元素分析-同位素比质谱法测定食醋总碳同位素比值

本文建立了一种利用元素分析-同位素比质谱法(Elemental analyzer-Isotope ratio mass spectrometry,EA-IRMS)测定食醋总碳同位素比值的方法,并对食醋进行聚类分析。优化了样品稀释倍数及进样量。2 g芳香醋用4 m L超纯水进行稀释,2 g糯米酿造食醋用2 m L超纯水进行稀释,苹果醋、配制白醋不稀释,进样量均为1μL,样品分析时间为670 s。结果显示:芳香醋、糯米酿造食醋、苹果醋及配制白醋的δ~(13)C值范围分别为-26.94‰~-23.46‰、-25.06‰~-22.40‰、-27.99‰~-22.76‰、-19.06‰~-13.74‰,聚类分析可将不同产地、不同原料、不同生产方式的食醋进行初步归类,并且该方法可鉴别出芳香醋和掺入≥4%糯米酿造食醋、≥6%苹果醋、≥2%配制白醋的芳香醋混合样品。食醋及质控样品(咖啡因)的测试精度(SD)在0.02‰~0.25‰(n=6)之间,均小于0.3‰,满足方法检测分析要求。结果表明,所建EA-IRMS方法结合聚类分析可用于食醋分类及掺假鉴别。     

乳及乳制品中稳定碳同位素比的研究

目的建立元素分析-稳定同位素比质谱法(elemental analyzer-isotope ratio mass spectrometry,EA-IRMS)测定乳及乳制品中δ~(13)C值的检测方法。方法本文研究了样品前处理、进样量、不同标样标定等对测定结果的影响,通过优化仪器工作条件,建立了稳定同位素比质谱仪测定乳及乳制品中碳同位素比(δ~(13)C)的方法,并用该方法对20余种品牌的乳及乳制品及3位哺乳期的母乳进行检测。结果研究数据表明,不同种类的乳汁δ~(13)C数值有明显差异:牛乳及其制品δ~(13)C值位于-16.50‰~-20.42‰,羊乳及其制品δ~(13)C值位于-22.38‰~-22.95‰,母乳δ~(13)C值为-23.17‰~-27.30‰。结论本方法根据羊乳和与牛乳δ~(13)C特征数值的差异,可以进行乳品纯正性判别。该方法精密度为0.04‰~0.24‰,小于常规0.3‰的要求,稳定性好、准确度高,操作简便,为乳及乳制品的鉴别提供了技术支持和理论基础。     

乙醇C、O、H稳定同位素在白酒掺伪鉴别中的潜在差异分析

采用气相色谱-稳定同位素比质谱(GC-IRMS)建立了白酒、食用酒精和工业酒精中乙醇C、H、O稳定同位素比值的测定方法,并优化了稀释倍数、进样体积和分流比等前处理。通过检测分析28种白酒、7种工业酒精和5种食用酒精的乙醇δ¹³C、δ¹⁸O和δ²H值发现：工业酒精与白酒之间乙醇δ¹³C和δ¹⁸O值差异较大,食用酒精与白酒之间乙醇δ¹³C值差异较小但乙醇δ¹⁸O值差异较大,三者的乙醇δ²H值差异较小;在鉴别白酒是否掺假工业酒精或食用酒精时,鉴别能力：氧稳定同位素>碳稳定同位素>氢稳定同位素。     

基于稳定氢氧同位素技术的花生油掺假检测技术研究

建立了高温裂解/元素分析-稳定同位素比值质谱联用技术（TC/EA-IRMS）测定油脂稳定氢氧同位素比值（δ2H和δ18O）的方法,并根据氢氧同位素特征开展花生油掺假检测技术研究。对28个花生样品、5个大豆样品和6个油菜籽样品榨油后测定δ2H值和δ18O值,结果发现三种油的δ2H值分布范围分别为-231.50‰~-213.69‰、-183.11‰~-169.53‰和-192.17‰~-175.82‰;δ18O值分布范围为14.06‰~16.77‰、19.77‰~20.98‰和24.31‰~27.45‰;其中花生油的δ2H值与大豆油和菜籽油存在显著性差异（p＜0.01）,模拟实验表明根据氢氧同位素特征可检测花生油中掺入大豆油或菜籽油。通过对氢氧同位素比值的二维分布对比,可以更为全面的评价和鉴别花生油的掺杂掺假情况,为花生油的掺假鉴别提供了研究基础和技术支持。     

