N-nitrosodimethylamine analysis in Estonian beer using positive-ion chemical ionization with gas chromatography mass spectrometry

N-nitrosodimethylamine (NDMA) is a potent animal carcinogen that has been detected in trace levels in beers. A total of 264 beer samples were analyzed for their NDMA content. For cleaning of the sample the two-step solid-phase extraction with Extrelut and Florisil sorbents were used. NDMA was separated by gas chromatography and detected by positive-ion chemical ionization using ammonia as reagent gas. The HP 6890 Plus GC/HP 5973 MSD with positive-ion chemical ionization option was used in the selected ion-monitoring mode. The limit of detection for NDMA using this method was 0.15 ppb with about 70–80% recovery. Of 158 Estonian beers analyzed during 2003–2004, the average NDMA level was found to be 0.20 ppb. Of 106 imported beer samples the average NDMA level was found to be 0.21 ppb.     

Characterization of new nitrosamines in drinking water using liquid chromatography tandem mass spectrometry

N-Nitrosodimethylamine (NDMA), a member of a group of probable human carcinogens, has been detected as a disinfection byproduct (DBP) in drinking water supplies in Canada and the United States. To comprehensively investigate the occurrence of possible nitrosamines in drinking water supplies, a liquid chromatography-tandem mass spectrometry technique was developed to detect both thermally stable and unstable nitrosamines. This technique consisted of solid-phase extraction (SPE), liquid chromatography (LC) separation, and tandem quadrupole linear ion trap mass spectrometry (MS/MS) detection. It enabled the determination of sub-ng/L levels of nine nitrosamines. Isotope-labeled N-nitrosodimethylamine-d6 (NDMA-d6) was used as the surrogate standard for determining recovery, and N-nitrosodi-n-propylamine-dl4 (NDPA-dl4) was used as the internal standard for quantification. The method detection limits were estimated to be 0.1-10.6 ng/L, and the average recoveries were 41-111% for the nine nitrosamines; of these, NDMA, N-nitrosopyrrolidine (NPyr), N-nitrosopiperidine (NPip), and N-nitrosodiphenylamine (NDPhA) were identified and quantified in drinking water samples collected from four locations within the same distribution system. In general, the concentrations of these four nitrosamines in this distribution system increased with increasing distance from the water treatment plant, indicating that the amount of formation was greater than the amount of decomposition within this time frame. The identification of NPip and NDPhA in drinking water systems and the distribution profiles of these nitrosamines have not been reported previously. These nitrosamines are toxic, and their presence as DBPs in drinking water may have toxicological relevance.     

Headspace solid-phase micro-extraction gas chromatography method for the determination of methanol in aspartame sweeteners

A headspace solid-phase micro-extraction (HS-SPME) method for the extraction and determination of residual methanol in artificial sweeteners by capillary gas chromatography with flame ionization detection (GC-FID) is described. A manual SPME holder with an 85-µm polyacrylate fibre was used. The optimized conditions for methanol extraction by SPME were: sample agitation, absorption temperature of 30°C, absorption time of 10 min, desorption time of 2 min and sample volume in the vial of 400.0 µl. Under these conditions the calibration graphs were linear in the range 2.50-31.60 mg l^-1, and the precision was good (relative standard deviation 4.9%). The detection limit was 0.40 mg l^-1; the quantification limit was 2.06 mg l^-1.     

