Environmental Engineering Reference
In-Depth Information
predicts that after the radius of the droplet decrease to a given size, direct emission
of an ion from the droplet becomes possible [
17
]. This particular model is known as
the
ion evaporation theory
.
8.2 Nanochips for Electrospray Ionization Mass
Spectrometry
In the development of miniaturized micro- and nanofluidic systems a significant
progress in the past decade took place primarily due to numerous advantages of
nanochip analysis, including the ability to analyze minute samples, the increased
throughput and performance, as well as reduced costs [
18
-
20
]. In addition, several
laboratory procedures such as sample preparation, purification, separation, and
detection have been integrated onto a single microchip unit forming the so-called
micro-total analysis systems (
μ
TAS) to allow enhancement in sensitivity, speed,
and accuracy.
In the last years, by introducing MS as a detector, the potential and the applica-
bility of
TAS have been significantly extended. On the other hand, the option for
miniaturized, integrated devices for sample infusion into MS was driven by several
technical, analytical, and economical advantages [
21
] such as simplification of the
laborious chemical and biochemical strategies required currently for MS research,
minimization of sample handling and sample loss, elimination of possible cross-
contamination, increased ionization efficiency, high quality of spectra, possibility
for unattended high-throughput experiments, and the flexibility provided by the
microchips for coupling to different MS configurations.
In the field of ESI MS, two types of chip-based devices are most popular and
widely used. The first category [
22
,
23
] is represented by the out-of-plane devices,
where 100 or 400 nanospray emitters are integrated onto a single silicon substrate,
from which electrospray is established perpendicular to the substrate. These sys-
tems are known under the commercial name of NanoMate robot (Fig.
8.3
).
NanoMate 100 or 400 is produced by Advion BioSciences and represents the
world
μ
s first fully automated nanoelectrospray system, as a robotic device that
provides an automated nanoelectrospray ion source for mass spectrometers [
24
,
25
]. In this system, by an automatic infusion, samples are infused directly into MS
at low flow rates in the nanoliter range (only 50-100 nL/min). In addition to the
robot itself, the main element of the system is the ESI chip. The robot holds a
96-well sample plate and a 96-pipette tip tray (Fig.
8.3
). Automated sample analysis
is achieved by loading a disposable, conductive pipette tip on a movable sampling
probe, aspirating sample via a syringe pump, and moving the sampling probe to
engage against the back of the ESI chip. ESI process is initiated by applying a head
pressure and voltage to the sample in the pipette tip. Each nozzle and tip is used
only once in order to eliminate carryover and contamination typical to conventional
autosamplers. The ESI chip is an array of nanoESI nozzles of 2.5 or 10
'
μ
m internal