牛奶中矿物元素和稳定同位素比的测定及在产地分析中的应用

本文应用电感耦合等离子质谱仪（ICP-MS）,同位素比质谱仪（IRMS）对牛奶中Li、Na等40种元素含量和碳、氮、氢、氧稳定同位素比值进行测定,并应用于牛奶产地分析中。牛奶样品经冷冻干燥成粉末后,通过ICP-MS对元素含量进行测定,EA-IRMS测定氮稳定同位素比值（δ15N）,通过EA-IRMS直接测定牛奶中碳稳定同位素比值（δ13C）,GasBench-IRMS测定牛奶水中的氢和氧稳定同位素比值（δ2H和δ18O）。应用上述方法对德国、西班牙、意大利、澳大利亚、新西兰、中国和奥地利的牛奶样品进行检测,并对测定结果进行多元统计分析（方差分析、主成分分析、聚类分析和判别分析）,对牛奶产地的归属进行研究。研究结果表明,有10种元素（As、Se、Rb、Sr、Mo、Cd、Cs、Ba、Tl、Bi）和4种稳定同位素比（?13C、?15N、?2H、?18O）在不同国家和地区的牛奶中存在显著性差异（p?0.05）,德国和意大利,中国,奥地利,澳大利亚和新西兰的牛奶可进行一定的聚类区分,应用As、Se、Rb、Sr、Mo、Cs、Ba、Tl、δ13C、δ15N和δ2H指标的组合分析,对7个国家牛奶产地的整体判别准确率为92.4%。     

元素分析-同位素比质谱法与液相色谱-同位素比质谱法测定乙醇中δ13C值

目的研制木薯乙醇和玉米乙醇中碳同位素标准物质,探讨碳同位素准确定值技术。方法定值分别采用元素分析-稳定同位素比质谱法(elemental analyzer-isotope ratio mass spectrometry, EA-IRMS)和液相色谱-稳定同位素比质谱法(liquid chromatography-isotope ratio mass spectrometry, LC-IRMS)。LC-IRMS分析过程中,将标准物质BCR657分别与待测样品和标准物质BCR660混合,可以实现对乙醇和蔗糖δ~(13)C值的同时测定。结果LC-IRMS方法验证结果显示使用该方法检测的标准物质BCR660的测量值在标准值的不确定度范围内,证明了混合检测方法的可行性。使用E_n值核查法对2种检测方法检测得到的乙醇样品δ~(13)C值进行检验,|E_(ncassava)|=0.952,|Enmaize|=0.551,En值均小于1,证明2种检测方法所测结果等效一致。结论该方法不但有利于对乙醇进行多方法定值,且弥补了气相色谱-稳定同位素比质谱法(gas chromatography-isotope ratio mass spectrometry, GC-IRMS)标准物质有限的缺陷。本研究建立的分析技术和研制的标准物质可用于食品真实性鉴别。     