Application of the standard addition method for the determination of acrylamide in heat-processed starchy foods by gas chromatography with electron capture detector

A gas chromatography electron capture detector (GC-ECD) using the standard addition method was developed for the determination of acrylamide in heat-processed foods. The method entails extraction of acrylamide with water, filtration, defatting with n-hexane, derivatization with hydrobromic acid and saturated bromine-water, and liquid–liquid extraction with ethyl acetate. The sample pretreatment required no SPE clean-up and concentration steps prior to injection. The final extract was analyzed by GC-ECD. The chromatographic analysis was performed on polar columns, e.g. Supelcowax-10 capillary column, and good retention and peak response of the analyte were achieved under the optimal conditions. The qualification of the analyte was by identifying the peak with same retention time as standard compound 2,3-DBPA and confirmed by GC–MS. GC–MS analysis confirmed that 2,3-DBPA was converted to 2-BPA nearly completely on the polar capillary column, whether or not treated with triethylamine. A four-point standard addition protocol was used to quantify acrylamide in food samples. The limit of detection (LOD) was estimated to be 0.6 μg/kg on the basis of ECD technique. Validation and quantification results demonstrated that the method should be regarded as a low-cost, convenient, and reliable alternative for conventional investigation of acrylamide.     

原料及加工工艺对包馅鱼肉卷N-亚硝胺含量的影响

为评价原料及加工工艺对包馅鱼肉卷中N-亚硝胺含量的影响,分别测定包馅鱼肉卷馅和皮加工过程中9 种挥发性N-亚硝胺含量、亚硝酸盐含量、硫代巴比妥酸反应物（thiobarbituric acid reaction substances,TBARs）值以及挥发性盐基氮（total volatile nitrogen,TVB-N）含量的动态变化。结果表明：经过加工后鱼肉卷馅和皮中的TVB-N含量均下降,TBARs值和亚硝酸盐含量均上升;鱼肉卷馅的各种原料中含有不等量的N-二甲基亚硝胺（N-nitrosodimethylamine,NDMA）（0～27.51 μg/kg）、N-二乙基亚硝胺（N-nitrosodiethylamine,NDEA）（0～3.39 μg/kg）、N-甲基乙基亚硝胺（N-nitrosoethylmethylamine,NMEA）（0.11～4.33 μg/kg）以及N-亚硝基二苯胺（N-nitrosodiphenylamine,NDPheA）（0～0.82 μg/kg）;在鱼肉卷皮原料中检出了NDEA（0～12.56 μg/kg）、NMEA（0.08～15.26 μg/kg）以及N-亚硝基哌啶（N-nitrosopiperidine,NPIP）（0～8.13 μg/kg）;馅中NDMA、NMEA、NDEA及皮中NDMA、NMEA主要在盐擂期间形成,并在加工后期逐渐下降;NDPheA及NPIP含量在馅和皮的加工过程中始终低于检出限;鱼肉卷成品馅料中NDMA含量为（1.9±0.2） μg/kg,低于国家标准中的限量,而皮中未检出NDMA。     

Rapid detection of Listeria monocytogenes in food using culture enrichment combined with real-time PCR

A rapid method for the detection of Listeria monocytogenes in foods combining culture enrichment and real-time PCR was compared to the ISO 11290-1 standard method. The culture enrichment component of the rapid method is based on the ISO standard and includes 24 h incubation in half-Fraser broth, 4 h incubation in Fraser broth followed by DNA extraction and real-time PCR detection of the ssrA gene of L. monocytogenes. An internal amplification control, which is co-amplified with the same primers as the L. monocytogenes DNA, was also included in the assay. The method has a limit of detection of 1–5 CFU/25 g food sample and can be performed in 2 working days compared to up to 7 days for the ISO standard. A variety of food samples from retail outlets and food processing plants (n = 175) and controls (n = 31) were tested using rapid and conventional methods. The rapid method was 99.44% specific, 96.15% sensitive and 99.03% accurate when compared to the standard method. This method has the potential to be used as an alternative to the standard method for food quality assurance providing rapid detection of L. monocytogenes in food.     

