Food and Nutritional Analysis Packaging Materials

7/26/2019 Food and Nutritional Analysis Packaging Materials

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Further Reading

AOAC (1990) AOAC Official Methods of Analysis, 15thedn. Arlington, VA: AOAC.

Codex Alimentarius (1969) Codex Alimentarius SamplingPlan for Prepackaged Foods. Arlington, Virginia CAC/RM 42-1969.

Hulme AC (1970) The Biochemistry of Fruits and TheirProducts. London: Academic Press.

Kirk RS and Sawyer R (1991) Pearsons Composition andAnalysis of Foods, 9th edn. London: Longman Scientificand Technical.

Kratochvil B and Taylor JK (1981) Sampling for chemicalanalysis.Analytical Chemistry 53(8): 924A938A.

Nagy S and Attaway JA (1980) Citrus Nutrition andQuality. Washington DC: American Chemical Society.

Pomeranz Y and Meloan CE (1987)Food Analysis, Theoryand Practice, 2nd edn. New York: AVI.

Packaging Materials

A W Lord, Pira International, Leatherhead, UK

& 2005, Elsevier Ltd. All Rights Reserved.

This article is a revision of the previous-edition article by Philip

Tice, pp. 36983706, & 1995, Elsevier Ltd.

Introduction

Analytical measurements on food packaging materi-als are generally carried out for three main purposes:

To identify the components of the packaging.

To identify and measure substances present thatcould migrate into the packaged foods and cause ahealth hazard to the consumer of the food. This work

is often accompanied by measurements of the migra-tion of particular substances into either the actualpackaged foods, or into food simulants.

To identify and measure substances present thatcould migrate into the packaged foods and result inadverse effects on the organoleptic properties, suchas taste or odor.

Food Packaging Materials

The main categories of basic materials used for food

packaging are:

* plastics,* regenerated cellulose films,* paper and board,* metal, and* glass.

Of these, plastics are the most widely used and with-in this category there are also the largest numbers ofvariants. Many packaging materials are, however,multilayered with either different layers of plastics or

combinations of plastics with paper/board, metal, or

glass. The individual properties of the different ma-terials are used to produce food packaging with therequired characteristics. For example, in a packagingmaterial with two layers of different plastics, onelayer might provide the basic strength whilst theother layer enables the packaging to be easily heat-sealed. Coatings are also often added to the basicplastic packaging material to provide additional bar-riers to the permeation of oxygen and water vapor.These coatings can be polymeric or vacuum depos-ited aluminum.

With some metal cans used for foods andbeverages there is an inner lacquer (plastics) coatingfor the purpose of either preventing corrosion ofthe metal by the food/beverage, or preventing con-

tamination of the food/beverage by the can metal.A combination of a polymer layer with a board isused to package liquids such as milk, where theplastic layer provides the barrier to contain the milkwithin the package and the board the basic strength.Where it is necessary to store the beverage for longperiods, such as fruit juices, additional barrier prop-erties are required to prevent permeation of oxygeninto the food product. To achieve this additionalprotection, an aluminum layer is incorporated withina plastic/board composite.

With many of the multilayer packaging materials

adhesives are used to bind the layers together. Theprinting on the outside is a further important com-ponent of food packaging.

Identifying the Components of

Packaging Materials

It is often necessary to identify or confirm the basiccomposition of the packaging materials. This appliesparticularly with plastics due to the range of polymertypes that are used. Six major polymer types are used

for packaging and these are shown in Table 1, with

FOOD AND NUTRITIONAL ANALYSIS/Packaging Materials 341


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typical uses. In addition to these basic polymer types,various copolymers are also used. For example, eth-ylene is copolymerized with vinyl acetate to produceethylene vinyl acetate, styrene is copolymerized with

both acrylonitrile and butadiene to produce the ter-polymer ABS.

On simple, one- or two-layer structures, identifi-cation of the polymer type is conveniently achievedusing Fourier transform infrared spectroscopy(FTIR). Each of the major polymer classes or copol-ymers has unique infrared spectra and are easilyidentified by comparison of the spectra to referencespectra.

The infrared spectrum of a plastic packaging ma-terial is most easily obtained when the sample is inthe form of a film sufficiently thin to allow the in-frared spectrum to be obtained through the film.However, with most plastic packaging, even thosethat are used in the form of films, the thickness isusually too great to obtain a good transmission spec-trum. With some film materials stretching can ade-quately reduce the thickness. Alternatively, it may bepossible to produce a solvent solution and cast a filmof the required thickness. Thin films may also bepressed from the sample by careful melting on a hot-plate. Caution should be exercised with melt pres-sing, as apart from polymer degradation, there is therisk of altering the structure, for example, by skewinga polymer layer away from the region of analysis.

Infrared spectra may be obtained from surfacesusing a variety of techniques. These included atten-uated total internal reflectance (ATR) and specularand diffuse reflectance. These techniques involve theinfrared beam passing through only the outer fewmicrometers of the sample. The most widely appli-cable is ATR. A typical two-layer plastic materialused for lidding on plastic food trays consists of po-lyethylene and poly(ethylene terephthalate) boundtogether with an adhesive. ATR infrared spectra of

the two surfaces will easily identify one surface as

polyethylene and the other surface as poly(ethyleneterephthalate) by the very different spectra obtained.With the standard KRS5 (thallium bromide/iodide)ATR crystal the depth of penetration of the infraredradiation is a few micrometers. This is less than theindividual polymer layers and consequently the ad-hesive is not shown in either of the ATR spectra.