不同产地库尔勒香梨果实生育期氢、氧稳定同位素特征

分析库尔勒香梨果实生育期氢（H）、氧（O）稳定同位素比值及其变化规律,比较不同产地香梨果实δ2H、δ18O差异,为库尔勒香梨产地真实性鉴别提供参考。以不同产地库尔勒香梨为研究对象,采集花后60~150天（d）的果实样本,采用真空冷凝提取法抽提果实中的水分,用高温裂解－同位素比值质谱法（HT-IRMS）测定其δ2H、δ18O值,分析香梨生育期H、O同位素特征,通过方差分析法探讨各产地果实水分δ2H、δ18O值的差异。新疆库尔勒市、阿克苏市和甘肃酒泉市三个产地的香梨生育期果实水δ2H的变化范围分别为-49.9‰~-15.4‰、-62.0‰~-28.2‰、-61.5‰~1.5‰,δ18O的变化范围分别为-2.5‰~6.7‰、-5.3‰~3.4‰、-3.5‰~14.2‰,成熟期三个产地δ18O值均存在极显著性差异(P＜0.01)。整个生育期三个产地δ2H、δ18O蒸发线均位于当地大气水线右下方,香梨果实水富集作用明显,相较其他两地库尔勒的蒸发线斜率和截距更低,果实水蒸发富集2H、18O的能力更强。新疆库尔勒市、阿克苏市和甘肃酒泉市香梨果实H、O同位素具有各自的指纹特征。     

气相色谱-燃烧-同位素比质谱法测定鱿鱼中甲醛稳定碳同位素比值

建立了一种气相色谱-燃烧-同位素比质谱法(GC/C/IRMS)测定鱿鱼中甲醛(FA)稳定碳同位素比值的方法。鱿鱼样品经水充分提取后,高速离心除油脂,上清液与2,4-二硝基苯肼在酸性、60℃条件下发生液相衍生化反应1 h,衍生液经正己烷萃取,氮吹干后复溶即可进行稳定碳同位素测试。二氯甲烷、甲醇、正己烷、乙腈均可作为衍生产物甲醛2,4二硝基苯腙的同位素测试的溶剂。甲醛的衍生化反应未发生碳同位素分馏,由质量平衡方程计算得到的衍生产物甲醛2,4二硝基苯腙的δ¹³C值与实测值差值的标准偏差为0.215‰。分析9个市售不同产地鱿鱼中甲醛的含量为0.341~39.132 mg/kg,内脏部分含量较高。甲醛含量较高的2、3、4、5号样品δ¹³C值差异高达23.653‰。水产品中甲醛稳定碳同位素指纹特征可作为其来源解析的特征性指标。     

气相色谱-燃烧炉-同位素比质谱法测定奶粉中 孕酮δ13C值

目的基于高效液相色谱纯化分离,应用气相色谱-燃烧炉-同位素比质谱法(gas chromatography-combustion-isotope ratio mass spectrometry,GC-C-IRMS)建立奶粉中测定孕酮激素碳同位素比值的方法,以气相色谱-质谱法提供定量支持。方法样品经水溶解和乙腈提取,经乙腈饱和的正己烷除脂肪和过C18固相萃取柱净化,经高效液相色谱纯化、浓缩后进行GC-C-IRMS检测。结果外源性孕酮δ~(13)C平均值为-32.297‰,内源性孕酮δ~(13)C平均值为-21.387‰,方法回收率为52.9%,检出限为22.7μg/kg,相对标准偏差小于5%(n=6)。结论内源性和外源性孕酮δ~(13)C值有显著性差异,本方法可以区分内外源性孕酮。但由于方法局限性,只能检测孕酮大于22.7μg/kg的样品。     

梨白兰地中乙醇碳同位素分布特征研究

利用元素分析-稳定同位素比值质谱仪测定梨白兰地原料的糖中δ13C,发酵后用气相色谱-燃烧-同位素比值质谱法分析乙醇中碳稳定同位素比值(δ13C)。结果显示梨的糖中δ13C值分布在-27‰~-25‰,而发酵后的乙醇δ13C集中在-30‰~-27‰,且糖与乙醇的δ13C具有良好的线性正相关关系(R2=0.98);白兰地精馏过程中乙醇出现反蒸汽压分馏效应,但酒体部分(50%vol~80%vol)δ13C值波动较小,重现性较好,且与发酵醪中的δ13C值较一致。模拟实验表明,乙醇δ13C值与玉米酒精含量和蔗糖含量成正相关关系,发酵前添加蔗糖和玉米酒精均会改变产品中乙醇δ13C值,因此碳稳定同位素技术可作为检测白兰地中C4来源的酒精或发酵前C4植物糖掺假的鉴别手段。     

