(RSC food analysis monographs) r self extraction of organic analytes from foods a manual of methods royal society of chemistry (2005)

Extraction of Organic Analytes from Foods
A Manual of Methods

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RSC Food Analysis Monographs
Series Editor: P.S. Belton, School of Chemical Sciences, University of East
Anglia, Norwich, UK
The aim of this series is to provide guidance and advice to the practising food
analyst. It is intended to be a series of day-to-day guides for the laboratory
worker, rather than library books for occasional reference. The series will form
a comprehensive set of monographs providing the current state of the art on food
analysis.
Other titles in this series:
Chromatography and Capillary Electrophoresis in Food Analysis
By H Sorensen, S Sorensen and C Bjergegaard, Royal Veterinary and
Agriculteral University Frederiksberg, Denmark and S Michaelsen, Novo
Nordisk A/S, Denmark
Dietary Fibre Analysis
By D A T Southgate, Formerly of the AFRC Institute of Food Research,
Norwich, UK
Mass Spectrometry of Natural Substances in Food
By F Mellon, Institute of Food Research, Norwich, UK, R Self, University of
East Anglia, Norwich, UK, and J R Startin, Central Science Laboratory, York,
UK
Quality in the Food Analysis Laboratory
By R Wood, MAFF, Norwich, UK, H Wallin, VTT Biotechnology and Food
Research, Finland, and A Nilsson, National Food Administration, Sweden
The Maillard Reaction

By S E Fayle, Crop and Food Research, New Zealand and J A Gerrard University of Canterbury, New Zealand
How to obtain future titles on publication
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Extraction of Organic Analytes
from Foods
A Manual of Methods

Ron Self
University of East Anglia, Norwich, UK

advancing the chemical sciences

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ISBN 0-85404-592-9
A catalogue record for this book is available from the British Library
© The Royal Society of Chemistry 2005
All rights reserved
Apart from fair dealing for the purposes of research for non-commercial purposes or
for private study, criticism or review, as permitted under the Copyright, Designs and
Patents Act 1988 and the Copyright and Related Rights Regulations 2003, this
publication may not be reproduced, stored or transmitted, in any form or by any means,
without the prior permission in writing of The Royal Society of Chemistry, or in the
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concerning reproduction outside the terms stated here should be sent to The Royal
Society of Chemistry at the address printed on this page.
Published by The Royal Society of Chemistry,
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Cambridge CB4 0WF, UK
Registered Charity Number 207890
For further information see our web site at www.rsc.org
Typeset by the Charlesworth Group, Wakefield, UK
Printed by Athenaeum Press Ltd, Gateshead, Tyne and Wear, UK

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Preface
A wide range of analytical protocols, including extraction procedures to measure the concentration of an analyte in stated food matrices, are published by the
Association of Official Analytical Chemists (AOAC). These are kept up to date
through their validation procedure, which differentiates between methods that
are under development and those that have been approved through collaborative trials and other tests as statistically reliable. The chemical composition of a

particular food can be found by consulting compilations, e.g. The Composition
of Foods by McCance and Widdowson that provides an updated source of
information on new and existing foods in common use, via regularly published
supplements. Other monographs in this RSC series on food analysis have
already dealt with Quality in the Food Analysis Laboratory (including sampling), Dietary Fibre Analysis, Chromatography and Capillary Electrophoresis in
Food Analysis, Mass spectrometry of Natural Substances in Foods, and The
Maillard Reaction. This contribution sets out to compile a laboratory manual of
methods used for the preparation and extraction of organic chemical compounds
from food sources.
Chapter 1, introducing extraction methodology, Chapter 2, compiling and
differentiating sample preparation for extraction procedures, and the introductory sections of the subsequent chapters are pitched at the undergraduate level.
Practising food analysts may find the compilation of extraction techniques
into five physical groups: partition, solvation, distillation, adsorption and diffusion (Chapters 3–7, respectively) a useful structure and content for training
programmes, and the applications (referenced in subject indices organised by
commodity, method, chemical class and analyte) may provide useful examples
from the literature to illustrate the historical development of the physical
methods applied to food analyses.
It must be emphasised, however, that the examples have been chosen to illustrate the analytical processes and are not intended to be a comprehensive record
of work, or even the major work, done using that process. One serious incursion
into the literature on extraction methodology will highlight the enormity of the
task in making such a record.
To some extent, the selection of extraction methods for separate study is
arbitrary since the various stages of analysis cannot be always cleanly dissected