Where the polymer material is a copolymer it isoften possible to obtain a measurement of the re-lative amounts of the various monomer componentsfrom an infrared spectrum. For example, with anethylenevinyl acetate copolymer the relative heightsof absorption bands from both the ethylene and vinylacetate are measured and ratioed with the spectrumrecorded in the absorbance mode. The most conveni-ent absorbance bands are: 720 cm1 for polyethyl-ene and 1235 or 1740 cm1 for vinyl acetate.Copolymers of known composition are required forcalibration. It is possible to obtain an assessment on

the butadiene and acrylonitrile contents in styrene/butadiene/acrylonitrile copolymers. The bandsusually used are: for styrene 1600 cm1, for acrylo-nitrile 2240 cm1, and for butadiene 996 cm1.

Modern packaging materials are very often mul-tiple-layered structures. If the packaging material is alaminate or coextrusion each layer will produce aninfrared spectrum. The resulting composite spectrumbecomes difficult to interpret. In most cases lami-nates are manufactured using adhesive to bond thelayers together. It is sometimes possible to select asolvent to dissolve the adhesive thereby enablingthe individual polymer layers to be separated. Theseparated polymers can then be identified by theirinfrared absorption spectra. Spectra from a polyeth-ylene/poly(ethylene terephthalate) laminate and theseparated layers are shown in Figures 1A1D.Polyurethane-based adhesives are widely used tobond poly(ethylene teraphthalate) to polyolefins.Hot benzylalcohol is a good solvent for a range ofpolyurethanes. Other solvents include tetrahydro-furan and chloroform for acrylate-based adhesives.This approach also enables the adhesive to beidentified.

An approach that can be applied to laminates andcoextrusions is to selectively dissolve and removepolymer layers by careful selection of solvents. Thus,the nylon layer in a polyethylene/nylon/polyethylenecoextrusion can be isolated by boiling in xylene. Al-ternatively, the nylon could be removed by boilingin formic acid. Solvents for the selective removal ofpolymers are listed inTable 2. Acids or alkalis shouldbe avoided on some polymers where there is a risk ofreaction with the polymer. An example would be theuse of concentrated sodium hydroxide solution on a

metallized film comprising certain acrylic/ethylene

Table 1 Types of plastics used for food packaging and typical

uses

Plastic type Typical uses

Polyethylene Bags and bottles

Polypropylene Wrapping films and pots

Poly(vinyl chloride),

unplasticized

Trays, bottles, and containers

Poly(vinyl chloride), plasticized Wrapping film and cling filmPolystyrene Trays, pots, and containers

Poly(ethylene terephthalate) Lidding films and oven

containers

Polyamide (nylon) Laminated with polyethylene,

boil-in-bag pouches

342 FOOD AND NUTRITIONAL ANALYSIS/Packaging Materials


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ionomer types, where marked alterations to theinfrared spectra can result from such treatment.

It is sometimes difficult to obtain thickness meas-urements on layers due to swelling of layers with thesolvent or partial break up of thin layers. If the den-sity of the polymer is known or measured the thick-ness of a layer may be calculated from the weight ofthe polymer.

Although infrared spectroscopy is a useful tech-nique for identifying polymers in packaging materi-als it is important to emphasize that as a result of the

development of packaging technology, it is now

rarely possible or wise to use the technique on itsown without recourse to other analytical techniques.There has in recent years been a trend toward the useof coextrusions, and away from adhesive bondedlaminates. Coextrusions of a wide range of polymerscan be produced using thin tie layers (a few microm-eters) of polymer with compatibility for the differentpolymer types. For example, polypropylene and eth-ylene vinyl alcohol can be extruded into films andbottles. Layers within coextrusions cannot be readilyseparated using solvents. In addition, the time andcost constraints upon the analysis of coextrusionsmean that physical isolation of layers is oftenimpractical.

The most efficient approach to establishing thestructure of packaging is a combination of opticalmicroscopy, differential scanning calorimetry (DSC),and infrared spectroscopy. The first stage in estab-lishing the construction of an unknown packagingmaterial is to subject it to the following optical mi-croscopy techniques. A section (typically 510mm) iscut from a 1010 mm area using a microtome. It isimportant that the sample is held rigid but strain freeand cut with a very sharp knife. The best knife for

packaging material is usually a freshly made glass

Figure 1 Infrared transmission spectra of: (A) polyethylene/poly(ethylene terephthalate) laminate; (B) separated poly(ethylene

terephthalate) layer; (C) separated polyethylene layer plus adhesive; and (D) separated polyethylene layer with adhesive removed.

Table 2 Solvents for plastics

Plastic type Solvents

Polystyrene and copolymers Chloroform, ethyl acetate,

ketones

Polyethylene Decalin, hot toluene

Polypropylene Decalin, hot xylene

Poly(vinyl chloride) Tetrahydrofuran,

cyclohexanone

Poly(ethylene terephthalate) o-Chlorophenol, trichloroacetic

acid

Polyamide Formic acid, phenols



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knife. Thicker sections (42mm) require use of asteel knife. It is sometimes beneficial to cool samplesbelow their glass transition temperature (Tg) in orderto provide a more rigid structure to section. It mayalso be necessary to mount samples in potting resinfor support prior to sectioning through the sampleand resin.