Soil phosphate stable oxygen isotopes across rainfall and bedrock gradients

The stable oxygen isotope compositions of soil phosphate (δ(18)O(p)) were suggested recently to be a tracer of phosphorus cycling in soils and plants. Here we present a survey of bioavailable (resin-extractable or resin-P) inorganic phosphate δ(18)O(p) across natural and experimental rainfall gradients, and across soil formed on sedimentary and igneous bedrock. In addition, we analyzed the soil HCl-extractable inorganic δ(18)O(p), which mainly represents calcium-bound inorganic phosphate. The resin-P values were in the range 14.5-21.2‰. A similar range, 15.6-21.3‰, was found for the HCl-extractable inorganic δ(18)O(p), with the exception of samples from a soil of igneous origin that show lower values, 8.2-10.9‰, which indicate that a large fraction of the inorganic phosphate in this soil is still in the form of a primary mineral. The available-P δ(18)O(p) values are considerably higher than the values we calculated for extracellular hydrolysis of organic phosphate, based on the known fractionation from lab experiments. However, these values are close to the values expected for enzymatic-mediated phosphate equilibration with soil-water. The possible processes that can explain this observation are (1) extracellular equilibration of the inorganic phosphate in the soil; (2) fractionations in the soil are different than the ones measured at the lab; (3) effect of fractionation during uptake; and (4) a flux of intercellular-equilibrated inorganic phosphate from the soil microbiota, which is considerably larger than the flux of hydrolyzed organic-P.     

HS‐SPME/GC‐MS and chemometrics for volatile composition of Chinese traditional aromatic vinegar in the Zhenjiang region

The main purpose of this study was to determine the volatile composition of Zhenjiang aromatic vinegar, one of the four famous China‐style cereal vinegars, by using headspace solid‐phase microextraction (HS‐SPME)/gas chromatography‐mass spectrum (GC‐MS) and chemometrics. For this purpose, the HS‐SPME sampling method for the volatile compounds of Zhenjiang aromatic vinegar was optimized by a second‐order rotatable central composite experimental design (CCD). A HS extraction of the volatile compounds by incubation on a 65 µm thickness polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibre during 44.2 min at 69.5°C with 1.9 g NaCl add gave the most effective and accurate extraction. By the optimized method, a total of 58 volatile compounds, including 9 alcohols, 13 acids, 16 esters, 5 aldehydes, 4 ketones and 8 heterocycle compounds, were identified from 13 aromatic vinegar samples manufactured in Zhenjiang region. By principal components analysis (PCA), the thirteen vinegar samples were classified into 3 groups, and 10 volatile compounds were chosen as characteristic compounds of Zhenjiang aromatic vinegars. Copyright © 2012 The Institute of Brewing & Distilling     

吴起荞麦醋与镇江香醋、山西老陈醋比较研究

比较了吴起荞麦醋、镇江香醋及山西老陈醋的生产原料、生产工艺、产品质量和风味等方面的异同。结果表明,镇江香醋以江米为主料,后期添加炒米,制作考究,所以产品风味酯香浓郁而偏甜;山西老陈醋主料为玉米,后期制作有熏制环节,所以熏香浓郁;吴起荞麦醋以荞麦为主料,后熟靠陈酿,长达半年以上,虽然没有浓郁的炒米香和熏香,但陈酿产生的酯香醇香也很绵长。     

Multicomposition analysis and pattern recognition of Chinese geographical indication product: vinegar

