102nd AOCS Annual Meeting & Expo Validation of Quantitative Method for Glycidol Fatty Acid Esters (GEs) in Edible Oils Hiroki Shiro, Naoki Kondo and Yoshinori Masukawa * Tochigi Research Labs Kao corporation Japan May 3, 2011
Summary In response to great concerns on contaminants, GEs, in edible oils, we developed a new method for quantification of GEs in edible oils (J. Oleo Sci. 58: 81-88, 2010, J. Am. Oil Chem. Soc. 88: 15-21, 2011 and Euro. J. Lipid Sci. Technol. 113: 356-360, 2011). In this study, we changed mobile phase composition to avoid overlapping C18:1-GE with a contaminant peak. Herein, the validation data of the final method is presented. The study demonstrates that this method is sufficiently accurate and simple under practical use situations.
100 mg The First Method (JOS) Pretreatment Edible oil GE-rich fraction Dispersed in acetonitrile Reversed-phase SPE using acetonitrile Normal-phase SPE using chloroform Time: half day Fast HPLC under linear gradient Single quadruple MS (positive APCI, SIM) ODS column for UPLC LC-MS quantification Run: 17 min Total: 40 min
The Second Method (JAOCS) Pretreatment 1 g 10 mg Edible oil GE-rich fraction Dissolved in chloroform /acetone Reversed-phase SPE using acetonitrile Normal-phase SPE using chloroform Time: half day Conventional HPLC under linear gradient Single quadruple MS (positive APCI, SIM) ODS column for HPLC LC-MS quantification Run: 17 min Total: 35 min
The Third Method (EJLST) Edible oil Pretreatment 1 g 10 mg External STD or Internal STD GE-rich fraction Dissolved in TBME/ethyl acetate Reversed-phase SPE using MeOH Normal-phase SPE using haxane/ethyl acetate Time: 3 h Conventional HPLC under step gradient (A: MeOH, B: IPA) Single quadruple MS (positive APCI, SIM) ODS column for HPLC LC-MS quantification Run: 5.5 min Total: 22 min
Appearance of Contaminant Peak A contaminant peak sometimes appeared in the chromatogram with almost same retention time and m/z as C18:1-GE. SPE column Manifold Vial stop valve (PP) disposable liner (PTFE) cushion (partially PP) Contaminants seemed to be mainly derived from plastic implements.
Appearance of Contaminant Peak contaminant SPE column only solvent (blank) stop valve (PP) almost same retention time with C18:1-GE m/z 339.4 Fig. Chromatogram for blank SPE treatment If only glass implements are used in the experiment, there are no problems. However, the method should be revised from the standpoint of universal usage.
Improvement of LC conditions We improved the mobile phase A, MeOH into water/meoh = 8/92 (v/v) to separate C18:1-GE with the contaminant. m/z 313.5 C16:0-GE m/z 335.4 C18:3-GE C18:2-GE m/z 337.4 m/z 339.4 C18:1-GE +contaminant C18:1-GE contaminant m/z 34 C18:0-GE 5.5 min 25 min Mobile phase A; MeOH Water/MeOH = 8/92 (v/v)
Materials and Methods Standards C16:0-GE (purity 99.3%) Wako Pure Chemical Industries C18:0-GE (purity 97.6%) Tokyo Chemical Industry C18:1-GE (purity 99.8%) Wako Pure Chemical Industries C18:2-GE (purity 99.2%) Wako Pure Chemical Industries C18:3-GE (purity 99.4%) Wako Pure Chemical Industries Test Oils Sample-A (Olive, liquid at RT, GE free) TAG 97.8%, DAG 2.0%, MAG 0.2% Sample-B (Palm, solid at RT) TAG 95.2%, DAG 4.8%, MAG 0.0% Sample pretreatment preparation Same as a procedure published in EJLST. LC-MS conditions Mobile phase: (A) Water/MeOH = 8/92, (B) 2-propanol Gradient: 0 min A100% 18 min A100% 18.1 min A0% 25 min A0% 25.1 min A100% 35 min A100% Except the above, same as a procedure published in EJLST.
Chromatogram of Standard GEs m/z 313.5 C16:0-GE m/z 335.4 C18:3-GE Abundance [x10 3 ] m/z 337.4 m/z 339.4 C18:2-GE C18:1-GE m/z 34 C18:0-GE 0 6 12 18 min Fig. Standard Chromatograms of 100 ng/ml GEs.