The section is then examined under polarized light(using cross-polars). A tint plate is useful to providecolor differentiation of layers. This enables thenumber and thickness of each layer to be estab-lished. Thickness measurements are made by calcu-lation after measuring the total thickness of thesample using a micrometer. The ratio of total thick-ness to layer thickness is calculated in arbitrary unitsusing the scale graduations on the microscope. Thethickness of each layer is then calculated from theratios knowing the true total thickness. An exampleof a typical cross-section of a coextrusion is shown

in Figure 2.Information on the composition of individual lay-

ers in the structure can then be obtained by observat-ions of the layer under the microscope. Differenttypes of polymers have a recognizable morphology.Polypropylene has very large spherulites distinctfrom many other polymers. Figure 3 shows aphotograph obtained from polypropylene cooledslowly from a melt. Compounded poly(vinyl chlo-ride) (PVC) can also be quite characteristic due to thedifferent phase regions arising from the presence ofimpact modifiers as well as pigment specks from col-or adjusters. Calcium carbonate filler and talc anti-blocking agent have recognizable morphologies. It isalso possible to determine whether a layer contains

recycled process scrap. It is quite common for off-cuts to be recycled in an inner layer of a coextrusion.

Infrared spectra are then obtained from the sur-faces of the packaging material after solvent removalof any print or lacquer. Spectra are best obtained byATR. A further portion of the packaging material isthen subjected to DSC. This is a technique where a

few milligrams of the sample is subjected to aprogrammed temperature ramp in a specified atmos-phere inside a sample chamber. The heat flow (pow-er) to the sample is monitored against temperature asthe sample is subjected to the heating ramp. For thepurposes discussed here this provides a trace showingthe melting points of the polymers present. Typicalmelting ranges for common packaging polymers aretabulated in Table 3.

The technique cannot be used to obtain meltingpoints for amorphous polymers. The sample polymeris heated and cooled and then reheated at a control-

led rate to record the meting points. This procedureremoves hysterisis effects that may be present in thepolymer as a result of the manufacturing process andwhich may alter the perceived melting point. DSC iscapable of identifying polymers and polymer blends

Foil

Polyurethaneadhesive

PET

Polyurethaneadhesive

Nitrocelluloselacquer/print

Surlyn

(LD-MD) PE

Ethylene-co-acrylicacid (ionomer)

Figure 2 Cross-section of a coextrusion viewed through a tint

plate on an optical microscope. PETPoly(ethylene terepha-

late), (LD-MD) PE? (Reprinted with permission from Mr R

Musgrove, Pira International.)

Figure 3 Polypropylene spherulites viewed through a tint

plate. (Reprinted with permission from Mr R Musgrove, Pira

International.)

Table 3 Typical melting ranges for common polymers

Polymer Melting range ( 1C)

Linear low-density polyethylene 115130

Low-density polyethylene 100115

Ethylene vinyl acetate 100110

Polyamide 210260

Poly(ethylene terephthalate) 240260

Poly(vinylidene chloride) 220

Polypropylene 160170

Ethylene propylene random co polymer 149



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not readily identifiable in packaging materials usinginfrared spectroscopy. Examples of these include,low-density polyethylene, linear low-density poly-ethylene, high-density polyethylene, and blends ofthese polymers. The blend ratios of these polyolefinscan be estimated after calibration using the purepolymers.

The construction of the packaging material is thendetermined by comparing the data obtained from allthe analytical techniques. Any layers that are difficultto identify are then identified by either detailed ana-lysis on the isolated layer using FTIR and otheranalytical techniques, or by applying additionalanalytical techniques to the whole structure. Forexample, pyrolysis gas chromatographymass spec-trometry (GCMS) can confirm the presence of astyrene/acrylate copolymer adhesive or vinylidenechloride/acrylate copolymer coating. The pyrolysiscauses depolymerization, often to the starting mon-

omers, which are then identified from their massspectra. The technique can be applied to the wholeconstruction. This is useful when FTIR analysis is notconclusive, or where the layer cannot be isolated forFTIR analysis. In the absence of a pyrolyser instru-ment, it is possible to perform the technique bybriefly heating the sample in an inert atmosphere in asealed headspace vial over a gentle Bunsen burnerflame. Static headspace GCMS analysis of thepyroloysate is then carried out. Hot stage micros-copy is a particular useful technique for identifyinglayers. A key advantage of the technique is the abilityto identify layers that cannot be isolated for analysis.In this technique, the packaging material cross-section is heated at a controlled rate under the mi-croscope. The melting ranges of the individual layerscan be observed and compared with the meltingranges observed by DSC. It should be noted thatthere is a difference of a few degrees centigrade inthe melting ranges observed by DSC and hot stagemicroscopy:

The strategy for identification of a packagingmaterial construction is summarize:

1. Examine a cross-section by optical microscopy;determine the number of layers and their thick-ness, tentatively identify the polymers in the lay-ers.

2. Obtain a DSC of the whole material. This willidentify all the crystalline polymers present in thestructure.

3. Obtain infrared spectra from the surfaces. Thiswill confirm the composition of the outer layers.Isolate fractions of the construction and obtaintheir infrared spectra to confirm the identifications

made by DSC and optical microscopy.

Optical microscopy techniques can also be appliedto packaging failure problems. Sections can be takenthrough a heat seal region to establish the integrity ofthe seal. Molecular orientation, melt flow, blendhomogeneity, and crystallinity can be observed thatcan reveal the cause of stress cracking and othertypes of packaging failures.

