皮革中六价铬的研究进展

对国内外有关皮革中六价铬形成的原因、检测方法和预防措施的研究现状进行了总结 ,并提出了一些自己的观点     

石墨炉原子吸收法测定食品中六价铬

建立食品中Cr(Ⅵ)的测定方法。方法 以10%的盐酸作为浸提液,样品通过微波120℃浸提15min,提取液经Waters MAX小柱(500mg,6cc)分离后用5%氨水淋洗,然后将淋洗液定容,经石墨炉原子吸收法间接测量Cr(Ⅵ)含量。结果 该方法在1～10μg/L的线性范围内具有良好的线性关系,r＞0.999,方法检出限为0.0087mg/kg,回收率均在90.24%～108.06%之间,RSD为3.19%～6.01%。结论 该方法简便、快速、灵敏和准确,适合蔬菜、水果、谷物以及保健食品中Cr(Ⅵ)的检测。     

深色皮革中六价铬含量测定方法的研究

在不改变DIN5 3 3 1 4检测方法的前提下 ,采用特效脱色剂对深色皮革的提取液进行脱色 ,解决了深色皮革中六价铬含量的测定难题     

HPLC法测定纺织品中可萃取六价铬

建立了柱前衍生高效液相色谱测定纺织品中可萃取六价铬的方法.用二苯基碳酰二肼与纺织品水萃取液中的六价铬在酸性条件下进行衍生反应,以甲醇和10 mmol/L H3PO4水溶液为流动相,ZORBAX SB-C18柱分离,采用高效液相色谱于540nm波长处对衍生物进行检测.该方法可有效消除颜色的干扰,且精确、可靠、快速、重现性好、灵敏度高,在0 ～ 1.2 mg/kg织物的范围内,线性相关系数r=0.99982,检测限达0.02 mg/kg织物.     

Reduction of hexavalent chromium with the brown seaweed Ecklonia biomass

A new type of biomass, protonated brown seaweed Ecklonia sp., was used for the removal of Cr(VI). When synthetic wastewater containing Cr(VI) was placed in contact with the biomass, the Cr(VI) was completely reduced to Cr(III). The converted Cr(III) appeared in the solution phase or was partly bound to the biomass. The Cr(VI) removal efficiency was always 100% in the pH range of this study (pH 1 to approximately 5). Furthermore, the Cr(VI) reduction was independent of the Cr(III) concentration, the reaction product, suggesting that the reaction was an irreversible process under our conditions. Proton ions were consumed in the ratio of 1.15 +/- 0.02 mol of protons/mol of Cr(VI), and the rate of Cr(VI) reduction increased with decreasing the pH. An optimum pH existed for the removal efficiency of total chromium (Cr(VI) plus Cr(III)), but this increased with contact time, eventually reaching approximately pH 4 when the reaction was complete. The electrons required for the Cr(VI) reduction also caused the oxidation of the organic compounds in the biomass. One gram of the biomass could reduce 4.49 +/- 0.12 mmol of Cr(VI). From a practical viewpoint, the abundant and inexpensive Ecklonia biomass could be used for the conversion of toxic Cr(VI) into less toxic or nontoxic Cr(III).     

Co-removal of hexavalent chromium through copper precipitation in synthetic wastewater

The mechanisms of hexavalent chromium [Cr(VI)] co-removal with copper [Cu(II)] during homogeneous precipitation were studied with batch tests using a synthetic solution containing Cr(VI) and Cu(II). Metal precipitation was induced by adding Na2CO3 stepwise to different pH, and the respective removals of Cu(II) and Cr(VI) were measured. At the same time, the relative quantities of Cu(II) and Cr(VI) in the precipitates were also analyzed to establish their stoichiometric relationship. The results indicated that, in a solution containing 150 mg/L Cu(II) and 60 mg/L Cr(VI), the initial co-removal of Cr(VII with Cu(II) began at pH 5.0 and completed at pH 6.2. At pH 5.0-5.2, coprecipitation took place through the formation of copper-chromium-bearing solids [such as CuCrO4 and/or CuCrO4 x 2Cu(OH)2]. Thereafter, the remaining soluble copper started to react with carbonate in a heterogeneous environment to form the negatively charged basic copper carbonate precipitates [CuCO3 x Cu(OH)2], which subsequently adsorbed additional Cr(VI) (or HCrO4-) at pH 5.2-6.2. The maximum Cr(VI) co-removal took place at pH 6.2. Between the two mechanisms, co-precipitation accounted for about 29% of the total chromium's co-removal while the remaining 71% was attributed to surface adsorption, mainly through electrostatic attraction and ligand exchange. When the solution pH was increased to beyond 7.5, a surface charge reversal took place on the basic copper carbonate solids, and this led to some Cr(VI) desorption. Thus, the extent of Cr(VI) adsorption is highly pH dependent.     

