Rapid Method for the Determination of the Stable Oxygen Isotope

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A rapid method for determination of stable oxygen isotope ratio of water in alcoholic beverages Daobing Wang, Qiding Zhong, Guohui Li, and Zhanbin Huang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b00636 • Publication Date (Web): 16 Sep 2015 Downloaded from http://pubs.acs.org on September 29, 2015

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Journal of Agricultural and Food Chemistry

A rapid method for determination of stable oxygen isotope ratio of water in alcoholic beverages

Wang Daobing1,2 Zhong Qiding1* Li Guohui1 Huang Zhanbin2 (1. China National Research Institute of Food and Fermentation Industries ,Beijing, 100015 ; 2. School of Chemical and Environmental Engineering,China University of Mining and Technology(Beijing),Beijing,100083)

1

ACS Paragon Plus Environment


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Abstract: It was demonstrated that the first successful application of on-line pyrolysis technique for direct determination of oxygen isotope ratios (δ18O) of water in alcoholic beverage. The similar water concentration in each samples was achieved by adjusting with absolute ethyl alcohol and then a fixed GC split ratio can be used. All the organic ingredients were successfully separated from the analyte on a CP-PoraBond Q columnand subsequently vented out, while water molecules were transferred into the reaction furnace and converted to CO. With the system presented, based on the system presented, 15 ~ 30 µL raw sample was diluted and can be analyzed repeatedly , the analytical precision was better than 0.4 ‰ (n=5) in all cases, and more than 50 injections can be made per day. No apparent memory effect was observed even if water samples were injected using the same syringe; a strong correlation (R2 = 0.9998) was found between the water δ18O of measured sample and that of working standards. There was no significant difference (p>0.05) between the mean δ18O value that obtained by the traditional method (CO2-water equilibration / isotope ratio mass spectrometry ) and the newly developed method in this study. The advantages of this new method are rapid and straightforward, and

less test portion

required. Keywords: Stable oxygen isotope ratio; pyrolysis; water; alcoholic beverage

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INTRODUCTION 1

As a result of the natural oxygen isotope variation in meteoric water and the

2

fractionation during plant transpiration, the oxygen isotope ratio (δ18O) in

3

groundwater varies from region to region due to the effects of temperature, altitude,

4

distance from the sea, and amount of precipitation. The δ18O in groundwater is usually

5

lower than the water from plant tissue, so that this quantitative information is

6

extremely useful for the discrimination of geographic origin and detection of added

7

water in wines and spirits.[1-4] Thus, a reliable and rapid δ18O analysis of water from

8

alcoholic beverage has become an attractive goal in recent years.

9

The isotopic ratio of oxygen in water has been measured by many different

10

techniques; the classical analytical procedure was described as early as the 1950s,

11

when CO2-water equilibration was used.[5] The automated devices based on this

12

method are commercially available, and generally provide accurate and precise results;

13

however, a large test portion is required and it is usually time consuming.[6-8] It was

14

not until 1990s, a more rapid measurement of oxygen-18 abundance was achieved by

15

high-temperature conversion isotope ratio mass spectrometry [9-15] and by isotope ratio

16

infrared spectroscopy(IRIS).[16-19] These techniques provide fast, accurate and precise

17

δ18O analysis of water; the total running time is less than 10 minutes with precision

18

better than 0.5 ‰, and the test portion is as small as 0.1 µL. Nevertheless, it was

19

indicated by literatures that the trace amount of organic contaminants may interfere

20

with IRIS and thus adversely impacts on data quality, and thus it can only be used for

21

pure water analysis.[18-19] As for high-temperature conversion isotope ratio mass

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22

spectrometry, the “carbon reduction” was used to convert H2O to CO, but other

23

oxygen containing compounds together with water injected into furnace will also be

24

converted into CO indiscriminately.[20] Therefore, both the two new techniques are not

25

suitable for direct determination of δ18O of water in alcoholic beverages.

26

Compound-specific stable-isotope analysis (CSIA) has been achieved by coupling a

27

GC system to an IRMS for more than 20 years , and it appears to be that published

28

reports focus primarily on direct carbon isotope analysis for aqueous samples.[21-24]

29

however, all GC-IRMS analyses of oxygen isotope ratio rely on pyrolysis and

30

reduction of organic molecules over carbon to quantitatively yield CO as the analyzed

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species, the crucial step for an accurate analysis is to separate the target compound;

32

for this reason, only pure analytes[14, 25-26 ] or organic compounds dissolved in organic

33

reagents[27-28 ] can be measured. Clearly therefore, water molecules can not be easily

34

separated by extraction methods[25-26] or routine GC methods[24] from organic

35

compounds for further analysis, as alcohols and organic acids are miscible with water .

