ION MOBILITY SPECTROMETRYa strawberry case study

Dr. Thomas Vandendriessche

02/04/2015

“SENSOR DEVICES”

Ease-of-use

Speed

Price

Sensitivity

Separation power

Identification of artefacts

Introduction

• 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

Introduction

• However– Resistance, health– Biotic factors– Off-flavor development– Altered external appearance

High – throughput volatile analysis?

Introduction

MCC-IMS

What?

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

Sample introduction

Ionization

Beta radiation (100 or 300 MBq, 63Ni or 3H)

Reactant ions: H+(H2O)n, (H2O)n, NO+(H2O)n (H2O)n

Product ions: M + H+(H2O)n MH+(H2O)n-x + xH2O(clusters, dimers, clustered proton-bound dimers)

• 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)

Ion separation

Drift tube

• 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)

Ion separation

• 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

Detection

Typical result

Application: shelflife

Application: shelflife

Application: shelflife

Conclusions

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

Conclusions