This thesis begins with an examination of the feasibility of using the Quick, Easy, Cheap,
Effective, Rugged, and Safe (QuEChERS) method, and its variants, for the co-extraction of
nonpolar and polar pesticides, including highly polar quaternary ammonium salts (QA) and
organophosphates (OP). QuEChERS was performed on a mixture of nine different chemical
classes of pesticides, with triphenyl phosphate (TPP) as the internal standard, on aqueous
Chinese lettuce samples, at 0.1 and 1.0 μg/mL levels. QuEChERS provided superior sample
recovery and precision (RSD) for nonpolar pesticides than it did for its polar variants, including
most of the polar pesticides and several carbamates, as judged from quintuplicate analyses. A
modification of the extraction buffer and cleanup reagent significantly enhanced the recovery of
highly polar QA and carbamates at sub–microgram-per-milliliter levels, while maintaining the
performance of the other nonpolar pesticides. Thus, QuEChERS is a versatile and convenient
methodology for multi-residue analyses, although unambiguous confirmation and quantification
of some polar pesticides, namely chlormequat, mepiquat, and glyphosate, required separate
analyses using tedious and time-consuming single-residue methods.
Liquid chromatography/tandem mass spectrometry (LC-MS/MS) provides the potential
advantages of low detection limits, simple sample preparation procedures, and high selectivities
for multi-residue analyses of organic toxics in food. In this study, a novel methodology based on
LC-MS/MS was developed for the simultaneous analyses of both polar and nonpolar pesticides;
an online-coupled hydrophilic-interaction chromatography/reversed-phase (HILIC-RP)
separation platform, featuring a HILIC column for online sample enrichment and a downstream
high-flow injector for solvent mixing and reconditioning, was constructed to allow efficient,
concomitant analyses of both hydrophilic and hydrophobic pesticides from a single sample
injection event. The performance of the HILIC-RP system, verified using a standard pesticide
mixture, was satisfactory. 6 out the 7 polar pesticides were successfully retained on the HILIC
column and 11 out of the 15 nonpolar pesticides were transferred to and separated by the RP
column; the remaining compounds were determined as flow-through prior to the HILIC
separation. No sensitivity loss of the polar pesticides was observed when using this hyphenated
system. The calibration curves for 20 out of the 22 standard pesticides exhibited excellent linear
responses (R2 > 0.995) over a typical working concentration range. The performance of the
HILIC-RP platform was comparable with those of individual one-dimensional HILIC and RP
analyses, thereby potentially eliminating redundant quantification procedures and allowing highthroughput
multi-residue analyses of toxic organic compounds. / published_or_final_version / Chemistry / Master / Master of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/161555 |
| Date | January 2011 |
| Creators | Lo, Fu-kiu., 盧富嬌. |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47869951 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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