Page 48 - Modern Derivatization Methods for Separation Sciences

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organophosphorous pesticides, food additives such as antioxidants and preservatives, synthetic
antibacterials and antibiotics used for drugs in feeds and animals, have been used for purposes of
insecticide, preservation, disease control in the process of culturing, harvesting, and food preparation.
Criteria of usage and residue levels are set on these compounds. Controlled by the Food Sanitation Act,
some of these compounds are subjected to administrative examination. To analyze these compounds
under the food regulation, accurate, easy, quick and sensitive methods are required.

In food analysis, the most significant and major part of the procedure involves how effectively to
extract trace analytes of interest from the complicated matrix composed of fats, proteins and minerals.
Sample pretreatment, i.e. separation, clean-up, concentration of analytes from food materials is
inevitable for HPLC and CE measurement with derivatization. It is no exaggeration to say that the
performance of the method is evaluated by the sample pretreatment stages.

1.2.1.1—
Sample Preparation

Organic solvents such as acetone, acetonitrile and chloroform have been traditionally used for the
extraction of analytes of interest, followed by a clean-up procedure. It incorporates liquidliquid
extraction with nhexane/methanol and nhexane/acetonitrile, solid-phase extraction(SPE) with ODS
cartridges containing silica gel-based, chemically bonded ODS phase packings, and column
chromatography to eliminate interferences. Prior to describing derivatization, this chapter discusses up-
to-date extraction and clean-up procedures in food analysis.

Matrix Solid-Phase Dispersion (MSPD)

Simultaneous extraction and clean-up pretreatment, MSPD, has been developed in recent years. The
procedure includes blending of the sample and C18 packing, followed by packing into a disposable
syringe. Fat is removed with nhexane and the analytes of interest are eluted

with dichloromethane or methanol. The method is widely accepted by the residual analysis of synthetic
antibacterials such as sulfonamides [1-7] and furazolidone [8,9] in fish, meat and milk, nicarbazin [10]
in chicken meat, oxolinic acid [11] in fish; anthelmintics such as benzimidazoles [12], ivermectin [13]
and hygromycin B [14] in meat. The method is also suitable for residual analysis of pesticides such as
oxamyl and methomyl [15] in fruits. To analyze organochlorine pesticides [16,17] in oysters and beef
fat, sample-combined C18 packing stacked on Florisil is carried out. MSPD distinctly yields target
analytes without loss during the extraction process.

Gel Permeation Chromatography (GPC)

A preliminary separation column for GPC is used for the clean-up procedure of pesticide residue
analysis. GPC employs column packings based on styrene-divinyl benzene cross-linked
macromolecular polymers and mixed solvent of dichloromethane, cyclohexane or ethyl acetate for
eluent. High molecular weight compounds such as phosphoric lipids, chlorophyll and polymers travel
with the solvent front. On the other hand, low molecular weight compounds such as pesticides, are PCB
retarded in their progress down the column and exit. The low molecular weight compounds are
collected and concentrated and then subjected to instrumental measurement of HPLC and GC-MS.
Exemption from degradation and absorption loss in pesticide residue analysis is a distinguishing feature
of GPC, which is adopted as an official method by FDA, AOAC, USDA, and EPA. GPC columns are
available from Bio Beads SX-3, Optima GPC, Shodex CLNpak and EnviroSep-ABC. Application of
residue analysis for food materials has been reported for organotin [18] in fish, organochlorine

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