36

Fortunately, chromatography columns bonded porous polymers have become very

37

popular because of their high retention, inertness and selectivity, and more

38

importantly is its high hydrophobicity. It is therefore applied in the GC method with

39

the use of porous polymer column for the determination of trace water in solvents.[29]

40

According to the advantages mentioned above, GC-P-IRMS equipped with a porous

41

polymer column was proposed for water δ18O analysis in aqueous samples. The aim

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of this study was to investigate the feasibility and efficiency of porous polymer

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column, and to develop a rapid and simple GC-P-IRMS method that could be applied

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directly to alcoholic beverages for water δ18O measurement.

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MATERIALS AND METHODS

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Chemicals. Carbon monoxide and helium, both 99.999% purity, from Air Products

47

and Chemicals, Inc.(Beijing, China) were used as reference gas and inert carrier gas,

48

respectively; 1.8% hydrogen in helium was used as an auxiliary (“magic-mix”) gas;

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Methane (99.999% purity) was used as working gas to deposit element carbon.

50

Ethanol reagent (HPLC grade), used as diluents, was purchased from Sinopharm

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Chemical Reagent Co., Ltd (Beijing, China). The anhydrous alcohol was obtained

52

while the trace water in ethanol regent was trapped by storing for at least 24 h on

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molecular sieve (2 mm beads, UOP type 3Å, Fluka Chemie GmbH, Buchs,

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Swizerland).

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Three distilled water, Std-1, Std-2 and Std-3, used as working standards for oxygen

56

isotope ratio analysis were purchased from supermarkets in China, the δ18Ocalibrated

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values determined by CO2-water Equilibration Method and normalized versus the

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VSMOW/SLAP scale were as follows: -6.01 ± 0.05 ‰ for Std-1, -11.91 ± 0.09 ‰ for

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Std-2, -18.53 ± 0.11 ‰ for Std-3.

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Samples. Some commercial alcoholic beverages were prepared: two traditional

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Chinese distilled spirit called baijiu (ca 52% vol), two pear spirit; one sparkling wine

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and seven kinds of wine, red and white. δ18O analyses of wine, spirits were performed

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using Isotope Ratio Mass Spectrometers (Delta Delta V Advantage, ThermoFisher

64

Scientific, Bremen, Germany) connected to a water/CO2 equilibration system 5



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(GasBenchII, ThermoFisher Scientific). All the procedures are described in the

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OIV-MA-AS2-12-MOU 18 method (2009) for grape derivates.

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GC-P-IRMS system. A Delta V Advantage isotope ratio mass spectrometer (Thermo

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Fisher Scientific) coupled by an open-split via a combustion/pyrolysis interface

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(Al2O3; 1.5 mm o.d., 320 mm; Pt, Ni) to a Trace GC Ultra gas chromatograph

70

(ThermoFisher Scientific) was used. The GC was equipped with a CP-PoraBOND-Q

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column（50 m length，0.32 mm i.d., 5.0 µm film thickness) and connected to a Triplus

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autosampler (Thermo Fisher Scientific).

73

Sample preparation. Following the rule of the ‘Identical Treatment’ (IT)

74

principle,[25,31] individual sample results versus a gaseous working standard could be

75

compared with results from reference material or working standard that had passed

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the full sample line in the same sequence of measurements, samples with different

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alcoholic strength were diluted with anhydrous alcohol to make the water content at

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the same level. In the present study, the water content of working standards and

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alcoholic beverage samples were dilute to 30 g/L. As for wine samples, the solutions

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were filtered using 0.45 µm syringe filters.[31-32]

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Analytical conditions. Helium was used as the carrier gas at a flow rate of

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1.2 mL/min; samples were injected through the injection port of the gas

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chromatograph using a 10 µL liquid sampling syringe. The injection port was

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operated in the split mode with a split ratio of 50:1. The injection port was held at

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180 °C, fitted with a straight-bore inlet sleeve containing a plug of nickel wool

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(Thermo Scientific, Bremen, Germany) to ensure complete vaporization of samples

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and to act as a trap for removal of nonvolatile components. For routine analysis, the

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inlet sleeve was cleaned and the nickel wool plug was replaced after 200 analyses.

