Measurement and Correlation of Citronellal and Methyl Anthranilate

Article pubs.acs.org/jced

Measurement and Correlation of Citronellal and Methyl Anthranilate Solubilities in Supercritical Carbon Dioxide Wen-Chyan Tsai and Syed S. H. Rizvi* Institute of Food Science, Stocking Hall, Cornell University, Ithaca, New York 14853, United States ABSTRACT: Citronellal and methyl anthranilate (MA) are both nonpolar molecules with similar physical properties except for their molecular structures. The solubility of citronellal in supercritical carbon dioxide (SC-CO2) was measured using a static equilibrium system in the pressure range of (9.1 to 14.2) MPa and at (313.15 and 333.15) K. For MA, (9.1 to 24.3) MPa was used at the same temperatures. Solubility data of citronellal and MA in SC-CO2 were well correlated using the Chrastil equation and Peng−Robinson equation of state. Under comparable operating conditions, the linear-chained citronellal solubility in SC-CO2 was three to four times higher than its aromatic derivative MA. The acentric factor of citronellal (ω = 1.004) is higher than that of MA (ω = 0.577), indicating that citronellal has larger molecular asymmetry. This difference allows less intermolecular binding energy but gives higher vapor pressure to citronellal, making it more readily soluble in SC-CO2. The results suggest that the acentric factor is a good indicator of molecular asymmetry of a solute and provides a preliminary estimate on solutes behavior in SC-CO2. Knowledge of the solubility behavior of such molecules in SC-CO2 is a prerequisite for designing efficient industry-scale systems for their extraction and fractionation.

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properties.9 The molecular structures of these two fragrant compounds are shown in Figure 1. Citronellal, a linear

INTRODUCTION A supercritical fluid (SCF), with its readily adjustable density, low viscosity, and gas-like diffusivity, is an attractive solvent in the food, pharmaceutical, and cosmetic industries for the extraction of natural compounds, fine particle formation, and microencapsulation.1−4 Supercritical carbon dioxide (SC-CO2) is an environmentally friendly solvent with relatively low critical temperature (304.25 K) and moderate critical pressure (7.4 MPa). The low critical temperature of SC-CO2 helps prevent heat-labile compounds from degradation during processing. The moderate critical pressure results in energy savings to reach a desired supercritical state. Designing an efficient processing unit based on SCFs requires the solubility information of compounds of interest. In addition to operating pressure and temperature, molecular structure of a solute has significant influence on its solubility in SCFs; however, this information is often lacking, which may limit development of the SCF-based technologies. Dynamic and static techniques are usually applied for measurements of solute solubilities in SCFs.5,6 The dynamic technique is a quick and simple procedure; however, it is challenging to ensure that the phase equilibrium is reached for a solute’s saturated solubility. The static technique is a timeconsuming and more complicated procedure, but its advantage of controlled recirculation guarantees a solute’s saturated solubility in equilibrium.7 Citronellal and methyl anthranilate (MA) naturally exist in citrus fruits.8 They are also the active compounds in the citrus essential oil. Citronellal possesses the sedative, antiviral, and antimicrobial activities while MA exhibits photoprotective © 2015 American Chemical Society

Figure 1. Molecular structures of (a) citronellal and (b) methyl anthranilate.

hydrocarbon aldehyde, has a molecular weight of 154.25 and a boiling point of 479.15 K at atmospheric pressure. It is a colorless to pale yellow liquid with intense lemon flavor. MA, an aromatic derivative, has a molecular weight of 151.16 and a boiling point of 510.15 K at atmospheric pressure. It is a pale yellow liquid with intense grape-like flavor and unique bluish fluorescence under UV excitation. Citronellal and MA are insoluble in water and soluble in most organic solvents. In the food industry, both compounds are often added to ice cream, candy, chewing gun, and nonalcoholic beverages. They also can be blended with each other for cosmetic products like perfumes, creams, and lotions. Because of their different molecular structures and similar physical properties, citronellal Received: May 17, 2015 Accepted: November 24, 2015 Published: December 7, 2015 182