Analysis of Substances Related to

Food Safety

It is sometimes necessary for technological reasons touse chemicals that have toxic properties in the man-ufacture of a food packaging materials. Also, there isthe possibility that some of the chemicals and com-ponents used for food packaging materials can con-tain trace levels of toxic contaminants. Where toxicsubstances are unavoidably present in a food packa-

ging material for any of these reasons, it is necessaryto ensure that levels of these substances are restrictedso that any transfer to packaged food does notexceed safety limits. The national regulations ofindividual countries control the safety of foodpackaging with respect to the substances with knowntoxic properties. In some countries the specific re-strictions are contained in official recommendationsor codes of practice. The primary restrictions are onthe levels that migrate or transfer to the packagedfood and are designated specific migration limits.However, in some cases the restriction is a permitted

level in the packaging material, while for others therestriction is a limit on the quantity, which can beextracted. As might be expected where the safety offood is concerned, the set limits are often low re-quiring sensitive analytical methods.

Food Contact Plastics

Vinyl chloride monomer used for the manufactureof PVC plastics intended for contact with foodsprovides an example where there is a low specificmigration limit, plus a low limit on the level allowed

to be present in the packaging material. These limitsare contained in an EC Directive 78/142/EEC onPVC plastics and are: 0.01 milligrams per kilogramof food (10 ppb), and 1 milligram per kilogram ofpolyvinyl chloride.

Vinyl chloride is a gas at ambient temperature andthe official EC analytical methods for both determi-nations use headspace GC with a flame ionizationdetector (FID). Where a determination exceeds thelegislation limit, confirmation is required with head-space GC using either a different chromatographycolumn, or a different detector, or with the gas chro-

matograph coupled to a mass spectrometer.



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For the determination of free vinyl chloride mon-omer in plastics, the test sample is dissolved or dis-persed inN,N-dimethylacetamide in a sealed vial andthen equilibrated at 601C before sampling the head-space. When determining vinyl chloride monomer infoods or food simulants, N,N-dimethylacetamide isagain used with the sample in a sealed vial, with

equilibration at 601C.Other volatile plastics monomers with similar

migration limits, such as acrylonitrile and butadiene,are also determined by the headspace GC technique.For the measurement of nonvolatile monomers inplastic food packaging and in foods or food simul-ants due to migration, high-performance liquid chro-matography (HPLC) and ion-exchange chroma-tography techniques can be employed. Food andfood simulants may give rise to interference problemswith the analysis. Sample clean-up procedures arewidely used such as solid-phase extraction of inter-

ference from extracts or size exclusion chromato-graphy to remove fats and oils. Selective detectorssuch as mass spectrometers are now widely used forboth liquid and gas chromatography.

Figure 4 is an ion-exchange chromatogram ofphthalic acids. Terephthalic acid and isophthalic acidare monomers of polyester plastics. Orthophthalicacid is the internal standard. There are migrationlimits for both terephthalic acid and isophthalic acidin EC regulations of 7.5 and 5.0 mg per kg of food.The other main classes of substances in the safetycategory, which can be present in food packagingplastics and for which analytical measurements arerequired, are the plastics additives. These substancesperform the functions of plasticizers, antioxidants,antistatics, slip agents, and stabilizers. Of these add-itives, the plasticizers have been most extensivelystudied and analytical methods developed for theirdetermination in the plastics and in packaged foods.The techniques are usually based on GC either withan FID or with a mass spectrometer as the detector.Key advantages offered by a mass spectrometer areselectivity of response and the ability to add a de-uterated internal standard to the sample to compen-sate for the incomplete and variable recovery of theanalyte in the analysis.

Migration testing of plastics packaging prior to usefor compliance with any legislation limits is usuallycarried out with food simulants rather than actualfoods. First, the analytical task is more often simpleand, second, testing with a food simulant or simul-ants for a class of foods covers use with all foods inthat class. The food simulants are simple liquids thatrepresent different classes of foods. For foods wherethe liquid phase is largely water, distilled water is

used as the simulant. For acidic foods (typically pH

4.5 or less) the simulant is an acetic acid aqueoussolution, and for alcoholic beverages and other foodscontaining alcohol, the simulant is an ethanol aque-ous solution with strengths more or less equal to thealcoholic concentration in the beverage or food.

Selecting a simulant for foods containing fats andoils has not been easy. In the USA, n-Heptane isspecified as the fatty food simulant in the Food andDrug Administration (FDA) regulations, although itis now recognized to give migration levels of specificsubstances well in excess of those that occur with thefoods even after applying a suitable reduction factor.

In Europe, olive oil has been selected as the fatty

Figure 4 Separation of terephthalic acid (TPA), isophthalic acid

(IPA), and orthophthalic acid (OPA) by ion-exchange chro-

matography. (From Ashby et al., 1992.)



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food simulant with alternatives of sunflower oil or asynthetic triglyceride, known as HB307, developedspecifically for migration testing. Alternatives toolive oil were considered necessary as it was knownthat various analytical problems arise with olive oil.The food simulants required for regulatory migrationtesting in the EC Member States on plastics packa-

ging intended for use with foods, are listed in ECDirectives 97/48/EEC and 85/572/EEC. These areshown in Table 4 together with the classes of foodsand beverages that they represent. The 85/572/EECDirective also contains a table that specifies thesimulant or simulants to be used for individualcategories foods and beverages, and the 97/48/EECDirective gives the test conditions of time and tem-perature corresponding to the intended conditions ofuse. Fatty foods contain various amounts of oils andfats. For those that have high oil or fat content theextent of migration of substances from the plastics is

often higher than for those with low oil or fat con-tents. Consequently, reduction factors are applied tomigration values obtained with olive oil to allow forthe various levels of oil and fat in particular foods.