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The pyrolysis furnace was set at 1280 °C, using auxiliary (“magic-mix”) gas (1.8%

90

hydrogen in helium, flow rate of 0.5 mL/min) to avoid oxygen exchange between CO

91

and Al2O3. Elemental carbon was used to provide a reactive layer, which should be

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well distributed. This was done for independent samples, by flushing the reactor with

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high concentrations of methane while diverting the flow from the IRMS instrument.

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The syringe carried 1 µL solutions penetrates a septum, waited 0.5s (pre dwell time)

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before injecting the sample and then waited another 0.5s (post dwell time) before

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withdrawing again. Prior to the sample injection the syringe was washed with sample

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water 10 times. In each wash cycle 1.5 µL of sample solution was taken up and

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injected into a waste vial.

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The backflush button of the GC/IRMS instrument was kept open all the time except

100

for from 60 s to 210 s.

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Isotopic calculation. One pulses of CO reference gas were admitted into the inlet

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system for about 20 s at the beginning and Three at the end of the run. The ion

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currents of m/z of 28-30 were registered and the results were calculated relative to a

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CO reference gas.

105 106 107 108

The delta notation is defined as δ18O[‰] = (18O/16O)sample/(18O/16O)reference-1 The duration of one sample run was 850s; details of time programming and the mass traces m/z of 28, 29 and 30 are shown in Figure 2.

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The working standards were analyzed at the beginning and the end of the sample

110

determination to verify the linearity of the spectrometer; the Std-1 was injected

111

systematically (every five samples) in order to correct the drift of the instrument.

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RESULTS AND DISCUSSION

113

Background

114

Oxygen isotope ratios are determined by the M[30]/M[28] [(12C18O)/(12C16O)] ratio.

115

Gas leak will give rise to the error of determination, for N2 has the same mass as CO ,

116

and the reaction of N2 and H2O will cause the increased ion current of m/z 30. It is

117

critical that the system must be leak-free. In this study, the GC-P-IRMS system was

118

thoroughly leak checked, no leak was found as the ion current of m/z 40 was lower

119

than 70mV, which meets the Thermo Fisher Scientific GC IsoLink™ Operating

120

Manual (2010).[33]

121

To ensure the quality of data, the backgrounds of m/z 28 and m/z 30 lower than 70

122

mV was recommended by F. Thomas et al for the oxygen isotope ratio analysis using

123

TC/EA-IRMS.[34] However, higher backgrounds of m/z 28 and m/z 30 were (see

124

Figure 1-2) observed in GC-P-IRMS while the backflush button was closed; it is

125

reasonable to assume that this is caused by the reaction of elemental carbon and

126

oxygen originating from the ceramics tube at higher temperatures, which is in line

127

with some previously published work on the subject.[14-15] Fortunately, the monitored

128

ion current ratio 30/28 was in a steady state, which can be considered as a constant,

129

therefore the background can be corrected mathematically.

130

Blank

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In this study, in order to simultaneously measure a series of samples with different

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alcoholic strength, the ethanol reagent was used as a diluent for sample preparation.

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However, ca. 1100 mV ion current of m/z 28 (Figure 1 a) above the background was

134

observed while 1 µL ethanol reagent injected into GC-P-IRMS. While the amount and

135

δ18O value of water in the mentioned diluent is difficult to estimate, there is no doubt

136

that this dissolved water in ethanol will influence the accuracy of the water stable

137

isotope determination in aqueous samples . Thus, it is necessary to eliminate the

138

dissolved water in the reagent first, and the anhydrous alcohol is created by storing for

139

at least 24h on molecular sieve. In this case a small CO peak is observed (area ca.

140

0.59 nAs), which is negligible compared with the CO peak of 41-49 nAs obtained by

141

the pyrolysis of sample analytes. In addition, more than 30 µL sample can be used to

142

increase the amount of analyte in the solution, thus the injection volume will be

143

decreased.

144

Nitrogen

145

The autosampler (Triplus) was used to improve the sampling reproducibility,

146

with which a small volume of air in the syringe is needed. However, it is well known

147

that the atmosphere is a

148

the same mass as CO.

149

ioncurrent of m/z 28 nearly 3000 mV, it can be separated chromatographically in

150

GC-P-IRMS from the N2 and CO, employing a CP-PoraBOND Q column (Figure 2).

