caution on the storage of waters and aqueous solutions in plastic containers for hydrogen and oxygen...

Research Article

Received: 11 July 2012 Revised: 25 August 2012 Accepted: 25 August 2012 Published online in Wiley Online Library

Rapid Commun. Mass Spectrom. 2012, 26, 2627–2636

Caution on the storage of waters and aqueous solutions in plasticcontainers for hydrogen and oxygen stable isotope analysis

Jorge E. Spangenberg*Institute of Mineralogy and Geochemistry, University of Lausanne, Anthropole Building, CH-1015, Lausanne, Switzerland

RATIONALE: The choice of containers for storage of aqueous samples between their collection, transport and waterhydrogen (2H) and oxygen (18O) stable isotope analysis is a topic of concern for a wide range of fields in environmental,geological, biomedical, food, and forensic sciences. The transport and separation of water molecules during water vaporor liquid uptake by sorption or solution and the diffusive transport of water molecules through organic polymer materialby permeation or pervaporation may entail an isotopic fractionation. An experiment was conducted to evaluate theextent of such fractionation.METHODS: Sixteen bottle-like containers of eleven different organic polymers, including low and high density polyethylene(LDPE and HDPE), polypropylene (PP), polycarbonate (PC), polyethylene terephthalate (PET), and perfluoroalkoxy-Teflon(PFA), of different wall thickness and size were completely filled with the samemineral water and stored for 659 days underthe same conditions of temperature and humidity. Particular carewas exercised to keep the bottles tightly closed and preventloss of water vapor through the seals.RESULTS: Changes of up to +5% for d2H values and +2.0% for d18O values were measured for water after more than1 year of storage within a plastic container, with the magnitude of change depending mainly on the type of organicpolymer, wall thickness, and container size. The most important variations were measured for the PET and PC bottles.Waters stored in glass bottles with Polyseal™ cone-lined PP screw caps and thick-walled HDPE or PFA containers withlinerless screw caps having an integrally molded inner sealing ring preserved their original d2H and d18O values. Thecarbon, hydrogen, and oxygen stable isotope compositions of the organic polymeric materials were also determined.CONCLUSIONS: The results of this study clearly show that for precise and accurate measurements of the water stableisotope composition in aqueous solutions, rigorous sampling and storage procedures are needed both for laboratorystandards and for unknown samples. Copyright © 2012 John Wiley & Sons, Ltd.

(wileyonlinelibrary.com) DOI: 10.1002/rcm.6386

Storage of waters, aqueous solutions and humid material inorganic polymer (plastic) containers for chemical and isotopicanalysis is a common practice in a wide variety of fields suchas hydrology, geology, medicine, biology, chemistry, agricul-ture, environmental, forensic and food sciences. It is welldocumented that potential contamination from samplingand storage containers as well as sorption on the walls ofplastic container may seriously affect the accuracy ofthe determination of trace elements in liquid samples.[1–8]

Contamination induced by filters and storage in containersof different plastic material may also influence measure-ments of dissolved organic carbon (DOC) in naturalwaters.[9,10] Adsorption of pharmaceuticals in aqueoussolutions to the surface of various plastic materials will, forexample, lead to incorrect assessments of the stability of thecompound or its permeation properties in tissues.[11–14]

Organic polymeric materials may behave as permeable orsemi-permeable barriers that permit the exchange of lowmolecular weight compounds, e.g., gases and vapors,

* Correspondence to: J. E. Spangenberg, Institute of Mineralogyand Geochemistry, University of Lausanne, AnthropoleBuilding, CH-1015 Lausanne, Switzerland.E-mail: [email protected]

Rapid Commun. Mass Spectrom. 2012, 26, 2627–2636

262

between inner and outer sites of the container wall.[15,16] Thepermeation of gases, water vapor, volatile organic compounds,and contamination by plastic additives from organic polymerpackaging materials are major concerns for the storage anddistribution of drinking water, food, beverages, pharmaceuticalsand cosmetic products, as well as the safe protective coatingsused for municipal waste landfills.[17–28]

The exchange of molecules that penetrate polymericmaterials is determined by their capacity to adsorb onto theorganic polymer and their facility to diffuse through it.[15]

Sorption on the wall, dissolution, and diffusion of liquid waterand water vapor within a polymeric organic material dependon the composition of the polymer, the nature and density ofcrosslinks, its crystallinity, temperature, time, and wallthickness.[15,16,29] Different water activity (humidity) or thegradient in chemical potential (i.e., humidity gradient) acrossthe organic polymer is the driving force for mass transport inthis case.[30] The presence of other small or low molecularweight compounds (e.g., O2) in the polymermatrixmay changethe interaction mechanisms of sorption and diffusion in theorganic matrix of the permeant.[31]

The transport of water molecules through organic polymericmaterial by evaporation of liquid water and gas-diffusion(pervaporation) or water-vapor permeation[30,32] and exchangewith hydrophilic polar groups in the polymer have the

Copyright © 2012 John Wiley & Sons, Ltd.

7

J. E. Spangenberg

2628

potential to modify the original hydrogen and oxygen stableisotope composition of the water or aqueous solution. Theextent of such isotopic fractionation in or across such organicpolymers used for packaging and storage has, as yet, beenpoorly studied. It is common and good practice to storewater reference samples in glass or metallic containers inthe dark at low temperatures, but the same procedure is notalways followed for unknown samples for stable isotopeanalysis. The stable isotope abundances are reported in thedelta (d) notation (e.g., d2H and d18O values) in per mil (%)variations relative to an international standard; where thed-value = (Rsample – Rstandard)/Rstandard� 1000 and R is themolar ratio of the heavy to light most abundant isotope(e.g., 2H/1H or 18O/16O). Variations of the d2H and d18Ovalues of water during storage in polyethylene terephthalate(PET) bottles was recently addressed for a single naturalspring water (Evian water, Cachat spring of Evian-les-Bains,France) distributed worldwide.[33] Changes of about +4%per mil for d2H and +0.7 per mil for d18O values weremeasured for Evian water stored in 500 mL PET bottles for253 days.[33] Here, the d2H and d18O variations from a first con-trolled experiment are reported, with storage under naturalconditions of a natural mineral water for 659 days in bottle-likecontainers made of glass and different plastic material,including high density polyethylene (HDPE), low densitypolyethylene (LDPE), polypropylene (PP), polycarbonate(PC), perfluoroalkoxy-Teflon (PFA), and PET (Fig. 1) of dif-ferent size and wall thickness. In addition, we report for thefirst time, to the best of our knowledge, the carbon, hydrogen,and oxygen stable isotope compositions of the organic poly-meric materials.