液相色谱-电感耦合等离子体质谱法测定饲料中的六价铬

目的建立液相色谱-电感耦合等离子体质谱法(liquid chromatography-inductively coupled plasma mass spectrometry,LC-ICP-MS)测定饲料中六价铬含量的分析方法。方法以碱性溶液和磷酸缓冲液为提取溶剂,100 mmol/L硝酸铵溶液(pH值7.5)为流动相,采用Dionex IonPac AG19(4 mm×50 mm,4μm)+Dionex IonPac AS19阴离子柱(4 mm×250 mm,4μm)对样品提取液进行分离,电感耦合等离子体质谱进行测定。结果该方法检出限为0.30 mg/kg,线性相关系数大于0.999,精密度RSD5%,回收率在80%～110%之间。结论该方法科学准确、操作简单快速,可满足各种饲料中六价铬含量的测定。     

番茄红素中总铬和六价铬本底值分析及健康风险评估

了解保健品中化学污染物的本底水平,有利于科学地进行综合判定,为制定相关的标准和法规提供理论依据。本文采用微波消解-离子交换分离-石墨炉原子吸收法对12种番茄红素胶囊中铬本底值水平进行测定和分析。结果表明,番茄红素样品中Cr本底值为401⁴521μg/kg,Cr(VI)本底水平为0.74521μg/kg,Cr(VI)本底水平为0.7²66μg/kg,仅占Cr的0.9%266μg/kg,仅占Cr的0.9%⁷%,番茄红素中的铬主要以Cr(Ⅲ)形式存在;Cr、Cr(VI)暴露健康风险指数分别为0.007和0.0006,无健康风险。本研究为正确认识番茄红素中铬天然水平及健康风险评估提供了数据支持。     

Removal of hexavalent chromium by biosorption process in rotating packed bed

Removal of hexavalent chromium ions from an aqueous solution by crude tamarind (Tamarindus indica) fruit shell was examined in a rotating packed bed contactor by continuously recirculating a given volume of solution through the bed. Reduction of Cr(VI) to Cr(III) within the biosorbent appeared to be the removal mechanism. Depletion rate of Cr(VI) from, and release of reduced Cr(III) ions into the aqueous phase, was influenced by mass transfer resistance besides pH and packing depth. A mathematical model considering the reduction reaction to be irreversible and incorporating intraparticle and external phase mass transfer resistances represented the experimental data adequately. The study indicated that the limitations of fixed bed contactor operating under terrestrial gravity in intensifying mass transfer rates for this system can be overcome with rotating packed bed due to liquid flow under centrifugal acceleration.     

杂醇油酶法制备天然等同酯香料的研究

研究了无溶剂体系中杂醇油酶法转化制备天然等同酯香料的影响因素,筛选适宜脂肪酶,优化工艺条件,研究超声处理对酶法制备酯香料的作用.结果表明:在无溶剂体系中固定化脂肪酶Novozym 435 FG的酯化活力高且易回收,乙酸异戊酯产率达到92.62％;除水剂分子筛的加入促进了酯化反应,乙酸加入次数和间隔时间、反应温度和反应时...     

Reduction of hexavalent chromium by H2O2 in acidic solutions

The rates of the reduction of Cr(VI) with H2O2 were measured in NaCl solutions as a function of pH (1.5-4.8), temperature (5-40 degrees C), and ionic strength (I = 0.01-2 M) in the presence of an excess of reductant. The rate of Cr(VI) reduction is described by the general expression -d[Cr(VI)]/dt = k2[Cr(VI)](m)[H2O2](n)[H+](z), where m = 1 and n and z are two interdependent variables. The value of n is a function of pH between 2 and 4 (n = (3 x 10(a))/(1 + 10(a)), where a = -0.25 - 0.58pH + 0.26pH2) leveling off at pH < 2 (where n approximately = 1) and pH > 4 (where n approximately = 3). The rates of Cr(VI) reduction are acid-catalyzed, and the kinetic order z varies from about 1.8-0.5 with increasing H2O2 concentration, according to the equation z = 1.85 - 350.1H2O2 (M) which is valid for [H2O2] < 0.004 M. The values of k2 (M(-(n+z)) min(-1)) are given by k2 = k/[H+](z) = k1/[H2O2](n)[H+](z), where k is the overall rate constant (M(-n) min(-1)) and k, is the pseudo-first-order rate constant (min(-1)). The values of k in the pH range 2-4 have been fitted to the equation log k = 2.14pH - 2.81 with sigma = +/- 0.18. The values of k2 are dependent on pH as well. Most of the results with H2O2 < 3 mM are described by log k2 = 2.87pH - 0.55 with sigma = +/- 0.54. Experimental results suggest that the reduction of Cr(VI) to Cr(III) is controlled by the formation of Cr(V) intermediates. Values of k2 and k calculated from the above equations can be used to evaluate the rates of the reaction in acidic solutions under a wide range of experimental conditions, because the rates are independent of ionic strength, temperature, major ions, and micromolar levels of trace metals (Cu2+, Ni2+, Pb2+). The application of this rate law to environmental conditions suggests that this reaction may have a role in acidic solutions (aerosols and fog droplets) in the presence of high micromolar concentrations of H2O2.     