Preconcentration of trace levels of cadmium (ІІ) ion using <Emphasis Type="Italic">Descurainia Sophia</Emphasis> seeds as a green adsorbent for solid phase extraction followed by its determination by flame atomic absorption spectrometry

For the first time, Descurainia Sophia (DS) seeds as an efficient and green adsorbent were used in solid phase extraction for preconcentration of trace levels of cadmium prior to its determination by flame atomic absorption spectrometry (FAAS). By using a batch method, Descurainia Sophia seeds were used as adsorbent to retain cadmium (??) ions in the sample solution. After eluting the adsorbent with 3 mol L^?1 HCl, the retained cadmium (??) was determined by flame atomic absorption spectrometry. Different parameters affecting the extraction efficiency such as pH, amounts of adsorbent, type and concentration of eluent solvent, extraction and desorption time were investigated and optimized. Under the optimum conditions, the calibration curve was linear in the range of 5–300 µg L^?1 cadmium (??) with a correlation coefficient of 0.998. The limit of detection (LOD) was 1.0 µg L^?1 and the relative standard deviation (RSD, %) based on seven replicate analysis of 25 µg L^?1 cadmium (??) was 3.2%. The accuracy of the proposed method was checked by the analysis of certified reference material (CRM) and spike methods. The results show a good agreement with certified values. The proposed method was successfully applied to determination of trace levels of cadmium in different water and rice flour samples.     

基于全自动核酸提取的荧光定量PCR鉴别羊肉制品真伪

摘要：目的 建立一种基于自动化的快速核酸提取方法,联合三重实时荧光定量PCR技术,提高羊肉制品真伪鉴别的检测效率。方法 分别采用全自动核酸提取法、磁珠手提法与柱提法对不同状态羊肉制品进行核酸提取,比较不同方法的提取时间差异,通过三重实时荧光定量PCR扩增结果评估不同方法的提取效果。以国标法为对照,对市售的羊肉制品进行平行检测,评估本方法的检测性能。结果 与磁珠手提法、柱提法相比,全自动核酸提取法的提取时间缩短了15-30 min,且提取的核酸扩增效果更好。全自动核酸提取法在羊猪混合样本中羊源核酸检出限为0.010 mg·g-1。全自动核酸提取法在生鲜肉、生肉及熟肉制品等多种类型产品中提取的羊源核酸PCR检测结果的CV值均<3.000%。分别采用三重实时荧光定量PCR法与国标法对全自动提取的21份市售的涵盖不同类型的羊肉制品核酸进行平行检测,符合率为100.00%。结论 本研究方法可为羊肉制品掺假的快速真伪鉴别提供操作简便、稳定灵敏、快速准确的整套解决方案。     

八角和丁香提取物对腊肠中亚硝胺的阻断效果

为研究阻断亚硝胺形成的抑制剂,降低腌腊肉制品中亚硝胺的形成,以腊肠为研究对象,分别添加VCNa、异抗坏血酸盐、VE,外购的八角和丁香精油,超声-微波萃取的八角和丁香萃取液,测定腊肠烘烤结束后的亚硝胺含量。结果表明:添加超声-微波萃取法得到的八角精油能减少腊肠中87%的亚硝基二甲胺(NDMA);丁香精油则可以减少79%的NDMA。八角精油和丁香精油对亚硝胺的阻断效果均好于VCNa、D-异VCNa和VE的阻断效果。     

分散固相萃取-气相色谱-三重四极杆串联质谱法同时测定沙拉酱中3种防腐剂

建立气相色谱-三重四极杆串联质谱（GC-MS/MS）法同时测定沙拉酱中的3种防腐剂（山梨酸、脱氢乙酸、苯甲酸）的方法。对样品前处理条件的提取方式、涡旋时间、萃取溶剂进行优化,通过分散固相萃取技术净化后,采用气相色谱-三重四极杆串联质谱仪（GC-MS/MS）进行测定,外标法定量。结果表明,3种防腐剂在0.001～0.100 mg/L质量范围内呈现良好的线性关系,相关系数R2均>0.999,回收率为88.6%～104.8%,精密度试验结果相对标准偏差（RSD）为2.0%～5.3%,方法检出限为0.002～0.010 mg/kg,定量限为0.006～0.030 mg/kg。该方法操作简单、灵敏度高、抗干扰能力强、结果准确可靠,可作为沙拉酱中多种防腐剂的测定方法。     