EXPERIMENTAL

Samples and experiment setup

Eleven sets (coded as A–K) of sixteen bottle-like containers ofdifferent type of organic plastic material (two of HDPE, fiveof LDPE, one of PP, one of PC, one of PAF, and one of PET),

a)

e) d)

c) b)

Figure 1. General structural formulas of organ(a) polyethylene (PE), (b) polypropylene (PP), (c) p(PFA), and (e) polyethylene terephthalate (PET).

wileyonlinelibrary.com/journal/rcm Copyright © 2012 John Wil

wall thickness (0.27 to 1.68 mm), size (10, 15, 30, 50, 200and 500 mL) and producer (Nalgene, Denmark; Kautex,Germany; KJS, Germany; Triforest, USA; and Vitlab, Germany)commonly used for storage of aqueous solutions or humidmaterial of a wide range of hydrological, geochemical, pharma-ceutical, medical, biological and forensic originwere purchasedfromVWRInternational LLC atDietikon, Switzerland (Table 1).All the plastic bottles were used with the original plastic screwcaps. The Nalgene narrow-mouth HDPE (coded A and B),LDPE (coded F) and PP (coded G) bottles, as well as the wide-mouth PC bottle from Triforest (code I), had linerless PP screwcaps with a sealing ring molded inside the closure for a leakresistant closure. The other plastic bottles (coded as C, D, E,H, J and K) had linerless screw caps made with the samematerial as the bottle body. A set of 50 mL dark borosilicateglass bottles with LDPE conical-insert Polyseal™ PP screwcaps (coded as L) was treated in the same way as the plasticcontainers. The cone-lined caps are known to provide anexceptionally tight wedge-type seal that serve as a barrieracross both the top of the container and the inside diameter toprevent leakage and evaporation. Evian freshly plastic bottledwater was chosen as the test water because of its homogeneityand d2H and d18O values within analytical error similar to thosereported for the source Cachat spring and those measured inthe glass bottled water.[33] All the containers, as received, werecompletely filled (without headspace) with Evian waterobtained from 1500mLPET bottles acquired from a local super-market in Lausanne (Switzerland). The expiry date of thebottled Evianwaterwas 3October 2010. Each set of the test con-tainers was filled on 17 November 2008 with Evian water pre-viously homogenized by manual vigorous shaking of the1500 mL bottles of the same batch for a few seconds. Particularcare was taken to ensure no loss of water and water vaporacross the sealing system of the bottles. The bottles were prop-erly closed with their original plastic screw cap and the topsof the container tightly wrappedwith two layers of paraffin foil(Parafilm ’M’, AmericanNational Can, Chicago, IL, USA). A setof 16� 500 mL Evian PET-bottled waters obtained on the sameday and from the same supermarket as the 1500 mL Evianbottles was included in the experiment. All the bottles and

ic polymers used for making plastic bottles:olycarbonate (PC), (d) perfluoroalkoxy-Teflon

ey & Sons, Ltd. Rapid Commun. Mass Spectrom. 2012, 26, 2627–2636

Table

1.Mainch

aracteristicsan

dd1

3 C,d

2 Han

dd1

8 Ova

lues

oftheorga

nicplasticbo

ttle-likecontaine

rs

Con

tainer

VWRP/

Na

Con

tainer

materialb

Cap

type

cVol.

(mL)

Wallthickne

ss(m

m)d

d13 C

(%,V

PDB)

d2H

(%,V

SMOW)

d18 O

(%,V

SMOW)

Ave

rage

eSD

Ave

rage

SDAve

rage

SDAve

rage

SD

A215-0997

HDPE

PPsc,isr

300.76

(4)

0.15

�30.

9(3)

0.08

�95(4)

2.8

B215-7503

HDPE

PPsc,isr

151.10

(4)

0.05

�31.4(3)

0.03

�85(5)

1.4

C215-9018

LDPE

LDPE

sc,isr

100.77

(4)

0.16

�28.2(3)

0.03

�92(4)

1.3

Df

215-9021

LDPE

LDPE

sc,isr

501.12

(4)

0.02

�28.2(3)

0.06

�90(6)

2.5

E215-9023

LDPE

LDPE

sc,isr

200

0.90

(4)

0.01

�28.9(3)

0.05

�92(6)

1.2

F215-7523

LDPE

PPsc,isr

151.09

(4)

0.08

�33.3(3)

0.05

�72(6)

1.6

G215-7563

PPPP

sc,isr

151.07

(5)

0.03

�30.5(3)

0.06

�108

(6)

2.7

Hf

215-5671

LDPE

LDPE

sc,isr

501.05

(4)

0.04

�31.2(4)

0.11

�104

(3)

1.5

I215-2203

PCPC

sc,isr

125

1.68

(5)

0.26

�27.5(5)

0.07

�84(5)

2.5

22.6

(4)

0.49

J215-4591

PFA

PFA

sc,isr

501.02

(5)

0.02

�43.0(4)

0.04

KPE

TPE

Tsc

500

0.27

(5)

0.03

�28.9(3)

0.03

�81(3)

2.6

22.5

(4)

0.26

L215-1831

Glass

Polyseal

cl50

a VWRpa

rtnu

mbe

r,containe

rsA,B

,Fan

dFarefrom

Nalge

ne;C

,Dan

dEfrom

Kau

tex,

Hfrom

KJS,I

from

Triforest,an

dJfrom

Vitlab.

bHDPE

,highden

sity

polyethy

lene

;LDPE

,low

den

sity

polyethy

lene

;PP,

polyprop

ylen

e;PC

,polycarbo

nate;P

FA,p

erfluo

roalko

xy-Tefl

on;P

ET,

polyethy

lene

tereph

thalate.

c sc,screw

cap;

isr,molded

inne

rsealingring

;Polysealc

l,LDPE

cone

-lined

PPscrew

cap.

dWall-thickn

essmeasu

redat

differen

the

ightsof

thecontaine

r.e N

umbe

rin

parenthe

sesstan

dsfornu

mbe

rof

replicatean

alyses.

f Dan

dH

are50

mLLDPE

containe

rsprod

uced

byKau

texan

dKJS

(German

y),respe

ctively.