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vi

Preface

one from the other. This is apparent when the first chromatographic method in
series with another can be seen as a microextraction (separation) process.
Sometimes, the relatively simple procedures involved in the extraction of
target compounds may be mistakenly considered to be less of an intellectual
challenge than the more sophisticated separation and detection techniques. But,
because the extraction stage is often identified as the major source of error in
the total analysis, there is justification for paying extra attention to this area,
especially now that it is being put on-line in automated assays.
In the appendices, examples of methods that have been compared, combined
or used in collaborative trails have been correlated and used to form the beginnings of a database.
Ironically, remote sensing methods of acquiring compositional information
from foods are developing rapidly and making the classical “sampling” and the
current “extraction for analysis” methods redundant! Fortuitously, the equally
rapid development of on-line extraction and separation/detection methods
requires easy access to existing information. This collation of methods and
applications may be a handy reference for the developers of the “extractionless”
methodology of the future.
Ron Self
Norwich, UK, 2005

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Contents
Acknowledgements

xiv

Abbreviations

xv

Chapter 1 Methodology and Proximate Analysis
1 Extraction of Organic Analytes
Opening Statement
Food Sample for Analysis
Analysis of Foods
Stages in Food Analysis
2 Sampling
Introduction
Standardisation and Validation of Methods
Remote Sampling
3 Preparation for Extraction (Resumé of Extraction Aids)
Introduction
Change of Volume
Change of pH
Change of Structure (Cell Disruption)
Change of State
Change of Chemical Composition
Flow Switching and Automation
4 General Approach to the Extraction of Analytes
Phase Separation
Consider the Resolution of the Total Assay
Special Case of Labile Samples
Classification of Plant Crops for Extraction
Classification of Foods for Pesticide Analysis
5 Resumé of Extraction Methods
Introduction
Partition (Chapter 3)

Solvation (Chapter 4)
Distillation (Chapter 5)
Adsorption (Chapter 6)
Diffusion (Chapter 7)

1
1
1
2
2
4
6
6
6
8
9
9
9
9
9
10
11
11
12
12
15
15
16
16
17

17
17
18
19
20
22

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viii

Contents

6

Proximate Analysis of the Major Food Components
Introduction
Water Content – Direct Methods
Water Content – Indirect Methods
Total Solid
Total Lipid
Total Protein
Total Carbohydrate
Automation and Multicomponent Analysis
7 References
Chapter 2 Sample Preparation for Extraction
1 Introduction
2 Change of Volume
Dilution

Evaporation
Condensation
3 Change of pH
pH Measurement
4 Change of Structure
Ultrasound
Microwaves
Divide into Parts
Lysis
Homogenise
5 Change of State
Vaporise (Volatilise)
Dissolve or Liquify
Slurry
Solidify
Precipitate
Coagulate
6 Change of Chemical Composition
React
Defat
Dehydrate or Lyophilise
Inactivate
Deproteinise
7 Automation and Miniaturisation
Flow Switching of Flowing Food Matrices
Automation of the GC Injection
Automation of Coupled Sample Preparation
and Separation
“Extractionless Techniques”
µ-TAS

8 References

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23
25
26
27
27
30
37
41
43
47
47
47
47
48
48
48
49
49
49
52
54
55
69
69
69

70
70
70
70
70
71
71
73
73
73
73
74
74
75
76
85
87
87


Contents

ix

Chapter 3 Partition
1 Introduction and Nomenclature
Partition Equilibrium
Partition-extraction of Food Samples
Solvent and Solid-Phase Extraction
2 Gas/Liquid Partition (GLP)

