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The complicated
determination of these herbicides is done by a two-phased, extractive
derivatisation with a subsequent GC-NPD or GC-MS/MS measurement.
The proof threshold is 0.1 to 0.5 mg/kg or 2-10µg/l..
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Thiabendazol/Carbendazim
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The determination
of these fungicides is done according to the collection of methods
for residue analysis of the DFG, No. 378. Water samples are
also subjected to an analog examination after a liquid extraction
of the active agents. The sample extract obtained after a corresponding
preparation of the samples (liquid extraction) is cleaned by
column chromatography and derivatised. The measurements are
done by means of GC-MS-NCI. Benomyl and partly also thiophanate-methyl
are converted into carbendazim in the course of the application
and also the preparation of the samples and therefore detected
and determined as carbendazim.
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Biphenyl
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Biphenyl
is extracted from the samples by means of water vapour distillation
and then measured by means of GC-MS. Orthophenyl phenol is also
detected in this determination. Both active agents are above
all used as surface treatment agents in citrus fruits.
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Piperonyl butoxid
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This
synergist, which is frequently used together with pyrethrum,
excels through a distinctly greater persistence compared with
pyrethrum, which is decomposed within a few days. Piperonyl
butoxide (PBO) is extracted from the sample material according
to item 1, only in this case the measurement method must be
mass spectrometry under electron impact conditions (MS or better
MS/MS). In this way, a further measurement is necessary in any
case.
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Chlormequat/Mepiquat
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Chlormequat
(CCC) is used:
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as a
growth regulator (shorter and stronger stems) in cereal cultivation
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in order
to increase the number of fruits in pears, almonds, grapevines,
olives, tomatoes
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to prevent
premature dropping of ripe fruits in pears, apricots, plums
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in cultivation
of cotton, vegetables, tobacco, sugar cane, mango, field crops
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Ethylene
oxide/propylene oxide
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These
gasification agents are used against pests in herbs and spices
and converted into chlorine ethanol and chlorine propanol. According
to Jensen's method, the preparation of the samples and implementation
of the extraction are done by distillation of the free or released
ethylene oxide(Eto)/propylene oxide(Ppo). In the receiver, Eto
and Ppo are converted into 2-iodine ethanol and 2-iodine propanol
respectively. These derivatives are extracted and measured by
means of GC-MS. The statement of results is done as chlorine
ethanol or chlorine propanol. For a determination of Eto alone
(without chlorine ethanol), the determination has to be slightly
modified.
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Bromide
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In an
analogy to DFG S18, propylene oxide is used instead of ethylene
oxide to convert the halogenide ions in the propylene oxide
method. According to a ring test of the Pesticides Study Group,
both methods are to be regarded as equivalent. The determination
itself is possible with justifiable efforts and also sufficiently
safe in the case of double determinations. Merely the assessment
of the figures received is difficult. There are only few data
available on the bromide contents of the individual products
normally encountered. It is not admissible to deduce the application
of methyl bromide directly from a bromide content.
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Phosphine
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Hydrogen
phosphide has been used as a gasification agent. It is gaseous
at room temperature and thus steam space analysis can be used
for the determination. The determination is done by head space
technique on a specific separation column with gas chromatography
phosphor detection (GC-NPD).
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