151

Thus, the impact of air on CO analysis can be considered insignificant, also, a high

152

split ratio can be used to reduce the atmospheric nitrogen amount.

nitrogen pool, which may be another concern that N2 has Fortunately, although the atmospheric nitrogen generates

9



153 154

Memory effect It has been noted that the effect of memory may be caused by the syringe that

155

carried reminiscences of last sample,[35 ] and a negative correlation between the

156

memory effect and the sample size was observed.[36] In order to eliminate the memory

157

effect of syringe, 1 µL injection was used and syringe cleaning procedure was

158

supplemented by flushing the syringe using samples as a washing agent for 10 cycles.

159

In addition, to eliminate the memory of reactor, one pulse of methane was introduced

160

into reactor for conditioning prior to the next sample analysis.

161

To evaluate the overall memory effect of the system, the working standards Std-1

162

was measured consecutively 5 times before alternating and measuring Std-3 five

163

times and each of them was analyzed consecutively for five times. Raw data are

164

shown graphically in Figure 3 and clearly demonstrates that the memory effect in the

165

GC-P-IRMS systemis negligible.

166

Normalisation

167

The oxygen isotope ratios of three working standards were determined by

168

GC-P-IRMS (Table 1). The discrepancy

between the mean value determined by

169

GasBench II-IRMS and the raw data by GC-P-IRMS indicates that there was an

170

isotopic fractionation which was caused by the split injection port (1:50) and ConFlo

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IV open split interface in the GC-P-IRMS system. However, the difference for three

172

working standards are -3.26 ‰, 0.78 ‰ and 2.26 ‰, respectively, meanwhile, a very

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strong correlation (R2 = 0.9998) between the water δ18O values was obtained by

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GasBench II-IRMS and those from the proposed new methodology, which

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demonstrates a systematic error introduced during pyrolysis.[37] An equation is generated by comparing the real values and measured values of standard samples as provided below: δ18Ocorrected = 1.7997 δ18OGC-P-IRMS + 10.822

Equation 1

179

As all the samples underwent the identical experimental processes with standard

180

samples according to the identical treatment (IT) described by Werner and Brand, this

181

equation was used to calibrate the measured value of each sample to get more

182

accurate results.

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Application to samples

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The δ18O values of water in 12 alcoholic beverage samples (including wines and

185

spirits) were determined by the official method (GasBench II-IRMS based on

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CO2-water equilibration) in order to evaluate the procedure developed in this study for

187

the on-line analysis of water in alcoholic beverage. Each sample was repeatly

188

analyzed three times and the data was calculated as the mean value of 10 injections in

189

a single repeat . The averaged δ18O value of each sample are shown in Table 2. The

190

stable oxygen isotope ratios of the samples (1-12) ranged from -10.37 ‰ to 9.47 ‰,

191

with a mean of -0.39 ± 1.88 ‰.

192

These 12 samples analyzed previously by GasBench II-IRMS were also measured

193

by GC-P-IRMS, and each sample was repeated 5 times. The samples were diluted,

194

filtered and processed through the GC column and were subsequently pyrolyzeed in

195

order to study the δ18O value of water in alcoholic beverages. All the samples showed

196

an appropriate chromatographic profile including baseline separation of the peak of

11



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197

analyte, and the results are shown in Table 2. The normalized δ18O value of all

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samples ranged from -9.78 ‰ to 10.17 ‰, with a mean of 0.26 ± 2.09 ‰.

199

As is known that individual mass spectrometers may produce machine specific and

200

systematically different values for international standards, and a normalization should

201

be used to eliminate this effect.[6] The normalization is applied under the assumption

202

that any systematic error introduced during mass spectrometric analyses is linear in a

203

dynamic range.[38] In this study, Std-1, Std-2 and Std-3 range from -6.01 ‰ to

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-18.53 ‰ were used.

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As can be seen in Figure 4, the δ18O values of water in alcoholic beverages obtained

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by GasBench II-IRMS and GC-P-IRMS(calculated following Equation 1) are strongly

207

correlated (R2 = 0.98), but the slope is not one and the y-intercept is not zero for these

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two sets of data. It is hypothesized that the measured value of δ18O and natural

209

abundance of δ18O are not related in a linear manner, just as suggested in Gehre’s

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study that the water δ2H values for identical samples determined at different reaction

211

conditions has deviations and their extents of fractionation are related in a non-linear

212

manner to the natural abundance of D/H in water,[15] thus suitable reference materials

213

or working standards in dynamic range should be used for normalization. For sample

214

1-7, the slope and intercept of the linear equations generated from the measured value

215

of δ18OGasBench II-IRMS and δ18OGC-P-IRMS are 1.0046 and 0.0007 ‰ , and there is a very