Introduction
Air/water Partition Constants (KA/W)
Water/air/water Partition in Microdiffusion
Extraction
3 Liquid/Liquid Partition (LLP)
Organic Solvent/water Partition Constant
Oil/water Partition Constants
4 Solid/Liquid Partition (SLP)
Introduction
Solid/liquid Partition Constants
5 Applications of Partition–Extraction
Liquid/liquid Partitioning of Liquid Foods
Solid/liquid and Liquid/liquid Partitioning of
Liquid Foods
Multiple Liquid/liquid Partitioning of Liquid
Foods
Liquid/liquid Partitioning of Liquid and Solid
Foods
Liquid/liquid Partitioning of Solid Food Samples
Liquid/solid/liquid Partitioning of Solid Foods
Sodium Sulphate Drying in Liquid/liquid
Partitioning
6 References
Chapter 4 Solvation
1 Introduction
Solvent Extraction
Matrix Solid phase Dispersion
Subcritical Fluid Extraction
Supercritical Fluid Extraction
2 Solvent Extraction

Liquid/liquid Extraction
Solid/liquid Extraction
Multiple Liquid/liquid Extractions
Countercurrent Distribution
3 Matrix Solid-phase Dispersion
Introduction
Development
Applications
MSPD in Combination with Other Extraction
Methods

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94
94
95
97
97
97
98
101
102
102
104
105
105
105
105
105

106
106
107
107
108
108
108
111
111
111
111
112
112
112
112
114
120
122
124
124
125
128
131


x

Contents

4

Sub-critical Fluid Extractions
Pressurised Liquid Extraction (PLE)
Subcritical Water Extraction (SWE)
MSPD Cleanup for Combined SWE and SPME
Pressurised Hot-water Extraction
Comparison of PLE and SWE with the Soxhlet
Method
5 Supercritical Fluid Extraction
Developments
Applications
Supercritical Fluid Extraction Method Compared
to Others
Supercritical Fluid Chromatography
6 References
Chapter 5 Distillation
1 Introduction
Vapour Pressure of Binary Solutions and
Raoult’s Law
Vapour-liquid Equilibria of Fatty Systems
Vapour Pressures and GC Retention Data
Cooking, Distillation and Recovery of Volatiles
Reflux Mode Distillation
Fractional Reflux/Retort Distillation
Retort Mode Distillation
Distillation Processes
2 Steam Distillation
Introduction
Essential Oils
Taints and Off-flavours

Volatiles – Flavour and Aroma Compounds
Fumigants
Sulphites
Miscellaneous
Combination of Steam Distillation and SPME
Comparison of Steam Distillation to Solvent
Extraction
3 Organic Solvent Distillation–Extraction
Introduction
Continuous Extraction
Intermittent (Soxhlet) Extraction
Dean and Stark Extractor
Mineral Oil Distillation
4 Simultaneous Steam Distillation–Extraction
Introduction
Likens and Nickerson SDE Method
Vacuum Carbon Dioxide Distillation

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131
135
136
136
137
138
139
143
144

145
146
153
153
153
156
156
156
157
158
159
162
164
165
165
166
166
166
167
172
173
173
174
174
175
175
179
180
181
181

182
189


Contents

xi

5

6

Sweep Co-distillation
Introduction
Development
Applications
References

189
189
189
190
190

Chapter 6 Adsorption
1 Introduction and History
Food Colours
Food Flavours
Restricted Access Media
Cyclodextrin Extractions

Sol-gel Technology
Popularity Surveys of Adsorption Methods
2 Solid-phase Extraction
Introduction
Cartridge and Adsorbents
Adsorption processes
Applications
Developments
3 Solid-phase Microextraction (SPME)
Introduction
Practical Aspects
Background Literature Review
Theoretical Aspects
Development
Applications for GC and GC-MS Analysis
Gas/liquid Partition Constants from
SPME-GC-MS Data
Measurement of Oil/water Partition Constants
Partition Constants Correlated with Kováts’ Index
Case Study 1. Selective Extraction
Case Study 2. Isothiocyanate and Nitrile
Extraction Methods
Comparison of SPME with Other Extraction
Methods
Recent Progress in SPME Technology
Thin Film Microextraction
Multiple SPME
4 High Concentration Capacity Extractions
Stir-bar Sorptive Extraction
Solid-Phase Dynamic Extraction