DOI: 10.1021/acs.jced.5b00423 J. Chem. Eng. Data 2016, 61, 182−187

Journal of Chemical & Engineering Data

Article

The solubility data of MA in SC-CO2 were adopted from our previous study.7 The solubility measurements were conducted in the pressure range of (10.1 to 26.9) MPa at (313.15 and 333.15) K. Theoretical Models. The Chrastil equation11 and Peng− Robinson equation of state (PR EOS)12 were chosen for the solubility correlation of citronellal in SC-CO2. The details about these two types of mathematicl models were described in our previous study.7 Model comparison was also evaluated for their applicability. Owing to a lack of vapor pressure data for citronellal and MA, their acentric factors (ω) were estimated using the Lee and Kesler equation,13 as shown in eq 1:

and MA are also model compounds to evaluate the effect of molecular architecture on the solubility behavior of various solutes in SC-CO2. The objectives of this study were to measure the phase equilibrium solubility of citronellal in SC-CO2 using the static equilibrium system. The solubility data were then correlated with the Chrastil equation and Peng−Robinson Equation of State (PR EOS) to establish the solubility prediction models. The effects of molecular configuration of solutes in SC-CO2 were evaluated by comparing the solubility data of citronellal with those of MA, which were measured in our previous study.7

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EXPERIMENTAL SECTION Materials. Citronellal (3,7-dimethyloct-6-en-1-al, CAS No. 106-23-0, C10H18O) and MA (methyl 2-aminobenzoate, CAS No. 134-20-3, C8H9NO2) were supplied by Acros Organics (Fair Lawn, NJ). Carbon dioxide (CAS No. 124-38-9, purity > 0.999995 volume fraction) was used as the supercritical solvent and supplied by Airgas (Ithaca, NY). The specifications of citronellal, MA, and carbon dioxide are presented in Table 1.

ω=

(1)

where θ ≡ Tb/Tc. The goodness of fit was evaluated by the average absolute deviation (AAD), as shown in the following equation: AAD =

Table 1. Specifications and Sources of Carbon Dioxide, Citronellal, and Methyl Anthranilate chemical name

CAS number

citronellal

106-23-0

methyl anthranilate carbon dioxide

134-20-3 124-38-9

source Acros Organics Acros Organics Airgas

0.99b

GCc

0.99

GCc

N

∑ |di|

(2)

i=1

3. RESULTS AND DISCUSSION Figure 2 shows the solubility of citronellal in SC-CO2 as a function of temperature and pressure. In terms of mole fraction,

GC−MSd

0.999995

a

1 N

where di is the difference between the measured and calculated values, and N is the number of the data points.

analysis method

mass fraction puritya

−ln Pc − 5.92714 + 6.09648θ −1 + 1.28862 ln θ − 0.169347θ 6 15.2518 − 15.6875θ −1 − 13.4721ln θ + 0.43577θ 6

b

No additional purification was applied to the chemicals. The purity was tested and reported on Certificate of Analysis (Acros Organics, Belgium). cGas chromatography. dGas chromatography−mass spectrometry.

Some critical properties of citronellal, MA, and carbon dioxide are shown in Table 2. HPLC-grade hexane (purity > 997 g· kg−1, Fisher Scientific, Fair Lawn, NJ) was used as the flushing solvent for sample analyses. Apparatus and Procedure. The solubility measurements of citronellal in SC-CO2 were conducted in the pressure range of (9.1 to 14.2) MPa at (313.15 and 333.15) K. The static equilibrium system and detailed procedure for the composition analysis were shown in our previous study.7,10 Briefly, citronellal was loaded in a view cell inside the static equilibrium system. Carbon dioxide was then introduced into the cell until the desired pressure was reached. The operating temperature was controlled by proportional controllers and circulation fans to an accuracy of ± 0.3 K. During solubility measurements, the fluid and liquid phases coexisted and were recirculated in independent loops driven by a magnetic pump for 2 h to attain the phase equilibrium. The fluid and liquid phases in different loops were sampled in separate expansion vessels for composition analyses using the gravimetrical method.