Determination of Iron in Edible Oil by FAAS After Extraction with a Schiff Base

The synthesis of a new Schiff base has been achieved by condensation reaction of 1,3-diamino-2-propanol and 2-hydroxy-5-methoxy-benzaldehyde in alcoholic media. The Schiff base was characterized by elemental analysis, IR, UV–Visible, ¹H-NMR, and ¹³C-NMR spectroscopy and used for the extraction of iron in liquid edible oils. Iron complex with the Schiff base was investigated in order to determine experimental conditions of the complexation. The extraction of iron from oils to aqueous phase was succeeded by the complexation with the Schiff base. A central composite design was employed in order to optimize the extraction conditions of iron. Optimum conditions for the iron extraction with N,N′-bis(5-methoxy-salicylidene)-2-hydroxy-1,3-propanediamine were found to be 19.3 °C, 2.1 mL g^?1, 10.0 min for the temperature, the ratio of the volume of used Schiff base solution to the amount of oil, and the stirring time, respectively. Method validation was performed with recovery experiments in the analysis of the oil-based metal standard by flame atomic absorption spectrometry, limit of detection, and the relative standard deviation of the proposed method were found to be 0.09 μg g^?1 and 1.04 %, respectively. Additionally, an alternative determination procedure (inductively coupled plasma optical emission spectrometry) was applied for the comparison. This paper describes a simple, cheap, rapid, efficient, sensitive, and accurate alternative analytical method for the iron determination in oils. The proposed method was applied on six different oil samples and the iron concentration was found in the range of 0.38–0.70 μg g^?1.     

动物肌肉组织DNA的提取方法及实时荧光定量PCR检测

以生鲜羊肉、猪肉、鸡肉、牛肉、鸭肉为实验材料,采用SDS法、异硫氰酸胍法、试剂盒法提取动物肌肉组织基因组DNA,对提取的DNA进行琼脂糖凝胶电泳和实时荧光定量PCR检测。结果表明,试剂盒法提取的基因组DNA在浓度和纯度方面均优于SDS法和异硫氰酸胍法。通过对三种提取方法建立的标准曲线进行比较,回归系数(R2)按照质量排序为:试剂盒法≥异硫氰酸胍法>SDS法,扩增效率按照质量排序为:试剂盒法>异硫氰酸胍法>SDS法。三种提取方法的羊源性成分灵敏度检测,最低检出限均为80 pg/μL,但在低浓度检测时试剂盒法的相对标准偏差RSD为0.684%,小于异硫氰酸胍法0.734%和SDS法1.075%;猪源性成分灵敏度检测,SDS法的最低检出限为80 pg/μL,异硫氰酸胍法和试剂盒法的最低检出限均为16 pg/μL,但在低浓度检测时试剂盒法的相对标准偏差RSD为0.092%,小于异硫氰酸胍法4.640%;鸡源性成分灵敏度检测,SDS法和异硫氰酸胍法的最低检出限均为3.2 pg/μL,试剂盒法的最低检出限为640 fg/μL,明显高于SDS法和异硫氰酸胍法。综上所述,试剂盒法提取的基因组DNA更有利于运用实时荧光定量PCR技术进行食物掺假和物种鉴别工作。      

Application of Dispersive Liquid–Liquid Micro-extraction Using Mean Centering of Ratio Spectra Method for Trace Determination of Mercury in Food and Environmental Samples

In the present study, dispersive liquid–liquid micro-extraction has been applied for trace extraction and determination of mercury (Hg) ions in environmental samples. The mean centering of ratio spectra method was used to optimize the experimental parameters affecting the extraction of Hg. The factors influencing the extraction procedure such as type and volume of extracting and disperser solvent, concentration of chelating reagent, pH, salt effect, and centrifuge time were investigated and optimized. Under the optimized conditions, the limit of detection of the method was 0.15 μg l^?1 and enrichment factor was 39. The calibration curve was linear in the range of 0.5–100 μg l^?1 with a correlation of determination (R ²) of 0.998. The relative standard deviation for determination of 40 μg l^?1 of Hg(II) was 2.6 % (n?=?5). The proposed method was applied for the determination of Hg in pine leaf, sea and river fish, sand, and water samples as indicators of environmental pollution and cigarette with satisfactory analytical results. In comparison with other methods, the proposed method is very simple, easy, rapid, and sensitive for determination of Hg at trace levels in complex matrices.     