5 References

196
196
197
197
200
200
200
200
201
201
201
203
203
206
225
225
226
226
229
230
233

Chapter 7 Diffusion
1 Introduction
Migration (Diffusion/Equilibrium) of Volatiles
Use of Membranes in Food Technology

262

262
262
262

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236
237
239
244
247
247
248
249
250
250
253
254


xii

Contents

Transport Theory
Analytical Extractions using Membranes
Membranes as Couplers for Preparation and
Separation Stages
Microporous Membrane Liquid–Liquid Extraction

Application of Membrane-based Solvent
Extraction in the Food Industry
Membrane-assisted Solvent Extraction
Introduction
For Triazines
Application to PCBs in Wine and Apple Juice
Sorbent Impregnated Membranes
Supported Liquid Membrane Extraction (SLME)
Planar Supported Liquid Membrane
Hollow Fibre Supported Liquid Membrane
SLME and Enzyme-catalysed Reactions
Immuno-SLME
Applications
Pervaporation
Principles
Development
Applications
Dialysis
Introduction
Development
Applications
Electrodialysis
Microdialysis
Filtration
Increasing the Area of Filtration
Decreasing the Concentration Polarisation Layer
References

263
264

Chapter 8 Conclusion
1 Introduction
2 Recent Reviews
Introduction
Preparation Techniques
Extraction Techniques
Combining Extraction and Preparation
Techniques with Capillary Electrophoresis
The Extraction of Chemical and Generic Classes
of Compounds
Automated Preparation and Extraction Methods
Automated Preparation, Extraction and
Separation Methods

284
284
284
284
286
286

2

3

4
5

6

7

8

9

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268
269
269
270
271
271
272
272
273
273
273
273
275
275
275
276
277
277
278

279
280
280
280
281
281
281

292
292
298
298


Contents

xiii

3

4
5
6

Recent Developments
Acrylamide Analysis
Extracting Syringe Method
Automation
Field Flow Fractionation
Molecularly-imprinted Polymers

MSPD for PCBs in Fat
Pittsburgh Conference 2003
Scavenger Extractors
Food Sensor Network
Sulphite Measurement
Report on HTC-8
Training for Collaborative Studies
Application of SDME
Concluding Statement
Further Reading
References

300
300
301
301
303
303
303
304
304
304
304
304
305
305
305
306
306

1
2
3
4
5

Comparisons of Extraction Methods
Combinations of Preparation/Extraction Methods
Interlaboratory Collaborative Trials
Examples of Preparation and Extraction Schemes
Literature Examples of Soxhlet Extractions

310
323
328
334
344

Appendices

Subject Indices
1 General Index
2 Commodity/Extraction Method/Analyte
3 Extraction Method/Analyte/Commodity
4 Analyte/Extraction Method/Commodity
5 Chemical Class/Extraction Method/Commodity
6 Utility/Extraction Method/Commodity

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356
368
377
381
385


Acknowledgements
I wish to thank the authors of all the work referred to in the text, without which
a collation of methods would not have been possible. Where more than a brief
summary of the referenced method has been cited, permission has been obtained
from the publisher or author, as appropriate. In the case of the six classical
line illustrations (Figures 1.1, 1.2, 5.3, 5.4, 5.5, and 5.8), neither the Publisher
(William Heinemann Ltd.) nor the author (Dr F. Sherwood Taylor) owned the
copyright. Every effort was made to trace the owners of material used here, and
anyone not contacted is invited to write to me.

