Page 131 - Modern Derivatization Methods for Separation Sciences

Document Página 1 de 2

Page 55

extraction method: 1) the disposal of a great amount of solvents used causing related health problems;
2) low operation efficiency; 3) low reproducibility; and 4) low recovery of highpolarity compounds.

Solid Phase Extraction (SPE)

This method passes liquid samples through the columns which are packed with silica gel chemically
bonded with the octadecyl silyl (ODS) group, with active carbon or other packings used as trapping
agents to trap the analytes. Compounds trapped on packing are extracted into solvent or solution with a
different polarity from the sample solution, and then concentration and clean-up is carried out. The
trapping agents can be classified into adsorbents and chemically bonded reversedphase silica gel. The
former includes active carbon, ion exchange resin, and porous polymer. The latter uses silica gel as a
base, chemically bonded with ODS or the octyl group. Nowadays many mini-columns using such
packings are sold in the market. It is advisable to contact the manufacturers for the selection of the
columns to suit the required use. Regarding post-treatment, the eluent is generally subjected to GC or
LC either directly, or following concentration or derivatization, except in the case of samples with
complicated matrices.

For the determination of residual pesticides and herbicides in water samples using chromatography,
refer to several general remarks referenced in [12-15].

1.3.3—
Application

In the determination of environmental contaminants, the derivatization HPLC is applied to a far fewer
number of compounds than in other fields. Introduced below are the studies on individual compounds
which have mainly examined the precolumn derivatization method intended for highly sensitive
detection.

1.3.3.1—
Aldehydes and Ketones in Air

The pre-column derivatization method has been examined to determine aldehydes and ketones in the
air, the toxicity of which has recently attracted attention. The main principle is a reaction in which
hydrazone compounds are efficiently obtained from the carbonyl group and hydrazine compounds
under acidic conditions (Fig. 1.3.5). The basic operation flow is shown in Fig. 1.3.6. 2,4-dinitrophenyl
hydrazine (DNPH), which has a strong UV absorption characteristic advantageous to detection, has
been the most popular in applications using EPA TO-5 since it was confirmed that various hydrazone

Fig. 1.3.5.
Reaction of aldehydes and ketones with hydradine compound.

http://emedia.netlibrary.com/nlreader/nlreader.dll?bookid=17968&filename=Page_55.html 30/09/2003