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研究发现,在磷酸介质中,甲醛可以在一定温度下催化溴酸钾氧化二甲酚橙使其褪色,且褪色程度(ΔA)与甲醛的浓度在一定的范围内符合朗伯-比尔定律,据此建立了催化光度法测定甲醛含量的新方法。在最优的试验条件下,方法的线性范围为0.05~0.80μg/mL,检出限为0.013μg/mL,回收率在95%~110%之间。可用于虾仁中甲醛含量的测定,其效果令人满意。 相似文献
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本实验采用速差动力学分光光度法对酪氨酸和色氨酸的混合物进行不经分离的同时测定.在碱性介质下,KMnO4可以氧化酪氨酸和色氨酸,同时KMnO4被还原为浅绿色的MnO42-,测定反应过程中MnO2-的吸光度可推知其浓度的变化情况.测定所得的数据采用化学计量学.偏最小二乘方法解析,从而可对酪氨酸和色氨酸分别进行测定. 相似文献
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利用5-溴水杨基荧光酮,CTMAB与Fe(Ⅲ),Ti(Ⅳ)形成的三元配合物显色体系,采用联机检测技术,结合流动注射方法,对双组分金属离子进行了速差动力学同时测定的研究,并且测定了电铸液中Fe(Ⅲ)的含量。结果表明,该方法不仅排除了Ti(Ⅳ)的干扰,而且测定了Ti(Ⅳ)的含量。方法的回收率在96%~106%之间。样品处理简便,电铸液中其它组分基本不干扰测定。 相似文献
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对于分部传动的纸机,尤其是高速纸机,是通过纸幅将各个分部传动点联系在一起的,生产工艺不但要求各分部速度具有较高的稳定精度,而且要求各分部之间速度差具有一定灵活性的调整范围。在实际生产中,由于受浆料和纸张抄造条件的限制,经常要求调整车速,这种情况在纸机改造后试生产阶段尤为突出。在调试过程中,主要出现以下问题:1.运行中纸机车速逐渐调到每分钟几十米范围时,个别分部控制器出现饱和值,双闭环控制系统失去了最佳调节作用,分部间速差调整失灵,即运差电位器调到头了。2.某些分部在平时处理电气故障后需要分部速度重… 相似文献
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主要讨论了两种电路,即速差(实际上是频差)预置电路和脉冲迭加电路的设计。将它用于印染联合机的鉴频鉴相控制系统,可使该系统实现线速度相等的同步运行和高精度的速差同步运行。 相似文献
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本文研究不同浓度的Fe~(2+)和Fe~(3+)对菠萝蛋白酶活性和60℃下酶稳定性的影响,以及通过圆二色谱检测Fe~(2+)和Fe~(3+)对酶构象的变化,并初步探究EDTA-2Na结合超滤膜法在菠萝蛋白酶制备工艺中清除铁离子的应用效果。结果表明:Fe~(2+)浓度在0~0.75 mmol/L范围内,对菠萝蛋白酶活性有促进作用,以0.5 mmol/L促进效果最佳,但浓度大于0.75 mmol/L时,抑制酶活,且随浓度增加,抑制程度增强。Fe~(3+)对菠萝蛋白酶只有抑制作用,抑制程度与Fe~(3+)浓度成正比,且Fe~(3+)对酶的抑制作用强于Fe~(2+)。60℃下,Fe~(2+)在浓度为0.5 mmol/L对菠萝蛋白酶的稳定性表现出促进作用,延长了酶的半衰期。Fe~(3+)对酶的稳定性呈现抑制作用。Fe~(2+)和Fe~(3+)浓度大于0.5mmol/L时,随离子浓度的升高,对酶稳定性的抑制作用增强。采用圆二色谱检测酶的二级结构表明:Fe~(2+)和Fe~(3+)对酶抑制作用表现为α-螺旋含量下降,β-折叠和β-转角含量稍下降,无规卷曲含量明显提高。EDTA-2Na结合超滤膜法除铁的效果很明显,铁含量(干重)从291.63 mg/kg降低到142.99 mg/kg,铁离子去除率达50.97%,其酶活也由597.27 U/mg上升到808.52 U/mg,酶活提高了26.13%。 相似文献
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以2,5-呋喃二甲酸和六水硝酸锌为原料,N,N-二甲基甲酰胺为溶剂合成一种锌金属有机骨架材料[(Me_2NH_2)_2Zn_3(fdc)_4]_n·DMA(Zn-MOF)。用荧光光谱法对该材料的荧光特性进行研究,发现该材料在波长379 nm和398 nm处有很强的荧光发射峰。考察食品中可能存在的16种不同金属离子对该材料荧光强度的影响,研究表明,Fe~(3+)能选择性地令该材料产生荧光淬灭现象。此外,考察Fe~(3+)浓度、浸泡时间和2种混合金属离子(Fe~(3+)-M~(+/2+/3+))对荧光淬灭敏感度的影响。结果表明,锌金属有机骨架材料对Fe~(3+)具有高度选择性传感功能,可作为荧光探针应用到食品Fe~(3+)的检测中,并可以高效地检测出Fe~(3+)。 相似文献
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通过水热法合成Fe3O4@VC磁性纳米粒子,采用透射电镜、红外光谱和X射线衍射等表征手段对合成的粒子结构进行表征。探讨了pH值、吸附时间、吸附剂用量、溶液初始浓度等因素对六价铬Cr(VI)吸附的影响,并对Cr(VI)的吸附热力学和动力学进行了研究。结果表明,在pH为1.50,25 ℃条件下,磁性纳米粒子对Cr(VI)的饱和吸附量可达39.12 mg/g,吸附率为85%以上。吸附性能试验表明,磁性纳米粒子对Cr(VI)的吸附符合Langmuir热力学模型和HO准二级动力学吸附模型。 相似文献
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Ashok K. Shrestha Tharalinee Ua-arak Benu P. Adhikari Tony Howes Bhesh R. Bhandari 《International Journal of Food Properties》2013,16(3):661-673
Spray drying behavior of orange juice concentrate with various levels of maltodextrin (DE 6) was studied. Five combinations of orange juice concentrate and maltodextrin (25:75, 30:70, 35:65, 40:60, and 50:50) were spray dried at 160 and 65°C inlet and outlet temperatures, respectively. The product recovered with 50% maltodextrin concentration was sticky and only 20% powder was recovered. The recovery of orange juice powder increased as the amount of maltodextrin in powders increased. The particle size and bulk density remained almost the same in all except in 50% maltodextrin powder which was