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Abbreviations
2-ME
AC
AcCN
AcD
AcE
ACE
AcHyd
AEC

AEDA
Alc
AlkHyd
AOAC
APCI
Aq
ASE
ATP
B&D
BDC
BE
BFR
BHT
C18
C18 ec
CC
CCC
CCD
CCGC
CC-SFE
COVB
CE
CEC
CF
CFFE
CFS
CGE
CI
CIC
CITP

COI

2-mercaptoethanol
affinity chromatography
acetonitrile
acid distillation
acid extraction
angiotensin I converting enzyme
acid hydrolysis
anion-exchange chromatography
aroma extract dilution analysis
alcohol
alkaline hydrolysis
Association of Official Analytical Chemists
Atmospheric pressure chemical ionisation
Aqueous
Accelerated solvent extraction (see also PLE)
Adenosine triphosphate
Bligh and Dyer
buoyant density centrifugation
Babcock extraction
brominated flame retardant
butylated hydroxy toluene
octadecyl silica
octadecyl end-capped silica
column chromatography
countercurrent chromatography
countercurrent distribution
capillary column gas chromatography
countercurrent supercritical fluid extraction

carbowax divinylbenzene
capillary electrophoresis
capillary electrochromatography
continuous flow
continuous free flow electrophoresis
continuous flow system
capillary gel electrophoresis
chemical ionisation
capillary ion chromatography
capillary isotachophoresis
compound of interest

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Abbreviations

xvi

Conc
COP
CPCB
C(PR)
CRM
CTAB
(CS)5
CW-DVB
CW-TPR
CZE
Da

DAD
D&S
DC
DCM
DDT
DEC
Dep
DF
DH
DHPSE
D-HS
DI
Dil
Dist
DMDS
DMF
DMSO
DMTS
DPP
DS
DVB
ec
EC
ECD
EDB
EDC
EDTA
EI
ELISA
Enz

ENZ
EnzHyd
EO
EOF
e-scheme

concentrated
cholesterol oxidation product
coplanar PCB
colorimetric (pararosaniline)
certified reference material
cetyltrimethylammoniom bromide
collaborative study among 5 laboratories
Carbowax-divinylbenzene
Carbowax-templated Resin
capillary zone electrophoresis
dalton
diode array detection
Dean and Stark
dry column
dichloromethane
dichlorodiphenyltrichloroethane
disposable extraction cartridge
deproteinised
dietary fibre
dehydrated
dynamic high-pressure solvent extraction
dynamic headspace
direct injection
dilute

distillation
dimethyl disulphide
N,N-dimethylformamide
dimethyl sulphoxide
dimethyl trisulphide
differential pulsed polarographic
digestible starch
divinylbenzene
end capped
electron capture
electron capture detection
ethylene dibromide
ethylene dichloride
ethylenediaminetetraacetic acid
electron ionisation
enzyme-linked immunosorbent assay
enzymatic
enzymic method
enzyme hydrolysis
ethylene oxide
electro end osmotic flow
extraction scheme

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Abbreviations

ESE
ESI

ES-ITMS
ESO
ESy
EtOH
EU
FA
FAB
FAD
FAME
FAPAS
FD
FDA
FFA
FFF
FI
FIA
FID
FLD
FMASE
FMN
FMOC
FS
FSV
GC
GCO
GE
GLP
GLPA
GPC
h

H
HA
HAA
HBV
HCB
Hex
HFB
HLB
HPIC
HPTLC
HS
HSCCC
HSGC
HS-GC

xvii

enhanced solvent extraction (see also PLE)
electrospray ionisation
electrospray ion trap mass spectrometry
enzymatic sulphite oxidase
extracting syringe
ethanol
European Union
fatty acid
fast atom bombardment
flavin adenine dinucleotide
fatty acid methyl ester
Food Analysis Performance Assessment Scheme
freeze drying

Food and Drugs Administration
free fatty acid
field flow fractionation
flow injection
flow injection analysis
flame ionisation detector
fluorescence detection
focused microwave-assisted Soxhlet extraction
flavin mononucleotide
9-fluorenylmethyl chloroformate
flow switching
flow switching valve
gas chromatography
gas chromatography-olfactometry
gel electrophoresis
gas/liquid partition
gas/liquid partition analysis
gel permeation chromatography
hour
height of a theoretical plate
heterocyclic amines
heterocyclic aromatic amine
high-boiling volatile
hexachlorobenzene
hexane
heptafluorobutyrate
hydrophilic–lipophilic balance
high-performance ion chromatography
high-performance thin-layer chromatography
headspace

