Agriculture Reference
In-Depth Information
trade disruption. However, in certain cases where there
is an evident structural problem in complying with
requirements, the European Commission has imposed
protective measures, including import bans, pending
satisfactory resolution of the problem in the affected
third country. Such protective measures can include:
•
Certification by the third country of absence of
specific residues from each individual consignment
(e.g. this was imposed on aquaculture exports from
Thailand in respect of residues of the nitrofurans and
chloramphenicol).
•
Mandatory testing by EU member states of a
proportion (up to 100%) of individual consignments
from a third country for a specific residue (e.g. 100%
testing was required of all poultry imports from Brazil
in respect of residues of the nitrofurans).
•
A complete ban on imports of food of animal origin
from a third country (e.g. a complete ban on the
import of food of animal origin was imposed on
China).
Table 13.3
The relationship between mass fragments and IPs
earned
MS technique
IPs earned per ion
Low-resolution mass spectrometry (LR-MS)
1.0
LR-MS
n
precursor ion
1.0
LR-MS
n
transition products
1.5
High-resolution MS (HR-MS)
2.0
HR-MS
n
precursor ion
2.0
HR-MS
n
transition products
2.5
Each ion may only be counted once.
GC-MS using electron impact ionisation is regarded as being a
different technique to GC-MS using chemical ionisation.
Different chemical derivatives of an analyte can be used to
increase the number of IPs only if the derivatives employ
different reaction chemistries (e.g. trimethylsilyl and
heptafluorobutyryl derivatives).
For substances in Group A of Annex I of Council Directive 96/23/
EC, if the following techniques are used in the analytical
procedure - (i) HPLC coupled with full-scan diode array
spectrophotometry (DAD), (ii) HPLC coupled with fluorescence
detection, (iii) HPLC coupled to an immunogram or (iv) two-
dimensional TLC coupled to spectrometric detection - they may
contribute a
maximum
of one IP, providing that the relevant
criteria for these techniques are fulfilled.
Transition products include both daughter and granddaughter
products.
In the case of authorised substances, a similar system
applies. However, the imposition of import restrictions
for repeated non-compliant results of a licensed veteri-
nary medicine with an established MRL would, very
much, be a last resort.
Analytical methods: Technical aspects
This technical section will be of interest mainly to
analytical chemists but may be useful as background
to official veterinarians.
For authorised substances, the use of HPLC with
single wavelength ultraviolet absorbance is no longer
acceptable for use as a confirmatory method. HPLC
with fluorescence detection or GC-/LC-MS or MS
n
detection is acceptable for the confirmation of authorised
substances. For unauthorised substances, only GC- or
LC-coupled MS or MS
n
techniques are acceptable for use
as confirmatory methods.
Table 13.3 shows the number of IPs that each of the
basic mass spectrometric techniques can earn. However,
in order to qualify for the IPs, a minimum of at least one
ion ratio must be measured, all measured ion ratios must
meet the criteria described earlier, and a maximum of
three separate techniques can be combined to achieve
the minimum number of IPs.
When mass spectrometric determination is per-
formed by fragmentography, the molecular ion shall
preferably be one of the selected diagnostic ions (the
molecular ion, characteristic adducts of the molecular
ion, characteristic fragment ions and all their isotope
ions). The signal-to-noise ratio for each diagnostic ion
shall be ≥3:1. The relative intensities of the detected ions,
expressed as a percentage of the intensity of the most
intense ion or transition, shall correspond to those of the
calibration standard, either from calibration standard
Method specificity
A system of identification points (IPs) has been intro-
duced to ensure the specificity of analytical methods.
The concept of IPs is applicable to both qualitative and
quantitative methods of analysis. The basic idea of IPs is
that a laboratory is allowed to use any molecular spectro-
metric technique or combination of techniques in order
to obtain the minimum number of IPs necessary for the
proper identification of a component. The minimum
number of IPs that must be obtained for identification of
unauthorised substances is set at four. For authorised
substances, the minimum number of IPs required for
proper identification is set at three. However, in order to
qualify for the IPs required for confirmation:
•
A minimum of at least one ion ratio shall be mea-
sured.
•
All relevant measured ion ratios shall meet the criteria
described in the following text.
•
A maximum of three separate techniques can be
combined to achieve the minimum number of IPs.