液相色谱-质谱法测定保健食品中的三价铬及六价铬含量

目的建立液相色谱-质谱法测定保健食品中总铬、三价铬及六价铬含量的分析方法,并与原子吸收法的检测结果进行比较。方法利用液相色谱-质谱法测定提取和氧化反应前后样品溶液中六价铬,分别计算总铬、三价铬和六价铬的量。结果 8批样品(3批胶囊,5批片剂)测定六价铬和总铬含量分别为188.7~257.8mg/kg和189.1~257.4 mg/kg。该方法可以实现保健食品中总铬、三价铬和六价铬的测定,六价铬的方法检出限为0.03 mg/kg,RSD=3.72%(n=5),定量限为1.0 mg/kg,RSD=3.07%(n=5)。结论该方法简便易行,与原子吸收法测定总铬的结果一致,可用于保健食品中铬及其形态的测定。     

Carbothermal synthesis of carbon-supported nanoscale zero-valent iron particles for the remediation of hexavalent chromium

Nanoscale, zero-valent iron is a promising reagent for in situ reduction of a variety of subsurface contaminants, but its utility in full-scale remediation projects is limited by material costs. Iron nanoparticles (20-100 nm diameter) supported on carbon (C-Fe0) were synthesized by reacting iron salts, adsorbed or impregnated from aqueous solutions onto 80 m2/g carbon black, at 600-800 degrees C under Ar. Similar products were obtained by heating the reactants under air in a covered alumina crucible. X-ray powder diffraction patterns show that Fe3O4 particles are formed at 300-500 degrees C in the initial stage of the reaction and that these particles are reduced to a mixture of alpha- and gamma-Fe nanoparticles above 600 degrees C. When C-Fe0 was combined with carboxymethylcellulose in a 5:1 weight ratio in water, the resulting material had similar transport properties to previously optimized nanoiron/polyanion suspensions in water-saturated sand columns. At a 10:3 Fe/Cr mole ratio, C-Fe0 reduced a 10 ppm Cr(VI) solution to approximately 1 ppm within three days. The surface area normalized first-order Cr removal rate was 1.2 h(-1) m(-2) under these conditions. These results demonstrate that reactive nanoiron with good transport properties in water-saturated porous media can be made in a scalable process from inexpensive starting materials by carbothermal reduction.     

Removal of hexavalent chromium with a lignocellulosic substrate extracted from wheat bran

In this paper, a new recovery system of the toxic hexavalent chromium Cr(VI) is proposed that uses a lignocellulosic substrate derived from the industrial treatment process of wheat bran. We studied the adsorption mechanism of Cr(VI) onto the lignocellulosic substrate and showed that the adsorption reaction consumes a large amount of protons goes along the reduction of Cr(VI) into Cr(III). The oxidation of lignin moieties takes place concurrently to the chromium reduction and leads to the formation of hydroxyl and carboxyl functions. The latter contribute to an increase in the number of ion-exchange sites for the reduced chromium. The maximum adsorption capacity for hexavalent chromium was found at about 35 mg g(-1) in an acidic medium. This is comparable to other natural substrates and ordinary adsorbents.     

Removal of hexavalent chromium from wastewater using a new composite chitosan biosorbent

A new composite chitosan biosorbent was prepared by coating chitosan, a glucosamine biopolymer, onto ceramic alumina. The composite bioadsorbent was characterized by high-temperature pyrolysis, porosimetry, scanning electron microscopy, and X-ray photoelectron spectroscopy. Batch isothermal equilibrium and continuous column adsorption experiments were conducted at 25 degrees C to evaluate the biosorbent for the removal of hexavalent chromium from synthetic as well as field samples obtained from chrome plating facilities. The effect of pH, sulfate, and chloride ion on adsorption was also investigated. The biosorbent loaded with Cr(VI) was regenerated using 0.1 M sodium hydroxide solution. A comparison of the results of the present investigation with those reported in the literature showed that chitosan coated on alumina exhibits greater adsorption capacity for chromium(VI). Further, experimental equilibrium data were fitted to Langmuir and Freundlich adsorption isotherms, and values of the parameters of the isotherms are reported. The ultimate capacity obtained from the Langmuir model is 153.85 mg/g chitosan.     