Figure 2. Solubilities of citronellal in SC-CO2 at different temperatures and pressures obtained with the static equilibrium system: ●, 313.15 K; ▲, 333.15 K.

the solubility data obtained at 313.15 K were found to be four to eight times higher than those at 333.15 K in the pressure

Table 2. Physical Properties of Carbon Dioxide, Citronellal, and MA

a

compound

molecular weight

boiling point (K)

critical temperaturea, Tc (K)

critical pressureb, Pc (MPa)

acentric factorc, ω

CO2 citronellal MA

44.01 154.25 151.16

194.7 479.15 529.15

304.25 664.95 725.75

7.4 2.7 3.6

0.225 1.004 0.577

Estimated by the Ambrose group contributions.23 bEstimated by the Ambrose group contributions.23 cEstimated by the Lee and Kesler equation.13 183



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phase. Consequently, the higher solubility of citronellal was observed at higher temperature when the density of SC-CO2 was maintained constant. This enhanced solubility of citronellal in SC-CO2 at higher temperature was also consistent with the solubility reported for flurbiprofen and δ-tocopherol in SCCO2.14,15 Figures 4 and 5 are the binary phase diagrams of citronellal and SC-CO2, presented as SC-CO2 mole fractions at (313.15

ranging from (9 to 14) MPa. The solubility of a solute in a SCF is mainly influenced by two major factors: the vapor pressure of the solute, which is exponentially related to the absolute temperature, and the solvating effect of the fluid, which is controlled by its density. With increase in temperature, the solubility around the lower pressure region decreases when the solvent density falls, reducing the solvating effect to a lower degree than is compensated for by the enhancement of vapor pressure of the solute.7 As a result, the density of SC-CO2 decreasing with rising temperature from (313.15 to 333.15) K is considered to be the dominant factor that affects solubility behavior of citronellal in SC-CO2. Solubility Correlations. In Figure 3, the solubility data of citronellal are correlated with SC-CO2 density using the

Figure 4. Binary phase equilibrium solubility data for citronellal and SC-CO2 in the fluid and liquid phases at 313.15 K: ⧫, fluid phase; , PR EOS in fluid phase; ●, liquid phase; --- , PR EOS in liquid phase.

Figure 3. Solubility correlation of citronellal with SC-CO2 density using the Chrastil equation at (313.15 and 333.15) K: ●, solubility of citronellal at 313.15 K; , Chrastil regression of citronellal at 313.15 K; ▲, solubility of citronellal at 333.15 K; --- , Chrastil regression of citronellal at 333.15 K.

Chrastil equation. This model is based on the assumption that one molecule of a solute and several molecules of a fluid form a solvato complex in equilibrium.11 The points are the experimental solubility data of citronellal in SC-CO2. The solid and dashed lines represent the calculated solubility at (313.15 and 333.15) K, respectively. As with many solutes, a log−linear relationship is observed between the solubility of citronellal and SC-CO2 density. The saturated solubility of citronellal in SCCO2 was reached during the static solubility measurements at different temperatures and pressures. The R2 value is 0.98, which means that the data at (313.15 and 333.15) K were both well correlated with SC-CO2 density. As for the equation constants, k is 4.5, c1 is −361 and c0 is −22.5. The predictive model of citronellal solubility in SC-CO2 was successfully established within the range of temperatures and pressures studied. As shown in Figure 3, the solubility of citronellal at 333.15 K was slightly higher than that at 313.15 K for the same SC-CO2 density. The enhancement of vapor pressure of citronellal with rising temperature allowed more citronellal molecules to evaporate into the fluid phase. As expected, the viscosity of SC-CO2 also decreased with elevation of temperature, which made citronellal molecules diffuse more easily into the fluid

Figure 5. Binary phase equilibrium solubility data for citronellal and SC-CO2 in the fluid and liquid phases at 333.15 K: ⧫, fluid phase; , PR EOS in fluid phase; ●, liquid phase; ---, PR EOS in liquid phase.

and 333.15) K, respectively. PR EOS was employed for the solubility correlation of citronellal in SC-CO2. An open-endedtop saturation loop is also observed in both phase equilibria. Hence, the fluid and liquid phases coexist for all pressures in the range studied. They may become one homogeneous phase at higher pressures. The fluid−liquid phase equilibrium data of citronellal in SC-CO2 are presented in Table 3. The attraction pressure in PR EOS is adjusted by the molar volume and van der Waals covolume. PR EOS is reasonably suited for an asymmetric binary system.16 The experimental 184