Chromatogram of GEs in Sample-A m/z 313.5 C16:0-GE m/z 335.4 C18:3-GE Abundance [x10 3 ] m/z 337.4 m/z 339.4 C18:2-GE C18:1-GE m/z 34 Fig. Chromatograms of GEs in Sample-A (Olive oil) C18:0-GE 0 6 12 18 min
Chromatogram of GEs in Sample-B m/z 313.5 C16:0-GE Abundance [x10 3 ] m/z 335.4 m/z 337.4 m/z 339.4 C18:3-GE C18:2-GE C18:1-GE m/z 34 C18:0-GE 0 6 12 18 min Fig. Chromatograms of GEs in Sample-B (Palm oil)
Performance of LC-MS Table Percentage of relative standard deviation (RSD%) during consecutive runs, limit of detection (LOD), limit of quantification (LOQ), and calibration line obtained for standard GEs C16:0-GE C18:0-GE C18:1-GE C18:2-GE C18:3-GE RSD% a LOD b LOQ b Calibration line c GE R.T. Area (ng/ml) (ng/ml) Equation R 2 0.10 0.18 0.15 0.11 0.087 1.9 3.3 4.2 4.9 3.3 0.23 0.19 0.26 0.19 0.25 0.76 0.63 0.87 0.63 0.84 y = 1600x - 20 y = 1300x - 730 y = 1600x + 1600 y = 1500x + 3400 y = 1400x - 100 0.9999 0.9995 0.9998 0.9997 0.9999 a Obtained by six consecutive runs of the standard GE solution at a concentration of 100 ng/ml. b Defined as S/N = 3 for LOD and 10 for LOQ based on 20 µl injection of the standard GE solution at a concentration of 5 ng/ml. c Calculated from the equation y = Ax + B, where x is the injected concentration (ng/ml), y is the each standard peak area, A is the slope, and B is the intercept in the range between 5 and 200 ng/ml (5,10, 50, 100 and 200 ng/ml). The LC-MS method was demonstrated to be reproducible, high-sensitive and calibration-linear for standard GEs.
Accuracy Table Levels of GEs in commercial edible oils and recovery test Levels [mg/kg] a Recovery% a Edible oil GE Mean ± S.D. RSD% Mean ± S.D. RSD% Sample-A C16:0-GE < 0.5-99.5 ±6.9 6.9 C18:0-GE < 0.5-99.9 ±6.4 6.4 C18:1-GE < 0.5-94.8 ±6.2 6.6 C18:2-GE < 0.5-101.7 ±6.3 6.2 C18:3-GE < 0.5-102.2 ±4.5 4.4 Sample-B C16:0-GE 7.5 ±0.26 3.4 10 ±5.0 4.9 C18:0-GE 1.2 ±0.031 2.6 100.2 ±5.9 5.9 C18:1-GE 13.5 ±0.22 1.7 106.0 ±8.7 8.2 C18:2-GE 4.2 ±0.093 2.2 105.4 ±7.1 6.8 C18:3-GE < 0.5-109.0 ±0.63 0.58 a Analyzed in triplicate. Each standard 10µg was added in 1g edible oil. The recovery% values were sufficient enough to use (95-109%).
Comparison of new method and EJLST Table Levels of GEs in Sample-B (Palm oil) obtained by new method and EJLST Levels [mg/kg] a Levels [mg/kg] a new method EJLST GE Mean ±S.D. RSD% Mean ± S.D. RSD% C16:0-GE 7.5 ±0.26 3.4 8.4 ±0.23 2.8 C18:0-GE 1.2 ±0.031 2.6 1.2 ±0.015 1.2 C18:1-GE 13.5 ±0.22 1.7 12.4 ±0.059 0.47 C18:2-GE 4.2 ±0.093 2.2 3.6 ±0.025 0.71 C18:3-GE < 0.5 - < 0.5 - a Analyzed in triplicate. Quantitative levels derived from this new method were comparable with those derived from the EJLST one.
Conclusion The mobile phase A composition was changed from MeOH into water/meoh = 8/92 (v/v) in order to separate C18:1-GE with a peak contaminated from plastic implements. The validation data, such as LOD, LOQ, linearity, recovery% and actual levels in edible oils under modified LC conditions, were comparable with those published in EJLST, implying that this method can be used as a quantitative one. This method can be used as a globally standardized one, because of its accuracy and simplicity.
We wish to express our appreciation to, Dr. Tatsushi Wakisaka of Kao Corporation Ms. Takeko Takada Dr. Yoshihisa Katsuragi of Kao Corporation Mr. Naoto Kudo of Kao Corporation Mr. Koichi Yasunaga of Kao Corporation Dr. Nobuyoshi Suzuki of Kao Corporation Mr. Naoki Ooi of Kao Corporation Mr. Nobuyuki Kibune of Japan Food Res Labs. Thank you for your attention!