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翻译几段化学类英语~~~~
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Recovery Experiments. The recovery of benzo[a]- pyrene（苯并[a]芘） from roasted coffee was determined by applying with a microsyringe 20-pL aliquots of benzo[a]pyrene standard solutions (1.00 or 1.30 wg/mL), containing 20.0 or 26.0 ng of benzo[a]pyrene, to a 20-g portion of ground roasted coffee. To another 20-g portion nothing was added. The recovery of benzo[a]pyrene from coffee brew was determined by adding a 10-pL aliquot of a benzo[a]pyrene standard solution (1.32 pg/mL), which corresponds to 13.2 ng of benzo[a]pyrene, to 1 L of coffee brew prepared by a household coffee maker (coffee to water ratio 50 g/L). To another l-L portion of coffee brew, prepared in the same way, nothing was added. The samples were analyzed as described above. Percent recoveries were based on the difference between the total amount in the spiked vs. unspiked samples. RESULTS AND DISCUSSION Chromatography. Figure 1 shows a typical chromatogram of a benzo[a]pyrene standard solution. The detection limit, twice the base-line noise, was estimated to be 10 pglinjection, which corresponds to 0.1 pg of benzo-[alpyrenelkg for roasted coffee and spent grounds and 0.1 ng of benzo[a]pyrene/kg for coffee brew. In Figure 2 are shown a chromatogram obtained for a ground roasted coffee sample containing less than 0.1 pg of benzo[a]pyrene/ kg and a chromatogram for the same coffee sample fortified with 0.5 pg of benzo[a]pyrene/kg of coffee. Peak identification was established by comparing the retention times of peaks in the sample chromatograms with those in the standard chromatograms. Further confirmation of identity can be obtained by various methods that rely either on comparison of the chromatographic characteristics of the eluting components with benzo[a]ppene reference material or on the characteristics of the detection system (Parris, 1984). Roasted Coffee. A total of 55 ground roasted coffee samples, commercially available in The Netherlands, were purchased and analyzed between 1980 and 1984. These products included brands of all major coffee roasting companies in The Netherlands. All samples were analyzed in duplicate, and the results are presented in Table V. The benzo[a]pyrene levels in the roasted coffee samples analyzed range from approximately 0.1 to 0.5 jtg/kg. The results of this study are in good agreement with previously published data for normal roasted coffee that vary from 0.1 to 0.8 bg/kg (Fritz, 1968; Lintas et al., 1979; Bories and Gasc, 1980; Guyot et al., 1982). Coffee Brew. For all roasted coffee samples investigated in this study, benzo[a]pyrene levels of less than 0.5 jtg/kg were obtained. In view of these very low benzo- [alpyrene levels, these samples were considered not very suitable for an investigation of the benzo[a] pyrene content of coffee brew. Guyot et al. (1982), however, have reported higher values (up to 3.2 jtg/kg) for heavily roasted coffee. Also for a partially burnt coffee sample, investigated in a previously reported study on coffee roasting and benzo- [alpyrene (van der Stegen and van Overbruggen, 1982), a benzo[a]pyrene content of 22.7 jtg/kg was found. The samples investigated in the framework of this study on coffee roasting and benzo[a]pyrene were analyzed in the laboratory of TNO-CIVO by means of an HPLC method that is similar to the method applied in the present investigation. The benzo[a]pyrene content of an over-roasted coffee sample (supplied by Douwe Egberts Research and Development, Utrecht, The Netherlands) was determined, as well as brewed coffee prepared from that sample by two different methods, using a coffee to water ratio of 50 g/L. [This ratio will produce rather strong coffee brew by Dutch standards; in The Netherlands more common practice is the ratio of 40 g/L.J Both the coffee brews and the spent grounds were analyzed for benzo[a]pyrene. As demonstrated in Table VI, very low benzo[a]pyrene levels are found in brews prepared by two different methods from an over roasted coffee sample containing 2.0 jtg of benzo-[alpyrenelkg. Also from the results obtained for the determination of benzo[a]pyrene in spent grounds (Table VI), it is apparent that nearly a11 the benzo[a]pyrene present in the roasted coffee is retained in the spent grounds. The elevated benzo[a]pyrene content of the spent grounds compared to that of