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Panagiotopoulos and Reid mixing rule. A predictive solubility model of citronellal in SC-CO2 was successfully developed. In both diagrams, the rising pressure results in a lower mole fraction of SC-CO2 in the fluid phase, indicating that more citronellal molecules were dissolved in this phase, due to the enhanced solvent power of SC-CO2. The mole fraction of SCCO2 in the liquid phase increased, which means that more SCCO2 molecules were carried into the solute-rich phase. The increasing solubility of SC-CO2 in the liquid phase with the elevation of pressure could be described using the Krichevsky− Ilinskaya (KI) equation and Henry’s constant.18 Similar phase equilibrium phenomena have also been reported for the solubility measurements of fish oil ethyl esters, fatty acids, and triglycerides in SC-CO2.19,20 Model Comparison. The average absolute deviations (AADs) of the solubility correlation using the Chrastil equation and PR EOS are shown in Table 4. The AAD values of the solubility correlations at 333.15 K are similar. The AAD value of the Chrastil correlation at 313.15 K was higher than that of the PR EOS correlation, but it was still within the acceptable accuracy (≤0.05). Overall, both models provided good solubility prediction of citronellal in SC-CO2. The Chrastil equation is a direct and simple method to predict the solubility of a solute in SC-CO2, but this model lacks sound theoretical basis. The solubility correlation by using PR EOS is often more challenging because it requires complex computations and physical property values that are not readily available in the literature.7 Molecular Effects on the Solubility Behavior of Solutes in SC-CO2. Figures 6 and 7 show solubility

Table 3. Fluid−Liquid Phase Equilibrium Data of Citronellal in SC-CO2 Obtained Using the Binary Static Equilibrium Systema citronellal (mole fraction)b pressure (MPa)

fluid phase (YF)

liquid phase (YL)

40 °C 0.051 0.047 0.056 0.061 0.070 0.064 0.078 0.081 0.091 0.098 60 °C 0.009 0.013 0.022 0.028 0.037 0.038 0.041 0.058 0.058

9.13 9.17 9.21 9.52 9.70 9.71 10.15 10.94 11.51 11.87 10.25 10.92 11.94 12.64 12.63 12.95 13.00 13.48 13.93

0.257 0.279 0.258 0.242 0.234 0.242 0.224 0.208 0.195 0.179 0.333 0.326 0.306 0.289 0.264 0.279 0.229 0.237 0.224

a Standard uncertainties u for temperature T and pressure P are u(T) = 0.3 K and u(P) = 0.05 MPa. bStandard uncertainties u for citronellal are u(YF) = 0.006 and u(YL) = 0.01.

solubility data were correlated with the critical properties of citronellal and SC-CO2 presented in Table 2. The Panagiotopoulos and Reid mixing rule was applied to improve the accuracy of computing the fugacity coefficient in the fluid phase using equations of state. It has been shown that this mixing rule provides less correlation deviation when used with PR EOS.17 Two binary interaction parameters (kij and kji) were needed for this mixing rule. In this study, kij and kji were −0.001 and 0.0496, respectively. The subscript “i” meant SC-CO2 and “j” meant citronellal. The goodness of fit was evaluated by calculating average absolute deviation (AAD), as shown in Table 4. The AAD values in our study were much less than the reported values by Lee and Lee (1998).4 The experimental solubility data were well correlated using PR EOS with the Table 4. Average Absolute Deviations (AADs) of the Solubility Correlations of Citronellal Using the Chrastil Equation and PR EOS

Figure 6. Solubility comparison of citronellal and MA in SC-CO2 at 313.15 K: ●, solubility of citronellal at 313.15 K; , Chrastil regression of citronellal at 313.15 K; ▲, solubility of MA at 313.15 K; ---, Chrastil regression of MA at 313.15 K.

AADa 313.15 K Chrastil equation Peng−Robinson EOS a

333.15 K

fluid

liquid

fluid

liquid

0.013 0.008

NAb 0.007

0.014 0.011

NAb 0.005

comparison of citronellal and methyl anthranilate (MA) in SC-CO2 at (313.15 and 333.15) K, respectively, using the Chrastil model. The solubility of citronellal was found to be three to four times higher than that of MA. Under comparable operating conditions of (10.1 to 14.2) MPa and (313.15 to 333.15) K, SC-CO2 density and the vapor pressures of the solutes would not be the dominant factors to account for the observed solubility differences. Citronellal and MA possess different molecular structures with similar molecular weights. As shown in Figure 1, citronellal is a linear molecule and MA contains an aromatic ring. Table 2

Averag absolute deviation:

AAD = b

1 N

N

∑ |di| i=1

NA: not available. 185



Article

Figure 7. Solubility comparison of citronellal and MA in SC-CO2 at 333.15 K: ●, solubility of citronellal at 333.15 K; , Chrastil regression of citronellal at 333.15 K; ▲, solubility of MA at 333.15 K; ---, Chrastil regression of MA at 333.15 K.