Stable isotope variation of water stored in plastic bottles

wileyonlinelibrary.com/journal/rcmCopyright © 2012 John Wiley & Sons, Ltd.Rapid Commun. Mass Spectrom. 2012, 26, 2627–2636

2629

J. E. Spangenberg

2630

bottle-shaped containers were stored in an open stainless steelfive-shelf bookcase protected from direct sunlight in a room ofthe Anthropole Building of the Institute of Mineralogy andGeochemistry at the University of Lausanne (IMG-UNIL,Fig. 2). The containers were opened after homogenizing thewater by shaking one after the other over a period ranging from0 to 659 days between 17 November 2008 and 7 September2010, and two 10 mL washed and dried borosilicate glass vialswith aluminum-foil lined screw-caps were filled with the con-tainer’s water and closed. The tops of the vials were tightlywrapped with two layers of paraffin foil. These sample vialswere stored at +4�C in the dark prior to analysis. The experi-ment duration covered two annual seasonal cycles. Thetemperature and relative humidity (RH) of the ambient atmo-sphere, measured with a sensor (Ansen Electronics, HongKong, China) placed in themiddle shelf of the bookcase, variedbetween 18.6 and 29.7�C, and 19 and 42%RH. The average out-side air temperature and humidity varied between �7.8 and32.8�C, with an average value of 11.0� 8.0�C, and between 18and 100% RH, with an average of 71.3� 11.4%.[34] One plasticcontainer of each type was cut into pieces for determination ofwall thickness and stable isotope composition of the organicpolymer. All the stable isotope analyses were performed atthe Stable Isotope Laboratory of the IMG-UNIL usingautomated preparation methods.

Hydrogen and oxygen stable isotope analysis ofwater samples

The stable hydrogen isotope composition was measuredusing the H-Device hydrogen preparation system (ThermoFisher Scientific, Bremen, Germany) connected to a ThermoFisher Scientific Delta V Plus isotope ratio mass spectrometer.In the H-Device, H2 gas was produced by quantitative reductionof a volume of 1.2 mL ofwater over hot (840�C) chromiumwithin

Figure 2. Stainless steel bookcase used to store the bottle-likecontainers filled with the same mineral water for 659 days.A temperature and relative humidity sensor was placed inthe middle shelf of the bookcase.


a quartz reactor connected to the dual inlet system of the Delta VPlus. Oxygen isotope analyses were carried out throughequilibration of 0.5%CO2 in Hewith 1.2 mL of the water samplepreviously loaded in a exetainer glass vial (Labco Ltd., HighWycombe, UK) for 24 h at room temperature followed by CO2

extraction in a continuous He flow using a GasBench II gaspreparation system connected to a Delta Plus XL isotope ratiomass spectrometer (both from Thermo Fisher Scientific). Thestable hydrogen and oxygen isotope ratios (d2H and d18Ovalues)are reported relative to the Vienna Standard Mean Ocean Water(VSMOW). The standardization of the d2H and d18O valuesrelative to the international VSMOW scale was carried out byperiodic calibration of the reference gases and workingstandards with IAEA (Vienna, Austria) VSMOW2, SLAP2, andGISP standards. The calibration and assessment of the reprodu-cibility of the isotopic analyses were based on replicate analysesof at least four working water standards. These included twice-glass-distilled tap water (UNIL-INH, calibration performed on14 August 2009 gave the working values �113.1� 0.2% ford2H and �16.82� 0.07% for d18O), two bottled mineral watersthat were mixed in different proportions (UNIL-LIPE, workingvalues �53.9� 0.4% d2H, –8.50� 0.04% d18O; UNIL-SCH,working values�122.0� 0.1%d2H, –17.32� 0.05%d18O),waterfrom an Antarctic Lake (UNIL-ANLA, working values�146.8� 0.2% d2H, –16.22� 0.03% d18O), Mediterraneanocean water (UNIL-MOW, working values 5.7� 0.4% d2H,0.47� 0.03% d18O), and water produced by combustion ofnatural gas (UNIL-TOCH, working values �141.3� 0.8%d2H, 27.45� 0.06% d18O). All water samples were replicatedbetween two and ten times. The reproducibility was betterthan 0.3% and 0.1% (1s) for d2H and d18O values, respec-tively. The isotopic analyses of some samples were repeatedby Wavelength-Scanned Cavity Ring-Down Spectroscopy(WS-CRDS, Picarro L-1120i; Picarro Inc., Santa Clara, CA,USA). The differences between the IRMS and WS-CRDSvalues were generally lower than the reproducibility ford2H and d18O values.

Bulk carbon, hydrogen, and oxygen stable isotope analysesof the organic polymeric materials

The carbon isotope ratios (d13C values) were obtained bycontinuous flow elemental analyzer/isotope ratio massspectrometry (EA/IRMS) using flash combustion on a CarloErba 1108 elemental analyzer (Fisons Instruments, Milan,Italy) connected via a ConFlo III open split interface to a DeltaV isotope ratio mass spectrometer (Thermo Fisher Scientific,Bremen, Germany). Helium carrier gas was used at a flowrate of 80 mL/min. Aliquots of the organic polymer samplesand of the calibration standards (20–200 mg) were weighedin tin cups (Säntis Analytical, Teufen, Switzerland). The tincups were closed, folded, pressed to a small size and loadedin an AS 200 autosampler (Fisons Instruments). They werethen flush-combusted sequentially under a steam of He andoxygen at 1020�C in a quartz reactor filled with high-purityoxidizing agents (Cr2O3 and (Co3O4)Ag, Säntis Analytical).The combustion-derived gases (CO2, N2, NOx and H2O) werefirst passed through a quartz reactor filled with reducing(reduced elemental Cu wires) and oxidizing (CuO wires)agents (both from Säntis Analytical) at 640�C to convertNOx into N2. The gases were dried by passing them througha 10 cm long glass column filled with anhydrous Mg(ClO4)2,