216

strong strength of association (R2 = 0.985) between the δ18OGasBench

217

δ18OGC-P-IRMS with no significant difference between these two values (p =

218

0.9126, >0.05). For the sample 8-11, a very strong correlation (R2 =0.998) between the

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II-IRMS

and

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values get from δ18OGasBench

220

significant difference (p>0.05) can be found, however, there are large differences

221

between the figure of the each group of values. The reason for this large discrepancy

222

may be because the linear relationship varies with natural abundance of oxygen

223

isotopes, and then different equation will be followed. This explanation is also

224

supported by Schimmelmann1 et al. that the calibration may require two reference

225

materials with different isotopic ratios, and more ideally, the range of the standard

226

should cover the range of the value the sample need to be measured.[39] Also, Bièvre et

227

al. suggests that the more similar are sample and reference material to be compared,

228

the smaller becomes the uncertainty due to the measurement itself.[40] Therefore, it

229

can be inferred that a proper standard that can cover an appropriate range of the

230

isotopic ratio that need to be determined is crucial for the calibration of measured

231

isotope ratio.

232

AUTHOR INFORMATION

233

Corresponding Author

234

*(Q.D.Z.) E-mail: [email protected]

235

Funding

236

This research was supported by The National Natural Science Foundation of China

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(Grant No. 31101333), The National Key Technology R&D Program of China during

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the “12ed Five-Year Plan” (Grant No. 2012BAK17B11), The International S&T

239

Cooperation Program of China (Grant No.2011DFA33270) and by the FP7 project

240

Foodintegrity "Ensuring the integerity of the european food chain" (Grant No.613688)

II-IRMS

and δ18OGC-P-IRMS was also obtained, and no

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241

from European Union.

242

Notes

243

The authors declare no competing financial interest.

244

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Lebensmitteluntersuchung und-Forschung A, 1998, 206(3): 230-232.

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[28] Jung J, Jaufmann T, Hener U, et al. Progress in wine authentication: GC–C/P–IRMS

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measurements of glycerol and GC analysis of 2, 3-butanediol stereoisomers. European Food

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Research and Technology, 2006, 223(6): 811-820.

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[29] Zeeuw J, Luong J. Developments in stationary phase technology for gas chromatography. TrAC Trends in Analytical Chemistry, 2002, 21(9): 594-607. [30] RA Werner, WA Brand. Referencing strategies and techniques in stable isotope ratio analysis. Rapid Communications in Mass Spectrometry, 2001, 15(7): 501–519.

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[31] Thomas F, Jamin E. H NMR and 13 C-IRMS analyses of acetic acid from vinegar, 18

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O-IRMS analysis of water in vinegar : International collaborative study report. Analytica

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Chimica Acta,2009 (649): 98–105.

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[32] Low N H, McLaughlin M., Hofsommer H J., et al. Capillary gas chromatographic detection

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of invert sugar in heated, adulterated, and adulterated and heated apple juice concentrates

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employing the equilibrium method. Journal of Agricultural and Food Chemistry, 1999,

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47(10):4261–4266.

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[33] Thermo Fisher Scientific GC IsoLink™ Operating Manual. Thermo Electron Corporation: Bremen, Germany, 2010.

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[34] Thomas F, Jamin E, and david hammond. 18O Internal Referencing Method to Detect Water

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Addition in Wines and Fruit Juices: Interlaboratory Study. Journal of AOAC InternatIonal,

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2013, 96(3), 615-624.

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[35] Begley I S, Scrimgeour C M. High-precision δH and δ18O measurement for water and

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volatile organic compounds by continuous-flow pyrolysis isotope ratio mass spectrometry.

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Analytical Chemistry, 1997, 69(8): 1530-1535.

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[36] Olsen J, Seierstad I, Vinther B, et al. Memory effect in deuterium analysis by continuous

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flow isotope ratio measurement. International Journal of Mass Spectrometry, 2006, 254(1):

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44-52.

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[37] Koziet J. Isotope ratio mass spectrometric method for the on-line determination of oxygen-18 in organic matter. Journal of Mass Spectrometry, 1997, 32(1): 103-108. [38] Paul D, Skrzypek G, Forizs I. Normalization of measured stable isotopic compositions to

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isotope reference scales – a review. Rapid Commun. Mass Spectrom. 2007, 21: 3006-3014.

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[39] Schimmelmann A, Albertino A, Sauer P, Qi HP, Molinie R, Mesnard F. Nicotine, acetanilide

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isotope ratio mass spectrometry. Rapid Commun. Mass Spectrom. 2009, 23(22): 3513-3521.

