Fatty Acid Composition in Ergosteryl Esters and Triglycerides from the Fungus Ganoderma lucidum

Free and esterified ergosterols are detected almost solely in fungi and are often employed as a biomarker of living fungi. In this work, the fatty acid composition and δ¹³C values of major fatty acids in triglycerides and ergosteryl esters from the fungus Ganoderma lucidum were analyzed by gas chromatography–mass spectrometer and gas chromatography–isotopic ratio mass spectrometer, respectively. The results showed that the fatty acid profiles varied in triglycerides and ergosteryl esters. The percentage of saturated fatty acids in ergosteryl esters was remarkably higher than that in triglycerides, where C_18:1^Δ9c was the predominant fatty acid and constituted 61.26 % of the total fatty acids. In contrast, C_16:0 was the predominant fatty acid and constituted 71.88 % of the total fatty acids in ergosteryl esters. The study suggests that, after fungal death, free ergosterols in the cell membrane of the dead fungus were esterified with preferentially saturated fatty acids, mainly C_16:0, from triglycerides and then stored in lipid particles for a longer period while free ergosterol markedly decreased. The δ¹³C values of C_16:0, C_18:0, C_18:1 and C_18:2 in ergosteryl esters exhibit a pronounced depletion in ¹³C compared with that in triglycerides within the range of ?1.3 to ?0.9 ‰, supporting the above inference. It is again suggested that free ergosterol in the cell membrane should be used as an indicator of living fungi, and ergosteryl esters in the lipid particles should not be included in the measurement of living fungal biomass.     

Tissue turnover in ovine muscles and lipids as recorded by multiple (H,C, O,S) stable isotope ratios

Multiple stable isotope ratios (δ²H, δ¹³C, δ¹⁸O and δ³⁴S) were measured in muscle, muscle lipids and lipid fractions collected from 28 lambs, subjected to a diet-switch and raised on two energy allowances (EAs), to determine tissue turnover and diet-tissue fractionation. The diet-muscle fractionations prior to the diet-switch were estimated to be −44.0‰, +1.9‰ and 0‰ for H, C and S, respectively, while the drinking water was demonstrated to be the main source of muscle O and thus δ¹⁸O variation. The diet-intra-muscular lipid fractionations prior to the diet-switch were estimated to be −172.7‰, −1.3‰ and −11.5‰ for H, C and O, respectively. The C half-lives of muscle were determined to be 75.7 and 91.6 days for animals receiving the high and low EA, respectively. Extracting temporally resolved pre-slaughter dietary information from meat by analysing bulk muscle, muscle lipids and muscle lipid fractions appeared to be not practicable due to possible incomplete turnover of lipids.     

PreCon-IRMS测定土壤游离氨基酸态氮稳定同位素丰度

土壤氮大部分为有机氮,大分子类有机氮-蛋白质转化成可溶性氨基酸态氮是土壤氮循环的关键过程和土壤氮素有效性的主要限制因子,其中氨基酸态氮消耗速率在研究土壤肥力、生物机制等方面有着重要的指示作用.本研究建立了一种蒸馏结合化学转化N2 O产生法的氨基酸态氮稳定同位素丰度测定前处理方法,并结合气体预浓缩装置与稳定同位素质谱仪(...     

碳-4植物糖超标蜂蜜样品的多维分析

本文从124份市面蜂蜜样品中筛选出21份C-4植物糖超标蜂蜜样品,应用元素分析-同位素质谱联用技术（EA-IRMS）、液相色谱-同位素质谱联用技术（LC-IRMS）、液相色谱测定蜂蜜还原糖含量等检测方法,对C-4植物糖超标蜂蜜样品进行多维分析。结果表明：C-4植物糖超标样品在市面上仍占有一定比例,本批次检出超标率为16.94%,且存在少量严重超标样品,最高达到82.35%。C-4植物糖超标蜂蜜样品大致可归纳为以下三类：一是源于生产操作不规范的轻微超标型,该类样品的碳-4植物糖含量为7~10%之间,△δ13CF-G、△δ13Cmax跟真实蜂蜜要求相差不远;二是人为掺入碳-4植物源淀粉转化产物型,该类样品寡糖含量较高,△δ13Cmax较大。三是人为掺入碳-4植物源果葡糖浆型,该类样品本身不含寡糖,δ13CF、δ13CG完成丧失碳-3植物特征。     