and then directed through a 3 m long and 4 mm i.d. stainlesssteel gas chromatographic column packed with Porapack sta-tionary phase (Säntis Analytical) at 70�C for the separation ofCO2 which was analyzed for its isotopic composition on theDelta V mass spectrometer. Pure CO2 gas was inserted intothe He carrier flow as pulses of reference gas. The hydrogenand oxygen isotope ratios of the organic polymers were mea-sured with a Thermo Fisher Scientific high temperature con-version elemental analyzer (TC-EA) coupled to a Delta PlusXL isotope ratio mass spectrometer via a ConFlo III open splitinterface. The TC-EA consisted of an outer ceramic (Al2O3)tube and an inner glassy carbon reactor tube filled withhigh-purity glassy carbon granulates, silver and quartz woolfrom Säntis Analytical. For H and O isotope analyses, pyroly-sis of separated aliquots of the organic polymer samples wascarried out. Aliquots of the organic polymer samples and ofthe calibration standards were weighed in silver cups, carefullyclosed and loaded into an AS 128 autosampler (ThermoQuest,Milan, Italy). The silver cups were dropped sequentiallyunder a steam of helium into the reaction tube held at1350�C. The produced pyrolysis gases (H2, N2, CO) thenpassed a 0.6 m long and 4 mm id gas chromatographic col-umn packed with 5 Å molecular sieve (80–100 mesh) and heldat 70�C in a continuous stream of He (flow rate of 90 mL/min)for separation of the gases before entering the ConFlo III inter-face for d2H and d18O analysis on the Delta Plus XL. Pure H2

and CO gases were inserted into the He carrier flow as pulsesof reference gases.The stable isotope composition of carbon (d13C values) is

reported relative to the Vienna Pee Dee Belemnite limestone(VPDB) standard. Each analytical EA/IRMS and TC-EA/IRMSsequence consisted of two sets of calibration standards, one atthe beginning and one at the end of the sequence, twentyunknown samples and two standards in the middle for controlof the analysis quality. The standardization of the organic d13C,d2H and d18O values and precision and accuracy controlwere performed using the international reference materialsUSGS-24 graphite (�16.05% d13C), IAEA-CH7 polyethylenefoil (�32.15% d13C, �100.3% d2H), NBS-22 oil (�30.03% d13C,–120.0% d2H), IAEA-CH3 (�43.5% d2H, 32.6% d18O), IAEA-CH6 (�11.7% d2H, 36.4% d18O), IAEA-601 (23.3% d18O),IAEA-602 (71.4% d18O), and an in-house standards (glycine,–26.1% d13C; urea, –43.1% d13C; pyridine (�29.2% d13C);paper cellulose UNIL-TP5, 29.8% d18O). The reproducibilityof the EA-IRMS and TC/EA-IRMS measurements, assessedby replicate analyses of the standards and organic polymersamples, was better than �0.1% for d13C, and 0.3% and 1%with respect to VSMOW standard for both d2H and d18Ovalues, respectively. The nature of the polymer, containervolume, wall thickness, together with the carbon, hydrogenand oxygen isotope compositions of the organic polymers,are given in Table 1.

263

RESULTS AND DISCUSSION

The d2H and d18O variations of the waters stored in organicpolymer bottle-like containers (Figs. 3 and 4) were found tobe related to the nature of the organic polymer, container wallthickness and volume. Higher offsets, that is differencesbetween original and final values, were measured for waterstored in PC (enriched by +4.1% in 2H and +0.7% in 18O

Copyright © 2012 JRapid Commun. Mass Spectrom. 2012, 26, 2627–2636

compared with the water transferred at time 0 to 10 mLborosilicate glass vials) and PET containers (enrichedby +5.1% in 2H and +2.0% in 18O). In general, other thanfor containers I and K which were manufactured with PCand PET, no clear trend was observed in the d2H and d18Ovariations for water stored in the organic polymer bottles.No appreciable water loss due to permeation or pervapora-tion was observed when the plastic containers were openedand water transfered to the glass vials. There is a strongpositive correlation between the d2H and d18O values for allthe water samples (r2 = 0.840, n= 194). The d2H vs. d18Ocovariations observed for the waters stored in differentplastic containers varied between 0.098 and 0.923 (Table 2).

The permeation or pervaporation of water vapor or liquidwater through a polymeric membrane is related to a kinetichydrogen and oxygen isotopic fractionation associated withevaporative liquid-vapor separation and diffusion of theliquid or gas phases. Therefore, the processes of permeationand pervaporation, similarly to the evaporation of water inan open system, cause an enrichment of 2H and 18O in theresidual water, thereby producing a positive d2H-d18O trendrelative to the starting water compositions (Fig. 3, Table 2).The large diffusion isotope effect in membrane distillationexplains the enormously high 18O/16O and 2H/1H separationfactors for liquid/vapor permeation/pervaporation of waterthrough an organic polymer membrane.[34,36] Therefore,the water loss might have been smaller than a few percentfor the more positive offsets in d2H and d18O values. Thepermeation/pervaporation slopes of the d2H-d18O line forthe different plastic polymers vary between 0.04 and 2.53.The different d2H-d18O covariations (i.e., r2 and slopes ofd2H-d18O line) are related to the extent of isotopic fractiona-tion during transport of water or water vapor through thedifferent polymeric materials and/or oxygen and hydrogenexchange with the organic phases from the plastic containerwall or with plastizicers and plastic degradation productsreleased into the water.

The transport and separation of water molecules duringwater vapor permeation or liquid water pervaporationthrough an organic polymeric membrane involve three steps:(i) selective sorption or solution on one side of the membrane,(ii) diffusion through the polymer film as gas or liquid, and(iii) desorption/evaporation of the permeated water and itsrelease at the other side of the membrane as a low pressurevapor.[15,30,32,37] This water molecule flux is proportional tothe humidity differences between the two phases and can bedescribed in terms of Fick’s first law of diffusion.[15]

These processes depend on the physicochemical interactionsbetween membrane material and the permeating molecule,i.e. the chemical microstructure (degree of cristallinity, volumeof microporosity), hydrophilicity (water permeability) of theorganic polymeric material and thickness of the membrane,ambient humidity and temperature.[16,38] Lower differencesbetween the initial and final isotopic compositions andd2H-d18O covariations were found for borosilicate glassbottles and HDPE containers. The differences in the d2H-d18Ocovariations of LDPE containers (C–F andH) are best explainedby differences in container wall thickness and volume.The waters stored in HDPE (container B) and PFA (containerJ) polymers have d2H and d18O values very close to those ofwater stored in borosilicate glass containers. The differencesbetween the variations of the d-values of the waters stored in

wileyonlinelibrary.com/journal/rcmohn Wiley & Sons, Ltd.

