America) by replacing the ESI
source with a CSI source. This source is a T-shaped nebulizer that
is made with stainless steel. The nebulizer was fixed on a three-
dimensional platform, in which one end was connected with a
capillary (i.d., 250 mm) for sample introduction and the other
end was connected through a Teflon tube (o.d., 6.0 mm) for the
flow of nitrogen (99.9%). A schematic diagram of the CSI source
is shown in Fig. 1.
Experimental
Materials and instruments
CSI-MS was applied to characterize the solution structure of la-
bile self-assembling complexes. CSI apparatus features a liquid ni-
trogen cooling device to maintain the temperature of the
All chemicals were at least analytical grade. Hydrazine hydrate
(
N
2
H
4
Á H
2
O, purity ≥99%) and salicylaldehyde (purity ≥99%) were
purchased from Sigma-Aldrich and were used without any
pretreatment except dilution. Sodium hydroxide, DMSO and
ethanol were supplied by the Beijing Chemical Factory (Beijing,
China). Deionized water was purified by a Milli-Q reagent water
treatment system (Millipore, Milford, MA).
ꢀ
capillary and spray itself below À10 C. Typical measurement
conditions are as follows: ionization mode, positive-ion mode;
acceleration voltage, 5.0 kV; needle voltage, 0 kV; orifice voltage,
ꢀ
ꢀ
8
0 V; ion source temperature, 25 C; spray temperature, À10 C;
ꢀ
desolvation temperature, 150 C; solution flow rate, 3.0 ml/min;
gas flow rate, 0.5 MPa; and the analyte concentration in the
UV–vis spectra and fluorescence spectra were acquired using a
Nicolet 380 UV–vis spectrometer (Nicolet Company, USA) and
Cary Eclipse spectrophotometer, respectively. Each spectrum is
the average of three scans. FLM images were recorded on an
Olympus IX71 fluorescence microscope (Olympus, Japan). Scan-
ning electron microscope (SEM) characterization was performed
on the instrument (Hitachi S-4800) at 10 kV. Before SEM imaging,
a thin layer of Pt was coated on the film surface by an Auto Fine
Coater (JEOL) at a current of 20 mA for 100 s. X-ray crystallo-
graphic experiment was performed on Bruker Smart Apex II
CCD X-ray diffraction. Mercury (CSD software) was used for crystal
structure visualization.
À5
MS experiments was 5.0Â 10 M. ESI-MS experiments were
conducted under the same conditions, except that the spray
ꢀ
temperature was 100 C. All the mass spectra were recorded with
an average duration of 2 min and were background subtracted
using the MassLynx V4 software of the LCT instrument. To
further verify cluster ions, collision-induced dissociation (CID)
experiments were performed using an isolation window of
0
.5–1.5 mass/charge units and collision energy of 15–25
(
manufacturer’s unit).
Results and discussion
Synthesis of SAA and single crystal
Analysis of the results obtained by CSI-MS and ESI-MS
SAA (M
reported method. Briefly, a given amount of salicylaldehyde
1.10 g, 7.03 mmol) was dissolved in 50.0 ml ethanol in a flask,
and then hydrazine hydrate (0.20 g, 3.99 mmol) was added
drop-wise under vigorous stirring. Then, the stirred mixture
solution was left at room temperature overnight, and the resulting
r
= 240) was synthesized according to a previously
[4]
The traditional approaches could only yield surface topography
information when SAA self-assembled into nanorods. However,
these methods cannot be used to analyze the solution behavior
of SAA when the water fraction is quite low. Thus, to further
examine the behavior of SAA in the solution phase, CSI source
(
Figure 1. (A) Schematic diagram of the CSI source; (B) Partial magnified image of the setup.
wileyonlinelibrary.com/journal/jms
Copyright © 2013 John Wiley & Sons, Ltd.
J. Mass Spectrom. 2013, 48, 961–968