Stable carbon isotope content in ethanol of EC data bank wines from Italy, France and Germany

In the present work we discuss the usefulness of carbon isotope analysis of wine ethanol for the assignment of origin and the proof of adulteration of Italian, French and German wines. At first the comparability of the results from three laboratories is demonstrated by the results of inter-laboratory comparison measurement and by tests of the distillation procedures applied to the same samples. Furthermore, a close correlation of carbon isotope content in sugars from must and ethanol from the related wine could be found for samples from all countries. Using the ¹³C values of EC data bank wines from 1991 to 1993 for Italy, France and Germany, we describe and discuss the main factors of influence which are responsible for the variation of those values. By examination of spiked samples, the usefulness of the ¹³C analysis in the detection of certain types of wine enrichment is demonstrated; especially if the carbon isotope analysis by¹³C-8 isotope ratio mass spectrometry is employed as an additional tool for improving the security of the already officially performed determination of the site-specific hydrogen isotope content in wine ethanol by²H-NMR.     

同位素质谱联用技术鉴别无蛋白蜂蜜的真实性

本文从120份蜂蜜样品中筛选出15份无蛋白蜂蜜样品,应用元素分析-同位素质谱联用技术（EA-IRMS）、液相色谱-同位素质谱联用技术（LC-IRMS）、液相色谱测定蜂蜜还原糖含量等检测方法,进行无蛋白蜂蜜样品真实性系统研究。发现15份无蛋白样品皆为掺假掺杂蜂蜜,无蛋白蜂蜜样品的三类典型掺假掺杂手段为：一是掺入碳-4植物源水解产物;二是掺入碳-3植物源水解产物;三是以碳．3植物源高纯度果葡糖浆造假。     

Authenticity control and identification of origin of synthetic creatine-monohydrate by isotope ratio mass spectrometry

Synthetic creatine-monohydrate is consumed as a dietary supplement (DS) worldwide. Up to now no analytical technique for authenticity control or identification of origin of creatine-monohydrate products has been reported. Isotope ratio mass spectrometry (IRMS) of different creatine-monohydrate samples was performed allowing to differentiate between production sites located either in Germany or China. The results obtained indicate that the carbon and nitrogen isotopic composition of industrially synthesised creatine-monohydrate depends on the isotopic composition of the raw materials rather than on different production processes. Statistical pattern recognition of isotope data allowed for classification of most of the creatine-monohydrates sold as DS into German and non-German origin, respectively. Four DS, cross-contaminated with anabolic androgenic steroids (AAS), could not be allocated to a single producer. This suggests that contamination with AAS did not occur during synthesis, but during handling by the distributors.     

大气浓度下N2O中氮稳定同位素比值测定的GasBench-IRMS系统改造

为实现在线自动测定大气环境N₂O中氮稳定同位素比值,本工作对多用途在线气体制备和导入系统（GasBench）进行了改造。增加了化学阱和2个冷阱,与八通阀构成预浓缩装置,以期达到纯化和浓缩大气样品中N₂O的目的,同时更换大体积进样瓶及其配套样品盘,用于增加样品进样量。优化了质谱测定条件、样品收集和浓缩时间等关键参数,并进行了系统的线性、稳定性测试以及方法准确性验证。结果表明,在本方法条件下,当离子流强度在280～3000 mV时,系统线性关系良好,δ¹⁵N_Air值随离子流强度的增加而变化不大;不同压力条件下,δ¹⁵N_Air值的S.D<0.04‰,达到仪器稳定性指标的要求。利用该方法测量配制的400 mg/L N₂O标准样品气,δ¹⁵N_Air平均值为7.253‰,接近标准气的氮稳定同位素标准值,说明该方法准确性良好,可用于大气浓度下N₂O中氮同位素比值测定。