It has been generally accepted that migration frompackaging materials into dry foods will be low com-pared to moist, liquid, or fatty foods. Accordingly,more work has been completed in developing simul-ants for these foods than dry foods. At the presenttime the only regulatory or generally recognized si-mulant for dry foods is Tenax (poly(2,6-diphenyl-p-phenylene oxide)). Tenax has been adopted as a dryfood simulant because it is a dry porous polymerwith a large surface area that exhibits high-adsorp-tion characteristics for a wide range of volatileorganic compounds. Tenax is therefore considered tobe a worst-case dry food simulant for a wide range ofdry foods. Other food simulants have been investi-gated for use with paperboard. A semisolid foodsimulant consisting of a mixture of diatomaceousearth, water, and olive oil has been used, as well asfilter paper impregnated with olive oil.

In addition to the requirement to measure thelevels of individual specific substances that havemigrated from plastic food packaging into foods orfood simulants and have toxic properties, there issometimes also the necessity to measure the totalquantity of substances that are likely to transfer fromthe plastics to the food. This is called overall migra-

tion or global migration. The tests are carried outwith food simulants as they are impracticable withfoods. No attempt is made to identify the nature ofthe substances that have migrated from the plasticmaterial. In the current EC food contact plasticsregulations there is an overall migration limit of60 mg of substances from the plastics material perkilogram of food simulant (60 mgkg1), or ex-pressed alternatively as 10 mg of plastic substancesfrom 1dm2 surface area of plastics test specimen(10mgdm2). With the three aqueous based foodsimulants distilled water, acetic acid, and ethanol

solutions the overall migration is measured by de-termining gravimetrically the nonvolatile residue inthe simulant following exposure to the plastic testspecimen. The values normally obtained with theseaqueous-based food simulants are usually well belowthe regulation limit and in the region of 618mgkg1 (13mg dm2). As the tests are mostoften carried out on test specimens with a surfacearea of 13mgdm2 the total quantities of migra-ting substances are typically a few milligrams. Con-sequently, care has to be taken with the gravimetricmeasurement to ensure reliable results are obtained.After evaporating the simulant to dryness thenonvolatile residue is dried in an oven at 1101C un-til constant weight is obtained. It has been found,however, that particular care has to be taken whenusing glass evaporating dishes to ensure that there isadequate time allowed for both the heating period inthe oven and the cooling period in the desiccator forthe mass to stabilize before each weighing. Withmetal evaporating dishes the mass of the dish andresidue stabilize more quickly, but with the aceticacid simulant it is necessary to use dishes made ofplatinum, or a metal with similar chemical resist-ance, to prevent additional errors from corrosionproducts.

To measure overall migration with olive oil or alter-native simulants, the method used with the aqueous-based food simulants is obviously not applicable.With oil-type simulants the test is carried out bymeasuring the loss in mass of the test specimen afterexposure to the food simulant. However, most plas-tics absorb some of the oil that then has to be ex-tracted and quantitatively measured before the trueloss in mass can be calculated. The extraction solvent

that has been most commonly used in the past is

Table 4 EC food simulants for migration tests and the corre-

sponding classes of foods

Food simulant Class of food or beverage

Distilled water Aqueous foods and beverages

3% (w/v) aqueous solution of

acetic acid

Foods and beverages with

pH 4.5 or less

10% (v/v) aqueous solution of

ethanolaFoods and beverages with

15% or less alcohol

Olive oil or sunflower oil or

HB307

Foods containing fats and oils

aFor a food or beverage with an alcohol content greater than 10%

(v/v), a simulant with a similar ethanol concentration is used.



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1,1,2-trichlorotrifluoroethane, as it is a good solventfor olive oil but does not dissolve most plastics. Asthis solvent is a chlorofluorocarbon its main use andsupply is being phased out and pentane and diethylether are now used instead for the extractions.

Once the extraction has been completed the oliveoil is quantitatively analyzed by hydrolyzing to the

fatty acids, methylating to form the methyl esters,and measurement by GC. The value obtained is sub-tracted from the mass of the test specimen after ex-posure to the olive oil, to allow the overall migrationvalue to be calculated. The test method has a rep-utation of poor precision and reliability not only dueto the complex procedure, described above, but alsodue various other factors that are known to influenceresults, such as moisture absorption by the plastictest specimens, incomplete extraction of the olive oil,and change in composition of the extracted olive oil.The overall and specific migration analytical test

methods have been established as Standards by theEuropean Committee for Standardisation (CEN).Reference plastics are also available with certifiedmigration values in olive oil (Institute for ReferenceMaterials and Measurements BCR, Geel, Belgium,[email protected]).

Paper and Board

Most paper and board food packaging materials arenot used in direct contact with liquid foods and con-sequently migration tests with liquid food simulantsare not considered appropriate. Paper and boardpackaging does, however, come into direct contactwith various moist and fatty foods where migrationof substances into the food can sometimes occur. Nosimulants have yet been selected to specifically rep-resent these classes of foods in migration tests onpaper and board. To ensure that the paper and boardmaterial is suitable and safe to package foods, ex-traction tests are often carried out. The extractiontest is performed with cold or hot water, or some-times with dilute acids and solvents and is considered

to be a more severe test than a migration test. An-alytical measurements are then carried out forspecific substances on the extraction liquid. For ex-ample, tests are carried out for free formaldehyde,which can arise from wet-strength additives of themelamine formaldehyde or urea formaldehyde types.A typical analytical method for the determination offree formaldehyde in the extracts is based on colori-metric procedures using chromotropic acid or ace-tylacetone (pentane-2,4-dione). With paper andboard products there is concern that there could betoxic contaminants present that in turn could trans-