1

Figure 3. Hydrogen and oxygen isotope compositions of the same mineral water versus time of storage in bottles A–L of differentmaterial, size and wall thickness.

J. E. Spangenberg

2632

HDPE (containers A and B) and LDPE (containers C, D, F) areassigned to different crystallinity of the organic polymers.Depending on the polymer density and branching, the small(<10%) void space restricts the diffusion and movement ofmolecules within an organic polymer.[15] The lower proportionof crystalline regions, more molecular branches that limit theclose packing of chains, and weaker intermolecular forcesaccount for higher amounts of void spaces between molecularchains in LDPE than inHDPE polymers. Hence, easier diffusionofmolecules through the less crystalline branched polyethylene(LDPE) than through the more crystalline linear polyethylene(HDPE) results in higher water and oxygen permeability ofLDPE structures.[16] This explains the differences in the d2Hand d18O values of waters relative to their initial values andstored in the LDPE and HDPE containers of similar volume.The higher gas permeability of the thinner organic polymerwalls explains the higher offsets of the d-values of the watersstored in HDPE containers A than in B, and in LDPE containersC than in D and F. For containers (B, F, C) of the same volume


(15 mL) and similar wall thichness (~1.1 mm) the lowestisotopic changes were observed for containers of HDPEcompared with those of LDPE and PP. The waters storedin PP had d2H-d18O covariations (r2 and d2H-d18O-slope)intermediate between those in HDPE and LDPE containers.This can be explained by the intermediate level of crystallinityof PP polymer, and therefore water and oxygen permeabilitybetween those of LDPEandHDPE.[16] Previous studyhas shownthat PP polymer may absorb water (0.03% w/w after 1-monthimmersion in distilled water).[39] The effect of container sizecan be assessed by comparing containers E, H and F, all ofLDPE and a wall thickness ~1 mm, but different volume.Excluding a few outliers, the d2H and d18O correlations(r2 = 0.084, 0.111, and 0.492) and the regression slope(0.16, 0.48, 1.39) increase with a decrease in the volume of thecontainer (200, 50, and 15 mL). This volume effect, with betterpreservation of the primary isotopic composition in higherwater volumes, is explained by the lower molar ratios ofpermeant-pervaporate relative to bulk liquid water.


Figure 4. Boxplots of the hydrogen and oxygen isotopecompositions of the water samples stored in bottles A–L.


263

The higher d2H-d18O covariations (r2 >0.9) were observedfor waters in PC, PET, and Teflon-PFA containers. PC and PETare polymersmade of biphenolA (BPA) polycarbonate andpoly-ethylene terephthalate, respectively, which are more hydrophilicthan pure polyalkylene polymers (polyethylene, polypropylene).The hydrophilicity of polytetrafluoroethylene (PTFE) andits perfluoroalkoxy copolymer polytetrafluoroethylene-co-perfluoroalkoxy vinyl ether (PFA)[40] explains the relativelyhigh correlation coefficient and d2H-d18O slope of the50 mL PFA containers. The mass fluxes and oxygen andhydrogen isotope separation by water distillation through a<0.1 mm thick PTFEmembrane increased as the temperaturedifferences across the membrane interface increased.[35,36]

Polytetrafluoroethene (PTFE) and PFA chains are morecrystalline than HDPE, as the intermolecular chain van derWaals forces are stronger than in polyethylene due to higherelectron density and stronger packing, asfluorine atoms replacehydrogen atoms in the PE chain structure. Therefore, the lowfree volume and sorption sites and lower permeability to smallmolecules explain why, despite the relative hydrophilicity ofthe PFA membrane and significant d2H-d18O covariations, thed2H and d18O variations of water stored in the 1.0 mm thickTeflon-PFA container are indistinguishable from those forwaterstored in the glass container (Fig. 4, Table 2).Polymer chains with aromatic rings and strong polar

groups, such as the ketone group (C=O) of ester bridges inPET or carbonate groups in PC, are able to bind watermolecules by hydrogen bridges.[41] These hydrogenbridges and other interactions between hydrogen atomsattached to two highly electronegative atoms (F, O) orgroups (C=O, -COOH) could cause sorption of watermolecules by hydrogen bonding with polar groups onthe wall of PC, PET, and Teflon-PAF containers. Such sorp-tion may entail a kinetic isotope effect for both 1H/2H and16O/18O in the water molecules. However, in the carbo-nate linkage of PC chains the ketone carbon is bonded to


oxygen on both sites, which is considered to hinder theformation of hydrogen bonds.[42] This potential isotopeeffect due to sorbent-affected water molecules by thematerial of the container is most probably negligible, dueto the high relative concentration of free compared withbound water molecules. The free-bound water molecule isoto-pic exchange may explain some of the d2H and d18O variationsin the 10 mL LDPE container, where the volume ratio of wall-bound to liquid free water molecules was higher than for theother containers.

PC and PET are more permeable to water and oxygen thanthe other commercial plastics,[16] and the selective vaporizationof 1H- and 16O-enrichedwatermolecules from the polymerwallby the process of pervaporation may explain the high isotopicoffsets measured for the PC and PET containers. Furthermore,the higher variability of d2H and d18O values for some samplesin PC and PET containers suggest that these waters wereaffected by isotopic exchange with oxygen-bearing moleculestransferred from the organic polymer to the aqueous phase.The PC and PET organic polymeric material (�84 and �81%for d2H, and 22.6 and 22.5% for d18O values, respectively) isdepleted in 2H and enriched in 18O compared with the Evianwater (�73% d2H and �10.6% d18O values). The release ofbisphenol A (BPA) into liquid stored in PC containers is widelydocumented.[43] The rate of BPA release from the container wallto a natural water may increase with temperature and time ofstorage in the container.[44,45] BPA polycarbonate may undergoa photooxidative degradation to BPA-quinonewhen exposed tosunlight, humidity, high temperature and oxygen or reactiveoxygen species in water.[43,46] The water oxygen may exchangewith the free BPA and oxidation products. Furthermore, theBPA and BPA-quinone in the aqueous solution behave as aquinone/hydroquinone redox couple by exchange of twoelectrons and two protons, which may induce hydrogen/deuterium (1H/2H) exchange. The migration of plasticisersphthalic acid dialkyl esters, among them dimethyl phthalate(DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP),and di(2-ethylhexyl) phthalate (DEHP), from PET to thebottled water has been widely reported.[21,47–49] The hydrolyticphotolysis of these phthalates may produce diverse degrada-tion products, including 1-alkenes, alkyl alcohols, phthalic acidanhydride, 2-formyl benzoic acid esters and benzoic acidesters.[50,51] These hydrolytic photo-degradation productspotentially involve multiple 2H/1H and 18O/16O exchangereactions. Furthermore, the thermal degradation and hydroly-sis of PET cause the formation of aldehydes (formaldehyde,acetaldehyde, propionaldehyde, and n-butyraldehyde) in thepolymer structure that may migrate into the water.[22,52,53]