18


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[40] Bièvre P, Laeter J, Peiser H, Reed M.Reference materials by isotope ratio mass spectrometry. Mass Spectrometry Reviews. 1993, 12(3): 143-172.

19



353

Figure captions

354

Table 1 δ18O value of working standards

355

Table 2. Stable oxygen isotopic characterization of water in alcoholic beverages

356

Figure 1a. Mass traces 28, 29, 30 and the ratio 30/28 . The flat peak is due to the

357

monitoring gas injections introduced by the ConFlo IV interface, and the

358

chromatographic peak are CO gas that derived from water contained in the ethanol

359

reagent.

360

Figure 1b. Mass traces 28, 29, 30 and the ratio 30/28.The flat peak is due to the

361

monitoring gas injections introduced by the ConFlo IV interface, and the

362

chromatographic peak are CO gas that derived from water contained in the anhydrous

363

alcohol.

364

Figure 2. Mass traces 28, 29, 30 and the ratio 30/28. The flat peak is due to the

365

monitoring gas injections introduced by the ConFlo IV interface, the first

366

chromatographic peak (peak 2) is N2 gas introduced by the syringe, the second

367

chromatographic peak (peak 3) is CO gas that derived from water.

368

Figure 3 Effect of memory on analysis of δ18O of water samples (No.1-5, mean

369

-16.31 ‰ ± 0.36 ‰; No.6-10, mean -9.36 ‰ ± 0.18 ‰; No.11-15, mean -16.24 ‰ ±

370

0.27 ‰ and No.16-20, mean -9.28 ‰ ± 0.32 ‰).

371

Figure 4 Correlation of δ18O water (‰) of alcoholic beverage by GC-P-IRMS versus

372

δ18O water by GasBench II-IRMS

20


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Tables Table 1: Working Standard

Mean value (‰) Raw δ18O by GC-P-IRMS (‰) Offset from mean (‰)

Std-1

-6.01 ± 0.05

-9.27 ± 0.25

-3.26

Std-2

-11.91 ± 0.09

-12.69 ± 0.13

-0.78

Std-3

-18.53 ± 0.11

-16.28 ± 0.30

2.26

Table 2: δ18O(‰, vs. VSMOW ) Sample

Type by GasBench II-IRMS

1

Pear Spirit

-3.96

2

Pear spirit

-9.50

3

baijiu

-7.14

4

baijiu

-10.37

5

Red wine

-2.10

6

Red wine

-0.42

7

White wine

-0.29

8

Sparkling wine

2.21

9

Red wine

4.60

10

Red wine

5.70

11

White wine

7.14

12

Red wine

9.47

21



Figure graphics Figure 1a:

Figure 1b:

22


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Figure 2:

Figure 3:

Figure 4:

23



24


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TOC Graphics

25



Figure 1 a. Mass traces 28, 29, 30 and the ratio 30/28 . The flat peak is due to the monitoring gas injections introduced by the ConFlo IV interface, and the chromatographic peak are CO gas that derived from water contained in the ethanol reagent. 310x158mm (96 x 96 DPI)


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Figure 1 b. Mass traces 28, 29, 30 and the ratio 30/28.The flat peak is due to the monitoring gas injections introduced by the ConFlo IV interface, and the chromatographic peak are CO gas that derived from water contained in the anhydrous alcohol. 68x41mm (600 x 600 DPI)



Figure 2. Mass traces 28, 29, 30 and the ratio 30/28. The flat peak is due to the monitoring gas injections introduced by the ConFlo IV interface, the first chromatographic peak (peak 2) is N2 gas introduced by the syringe, the second chromatographic peak (peak 3) is CO gas that derived from water. 76x57mm (600 x 600 DPI)


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Figure 3 Effect of memory on analysis of δ18O of water samples (No.1-5, mean -16.31 ‰ ± 0.36 ‰; No.610, mean -9.36 ‰ ± 0.18 ‰; No.11-15, mean -16.24 ‰ ± 0.27 ‰ and No.16-20, mean -9.28 ‰ ± 0.32 ‰). 793x384mm (96 x 96 DPI)



Figure 4 Correlation of δ18O water (‰) of alcoholic beverage by GC-P-IRMS versus δ18O water by GasBench II-IRMS 1743x1092mm (96 x 96 DPI)


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TOC Graphic only 45x17mm (300 x 300 DPI)


Rapid Method for the Determination of the Stable Oxygen Isotope

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