high-speed ccc
high speed gas chromatography
headspace gas chromatography

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Abbreviations

xviii

HS-LC
HS-SE
HS-SPME
HVD
IAC
IAE
IC
ICM
IDF
IE
IEC
IEF
IexC
IFJU
IgG
ILC
IMP
IPA
IPT

IRMM
IRMS
ISO
ITC
ITP
IUPAC
KA/W
KO/A
KO/W
Koil/water
KS/M
LBV
LC
LE
LLE
LLLE
LLP
LLP-E
LME
LMW
L-N
LOD
LOQ
LPME
LRM
LSE
LSLE

headspace liquid chromatography
headspace sorptive extraction

headspace solid-phase microextraction
high vacuum distillation
immunoaffinity chromatography
immunoaffinity extraction
ion chromatography
Iodometric Committee Method (for sulphites)
insoluble dietary fibre
ion exchange
ion exchange chromatography
isoelectric focusing
ion exclusion chromatography
International Fruit Juice Union
immunoglobulin G
interlaboratory comparison
instant mashed potato
isopropyl alcohol
International Proficiency Test
Institute for Reference Materials and Measurements
isotope ratio mass spectrometry
International Standards Organisation
isothiocyanate
isotachophoresis
International Union of Pure and Applied Chemistry
air/water partition constant
octanol/air partition constant
octanol/water partition constant
oil/water partition constant
stationary phase/mobile phase partition constant
low-boiling volatile
liquid chromatography

leading electrolyte
liquid/liquid extraction
liquid/liquid/liquid extraction
liquid/liquid partition
liquid/liquid partition–extraction
liquid membrane extraction
low molecular weight
Likens–Nickerson
limit of detection
limit of quantification
liquid phase microextraction
laboratory reference material
liquid–solid extraction
liquid/solid/liquid extraction

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Abbreviations

LSLP
LTP
LTVD
LVI
MA
MAE
MAH
MALDI
MASE
MA-SOX

MBSE
MCAC
MD
MDE
MECC
MEE
MEECC
MemASE
MeOH
MESI
MIP
MISPE
MMLLE
M(MT)M
MMTSO
Mod
MOD
ModMEE
MOPSO
MPa
MRA
MRC
MRL
MRM
MS
MSn
MS-MS
MSPD
MTB
MW

MWCO
MWD
N2
NAA
NBS
n.d.

xix

liquid/solid/liquid partition
low temperature precipitation
low temperature vacuum distillation
large volume injection
microwave assisted
microwave-assisted extraction
monocyclic aromatic hydrocarbon
matrix-assisted laser desorption ionisation
microwave assisted solvent extraction
microwave-assisted Soxhlet extraction
membrane-based solvent extraction
metal chelate affinity chromatography
membrane diffusion
microdiffusion extraction
micellar electrokinetic capillary chromatography
Mojonnier ether extraction
microomulsion electrokinetic chromatography
membrane-assisted solvent extraction
methanol
membrane extraction with sorbent interface
molecularly-imprinted polymer

molecularly-imprinted solid-phase extraction
microporous membrane liquid/liquid extraction
methyl(methylthio)methyl
methylmethane thiosulphinate
modified
mineral oil distillation
modified Mojonnier ether extraction
OH-4-morpholinopropanesulphonic acid
mega Pascal
multiresidue analysis
Medical Research Council
maximum residue level
multiresidue method
mass spectrometry
multistage mass spectrometry
mass spectrometry-mass spectrometry (tandem method)
matrix solid-phase dispersion
S-Methyl thiobutanoate
molecular weight
molecular weight cut-off
Monier-Williams distillation
nitrogen
neutron activation analysis
National Bureau of Standards
not detected