Oxygen-exchange reactions between BPA-quinone, aliphaticaldehydes and ketones with water[54,55] in the PC and PETcontainers may at least partially account for the 18O enrichmentin some samples from containers I andK (Fig. 3)with no or littlechange in the 2H content. Furtherwork is needed to assess if therelative small masses of BPA or phthalates released to thewatercan affect significantly its hydrogen and oxygen isotopiccomposition. A final point to consider is a possible isotopicexchange between water within the plastic bottle and watervapor in the air near the plastic-water interface.[33] Such aprocess does not requires a net water loss, but tranport of watermolecules in both directions through organic polymer material.The likelihood of such a process is slim due to the very differentwater activity across the bottle plastic wall.


3

Table

2.Variation

sin

thed2H

andd1

8 Ova

lues

(in%

VSM

OW)of

theEvian

water

withresiden

ceof

upto

659day

sin

differen

tplasticcontaine

rs

Bottle

Material/

Volum

ea

d2H

d18 O

r2

d2H=xd

18O+y

Min.

Max

.Ran

geAve

rage

bs

Min.

Max

.Ran

geAve

rage

bs

xy

AHDPE

/30

�72.8

�71.3

1.5

�72.1(17)

0.43

�10.6

�10.1

0.5

�10.3(17)

0.16

0.051(17)

0.13

�70.7

BHDPE

/15

�72.7

�71.2

1.6

�72.0(17)

0.40

�10.5

�10.1

0.9

�10.2(17)

0.12

0.129(17)

0.42

�67.6

CLDPE

/10

�72.4

�69.7

2.7

�71.4(17)

0.70

�10.5

�9.6

1.0

�10.1(17)

0.23

0.376(16)

1.13

�60.0

DLDPE

/50

c�7

2.7

�70.7

1.9

�71.6(17)

0.51

�10.6

�10.1

0.5

�10.3(17)

0.16

0.162(17)

0.52

�66.2

ELDPE

/200

�73.2

�71.2

2.0

�72.2(17)

0.43

�10.5

�9.9

0.6

�10.3(17)

0.19

0.084(16)

0.16

�70.6

FLDPE

/15

�73.4

�70.5

2.9

�71.9(17)

0.65

�10.6

�9.9

0.8

�10.2(17)

0.23

0.493(17)

1.39

�57.8

GPP

/15

�72.5

�71.3

1.2

�71.9(17)

0.42

�10.6

�9.8

0.8

�10.2(17)

0.24

0.243(17)

0.46

�67.2

HLDPE

/50

c�7

2.9

�69.9

3.0

�71.7(17)

0.79

�10.6

�9.8

0.8

�10.3(17)

0.19

0.111(17)

0.48

�66.8

IPC

/12

5�7

2.8

�67.7

5.1

�69.9(17)

1.84

�10.6

�8.6

2.0

�9.4

(17)

0.69

0.923(17)

2.48

�46.5

JPF

A/50

�72.9

�71.9

1.0

�72.3(7)

0.30

�10.5

�10.2

0.3

�10.3(7)

0.11

0.578(7)

1.54

�54.4

KPE

T/500

�72.7

�67.5

5.2

�70.2(17)

1.77

�10.5

�8.8

1.8

�9.6

(17)

0.64

0.923(17)

2.53

�45.8

LGlass/50

�72.8

�71.8

1.0

�72.2(17)

0.29

�10.5

�10.3

0.2

�10.4(17)

0.07

0.009(17)

0.04

�71.9

All

�73.4

�67.5

5.9

�71.6(194)

1.17

�10.8

�8.6

2.2

�10.1(194)

0.44

0.840(194)

2.28

�48.5

a Materials:HDPE

,high

den

sity

polyethy

lene

;LDPE

,low

den

sity

polyethy

lene

;PP

,po

lyprop

ylen

e;PC

,po

lycarbon

ate;

PFA,pe

rfluo

roalko

xy-Tefl

on;PE

T,po

lyethy

lene

tereph

thalate.

Volum

ein

mL.

bNum

berin

parenthe

sesstan

dsfornu

mbe

rof

replicatean

alyses.

c Dan

dH

are50

mLLDPE

containe

rsprod

uced

byKau

texan

dKJS

(German

y),respe

ctively.

J. E. Spangenberg

wileyonlinelibrary.com/journal/rcm Copyright © 2012 John Wiley & Sons, Ltd. Rapid Commun. Mass Spectrom. 2012, 26, 2627–2636

2634


CONCLUSIONS

The transport of water molecules through organic polymericmaterial by liquid water evaporation and gas-diffusion(pervaporation) or water-vapor permeation and exchangewith hydrophilic moieties in the polymer have the potentialto modify the original hydrogen and oxygen stable isotopecomposition of the water or aqueous solution. In a previousstudy,[33] it was shown that the extent of such changes inisotopic composition is related to the time spent, temperature,and relative vapor pressures of water within the organicpolymer container and ambient air. In this study the extentof such changes in isotopic compositions in bottle-likecontainers of different organic polymers, including low andhigh density polyethylene (LDPE and HDPE), polypropylene(PP), polycarbonate (PC), polyethylene terephthalate (PET),and perfluoroalkoxy-Teflon (PFA), and of different size andwall thickness during storage at the same temperature andhumidity variationswas investigated. The results of this experi-ment indicate that changes of up to +5% for d2H and +2.0% ford18O values may occcur for water after 659 days of storagewithin plastic bottles, showing that the organic polymer, wallthickness and container volume were major variables affectingthe isotopic composition of the water with time of storage. Themost important offsets were measured for the PET and PCbottles. For accurate measurements of the water stable isotopecomposition in aqueous solutions, rigorous sampling, andstorage procedures preferably in glass or thick-wall HDPEbottles are needed. Systematic errors due to inadequate storageof aqueous solutions and interpretation of the hydrogen andoxygen stable isotope ratios should not be disregarded.