fer to the food when used as packaging. These

possible contaminants include: the toxic heavy ele-ments arsenic, mercury, lead, cadmium, and chro-mium, plus chlorophenols and polychlorinatedbiphenyls (PCBs). With extraction liquids such aswater or dilute aqueous acid solutions, the toxicheavy elements can be analytically determined usingatomic absorption spectroscopy. Arsenic can be

measured with the hydride generation technique,mercury with the cold vapor technique, and the othermetals by the standard flame technique. Inductivelycoupled plasma atomic emission spectroscopy is nowalso widely used. Pentachlorophenol and otherchlorophenols can be determined by either GC orHPLC. When using GC the chlorophenols are bestderivatized to form the methyl or acetyl derivativesin order to improve the chromatographic perform-ance and the analytical precision. These analyticaltechniques have also been used in the detection andanalysis of chlorophenols suspected of being respon-

sible for odors and food tainting, as described later.The PCBs are determined in extracts from paper andboard materials by GC with an electron capture de-tector or mass spectrometer.

Two compounds are currently of particular inter-est in paper and board. Diisopropyl naphthalene(DIPN) is a mixture of isomers that until recentlywere widely used in carbonless copy papers as inksolvents. Although it is currently being replaced itoccurs as a persistent contaminant in recycled paperand board. Various studies have shown that it is ableto migrate from paperboard into food. There is adraft CEN analytical method available. This methodinvolves acetone extraction and quantification byGCMS using diethyl naphthalene as an internalstandard. There is currently no limit for DIPN butlevels are being monitored to reduce concentrationsin recycled paperboard.

Two related compounds are 3-monochloropro-pane-1,2-diol (3-MCPD) and dichloropropanol.These arise in paper board due to the hydrolysis ofepichlorohydrin-based wet strength agents. 3-MCPDcan occur in food from hydrolyzed vegetable protein.The limit in food is 120 ppb. In packaging the spe-cific migration limit is 12 ppb in the food. The di-chloropropanol does not at present have a limit.However, the German BGVV recommendations(widely accepted as useful guidelines) list a limit of2 ppb in a hot water extract. A convenient method ofanalysis is to extract the two compounds with water.The water extract is then totally absorbed onto adiatomaceous earth cartridge. The cartridge is thenwashed with a large volume of diethyl ether. Thewater is retained on the cartridge and the 3-MCPDand dichloropropanol extracted and eluted by

the diethyl ether. The ether is then concentrated by



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evaporation and the two compounds derivatized andinjected for analysis by GCMS.

Metal Packaging

Cans are widely used to pack food. In some casestinplated steel cans are used, for example, forpacking fruit. Predominantly, the cans are internally

coated with a polymeric coating to prevent corrosionor food spoilage. A considerable amount of work hasbeen done in recent years investigating the extent towhich compounds present in the lacquers migrateinto food.

Attention has focused on the chemical compoundsbisphenol A, BADGE, and BFDGE. Bisphenol A ismanufactured from the reaction of phenol withacetone. The bisphenol A is further reacted with epic-hlorohydrin to produce bisphenol A diglycidyl ether(BADGE). BADGE is then polymerized and cross-linked in a stoving process to produce an epoxy phe-nolic coating that has high chemical and mechanicalresistance. These coating are called bisphenolA-epoxies.

Alternatively, phenol may be reacted with formal-dehyde to generate bisphenol F. Unlike bisphenol A,bisphenol F is a mixture of isomers rather than adiscreet compound. Bisphenol F can be subjected to acondensation process in which a polymeric resincalled Novalac is produced. The Novolac can be re-acted with epichlorohydrin to produce a polyglcidyl-ether and these are called novolac glycidyl ethers

(NOGE). NOGE is not used to produce epoxyphe-nolic coatings, as is the case with BADGE.Organosol coatings are dispersions of PVC in sof-

tener, solvent, and other resins. Solid contents aretypically 4080%. The coating is stoved to evaporateoff the solvents and cure the resin. BADGE is oftenadded as an additive to scavenge for hydrochloricacid generated from the PVC during curing. Alter-natively, NOGE is used as an additive instead ofBADGE.

The most widely used lacquer types for food cans,where the food is retorted in the can to ensure pre-

servation are:

* epoxyphenolic and* organosol

Epoxyphenolic lacquers are universally used for bothcan bodies and ends for two- and three-piece con-structions, although more usually for shallow drawcans. Beverage can bodies are commonly epoxyami-no coated, and the easy-open end and deeper drawtwo-piece cans are organosol coated. Coatings maycontain residual BFDGE and bisphenol F arising

from the NOGE in organosol coatings and bisphenol

A as well as BADGE arising from the use of BADGEin organosol and epoxy phenolic coatings. Possibleresidues remaining in the coatings are listed below,all of which have been found to contaminate thefood:

* BFDGE

* BADGE* Bisphenol A* Bisphenol F

BADGE and BFDGE undergo hydrolysis and addi-tion of hydrogen chloride released from the PVCorganosol in aqueous foods and a series of reactionproducts result. Concern has been raised over thesereaction products. These are listed below:

* BADGE HCl* BADGE 2HCl

* BADGE H2O HCl* BADGE H2O

These decomposition products result from the ringopening on the epoxy group of which there are two.The legislation (Directive 2002/16/EC, February 20,2002, on epoxy food contact materials) specifies amigration limit of 1 ppm in the food. This limit is thetotal of all the reaction products and BADGE addedto the BFDGE and its reaction products. In addition,there is a requirement of no detectable migration ofNOGE at a detection limit of 0.2mgkg 1 in the

food or 0.2 mg/6 dm2

in the can. The decompositionproduct BADGE 2H2O in food is ignored as this isnot of toxicological significance. However, it must beincluded if the migration test is done on food simul-ants as there is the risk of forcing decompositionthrough to the BADGE 2H2O and underestimatingthe other compounds. The legislation is due forreview in 2004 as the toxicity of the chlorohydrins isnot at present established.