Determination of Cobalt in Food and Water Samples by Ultrasound-assisted Surfactant-enhanced Emulsification Microextraction and Graphite Furnace Atomic Absorption Spectrometry

A novel method based on ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) has been developed for the preconcentration of cobalt prior to its determination by graphite furnace atomic absorption spectrometry. In the UASEME technique, chloroform was used as the extraction solvent, sodium dodecyl sulfate was adopted as emulsifier, and ultrasound was applied to assist emulsification. There is no need of using organic dispersive solvent which is typically required in conventional dispersive liquid–liquid microextraction method. Several parameters that affect the extraction efficiency, such as the kind and volume of the extraction solvent, the type and concentration of the surfactant, pH of sample solution, concentration of the chelating agent, and extraction time and temperature were investigated and optimized. Under the optimal conditions, the linearity of calibration curve was in the range of 0.1–5 ng mL^?1 with a correlation coefficient (R ²) of 0.9992. An enrichment factor of 58 was achieved with a sample volume of 5.0 mL. The detection limit of this method for Co was 15.6 ng L^?1, and the relative standard deviation (RSD) was 4.3 % at 1.0 ng mL^?1 concentration level of Co. The accuracy of the developed method was evaluated by analysis of the certified reference materials GBW07605 tea leaf and GBW10015 spinach. The method was successfully applied to determine trace cobalt in food and water samples with satisfactory results.     

电膜萃取-光度法测定食品中的砷

应用电膜萃取-紫外-可见分光光度法测定食品中砷。对影响实验的参数进行优化:有机溶剂为邻苯二甲酸二异壬酯在正辛醇溶液中体积分数2.5%、电压70 V、萃取时间15 min、接受相溶液pH 13、搅拌速率700 r/min。砷的检出限为1.5μg/L,回收率为96%~104%,相对标准偏差(n=5)为0.1%~3.6%。本方法具有选择性好、操作简单、成本低等特点,可用于食品中总砷的分析。     

Development and validation of a modified QuEChERS method coupled with LC-MS/MS to determine arbutin in pear peels

A new effective method was developed to determine the concentration of arbutin in pear peels using a modified QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The original QuEChERS was modified to enable the extraction of the polar arbutin molecule. Use of an initial 50:50 acetonitrile:water extraction solvent led to the highest extraction efficiency. The arbutin extracted from pear peels was found to be identical to the β-arbutin standard, as confirmed by NMR and LC-MS/MS analyses. For quantitative analysis, the mass spectra of the precursor ion [M+NH₄]⁺ at m/z 290.0 and the product ion of arbutin at m/z 163.0 were used. The limit of detection, limit of quantification, linearity, precision, accuracy, and recovery of the proposed method were evaluated. We successfully applied this method to pear samples and it may be suitable for the quantitative analysis of arbutin in other similar plant materials.     

Hydroxymethylfurfural in fruit puree and juice: preconcentration and determination using microextraction method coupled with high-performance liquid chromatography and optimization by Box–Behnken design

In the present study, a sensitive and rapid method for separation and determination of hydroxymethylfurfural (HMF) in fruit puree and juices was proposed. Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC) was used for extraction and quantitative determination of HMF in fruit puree and juices. The effective parameters such as the type and volume of extraction and dispersive solvents, pH and salt amount (NaCl) were studied and optimized with the aid of response surface methodology based on Box–Behnken design to obtain the best condition for HMF extraction. At the optimized conditions, parameter values were 60 µL extracting solvent, 600 µL dispersive solvent, 2 g NaCl and pH 5. Repeatability of the method, described as the relative standard deviation, was 3.1% (n?=?6) and the recovery was 98.4%. The limit of detection and limit of quantitation were 1.47 and 5.28 µg L^?1, respectively. The merit figures of DLLME–HPLC–UV method showed that the proposed method can be noticed as a new, fast and good alternative method for investigation of HMF in various fruit puree and juice samples.     