Figure 8. Binary phase equilibrium solubility data for citronellal + SCCO2 and MA + SC-CO2 at 313.15 K: ◇, fluid phase of MA; ◆, liquid phase of MA; ---, PR EOS for MA; △, fluid phase of citronellal; ▲, liquid phase of citronellal; , PR EOS for citronellal.

shows the acentric factors computed for citronellal (ω = 1.004) and MA (ω = 0.577). The larger ω value of citronellal suggests it is more asymmetric than MA. Generally, asymmetric molecules in a liquid rotate more freely and move further apart on average, as temperature rises. Their intermolecular binding energy is therefore reduced and they pass more easily into the gas or fluid phase. Thus, the vapor pressure will rise more rapidly for asymmetric molecules than for spherically symmetric molecules.21 This theory of molecular asymmetry would justify the measured solubility difference between citronellal and MA in SC-CO2. Constants of the Chrastil equation for citronellal and MA are also compared in Table 5. In the Chrastil equation, constant k Table 5. Constants of the Chrastil Equation for Solubility Correlations of Citronellal and MA

a

compound

ka

c1 a

c0 a

citronellal MA

4.5 4.8

−361 −1165.9

−22.5 −19.2

Figure 9. Binary phase equilibrium solubility data for citronellal + SCCO2 and MA + SC-CO2 at 333.15 K: ◇, fluid phase of MA; ◆, liquid phase of MA; ---, PR EOS for MA; △, fluid phase of citronellal; ▲, liquid phase of citronellal; , PR EOS for citronellal.

ln C = k·ln ρ + c1/T + c0.

represents an averaged equilibrium association number, which is a characteristic constant for a given fluid-solute equilibrium system. Citronellal and MA have similar k values, which means that both possess comparable affinity for SC-CO2. Constant c1 is defined as ΔH/R, where ΔH is the enthalpy of vaporization and salvation of a solute and R is the ideal gas constant. Constant c0 is dependent on the molecular weights of the solute and solvent. The values of c0 for citronellal and MA are comparable because their molecular weights are also similar. Calculated from the c1 values for citronellal and MA, the enthalpy of citronellal (−43.42 J·mol−1) is larger than the enthalpy of MA (−140.23 J·mol−1). This may suggest that the vaporization enthalpy of citronellal is larger than MA, resulting in the higher solubility of citronellal in SC-CO2. Similar results have been reported by Anderson et al. (2001).22 The critical properties of citronellal, MA, and carbon dioxide are listed in Table 2 for the PR EOS correlations. In Figures 8 and 9, the phase equilibrium solubilities of citronellal in SCCO2 are compared with the solubilities of MA in SC-CO2 at (313.15 and 333.15) K, respectively. The operating pressure for

citronellal to reach the critical homogeneous phase is consistently lower than that for MA due to the higher solubility of citronellal in SC-CO2. Deviations of the solubility correlations with PR EOS are presented in Table 6. The AAD values for the solubility correlations of both compounds indicate acceptable accuracy (≤0.05). It means that PR EOS provided good predictions for the solubilities of citronellal and MA in SC-CO2.

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CONCLUSIONS Solubility measurements of citronellal in SC-CO2 were successfully conducted using the static equilibrium system. The solubility of citronellal was found to have a linear relationship with SC-CO2 density as suggested by the Chrastil equation. The solubility data were also well correlated using PR EOS. Both models presented good accuracy with the AAD values of less than 0.05. 186



