3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
Table I
Sample preparation and GC-HT TOF MS instrumental set-up
Instrumental
set-up
Pesticides
(baby food)
PCBs
(fat)
Analytes group
PBDEs
(sewage water)
Pharmaceuticals
(river sediment)
Sample
preparation
Ethyl acetate extraction
of baby food followed
by HPGPC clean-up.
Soxhlet extraction of
adipose tissue using
Filtration of water followed
by microextraction in
Hexane:acetone (1 : 1,
v : v) extraction followed
6
hexane:dichlormethane
(1 : 1, v : v) followed by
packed siringe
(MEPS, C-18).
by SPE clean-up.9
8
HPGPC clean-up. 7
Injection: splitless 1 µl,
250 °C
Injection: pulse splitless Injection: PTV, 10 µl, Injection: pulse splitless
1 µl, 250 °C, 1.5 min 50 °C (2 min) 400 °C min–1 GC
Column: forte BPX-5
(40 m × 0.18 mm ×
0.18 μm) Temperature
programming: 70 °C
(1 min), 45 °C min –1
to 300 °C (3 min)
at 50 p.s.i.
Column: forte BPX-5
(30 m × 0.25 mm ×
0.25 µm) Temperature
programming: 80 °C
to 300 °C
Column: DB-XLB
(15 m × 0.25 mm ×
0.1 µm) Temperature
programming: 80 °C
1 µl, 250 °C, 2 min
at 90 p.s.i.
Column: forte BPX-5
(30 m × 0.25 mm ×
0.25 µm) Temperature
programming: 80 °C
(1.5 min) 45° C min–1 (2 min) 50 °C min –1 (2 min) 55 °C min –1
Column flow: 1 ml min –1 to 340 °C (6 min)
Column flow: 1 ml min
to 320 °C (4 min) to 330 °C (5 min)
–1 Column flow: 1.5 ml min –1 Column flow: 2 ml min –1
TOF MS
Detector voltage: 1,750 V
Time of analysis: 10 min
Detector voltage: 1,875 V
Time of analysis: 14 min
Detector voltage: 1,800 V
Time of analysis: 11 min
Detector voltage: 1,875 V
Time of analysis: 12 min
For optimization and validation purposes blank matrix
(pork fat, apple based baby food) was chosen. Sewage water
was obtained from local water treatment facility (Prague) and
sediment was sampled at Podoli site (river Vltava).
S a m p l e A n a l y s i s
Different sample preparation procedures for each analytes
group were applied. 6–9 Their brief overwiev can found
in Table I. The GC-HT TOF MS system consisted of a HP
6890 (Agilent Technologies, Palo Alto, CA, USA) gas chromatograph
with split-splitless injector (or Agilent PTV Inlet)
and LECO TruTOF HT time-of-flight mass spectrometer
(LECO, St Joseph, MI, USA). The detector operated in
electron impact ionisation mode (EI) or positive chemical
ionization mode (CI+). GC-TOF MS was performed using
set-up and conditions summarized also in Table I.
Results
F a s t A n a l y s i s a n d S p e c t r a l
D e c o n v o l u t i o n
To demonstrate the application potential of TruTOF
HT system and ChromaTOF software for detection/identification,
selected contaminats and residues were analyzed
under optimized conditions shown in previous chapter. All of
the analyzed sample has been processed by automated peak
finding and deconvolution function. Within peak finding,
the Chroma TOF software automatically detects peaks at
all acquired single masses (m/z 35–650 in our work) above
certain signal-to-noise level (S/n = 25 was used in the given
cases). After that, deconvolution alghoritm mathematically
separates mass spectra of chromatographically coeluted compounds.
Deconvoluted spectra are then compared to nIST
s565
library and the identification is performed automatically. As
the example Fig. 2. shows the Deconvoluted Total Ion Chromatogram
(DTIC) for matrix matched standard (25 µg dm –3 ).
Due to rapid analysis (fast temperature programming rate
45 °C), several coelutions occured (see Fig. 2.A). Successful
spectral deconvolution followed by positive identification
of overlapping chromatographic peaks have been enabled
by data acquisition rate of 15 Hz offered by the Tru TOF
(see Fig 2.B–C). Althought, within all tested analytes groups
and matrices certain coelutions occured, the quantification
Fig. 2. GC-hT TOF MS analysis of matrixe match standard of
pesticides at 25 µg dm –3 (apple based baby food). (A) Deconvoluted
TIC chromatogram. Measured mass spectrum (upper line)
of Fenthion (b), Chlorpyrifos (C) and Parathion (D) along with
respective NIST library hits (bottom line)