Analysis of Substances Causing Taint

Taint from food packaging is very rare when oneconsiders the tonnage of packaged food consumedeach year. Tainting chemical compounds present orderived from the food packaging are often volatilecompounds. With plastics these odorous volatiles canbe: monomer residues, reaction by-products fromthe polymerization process, breakdown products ofcertain additives and contaminants. For example,with polystyrene plastics high levels of styrene mono-mer produce a very characteristic odor and a numberof incidents of tainting from styrene monomerhave been reported. With polyethylene terephthalate

(PET) plastics, acetaldehyde can be formed during



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the polymerization process and when PET is used forbeverage bottles the acetaldehyde can cause taintingof the beverage. With paper and board materials thevolatiles arise mainly from natural lipids and resinsoriginating from the wood raw material, but somecan come from synthetic resins used in surface coa-tings that are applied for improved printability and

appearance. The predominant volatiles originatingfrom the wood lipids and resins are usually alde-hydes, carboxylic acids, and alcohols. The odors ofsome of these aldehydes are not unpleasant beingdescribed as grassy, but others have rancid odors.Many of the carboxylic acids and alcohols havestrong sharp odors. The synthetic resin binder used inthe surface coatings is typically a styrene/butadienecopolymer that can contain odorous reaction by-products such as 4-phenyl cyclohexene. If solvent-based adhesives are used in sealing the packaging orto bind layers together, and if the finished packaging

is printed with solvent-based inks, solvent residuescan add to the list of volatile substances. If the moreodorous of these print solvents and volatile sub-stances are present in sufficient quantities they cancause the packaging to be odorous and in turn resultin tainted foods.

Two classes of highly odorous substances that havebeen known to contaminate food packaging andresult in food tainting are the halophenols andthe related haloanisoles (methylated chlorophenolsand bromophenols). In the past contamination wasinvariably with the chlorophenols and correspondinganisoles from wooden pallets and surfaces treatedwith wood preservers or phenol-based disinfectants.The ansioles are generated by microorganisms suchas molds from the phenols. Recently, there has been anoticeable trend toward increased contaminationwith the bromophenol and corresponding anisoles.This reflects the substitution of bromophenolsfor chlorophenols in wood treatments. The odorthreshold for tribromoanisole in water is 8 pg l1

(81012 g l1 or 8 parts per trillion, ppt). Low-detection limits are therefore required for such taintinvestigations. Concentrations above 1 ppb in thepackaging are often sufficient for tainting to occur.Polyethylene is the most widely used polymer incontact with food, usually in the form of a thin innerlayer of a food pack. It therefore only requires con-tamination of a few sacks of polyethylene granuleswith the ansiole to result in tainting of a largeamount of food.

Analytical measurements and investigations aretherefore carried out to detect and measure volatileodorous substances in food packaging either forquality control purposes or when odor and taint

problems arise. The technique of choice is GCMS.

For odor investigation the chromatograph is fittedwith an odor port so that the flow from the analyticalcapillary column is split via a T piece to an odor port.By this means it is possible to smell compounds elu-ting from the capillary column simultaneously withtheir detection by the mass spectrometer. This ena-bles an odorous compound to be identified and

quantified in food and packaging.Isolation and concentration of tainting compounds

from the rejected food and packaging prior to ana-lysis is usually the most challenging step in theinvestigation. Dynamic headspace sampling is widelyused. In this technique, a sample of the packagingmaterial is placed in a vessel that is closed, heated toa temperature of B701C, and then purged with aninert gas such as nitrogen or helium. Volatiles re-leased from the packaging are removed by the purgegas, trapped, and concentrated on a porous polymersuch as Tenax. Transfer of the volatiles from the po-

rous polymer to the gas chromatograph is performedby thermal desorption or by solvent elution and in-jection as a solvent solution. The chromatogram inFigure 5 shows volatile substances that have beencollected by the dynamic headspace technique from aprinted carton-board that had caused tainting in apackaged cake. The tainting was attributed to thebenzophenone that appears as the large peak at justbelow 16 min. Benzophenone is used as an initiatorin ultraviolet radiation cured printing inks. The peakat 3.1 min is the aldehyde, hexanal, which originatedfrom the pulp used to make the board. The cluster ofpeaks from B5.5 to B7 min is volatiles from thesynthetic resin binder in the board coating. None ofthese substances produced detectable odors.

The LikensNickerson extraction technique canalso be used as a concentration technique, particu-larly for those volatile substances that are steamvolatile such as the chlorophenols and chloroani-soles, and also when carrying out an analysis for thepackaging volatiles in foods. The sample is boiled ina flask with water. Consideration must be given tothe pH of the sample in the water. Basic compoundswill be present as water-soluble involatile salts inboiling water at low pH, and acids as the corre-sponding salts in boiling water at high pH. The pro-cedure is therefore best carried out under basicconditions and then repeated after acidification witha few drops of nitric acid. The steam is condensedand continuously extracted with a suitable nonwater-miscible solvent, any solvent-soluble volatile sub-stances being transferred to the solvent. After con-centration of the solvent solution by evaporation ofthe solvent with a KudernaDanish apparatus, theanalysis is again performed using a gas chro-

matograph coupled to a mass spectrometer.