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(8) Saleh, M. M.; Hashem, F. A. E. M.; Glombitza, K. W. Study of Citrus taitensis and radical scavenger activity of the flavonoids isolated. Food Chem. 1998, 63, 397−400. (9) Edlich, R. F.; Winters, K. L.; Lim, H. W.; Cox, M. J.; Becker, D. G.; Horowitz, J. H.; Nichter, L. S.; Britt, L. D.; Long, W. B. Photoprotection by sunscreens with topical antioxidants and systemic antioxidants to reduce sun exposure. J. Long-Term Eff. Med. Implants 2004, 14, 317−340. (10) Yu, Z. R.; Rizvi, S. S. H. Phase equilibria of oleic acid, methyl oleate, and anhydrous milk fat in supercritical carbon dioxide. J. Supercrit. Fluids 1992, 5, 114−122. (11) Chrastil, J. Solubility of solids and liquids in supercritical gases. J. Phys. Chem. 1982, 86, 3016−3021. (12) Peng, D. Y.; Robinson, D. B. A new two-constant equation of state. Ind. Eng. Chem. Fundam. 1976, 15, 59−64. (13) Lee, B. I.; Kesler, M. G. A generalized thermodynamic correlation based on three-parameter corresponding states. AIChE J. 1975, 21, 510−527. (14) Duarte, A. R. C.; Coimbra, P.; Sousa, H. C. d.; Duarte, C. M. M. Solubility of flurbiprofen in supercritical carbon dioxide. J. Chem. Eng. Data 2004, 49, 449−452. (15) Pereira, P. J.; Coto, B.; Menduiña, C.; Azeved, E. G. d.; Ponte, M. N. d. High pressure phase equilibrium for δ-tocopherol+CO2. Fluid Phase Equilib. 2004, 216, 53−57. (16) Yu, Z. R., Phase equilibria and enzymatic esterification of anhydrous milk fat in supercritical carbon dioxide. Ph.D. Dissertation, Cornell University: Ithaca, N. Y., 1992. (17) Rodrigues, J. E.; Araújo, M. E.; Azevedo, F. F. M.; Machado, N. T. Phase equilibrium measurements of Brazil nut (Bertholletia excelsa) oil in supercritical carbon dioxide. J. Supercrit. Fluids 2005, 34, 223− 229. (18) Lee, M. J.; Chen, W. S.; Lin, H. m. Isothermal vapor-liquid equilibria for binary mixtures of carbon dioxide with hexyl acetate, cyclohexyl acetate, or phenyl acetate at elevated pressures. J. Chem. Eng. Data 2001, 46, 1410−1414. (19) Riha, V.; Brunner, G. Phase equilibrium of fish oil ethyl esters with supercritical carbon dioxide. J. Supercrit. Fluids 1999, 15, 33−50. (20) Bharath, R.; Yamane, S.; Inomata, H.; Adschiri, T.; Arai, K. Phase equilibria of supercritical CO2-fatty oil component binary systems. Fluid Phase Equilib. 1993, 83, 183−192. (21) Clifford, T. A single substance as a supercritical fluid. In Fundamentals of Supercritical Fluids; Oxford University Press: New York, 1999. (22) Andersen, W. C.; Sievers, R. E.; Lagalante, A. F.; Bruno, T. J. Solubilities of cerium(IV), terbium(III), and iron(III) beta-diketonates in supercritical carbon dioxide. J. Chem. Eng. Data 2001, 46, 1045− 1049. (23) Klincewicz, K. M.; Reid, R. C. Estimation of critical properties with group contribution methods. AIChE J. 1984, 30, 137−142.

Table 6. Deviations of Solubility Correlations of Citronellal and MA Using PR EOS AADa 313.15 K citronellal MA a

333.15 K

fluid

liquid

fluid

liquid

0.008 0.005

0.007 0.007

0.011 0.003

0.005 0.005

Average absolute deviation: AAD =

1 N

N

∑ |di| i=1

At comparable operating conditions, the solubility of citronellal in SC-CO2 was found to be three to four times higher than that of MA. The linear structure of the citronellal molecule enhanced its solubility in SC-CO2 more than the aromatic structure of the MA molecule, owing to the higher molecular asymmetry of citronellal than MA. It suggests that molecular asymmetry of a solute plays an important role in its solubility in SC-CO2. The acentric factor is a good indicator for molecular asymmetry of a solute and can provide a preliminary estimate on a solute’s behavior in SC-CO2. On the basis of the Chrastil equation, the enthalpy required for citronellal solubilization was three to four times higher than that for MA, which also supports the fact that citronellal is more soluble in SC-CO2 than MA. Understanding their solubility behaviors in SC-CO2 is critical to facilitate the development of efficient SC-CO2 systems for extraction and fractionation of bioactive compounds from natural matrices.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +1 607 255 7913. Fax: +1 607 254 4868. E-mail: ssr3@ cornell.edu. Notes

The authors declare no competing financial interest.

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REFERENCES

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Measurement and Correlation of Citronellal and Methyl Anthranilate

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