AcknowledgementsThe stable isotope facilities were supported by the Universityof Lausanne. I thank Torsten Vennemann and two anonymousjournal reviewers for detailed reading and constructivecomments.

263

REFERENCES

[1] W. G. King, J. M. Rodriguez, C. M. Wai. Losses of traceconcentrations of cadmium from aqueous solution duringstorage in glass containers. Anal. Chem. 1974, 46, 771.

[2] P. Bene�s, E. Steinnes. Migration forms of trace elements innatural fresh waters and the effect of the water storage.Water Res. 1975, 9, 741.

[3] G. E. Batley, D. Gardner. Sampling and storage of naturalwaters for trace metal analysis. Water Res. 1977, 11, 745.

[4] J. R. Moody, R. M. Lindstrom. Selection and cleaning ofplastic containers for storage of trace element samples. Anal.Chem. 1977, 49, 2264.

[5] R. Massee, F. J. M. J. Maessen, J. J. M. De Goeij. Losses ofsilver, arsenic, cadmium, selenium and zinc traces fromdistilled water and artificial se-water by sorption on variouscontainer surfaces. Anal. Chem. Acta 1981, 127, 181.

[6] R. Cornelis, J. Hoste, J. Versieck. Potential interferencesinherent in neutron-activation analysis of trace elements inbiological materials. Talanta 1982, 29, 1029.

[7] M. Gasparon. Trace metals in water samples: minimisingcontamination during sampling and storage. Environ. Geol.1998, 36, 207.


[8] C. Reimann, U. Siewers, H. Skarphagen, D. Banks. Doesbottle type and acid-washing influence trace elementanalyses by ICP-MS on water samples? A test covering 62elements and four bottle types: high density polyethene(HDPE), polypropene (PP), fluorinated ethene propenecopolymer (FEP) and perfluoroalkoxy polymer (PFA). Sci.Total Environ. 1999, 239, 111.

[9] L. M. Tupa, B. N. Popp, D. M. Karl. Dissolved organiccarbon in oligotrophic water: experiments on sample preser-vation, storage and analysis. Mar. Chem. 1994, 45, 207.

[10] S. C. Yoro, C. Panagiotopoulos, R. Sempere. Dissolvedorganic carbon contamination induced by filters and storagebottles. Water Res. 1999, 33, 1956.

[11] L. Illum, H. Bundgaard. Sorption of drugs by plasticinfusion bags. Int. J. Pharm. 1982, 10, 339.

[12] D. Song, L.-F. Hsu, J. L. S. Au. Binding of toxol to plastic andglass containers and protein under in vitro conditions.J. Pharm. Sci. 1996, 85, 29.

[13] C. Beitz, T. Bertsch, D. Hannak, W. Dchrammel, C. Einberger,M. Wehling. Compatibility of plastics with cytotoxic drugsolutions – comparison of polyethylene with other containermaterials. Int. J. Pharm. 1999, 185, 113.

[14] J. J. Palmgrén, J. Mönkkönen, T. Korjamo, A. Hassinen,S. Auriola. Drug adsorption to plastic containers andretention of drugs in cultured cells under in vitro conditions.Eur. J. Pharm. Biopharm. 2006, 64, 369.

[15] S. C. George, S. Thomas. Transport phenomena throughpolymeric systems. Prog. Polym. Sci. 2001, 26, 985.

[16] J. M. Lagaron, R. Catalá, R. Gavara. Structural characteristicsdefining high barrier properties in polymeric materials.Mater.Sci. Technol. 2004, 20, 1.

[17] G. A. Junk, H. J. Svec, R. D. Vick, M. Avery. Contaminationof water by synthetic polymer tubes. Environ. Sci. Technol.1974, 1974, 1100.

[18] F. Pellerin, D. Baylocq, D. Andre, C. Majcherczyk, N. Laham.Migrations between plastic containers and liquid pharmaceu-ticals: general criteria for study and detection methods. Ann.Pharm. Fran. 1984, 42, 15.

[19] A. Schwope, D. E. Till, D. Ehntholt, K. Sidman, R. Whelan,P. Schwartz, R. Reid. Migration of BHTand Irganox 1010 fromlow-density polyethylene (LDPE) to foods and food-simulatingliquids. Food Chem. Toxicol. 1987, 25, 317.

[20] G. Smistad, T. Waaler, P. O. Roksvaag. Migration of plasticadditives from soft poly(vinyl chloride) bags into normalsaline and glucose infusions. Acta Pharm. Nordica 1989, 1, 279.

[21] N. Casajuana, S. Lacorte. Presence and release of phthalicesters and other endocrine disrupting compounds indrinking water. Chromatographia 2003, 57, 649.

[22] J. Ewender, R. Franz, A. Mauer, F. Welle. Determinationof the migration of acetaldehyde from PET bottles intonon-carbonated and carbonated mineral water. DeutscheLebensmittel-Rundschau 2003, 99, 215.

[23] B. Marcato, S. Guerra, M. Vianello, S. Scalia. Migration ofantioxidant additives from various polyolefinic plastics intooleaginous vehicles. Int. J. Pharm. 2003, 257, 217.

[24] I. Skjevrak, A. Due, K. O. Gjerstad, H. Herikstad. Volatileorganic components migrating from plastic pipes (HDPE,PEX and PVC) into drinking water. Water Res. 2003, 37, 1912.

[25] C.-M. Chang, C.-C. Chou, M.-R. Lee. Determining leachingof bisphenol A from plastic containers by solid-phasemicroextraction and gas chromatography-mass spectrometry.Anal. Chim. Acta 2005, 539, 41.

[26] J. Bosnir, D. Puntaric, A. Galic, I. Skes, T. Dijanic, M. Klaric,M. Grgic, M. Curkovic, Z. Smit. Migration of phthalatesfrom plastic containers into soft drinks and mineral water.Food Technol. Biotechnol. 2007, 45, 91.

