用从国际原子能机构溯源得到的橄榄油标准物质［Cat No.B 2172-Batch 3130,其δ13CPDB为(-28.51±0.16)‰］作标准,应用稳定同位素比质谱法测定了苹果和苹果汁的δ13C值,并以此确定国产苹果的δ13C值的范围和鉴定制成的果汁的质量。苹果样品去皮后切碎,打成糊状,离心后取其上清液,在75 ℃加热2~3 h至呈黏稠状液体,冷却至室温。此时其糖度约为70 Brix。浓缩苹果汁样品是黏稠液体,其糖度一般也在70 Brix左右。取2 μL上述样品置于锡杯中,按方法处理后供质谱分析。标准物质的进样量为2 μL。按所测得碳的稳定同位素13C与12C的比值代入所给公式计算δ13C值。结果表明:方法的精密度较好,其相对标准偏差(n=11)均小于0.021%。根据测定结果发现,我国苹果的δ13C值在-29.1‰~-23.33‰之间。

The reference standard selected is traceable to the CRM of olive oil ［Cat. No.B 2172, Batch 3130, with its δ13C value (vs. PDB) of (-28.51±0.16)‰］ obtained from IAEA and the stable isotopes ratio mass spectrometry was used for the determination of δ13C of apple pulp and apple juice, on the base of which the range of δ13C values of apples produced in our country was determined and the quality of apple juice produced was appraised. The apple sample was peeled and the pulp was sliced and made into paste. After centrifuging, the supernatant was taken and heated at 75 ℃ for 2-3 h to condense it to a syrupy state, having its Brix degree of about 70. In general, the sample of apple juice concentrate was in syrupy state and having its Brix degree of around 70. Two μL of either of the above samples, as well as 2 μL of the olive oil standard were taken and placed in tin cups separately for MS analysis. Values of ratio of the stable isotopes of 13C and 12C were substituted into the given formula and the values of δ13C were calculated. Precision was tested and values of RSD′s (n=11) obtained were all less than 0.021%. The range of δ13C values for apples grown in various origin in our country was between -29.17‰ and -23.33‰.