响应面优化HS-SPME-GC/MS检测啤酒微量酯类物质条件

该研究采用Plackett-Burman和Box-Behnken试验设计,对顶空固相微萃取-气相色谱-质谱法（HS-SPME-GC/MS）检测啤酒中6种低含量酯类物质（辛酸乙酯、丁酸乙酯、乙酸异丁酯、乙酸苯乙酯、苯甲酸乙酯和3-苯基丙酸乙酯）的萃取条件进行优化,发现萃取温度、萃取时间和平衡温度为主要影响因素,通过响应面法分析得出最佳萃取条件为：萃取温度42 ℃、萃取时间30 min和平衡温度48 ℃;在该条件下,结合内标法定量,该方法的相关系数R2为0.990 0～0.999 9,回收率为93.43%～103.37%,检测限为0.01～0.05 μg/L,相对标准偏差（RSD）为1.75%～8.24%,表明该方法准确可靠,可应用于啤酒中微量酯类物质的检测。     

茄尼醇同步提取皂化-超高效液相色谱测定方法研究

为了建立高效、准确检测烟草总茄尼醇的方法,研究了超声辅助条件下,同步提取、皂化烟草茄尼醇的溶剂、温度、液料比、皂化剂用量、提取时间及超高效液相色谱测定的仪器条件。结果表明,烟草样品以正己烷为萃取剂,液料比为50:1,0.1 moL/L氢氧化钠的乙醇溶液为皂化剂,在超声频率45 kHz,恒温水浴40 ℃,提取时间30 min条件下,完成烟草茄尼醇的提取、皂化,且使茄尼醇的提取、皂化以及与皂化剂的分离在同一离心管中完成。以ACQUITY UPLC BEH C18为色谱柱,甲醇-乙腈(50:50)为流动相,流速为0.5 mL/min,柱温为35 ℃,在波长208 nm条件下,超高效液相色谱进行检测。方法的线性范围为0.67~84.1 mg/L,方法检出限为0.07 mg/L,定量限为0.012%,空白及样品加标回收率分别在97.9%~104.7%、93.4%~102.3%范围内,相对标准偏差为1.34%~2.43%。该方法简便、快速,且节约有机溶剂,精密度和准确度较高,可以实现烟草茄尼醇批量高效检测。     

UPLC-Q-TOF/MS法测定桂皮中香豆素含量

为降低基质干扰,样品经粉碎过筛后,通过响应面试验优化桂皮前处理条件,采用稳定同位素稀释结合超高效液相色谱-四极杆飞行时间质谱（UPLC-Q-TOF/MS）法测定香豆素含量,并进行方法学考察。结果表明,桂皮中香豆素的最优超声提取条件为甲醇作为提取溶剂,甲醇用量25 m L,提取时间25 min,提取温度50℃,重复提取2次。在此条件下,采用稳定同位素稀释结合UPLC-QTOF/MS测定香豆素,内标法定量,使用香豆素-d4为内标物进行基质效应的校正,香豆素质量浓度在0.01～2.0 mg/L范围内,线性关系良好,相关系数R2为0.999 3,平均回收率为89.9%～99.9%,精密度试验结果的相对标准偏差（RSD）为1.58%～3.22%,方法检出限（LOD）为0.3 mg/kg,定量限（LOQ）为1.0 mg/kg,说明该方法操作简便、灵敏度高,回收率及精密度较好,可应用于桂皮中香豆素含量的测定。