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Abbreviations

xx

NDMA
NFPA
NIR
NP
NPAH
NPD
NPLC
NPN
NPYR
NSP
NT
od
ODS
OEP
OM
Op
OP
OPP
Org
Pa
PA
PAC
PAD
PAH
PBDE
PBS
PCB

PCDD
PCDF
PCP
PCR
PDMS
PDMS-DVB
PEEK
PEG
Pet. Ether
PFE
PHWE
pI
PLE
PLM
POAE
pptn
PS
PSE

N-Nitrosodimethylamine
National Food Processors Association
near-infrared
normal phase
nitrated polycyclic aromatic hydrocarbon
nitrogen phosphorus detector
normal phase liquid chromatography
non-protein nitrogen
N-Nitrosopyrrolidine
non-starch polysaccharides
not tested

outside diameter
octadecylsilica
optimum extraction protocol
official method
optimised
organophosphorus
organophosphorus pesticide
organic
Pascal
polyacrylate
polyaromatic compound
pulsed amperometric detection
polycyclic aromatic hydrocarbon
polybrominated diphenyl ether
phosphate buffered saline
polychlorinated biphenyl
polychlorinated dibenzo-p-dioxin
polychlorinated dibenzofuran
pentachlorophenol
polymerase Chain Reaction
poly(dimethylsiloxane)
polydimethylsiloxane-divinylbenzene
polyetheretherketone
polyethyleneglycol
petroleum ether
pressurised fluid extraction (see also PLE)
pressurised hot water extraction (see also SWE)
isoelectric point
pressurised liquid extraction (also known as PFE, PSE, ASE,
ESE)

particle-loaded membrane
press oil aroma extraction
precipitation
phenylsilane
pressurised solvent extraction (see also PLE)

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Abbreviations

psi
PTFE
P&T
PVDF
RAG
RAM
RDS
R-G
RIs
RP
RP-IRLC
RP-LC
RRI
RRT
RS
RSD
RT
RmT
SAP

SAX
S-BSE
SC
SCoD
SD
SDE
SDF
SDME
SDS
SDSt
S-DVB
SE
SEC
SF
SFE
SGC
S-HS
SIM
SLE
SLM
SLME
SLP
s/n
SO
SolD
SOX
SPDE

xxi

pounds per square inch
polytetrafluoroethylene
purge and trap
polyvinyldifluoride
rapidly available glucose
restricted access media
rapidly digestible starch
Roese-Gottlieb
retention indices
reversed phase
reversed phase ion pairing liquid chromatography
reversed phase liquid chromatography
relative retention Index
relative retention Time
resistant starch
relative standard deviation
retention time
room temperature
saponification
strong anion exchange
stir-bar sorptive extraction
short-chain carbohydrate
sweep co-distillation
standard deviation
simultaneous steam–organic solvent distillation extraction
soluble dietary fibre
single drop microextraction
sodium dodecyl sulphate
slowly digestible starch
styrene-divinylbenzene

solvent extraction
size exclusion chromatography
shake flask
supercritical fluid extraction
silica-gel chromatography
static headspace
selected ion monitoring
solid/liquid extraction
supported liquid membrane
supported liquid membrane extraction
solid/liquid partition
signal-to-noise
sulphite oxidase
solvent distillation
Soxhlet extraction
solid-phase dynamic extraction

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Abbreviations

xxii

SPE
SPE/HPLC
SPME
SPR
SRMs
Std

StD
SWE

µ-TAS
TCA
TCB
TCE
TCP
TD
TDF
TE
TEA
TIC
TMS
TP
TS
p-TSA
TVA
UAE
UAMD
UASE
UDMH
UHT
USE
USEPA
VC
VIS
VLE
VOC
VSS

ZRM

solid-phase extraction
combined solid-phase extraction and high-performance liquid
chromatography
solid-phase microextraction
surface plasmon resonance
standard reference materials
standard
steam distillation
sub-critical water extraction (see also hot water extraction,
PHWE, pressurised water extraction, high temperature water
extraction, superheated water extraction, hot liquid water
extraction)
miniaturised total chemical analysis
trichloroacetic acid
trichlorobenzene
trichloroethylene
tetrachlorophenol
thermal desorption
total dietary fibre
terminating electrolyte
thermal energy analysis
total ion current
trimethylsilyl
theoretical plate
total starch
p-toluenesulphonamide
total volatile analysis
ultrasound-assisted extraction

ultrasound-assisted microwave digestion
ultrasound-assisted soxhlet extraction
unsymmetrical dimethylhydrazine
ultra-high temperature
ultrasonic Extraction
US Environmental Protection Agency
vinyl chloride
visible spectrophotometry
vapour–liquid equlibrium
volatile organic compound
vacuum steam-stripping
zero reference material