Multicomposition fingerprints with several chemical compositions containing inorganic elements and organic compounds (amino acids, polyhydric alcohols, organic acids) were measured to distinguish two geographical indication-protected vinegars (GIs) from general vinegars (nGIs). The two of GIs were named Shanxi extra aged vinegar and Zhenjiang vinegar from Shanxi and Jiangsu province, respectively. Principal component analysis and Fisher linear discriminant methods were applied for the pattern recognition and classification of GI product. It was not suitable by simply using one kind of composition to make a distinction between GIs and nGIs. However, by using multicomposition to build a classify model, the classification of SXVs was described by Co, As, Al, Mg, Ca, erythritol, arabitol, sorbitol, proline, lysine and pyruvic acid, while ZJVs classification was described by threonine, serine, glycine, lysine, Ba, erythritol, xylitol and lactic acid. The GI samples can be classified with high accuracy according to the discriminant model, of which the false rate is 3.88 % in SXVs model and 10.85 % in ZJVs model. This method can be a useful method for protecting the geographical indication vinegars from the fake or adulterate vinegar commodities.     

Stable carbon isotope ratio analysis of anhydrosugars in biomass burning aerosol particles from source samples

A new method for stable carbon isotope ratio analysis of anhydrosugars from biomass burning aerosol particle source filter samples was developed by employing Thermal Desorption--2 Dimensional Gas Chromatography--Isotope Ratio Mass Spectrometry (TD-2DGC-IRMS). Compound specific isotopic measurements of levoglucosan, mannosan, and galactosan performed by TD-2DGC-IRMS in a standard mixture show good agreement with isotopic measurements of the bulk anhydrosugars, carried out by Elemental Analyzer--Isotope Ratio Mass Spectrometry (EA-IRMS). The established method was applied to determine the isotope ratios of levoglucosan, mannosan, and galactosan from source samples collected during combustion of hard wood, softwood, and crop residues. δ(13)C values of levoglucosan were found to vary between -25.6 and -22.2‰, being higher in the case of softwood. Mannosan and galactosan were detected only in the softwood samples showing isotope ratios of -23.5‰ (mannosan) and -25.7‰ (galactosan). The isotopic composition of holocellulose in the plant material used for combustion experiments was determined with δ(13)C values between -28.5 and -23.7‰. The difference in δ(13)C of levoglucosan in biomass burning aerosol particles compared to the parent fuel holocellulose was found to be -1.89 (±0.37)‰ for the investigated biomass fuels. Compound specific δ(13)C measurements of anhydrosugars should contribute to an improved source apportionment.     

Comparison between isotope ratio mass spectrometry (IRMS) and cavity ring-down spectroscopy (CRDS) for analysing the carbon isotope ratio and detection of adulteration in coconut water

This study investigated the carbon isotope ratio (¹³C/¹²C, δ¹³C in unit of parts per thousand or per mill, ‰) of different coconut water samples using elemental analysis isotope ratio mass spectrometry (EA-IRMS) and combustion module cavity ring-down spectroscopy (CM-CRDS). Natural coconut water from young coconuts from 12 provinces in Thailand (n = 94), adulterated coconut water containing three sweeteners (sucrose, glucose and fructose) at different concentrations and eight brands of commercial coconut water were analysed. The δ¹³C of all samples were not significantly different (P > 0.05) between the EA-IRMS and CM-CRDS analyses. The natural coconut water (C3 plant) had δ¹³C ranging from −21.58‰ to −27.79‰ (mean −24.64 ± 0.91‰). Three sweeteners (C4 plant) contained δ¹³C between −11.46‰ to −13.16‰. The use of δ¹³C determination can detect adulteration of a singular extraneous sweetener (either glucose or sucrose) down to a level of 2% of adulteration. For the detected δ¹³C values of commercial products labelled as ‘no added sugar’, about 50% of products were adulterated. This study demonstrates that CM-CRDS can be used as an alternative analytical platform to EA-IRMS for detecting adulterated products, especially coconut water.     

