Nanospray Ionisation
Nanospray ionisation is a development of electrospray ionisation
(ESI) for performing analysis when you are either highly sample lim
ited or if the analyte is very
fragile. Nanospray only requires very low amounts (µL) of very low
concentration samples (nmol/mL). The technique also has an increased
tolerance to high aqueous solvents and salt contamination. Spectra can
be obtained from pg of material with very little clean up being
required. This increased performance is the result of lowering the
inner diameter of the spray needle and reducing potentials normally
used in ESI. Standard nanospray uses disposable tips, but has problems
with signal reproducibility between tips.
The nanospray system we have here at Bristol as the Advion TriVersa
Nanomate®. This is an automated system that uses chips (arrays) of 400
uniform nanospray needles which are each used once. The analyte
solution is sprayed from a non-conducting pipette tip pressed against
the rear of the chip. A small gas pressure is then used to create the
spray. In this way it is possible to typically spray for 20 to 30 mins
from only 5 µL of solution. Concentrations can also be considerably
reduced. We have the Nanomate® installed on our Waters Synapt. The
Bruker FT-ICR-MS instrument has an older Nanomate® HD system.
The nanospray chip system was developed by
Advion
Biosciences as an add-on to most commercial ESI instruments. The
array of needles is approximately the same size as a postage stamp
with each needle is just a few µm long. The figure shows a Scanning
Electron Micrograph images of a Nanomate® chip. Figure (a) is the
annulus and spray nozzle, figure (b) is a single spray nozzle (x1300).
In the example spectrum below, the sample is Leucine Enkephalin (a
peptide of mass 555 Da) at a concentration of 0.4µg/mL (in 50% MeCN/H
2O).
This was sprayed for 30 mins by the Nanomate, but only an 8 second
acquisition was required to record the spectrum on the FT-ICR. This is
equivalent to a sample consumption of about 30 pg (30x10
-12g)
of sample. The spectrum is recorded at a resolution of 50,000 (95%
valley definition) with a signal:noise ratio of 5000:1. The mass
accuracy is 1.4ppm.