[27] O.-G. Piringer. Permeation of gases, water vapor and volatileorganic compounds, in Plastic Packaging Materials for Food:


5

J. E. Spangenberg

2636

Barrier Function, Mass Transport, Quality Assurance, and Legisla-tion, (Eds: O.-G. Piringer, A. L. Baner), Wiley-VCH, Weinheim,Germany, 2007, DOI: 10.1002/9783527613281.ch09.

[28] R. S. McWatters, R. K. Rowe. Transport of volatile organic com-pounds through PVC and LLDPE geomembranes from bothaqueous and vapour phases. Geosynthetics Int. 2009, 16, 468.

[29] R. J. Ashley, Permeability and plastics packaging, in PolymerPermeability, (Ed.: J. Comyn), Elsevier, New York. 1985,pp. 269–308.

[30] X. Feng, Y. M. Huang. Liquid separation by membranepervaporation: A review. Ind. Eng. Chem. Res. 1997, 36, 1048.

[31] R. Hernandez. Effect of water vapor on the transport propertiesof oxygen through polyamide packagingmaterials. J. Food Eng.1994, 22, 495.

[32] B. Bolto, M. Hoang, Z. Xie. A review of water recoveryby vapour permeation through membranes. Water Res.2012, 46, 259.

[33] J. E. Spangenberg, T. W. Vennemann. The stable hydrogenand oxygen isotope variation of water stored in polyethy-lene terephthalate (PET) bottles. Rapid Commun. Mass Spec-trom. 2008, 22, 672.

[34] Available: http://www.meteoschweiz.admin.ch/web/en/weather.html

[35] G. Zakrzewska-Trznadel, A. G. Chmielewski, N. R. Miljevic.Separation of protium/deuterium and oxygen-16/oxygen-18by membrane distillation. J. Membrane Sci. 1996, 113, 337.

[36] J. Kim, S. E. Park, T. S. Kim, D. Y. Jeong, K. H. Ko. Isotopicwater separation using AGMD and VEMD. Nukleonika2004, 49, 137.

[37] R. Z. Hernandez, Plastics in Packaging, inHandbook of Plastics,Elastomers, & Composites, (Ed.: C. A. Harper), McGraw-Hill,New York, 2002, pp. 627–692.

[38] V. Morillon, F. Debeaufort, G. Blond, A. Voilley. Temperatureinfluence on moisture transfer through synthetic films.J. Membrane Sci. 2000, 168, 223.

[39] H. Deng, C. T. Reynolds, N. O. Cabrera, N. M. Barkoula,B. Alcock, T. Peijs. The water absorption behaviour of all-polypropylene composites and its effect on mechanicalproperties. Composites Part B 2010, 41, 268.

[40] L. Gao, T. J. McCarthy. Teflon is hydrophilic. Comments ondefinitions of hydrophobic, shear versus tensile hydrophobi-city, and wettability characterization. Langmuir 2008, 24, 9183.

[41] G. Baschek, G. Hartwig, F. Zahradnik. Effect of waterabsorption in polymers at low and high temperatures.Polymer 1999, 40, 3433.


[42] J. N. Clark, N. R. Jagannathan, F. G. Herring. A nuclearmagnetic resonance study of poly(aryl ether ether ketone).Polymers 1988, 29, 341.

[43] J. Sajiki, J. Yonekubo. Leaching of bisphenol A (BPA) toseawater from polycarbonate plastic and its degradationby reactive oxygen species. Chemosphere 2003, 51, 55.

[44] C. A. Pryde, M. Y. Hellman. Solid state hydrolysis ofbisphenol-A polycarbonate. I. Effect of phenolic endgroups. J. Appl. Polym. Sci. 1980, 25, 2573.

[45] H. E. Bair, D. R. Falcone, M. Y. Hellman, E. Johnson,P. G. Kelleher. Hydrolysis of polycarbonate to yield BPA.J. Appl. Polym. Sci. 1981, 26, 1777.

[46] M. Diepens, P. Gijsman. Photo-oxidative degradation ofbisphenol A polycarbonate and its possible initiationprocesses. Polym. Degrad. Stabil. 2008, 93, 1383.

[47] D. Biscardi, S. Monarca, R. D. Fusco, F. Senatore, P. Poli,A. Buschini, C. Rossi, C. Zani. Evolution of the migrationof mutagens/carcinogens from PET bottles into mineralwater by Tradescantia/micronuclei test, Comet assay onleukocytes and GC/MS. Sci. Total Environ. 2003, 302, 101.

[48] P. Schmid, M. Kohler, R. Meierhofer, S. Luzi, M. Wegelin.Does the reuse of PET bottles during solar waterdisinfection pose a health risk due to the migration ofplasticisers and other chemicals into the water? WaterRes. 2008, 42, 5054.

[49] P. Montuori, E. Jover, M. Morgantini, J. M. Bayona, M. Triassi.Assessing human exposure to phthalic acid and phthalateesters from mineral water stored in polyethylene terephthalateand glass bottles. Food Addit. Contam. Part A 2008, 25, 511.

[50] G. Hizal, Q. Q. Zhu, C. H. Fischer, P. M. Fritz, W. Schnabel.On the photolysis of phthalic acid dialkyl esters: a productanalysis study. J. Photochem. Photobiol. A Chem. 1993, 72, 147.

[51] T. K. Lau, W. Chu, N. Graham. The degradation of endocrinedisruptor di-n-butyl phthalate byUVirradiation: A photolysisand product study. Chemosphere 2005, 60, 1045.

[52] N. Sugaya, T. Nakagawa, K. Sakurai, M. Morita, S. Onodera.Analysis of aldehydes in water by head space-GC/MS.J. Health Sci. 2001, 47, 21.

[53] A. Dabrowska, A. Borcz, J. Nawrocki. Aldehyde contaminationof mineral water stored in PET bottles. Food Addit. Contam.2003, 20, 1170.

[54] M. Byrn, M. Calvin. Oxygen-18 exchange reactions ofaldehydes and ketones. J. Am. Chem. Soc. 1966, 88, 1916.

[55] K. W. Wedeking, J. M. Hayes. Exchange of oxygen isotopesbetweenwater und organicmaterial.Chem. Geol. 1983, 41, 357.


http://www.meteoschweiz.admin.ch/web/en/weather.html

http://www.meteoschweiz.admin.ch/web/en/weather.html

caution on the storage of waters and aqueous solutions in plastic containers for hydrogen and oxygen...

Documents