the roasted coffee is due principally to the removal of soluble solids, volatile aroma components, and water during the brewing process and the drying of the spent grounds. The benzo[a]pyrene levels in coffee brew found in the present work indicate benzo[a]pyrene extraction yields of about 1% for both preparation methods. This value is significantly lower than previously published benzo[a] pyrene extraction yields that vary from about 25 to 80%. These high benzo[a]pyrene extraction yields were obtained, however, by rather insensitive ultraviolet and/or fluorescence techniques (Fritz, 1969; Grimmer and Hildebrandt, 1966) or HPLC with UV detection (Guyot et al., 1982). This latter HPLC detection system is less sensitive and specific compared with the fluorescence detector used in this study and therefore more susceptible to interferences. CONCLUSION A relatively rapid and reliable method has been developed and applied to the determination of trace levels of benzo[a]pyrene in roasted coffee, coffee brew, and spent grounds. The results of this study indicate that benzo-[ alpyrene levels in roasted coffee commercially available in The Netherlands are generally below 0.5 jtg/kg. For coffee brews prepared from an over-roasted coffee sample with an elevated benzo[a]pyrene level of 2 pg/kg, benzo-[alpyrene contents of approximately 1 ng/L were found. It is apparent from these results that the benzo[a]pyrene content of coffee brew, prepared from normal roasted coffee with a benzo[a]pyrene level 10.5 pg/kg, will be less than 1 ng/L. The daily total food and beverage intake of benzo[a]pyrene by humans is estimated to range from 0.25 to 2.5 pg (Dennis et al., 1983; Fritz, 1983). These figures indicate that coffee contributes very insignificant quantities to the daily human intake of benzo[a]pyrene. In this study only the occurrence of benzo[a]pyrene in roasted coffee and coffee brew has been investigated. Future studies are planned in which the determination of various PAH in both coffee and tea samples will be investigated. [ Last edited by angelcarlos on 2010-3-3 at 18:04 ] |
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xiaoqihu
铁杆木虫 (著名写手)
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2楼2010-03-03 22:05:04
xiaoqihu
铁杆木虫 (著名写手)
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angelcarlos(金币+50): 2010-03-03 23:00
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回收实验 从烘焙咖啡中回收的benzo[a]- pyrene通过与加入了标准的benzo[a]- pyrene样品溶液(1.00 or 1.30 wg/mL)的20克咖啡来测定，其中含有20或26 ng的benzo[a]- pyrene。另一份20克的样品没有加入标准溶液。从调制咖啡中得到的benzo[a]- pyrene通过与加入了标准benzo[a]- pyrene溶液的1升调制咖啡样品测定，调制咖啡用家用咖啡机制备，咖啡与水的比例为50克每升。另一份1升的调制咖啡则没有家标准benzo[a]- pyrene溶液。 样品制备由上所述，回收比率是基于加入和没有加入的总量不同来决定的 结果讨论 色谱图1是标准的benzo[a]- pyrene溶液。检测限2倍于基线干扰噪音，估计是1pg每次注射，相当于含有benzo[a]- pyrene 0.1 pg每公斤的烘焙咖啡和咖啡残渣的含量， 或者含有benzo[a]- pyrene 0.1 ng 每公斤的 调制咖啡中的benzo[a]- pyrene的含量 图2 是从benzo[a]- pyrene含量少于0.1 pg每公斤的咖啡回收物和加入了0.5 pg标样的回收物中获得的谱图，样品峰的保留时间是通过和加入了标准benzo[a]- pyrene溶液的同样批次样品对比得来的，进一步确定地方法要么是通过和benzo[a]- pyrene流动参比对照，要么是通过监测系统本身来完成。(Parris, 1984). 烘焙咖啡 55克荷兰产咖啡购买和分析与1980到1984年，这种深度烘焙咖啡是荷兰市场上面主要的咖啡。所有的分析方法完全一样。数据结构展现于表格V，烘焙咖啡中benzo[a]pyrene含量从0.1到0.5，结果对比以前关于普通烘焙咖啡的发表文章是基本一致的，0.1 to 0.8 bg/kg (Fritz, 1968; Lintas et al., 1979; Bories and Gasc, 1980; Guyot et al., 1982). 调制咖啡 所有研究样本的benzo[a]pyrene含量均低于0.5 jtg/kg，对于那些非常低含量的样品是不是和作为benzo[a] pyrene含量研究的。但是Guyot et al 在1982年报道了高于3.2jtg的深度烘焙咖啡测试数据。同时有报道说局部燃烧咖啡benzo[a] pyrene含量是22.7jtg。 按照这种模式对研究benzo[a] pyrene含量的测试采用了TNO-CIVO实验室的HPLC测试方法，和以前报道的相同。 对于深度烘焙咖啡的样品测试（Douwe Egberts Research and Development, Utrecht, The Netherlands提供）和上述的调制咖啡样品制备方法一样，咖啡比水（50克比1升）这个比例稍大于目前荷兰所普遍采用的40克比1升。 调制咖啡和残渣都用来测试benzo[a]pyrene，入表格VI所示，深度烘焙咖啡中浓度很低的样品为2jtg每公斤，同时对于残渣测试，几乎所有的数据都表明benzo[a]pyrene有残留。这可能是因为相对于烘焙咖啡，咖啡残渣的提取过程中去除了可溶物，挥发性的芳香物质和水。目前对调制咖啡的benzo[a]pyrene的含量表明通过两种方法都只能提取1%的benzo[a]pyrene， 得出的数值很明显低于以前报道的25-28%的收率。但是高浓度的测试结果是通过采用低灵敏度的紫外或者荧光检测技术的HPLC得到的，或者通过只采用UV监测的HPLC。后者的监测系统的灵敏度低于本文采用的荧光检测器，因此更容易受到干扰，更加灵敏。 结论 发展和应用了相对快速可信赖的检测烘焙咖啡，调制咖啡和咖啡残渣中痕量benzo[a]pyrene的方法。结果表明了市售荷兰烘焙咖啡中benzo[a]pyrene含量基本上低于0.5jtg。对于深度烘焙咖啡的调制咖啡得到的benzo[a]pyrene含量提高了2 pg每公斤，大概为1 ng每升。明显高于普通烘焙咖啡的benzo[a]pyrene含量10 .5 pg每公斤， 普通的少于1 ng每升。人们每日通过食物和饮料摄取的benzo[a]pyrene大概为0.25到2.5 pg (Dennis et al., 1983; Fritz, 1983). 数据表明人们每日通过咖啡摄取的benzo[a]pyrene是很少量的。 在这项研究中，只有研究了烘焙咖啡和调制咖啡中的benzo[a]pyrene含量，下一步我们准备对咖啡喝茶叶中的PAH进行研究。 [ Last edited by xiaoqihu on 2010-3-3 at 23:47 ] |
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