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CHAPTER 1

Methodology and Proximate
Analysis
1

Extraction of Organic Analytes

Opening Statement
The preparation for analysis of a small amount of material (the sample), representative of the bulk food, and normally supplied to the analyst, can be divided
into the following stages:
1. The first stage for most food matrices is to prepare a weighed and calibrated aliquot – the sample for analysis – in preparation for quantitative
extraction of the compounds of interest (analytes).
2. For some food samples, the material has to be rendered accessible to the

extracting agent – preparation for analysis.
3. The next stage can then be either (a) removal of the analytes from the
sample matrix or (b) removal of interferents from the matrix – the
extraction. In each case, the analytes are in a form to be recognised and
quantified unambiguously in subsequent examinations.
4. The final stage is to examine the extract, which will normally contain
matrix components other than the target analytes, using various of
chemical and physical methods to make qualitative or quantitative
measurements of the analytes – the analysis.
One contemporary objective in the development of analytical methodology is
to automate the whole assay, and there are two ways forward. The classical
extraction procedure can be given over to robotic control, or the information
about the chemical composition can be “extracted” directly from the sample
matrix by remote sensing. Perversely, remote sensing makes extraction redundant. Thus, it is necessary at the outset to recognise that the future analysis may
be an extractionless, remote sensing, robotic operation. Although considerable
1

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Chapter 1

2

progress has been made already towards these goals, as a “hands on instrumental analytical chemist” the modus vivendi for this monograph was to present
classical and modern experiential and methodological data in ways that may be
a helpful record and also serve as a transitional reference of methodology to
facilitate the advancement of the era of robotic analytical workstations.

Food Sample for Analysis

Foods (and drinks) are nutrient-containing substances that can be metabolised
into body tissue and into energy to sustain body tissue. In modern parlance foods
are largely solid, and drinks are largely liquid. It is convenient to refer to all
nutrient sources as food – the nutrient-carrying matrix – and to consider the
removal of compounds from a sample of food as an extraction. However, the
English language has many words to express the idea of removing something
from the whole. In analytical chemistry, for example, there is no clear distinction between a separation method and an extraction method, and it gets worse
because chemists also fractionate, purify, isolate, partition, disperse and distribute components of mixtures. Here, an extraction is thought of as an operation
on a sample of food that concentrates the target components, normally by
removing them from the bulk of the food sample, often in preparation for further
examination such as chromatographic separation. In analytical chemistry, a
separation is seldom carried out on the raw material (however, see Chapter 8,
Section 2, direct injection), but on an extracted or cleaned up sample for analysis. In addition, there are many procedures associated with extraction that in
themselves do not actually remove anything from the sample. These processes
are dealt with in Chapter 2 (Sample Preparation for Extraction), and are treated
as extraction aids.
The natural origins of human foods are biologically diverse, ranging widely
in texture and composition – from nutmeg to oysters. The extremely complex
endogenous composition of food is made even more complex in the modern
environment where so many extrinsic, additional items – additives such as
antioxidants, contaminants from agriculture such as herbicides and industrial
adulterants such as hydrocarbons from petroleum – may also be present. This
extends the quantitative range of analyses practised by food analysts from the
gram amounts encountered in proximate analysis (Section 6) to picogram and
even lower amounts of highly toxic contaminants e.g. PCBs. To cover more
than 12 orders of magnitude requires an enormously diverse armoury of
techniques.

Analysis of Foods
It is usually a concern over the chemical composition or contamination of food

and the effect this has on its value to the consumer that generates the need for
analysis. The quality of food is based on the natural composition, the balance
between the nutrient and the anti-nutrient composition. The health and prosperity of early civilisations depended upon their ability to refine their food

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