Chemistry Reference
In-Depth Information
and reliable LC/MS instruments have been introduced commercially. The a
tmospheric
pressure interfaces has been used to broaden the range of analytes to be analysed by liquid
chromatography coupled with mass spectrometry [16-17].
Solvents such as acetone, ethyl acetate and acetonitrile may be used for extraction. However,
acetonitrile is the recommended solvent and is being used widely for QuEChERS method
because when salts are added, it separates more easily from water than acetone. Ethyl
acetate has the advantage of partial miscibility with water but it co-extracts with lipids and
waxes giving lower recoveries for acid-base pesticides [6]. A study by Lehotay S.J et al in
2010 [18] showed that results using acetate-buffered MeCN gave more accurate (true and
precise) results for all analytes in LC-MS/MS than EtOAc. On the contrary EtOAc is a better
solvent for GC rather than MeCN as demonstrated by the slightly more consistent
recoveries and reproducibility overall in GC-MS using EtOAc.
2. Materials and methods
2.1. Equipment
i.
LC/MS instrument
The chromatographic system used to analyse the extract is a Waters Alliance Separations
Module 2695 equipped with a quaternary solvent delivery system, autosampler and column
heater. A Waters ZQ 4000 single quadrupole Mass Spectrometer was used.
ii.
Chopper and Vortex mixer
Robot Coupe R5 V.V (Jackson, MS) and OMNI mixer homogenizer (OMNI International,
USA) were used to cut the fruit and vegetable samples into smaller pieces. Genie II vortex
mixer was used to swirl the tubes.
iii.
Centrifuge
Sorvall Legend RT Plus / Thermo Scientific were used for the centrifugation.
iv.
Balance
A Shimadzu top-loading balance Libror AEG-220 was used to weigh the chopped samples
and solid reagents and a Shimadzu analytical balance Libror EB-3200 HU was used in the
preparation of stock standard solutions.
v.
Vials and tubes
For the extraction step, 50mL centrifuge tubes were employed. 15mL graduated centrifuge
tubes were used for dispersive SPE in the method.
vi.
Solvent Evaporator
Zymark nitrogen evaporator Turbovap LP was used to concentrate the extracts and to
facilitate solvent exchange when necessary.