The application of SNIF‐NMR and IRMS combined with C,H and O isotopes for detecting the geographical origin of Chinese wines

The regional origin of Chinese wines was investigated using two important complementary techniques, site‐specific natural isotopic fractionation nuclear magnetic resonance (SNIF‐NMR) and isotope ratio mass spectrometry (IRMS). Twenty samples from five different grape varieties were collected from north Xinjiang in 2009, along with 100 wine samples from five different regions during 2010–2013. The (D/H)_I and (D/H)_II in wine ethanol ranged from 95.10 to 102.86 ppm and from 115.99 to 126.39 ppm using SNIF‐NMR, respectively. The ¹³C/¹²C of wine ethanol and ¹⁸O/¹⁶O of wine water were detected using IRMS. The δ¹³C value (?23.36‰) in coastal regions was higher than that in continental regions (?27.75‰). The temperature is the key for δ¹³C value. The δ¹⁸O ranged from ?1.94 to 4.57‰. The δ¹⁸O values were only positive in north Xinjiang which had the arid climate and strong sunshine. No difference was found for isotope ratios for wines made from five different grape varieties in north Xinjiang. All data evaluated by principal component analysis and linear discriminant analysis showed that the best method to distinguish the regional wine origin correctly is a combination of (D/H)_I, (D/H)_II, R, δ¹³C and δ¹⁸O. Therefore, natural multi‐elemental isotope ratios are effective in contributing to wine quality control in the Chinese market.     

HS-SPME-GC-MS测定中国四大名醋的香气成分

采用顶空固相微萃取气相色谱质谱联用仪对山西老陈醋、江苏镇江香醋、福建永春老醋、阆中保宁醋不同品牌和年份的8个 醋样进行香气物质检测分析。 结果表明,8个醋样含有酸类10种、酯类14种、醇类4种、酚类6种、醛类10种、酮类4种、吡嗪类5种、呋喃类 4种、其他类11种;四大名醋的香气成分种类繁多且差异明显,其具有各自的独有香气成分,其中山西老陈醋6种,镇江香醋5种,永春 老醋2种,保宁醋4种。 山西老陈醋的吡嗪类成分中2,3,5,6-四甲基吡嗪含量最高,平均580.75 μg/L;镇江香醋B2的乙偶姻中含量最高 为562.6 μg/L。 本研究为进一步研究各类食醋原料、微生物和香气成分之间的关系打下良好基础。     

基于液质联用技术的镇江香醋中十种黄酮类物质含量的同时测定

建立了超高效液相色谱-串联质谱（UPLC-MS/MS）同时测定镇江普通醋和陈年醋中十种黄酮类化合物含量的分析方法。采用体积分数为70%的甲醇水溶液超声提取的方法对食醋样品进行处理,提取液用C18柱进行分离,以0.1%的甲酸水和乙腈为流动相进行梯度洗脱,流速0.4 mL/min,柱温35 ℃。质谱测定为电喷雾负离子模式（ESI-）,多反应监测（MRM）。结果表明,十种黄酮类化合物在25.0～1 000.0 ng/mL线性关系良好（R2＞0.99）,平均加标回收率为93.9%～99.0%,精密度和稳定性试验结果的相对标准偏差（RSD）均≤3.8%,检出限在1.0～4.0 ng/mL。该方法简便、快速、灵敏度高、准确性好,可用于镇江普通醋和陈年醋等酿造食醋中黄酮类成分的检测。     

食醋中苯乳酸的提取、鉴定及含量比较

采用高效液相色谱-串联质谱联用（LC-MS/MS）结合核磁共振（NMR）法从山西老陈醋的乙酸乙酯萃取物中分离提取并鉴定出一种新型抗菌物质苯乳酸（PLA）。进一步分析发现,PLA主要在食醋酿造的醋酸发酵阶段产生。对77种来自不同国家食醋中的PLA含量进行分析,结果表明73种食醋中都检测到PLA,且谷物醋中PLA的含量均明显高于果醋中的PLA含量。