Ion-mobility spectrometry (IMS) is an analytical technique used to separate ionized molecules in the gas phase based on their mobility in a carrier buffer gas. The technique is widely used as a sensor for fast screening purposes. Although quite successful for straightforward applications, It suffers from lack of selectivity and specificity when more demanding challenges need to be addressed

1. ION MOBILITY SPECTROMETRY
a strawberry case study
Dr. Thomas Vandendriessche
02/04/2015

2. “SENSOR DEVICES”
Ease-of-use
Speed
Price
Sensitivity
Separation power
Identification of artefacts

5. • Strawberry is most popular soft fruit worldwide
• Yearly 25 % harvest loss due to grey mould
• Control:
– Fungicides
– Biological control agents
– Modified storage conditions
– UV or heat treatment

6. • However
– Resistance, health
– Biotic factors
– Off-flavor development
– Altered external appearance
High – throughput volatile analysis?

9. • Membrane inlets
• Coupling to GC (liquid injection)
• Headspace
• SPME
• Thermal desorption
• Purge and trap
• ESI
• Pyrolysis

10. Beta radiation (100 or 300 MBq, 63Ni or 3H)
28
63
Ni → β− + 29
63
Cu
N2 + β−
→ N2
+
+ β′
+ e−
Reactant ions: H+(H2O)n, NH4
+
(H2O)n, NO+(H2O)n O2
−
(H2O)n
Product ions: M + H+(H2O)n → MH+(H2O)n-x + xH2O
(clusters, dimers, clustered proton-bound dimers)

11. • Injection of product & reactant ions in drift tube
• Injection by ion shutter
– Removal of a strong electric field between parallel wires
extended over the cross-section of a ring in the drift tube
• Peak resolution and shape dependent on shutter
pulse width (100 - 300 µs)

13. • Ion separation based on ion mobility
• Ions moving through a gas under the influence of a
low electric field (E) obtain a certain drift velocity
(mobility)
Vd = KE
• The mobility coefficient (K) depends on:
– The strength of the electric field
– The drift gas pressure and temperature
– Characteristics of the ion (mass, structure and charge)
– Its interaction with the drift gas (collision cross section)

14. • Detector used = Faraday plate
– grounded metal plate connected to an inverting input of
an operational amplifier
• Aperture grid
– parallel wires at a potential above the Faraday plate
• Preventing of distortion or peak fronting and
preservation of the resolution in the spectra

20. • Relatively fast (2 min)
• Cheap
• Sensitive
• Low specificity
• Low selectivity
• QR-like data handling