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Solid-phase micro extraction is a useful techniquein which volatiles are partitioned from the sampleonto fibers coated with polar or nonpolar bondedphases. The fiber is then placed directly into theheated injection port of the GC where compoundsare volatilized and carried onto the capillary column.The technique is less sensitive than the techniquesdescribed above as it is an equilibrium process.However, modern ion trap mass spectrometers haveincreased in sensitivity and the technique is becomingwidely used.

Residual Solvents

Solvent residues from printing and adhesives have

the potential to cause food tainting. Typical solventsused in printing with characteristic, easily detectableodors are aliphatic esters, such as ethyl acetate, iso-propyl acetate, and n-propyl acetate, the alcoholsisopropyl alcohol and n-propyl alcohol and hydro-carbon mixtures, particularly aromatics. Regulartests are carried out by printers of food packagingto ensure that the concentrations of solvent residuesare maintained below the odor and tainting thresh-old levels. The most widely used analytical techniqueto measure the levels of solvent residues is GC head-space analysis. Portions of the packaging are placed

in sealed vials or other suitable containers and heated

at a set temperature for a prescribed period of time.The headspace is then sampled by means of a gassyringe or automatic sampling unit and injected intoa suitable gas chromatograph with an FID. As themeasurements are often carried out for quality con-trol purposes, short heating times are sometimes usedwith external calibration and the measurements donot always accurately determine the solvent residuesin the packaging, but do give reproducible results.This is the case with UK, BSI Standard BS6455 Monitoring the levels of residual solvents in flexiblepackaging materials and also the correspondingAmerican ASTM Standard F 151-86. There are twodraft EN standard methods in existence, prEN13628-1 (absolute method) and prEN 13628-2 (in-dustrial quality control monitoring method).

See also: Adhesives and Sealants. Food and Nutri-

tional Analysis: Oils and Fats. Infrared Spectroscopy:

Overview; Sample Presentation; Industrial Applications.

Liquid Chromatography: Food Applications. Plastics.

Sensory Evaluation.

Further Reading

Ashby R, Cooper I, Harvey S, and Tice P (1997) FoodPackaging Migration and Legislation. Leatherhead, UK:

Pira International.

Figure 5 Chromatogram of volatile substances from a carton-board food packaging printed with a UV-cured ink. Benzophenone, the

printing ink component responsible for tainting of packaged food, is represented by the peak at 15.7 min.



12/12

Bradbury S and Bracegirdle B (1998)Introduction to LightMicroscopy. Oxford: BIOS Scientific Publishers.

Bradbury S and Evennett PJ (1996) Contrast Techniquesin Light Microscopy. Oxford: BIOS ScientificPublishers.

Briston JA and Katan LL (1974) Plastics in Contact withFood. London, UK: Food Trade Press Ltd.

Crosby NT (1981)Food Packaging Materials Aspects ofAnalysis and Migration of Contaminants. London: Ap-plied Science Publishers Ltd.

Food Contact Materials, Practical Guide (March 2002) APractical Guide for Users of European Directives. Euro-pean Commission, Health and Consumer ProtectionDirectorate-General, http://cpf.jrc.it/webpack/.

FSA (April 2001) Survey of Bisphenols in Canned Foods.Food Surveillance Information Sheet Number 13/01,Food Standards Agency.

Haslam J, Willis HA, and Squirell DCM (1972) Identifi-cation and Analysis of Plastics. London: Iliffe Books.

Kolb B (1984) Analysis of food contamination by head-space gas chromatography. In: Gilbert J (ed.) Analysis ofFood Contaminants, pp. 117156. Barking, UK: Elsevier.

Krause, Lange, and Ezrin (1983) Schultheis KR (trans.)Plastics Analysis Guide Chemical and InstrumentalMethods. Munich: Carl Hanser Verlag.

Lord AWT (2003) Packaging materials as a source oftaints. In: Baigrie B (ed.) Taints and Off-Flavours inFood, pp. 64111. London: Woodhead Publishing.

MAFF (January 1999) Diisopropylnaphthalenes in FoodPackaging Made from Recycled Paper and Board. FoodSurveillance Information Sheet Number 169, MAFFJoint Food Safety Standards Group.

Synoptic Document (updated 15 January 2002) EuropeanCommission, Health and Consumer Protection Directo-rate-General, http://cpf.jrc.it/webpack/.

Tice PA (1993) Packaging as a source of taints. In: SaxbyMJ (ed.) Food Taints and Off-Flavours, pp. 202233.Glasgow: Blackie Academic Professional.

FORENSIC SCIENCES

Contents

Overview

Alcohol in Body Fluids

Arson Residues

Blood Analysis

Carbon Monoxide and Cyanide from Fire and Accident

DNA Profiling

Drug Screening in Sport

Explosives

Fibers

Fingerprint Techniques

Glass

Gunshot Residues

Hair

Illicit Drugs

Paints, Varnishes, and LacquersQuestioned Documents

Systematic Drug Identification

Thin-Layer Chromatography

Volatile Substances

Overview

P Margot, Universitede Lausanne, Lausanne, Switzerland

& 2005, Elsevier Ltd. All Rights Reserved.

Introduction

Forensic sciences group the scientific principles andtechnical methods applied to the investigation ofcrimes, litigations in civil matters, or regulatory and

state administrative matters. Results are presented as

352 FORENSIC SCIENCES/Overview

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