Effects of Several Variable Factors on the Isotope Ratio by HRGC-MS

Abstract

In the isotope ratio (Ir) analysis using GC-MS, several variable factors in sampling incidental to any food analysis were investigated for yuzu fruit. The Irs of ten monoterpene hydrocarbons in yuzu essential oils from each of six fruiting positions of three trees were measured. The sign test following t-test of all the Ir values demonstrated that there was no significant difference between both sampling years of 2001 and 2002. There was also no significant variation in the Ir values among the three trees and six fruiting positions in the individual two years.Key words: isotope ratio analysis; sampling variations; HRGC/MS; monoterpene hydrocarbon A determination of the isotope values of constituents is gaining increasing importance, especially in view of the increased demand in the fragrance and food industries for the authenticity control and origin determination of the production of essential oils and foods.1-3) Recently, many sensational articles have been reported on dishonest designations of raw foods, since the JAS (Japanese Agricultural Standards) were revised on July 2000. The authors 4) have developed a specific and convenient method for characterization of yuzu (Citrus junos Tanaka) fruits produced in different districts by the isotope ratio of monoterpene hydrocarbons with HRGC-MS. This method will be applicable to several cases such as differentiation of the quality, evaluation of genuineness of vegetable products from various producing districts, and classification of the species. It is noticed that this analytical method will be useful for chemical evaluation of agricultural products, in addition to DNA analysis. 5,6) The authors 7,8) have also reported successful results on the discrimination of commercial citrus essential oils of different origins, and the accuracy of the Ir method using 13 C-labeled compounds. There remain, however, some questions about samplings from the fundamental scope. In order to normalize this method, the variations or individual differences which each material substantially owns should be further investigated. This paper concerns the effects of variable factors involved in fruit samples regarding the isotope ratio analysis.Three yuzu trees (13-to 15-years age) were selected at random among a number of yuzu trees under the usual cultivation in the field of Kochi Fruit Tree Experimental Station, Kochi. The experiments were done from the following three viewpoints: (1) 9) The yield of CPO was 0.10-0.16 g/100 g of fresh fruit, and 0.34-0.59 g/100 g of flavedo. Each CPO sample was kept at À25 C until needed for analysis. Gas chromatography-mass spectrometry (GC-MS) was done with a Shimadzu GC-17A linked to a Shimadzu QP-5000. The GC column was a DB-Wax fused silica capillary (60 m  0.25 mm i.d., 0.25 m film thickness; J & W Scientific, Folsom, CA, U.S.A.) The analytical conditions of GC-MS and column temperature were the same as those of the previous paper.4) The isotope ratio (Ir) of the selected monoterpene hydrocarbons in CPO, m=z 137/136, was measured by selected-ion m...

MS Fragment Isotope Ratio Analysis for Evaluation of Citrus Essential Oils by HRGC-MS

“…Each component was initially identified by the GC retention index and the NIST library connected to the QP-5050 mass spectrometer, as described in previous papers. 12,13) Measurement of the MS fragment ratio. The MS fragment ratio was measured using the isotope ratio measurement method described in previous papers.…”

“…The MS fragment ratio was measured using the isotope ratio measurement method described in previous papers. [10][11][12] Selective ion monitoring (SIM) of GC-MS was done in order to estimate the intensities of ion peaks of each major MS fragments (m=z ¼ m) and of its þ1 fragment peaks (m=z ¼ m þ 1). The MS fragment ratio of each peak was calculated using the following equation:…”

“…Regarding the volatile compounds from food materials, this fragmentation analysis has been first done. These results suggest that in addition to enantiomeric analysis 14,15) and isotope ratio analysis of the molecular ion peaks on mass spectra, [10][11][12] this technique for MS fragment isotope ratio analysis can provide diverse information on the evaluation of natural essential oils. This technique is also applicable to the compounds of which peaks on gas chromatograms are very small or a molecular ion peak on a mass spectrum is not detectable.…”

“…10,11) Furthermore, it was statistically demonstrated that this method was not affected by such variations as sampling years, trees, and fruiting positions as long as the plants were grown under set conditions. 12) However, it is often difficult to measure the isotope ratio by ordinary GC-MS when the molecular ion peak is very small or not detected. In GC-IR-MS specialized for the measurement of isotope ratios, the value is determined as the whole molecule isotopic ratio.…”

Characterization by GC–MS of Vietnamese Citrus Species and Hybrids Based on the Isotope Ratio of Monoterpene Hydrocarbons

“…The isotope fingerprint of Japanese yuzu (Citrus junos Tanaka) essential oil has also been established as a result of various studies. [7][8][9] Citrus fruits are among the most easily hybridized species. It is natural that the composition of citrus essential oils often varies according to species, variety, ripening stage, growing place and other conditions.…”