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temperatures used by GC. For the analysis of these pesticides, the HPLC method has been developed.

N-methylcarbamates are carbamates with N-methyl substituents including carbamide acid ester and its
salts. These carbamates were analysed by following technique, which involved a reversed-phase
separation followed by a postcolumn base hydrolysis that liberated methylamine, which further reacted
with OPA/thiol reagents to form a highly fluorescent isoindole (λex340 nm, λem455 nm). The general
system includes separation of several N-methylcarbamates on a reversed-phase column with gradient
elution followed by hydrolysis (ca 100°C) with sodium hydroxide to form methylamine and
derivatization with OPA/2-ME (or 3-MP). Recently, hydrolysis without an alkaline solution was
developed, and the use of catalytic solid-phase hydrolysis such an anion-exchange resin as Aminex A-
27 and magnesium oxide (Fig. 1.2.12) [204,205], UV irradiation, decomposition with a photolysis
reactor [30] and a single-stage reaction of hydrolysis and derivatization with a mixed solution of
alkaline solution and OPA/thiol reagent was reported [15]. Preliminary treatment of GPC [25], SFE
[30], MSPD [15], and SPE [205,206] for several vegetables and fruits was investigated. Simultaneous
multicomponent analysis of N-methylcarbamates and their metabolites with gradient elution on
reversedphase HPLC is customarily carried out. This postcolumn method for N-methylcarbamates
offers simplicity and sensitivity, but numerous interference peaks from co-existents appeared when the
method was applied for the analysis of such citrus fruit as grapefruit. Therefore, this method is not
suitable for identification but screening.

The approach with liberation of methylamine from N-methylcarbamates using a post-column photolysis
reactor mentioned earlier has been examined for the analysis of other carbamates, nitorogenous
pesticides and organophosphates [207,208]. Depending on analyte pesticides, detection with fluorescent
or ECD sensitive products after photolysis [208], and with fluorescent OPA derivatives with a liberated
allylamine such as methylamine was reported [207]. These methods were applied to standards. For food
application, bentazon (BEN), pyrazoxyfen (PYR) and chinomethionate (CIN) in brown rice was
analysed by post-column photolysis with UV irradiation followed by fluorescent detection (λex329 nm,
λem415 nm for BEN; λex333 nm, λem405 nm for PYR; λex377 nm, λem450 nm for CIN) (Fig.
1.2.13) [209]. In this case, disappearance of interfering peaks and improvement of sensitivity was
observed compared to detection with UV 215 nm (for BEN), UV 251 nm (for PYR), and UV 260 nm
(for CIN) (Fig. 1.2.14). The detection limit was 10 ppb, respectively.

1.2.6—
Analysis of Natural Toxins

1.2.6.1—
Mycotoxins

Aflatoxins

Mycotoxins are toxic metabolites produced by fungi and more than 300 mycotoxins are known. Among
them, aflatoxins yielded by Aspergillus flavas are the most potent carcinogens in nature, and the
legislative level of aflatoxins is set in most countries. More than 10 analogues of aflatoxins B , B , G ,
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G , M , M , P , Q and aflatoxicol are recognized. Strong carcinogenicity and contamination prevalence
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of aflatoxin B , B , G , G and M in food necessitates the monitoring of these compounds. These
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aflatoxins have native fluorescence (λex365 nm, λem450 nm), but the fluorescence intensity of B and
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G is weaker than that of B and G . Therefore, the use of fluorescence enhancement by hydration of B
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and G with trifluoroacetic acid (TFA) to hemiacetals, i.e., reaction of double bonding of terminal furan
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ring in B and G with TFA is widely accepted [37]. In this case, B and G do not react with TFA. The
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