slightly larger and more dense. The moisture content of spray dried powders was high and desiccated before measuring glass transition temperature. The anhydrous spray dried powders showed increased Tg values with increasing maltodextrin concentration, from 66°C in 50% maltodextrin to 97°C in 75% maltodextrin containing powders. The glass rubber transition (Tg-r) values of all the products measured using novel Thermal Mechanical Compression Test (TMCT) were higher than Tg values measured by DSC; the difference in values increased with increase in maltodextrin concentration. 相似文献
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Rodríguez-Lucena P Benedicto A Lucena JJ Rodríguez-Castrillón JA Moldovan M García Alonso JI Hernández-Apaolaza L 《Journal of the science of food and agriculture》2011,91(3):395-404
BACKGROUND: During the last decade, environmental concerns regarding the use of recalcitrant synthetic chelates to overcome iron chlorosis has increased and new ligands such as lignosulfonates (LS) have been evaluated. However, the efficacy of these products is variable. In this work a hardwood (eucalyptus) and softwood (spruce) LS were compared to try to relate their physico‐chemical characteristics and their efficacy. Also two more products derived from the eucalyptus lignosulfonate were tested. RESULTS: All the LS tested presented a good ability to complex Fe, but only the spruce LS was capable to maintain significant amounts of soluble Fe above pH 8. According to the FTIR data, structural changes related to the Fe source (Fe2+ or Fe3+) used to form the complex occurred in the LS molecule and might influence their efficacy. Cucumber (Cucumis sativus L. cv Ashley) chlorotic plants were used to test lignosulfonate efficacy when applied through foliar sprays in comparison with FeSO4 and EDTA/57Fe3+. The 57Fe content of plants sprayed with LS was very low in respect to the EDTA treatment, but this was not reflected in the biomass and re‐greening rates. Eucalyptus LS modifications improve its efficacy for iron chlorosis recovery to levels similar to those found for the spruce LS. Two applications of the LS are recommended. CONCLUSIONS: Lignosulfonates did not require surfactants for their application; they did not burn the leaves, and had a stimulating effect on the vegetative growth of the plants. So these by‐products could be a good alternative when applied through foliar sprays for cucumber plants. Copyright © 2010 Society of Chemical Industry 相似文献
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目的建立石墨化碳黑净化-二苯碳酰二肼衍生-分光光度法测定着色明胶空心胶囊中六价铬的含量。方法样品经磷酸盐缓冲液Ⅰ提取,80℃水浴振荡1 h,碱性条件下用石墨化碳黑脱除色素,二苯碳酰二肼丙酮溶液酸性条件下衍生显色,10 mm石英比色皿比色,采用分光光度法在540 nm波长下检测,扣除本底后以外标法定量。结果 50 mg石墨化碳黑粉末(graphitized carbon black,GCB)对于明胶空心胶囊的着色剂具有较好的脱除效果,GCB在待净化液pH大于12.5的条件下对Cr(Ⅵ)的吸附作用不明显,回收率可达90%以上。样品中Cr(Ⅲ)的存在对于本方法测定Cr(Ⅵ)无显著影响。根据使用的比色皿光程,方法检出限为1.6 mg/kg或更低。结论本方法快速准确,适用于明胶空心胶囊中六价铬的检测。 相似文献
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在醋酸-醋酸钠缓冲溶液(pH 3.5)介质中,H2O2可以与Fe(Ⅱ)快速地发生氧化还原反应,所以H2O2对Fe(Ⅱ)-双吡啶(2,2’-bipyridine,BPY)显色体系有明显的阻抑作用,据此建立了一种测定食品中微量H2O2的新方法。试验考察了pH、缓冲溶液用量、显色剂用量、振荡时间和显色时间对H2O2测定的影响。在选定条件下,该方法的线性范围为0.004~0.02 mmol/L(R2=0.9988),方法的检出限为2 mg/kg。该法用于实际食物样品凤爪中H2O2含量的测定,其RSD均小于5%(n=6),在0.0103,0.0206和0.0309 mg/L三个质量浓度水平下其加标回收率在96.8%~99.1%之间。该法能满足食品中微量H2O2的测定要求。 相似文献