Behavior of hexavalent chromium in a polluted groundwater: redox processes and immobilization in soils

This work describes the chemical mechanisms governing transport and reduction of hexavalent chromium in soils of a contaminated industrial waste landfill. Groundwater and soil analyses indicate that the main source of chromium is a slag heap essentially consisting of mill tailings. In the groundwater, downstream migration of Cr(IV) is limited thanks to a redox mechanism involving chromate ions and ferrous ions or Fe(II)-bearing minerals. High Fe2+ concentrations in the groundwater are a result of pyrite residues from old activities at the site. Analyses of soil samples reveal that chromium is preferentially located in the soil profile at the fluctuation of the groundwater level. Grain size fractionation of four soil samples was performed, and fraction analyses show that chromium is preferentially accumulated in the clay fraction (<2 microm) and more specifically associated with montmorillonite particles. This work is a demonstration of the reduction of Cr(VI) by Fe(II) studied previously in the laboratory (Buerge, I. J.; Hug, S. J. Environ. Sci. Technol. 1997, 31, 1426-1432; Fendorf, S. E.; Li, G. Environ. Sci. Technol. 1996, 30, 1614-1617; Sedlak, D. L.; Chan, P. G. Geochim. Cosmochim. Acta 1997, 11, 2185-2192) in a field setting. Cr(VI) migration into the groundwater is stopped vertically by the very thick green clay unit and horizontally by the presence of Fe(II) acting as a chemical barrier. The specific site conditions safely prevent any extension of the Cr pollution.     

Natural occurrence of steroid hormones in food

The natural occurrence of the sex steroid hormones progesterone, testosterone, 17β-estradiol and estrone in food was investigated in a survey of the German market basket. The main metabolic precursors, intermediates and metabolites (pregnenolone, androstenedione, hydroxyprogesterone, dehydroepiandrosterone (DHEA), dihydrotestosterone, androsterone, 17α-estradiol and estriol) were also included in the investigation. Particular attention was paid to DHEA, which is said to have anti-aging properties. Analysis was carried out by gas chromato-graphy-mass spectrometry (GC-MS). The steroid patterns of pork, meat products, fish and poultry resemble those known for beef. Milk and milk products reflect the hormone profile of female cattle with high amounts of progesterone, which accumulates with increasing milk fat content. Milk products supply about 60–80% of ingested female sex steroids. Eggs are a considerable source of any of the investigated steroids and contribute to the nutritional hormone intake in the same order as meat and fish (10–20%). In vegetable food no estrogens could be detected. Plants supply testosterone in the same order as meat and milk products (20–40%) though. They contain considerable amounts of hormone precursors as well (contribution to DHEA supply: about 80%). In comparison to the human daily production of steroid hormones the nutritional supply (about 10 μgd⁻¹ progesterone, 0.05 μg d⁻¹ testosterone, 0.1 μg d⁻¹ estrogens, 0.5 μg d⁻¹ DHEA) is insignificant.     

Natural occurrence of bisphenol F in mustard

Bisphenol F (BPF) was found in mustard up to a concentration of around 8 mg kg^?1. Contamination of the raw products or caused by the packaging could be ruled out. Also, the fact that only the 4,4?-isomer of BPF was detected spoke against contamination from epoxy resin or other sources where technical BPF is used. Only mild mustard made of the seeds of Sinapis alba contained BPF. In all probability BPF is a reaction product from the breakdown of the glucosinolate glucosinalbin with 4-hydroxybenzyl alcohol as an important intermediate. Hot mustard made only from brown mustard seeds (Brassica juncea) or black mustard seeds (Brassica nigra) contained no BPF. BPF is structurally very similar to bisphenol A and has a similar weak estrogenic activity. The consumption of a portion of 20 g of mustard can lead to an intake of 100–200 µg of BPF. According to a preliminary risk assessment, the risk of BPF in mustard for the health of consumers is considered to be low, but available toxicological data are insufficient for a conclusive evaluation. It is a new and surprising finding that BPF is a natural food ingredient and that this is the main uptake route. This insight sheds new light on the risk linked to the family of bisphenols.     

Natural occurrence of aflatoxins in Korean meju

Aflatoxin B₁ (AFB₁) was found in 35 of 60 (58.3%) meju samples with an average concentration of 7.3ng/g by ELISA. Contamination of AFB₁ was confirmed in 25 of 60 samples (41.6%) using HPLC, with an average concentration of 6.9ng/g. Mean recoveries from meju ranged from 107% to 170% for AFB₁ using ELISA at a spiking range of 1 to 50ng/g. Over the same range, recoveries using HPLC were from 70% to 83%. The levels of AFB₁ determined by ELISA and by HPLC demonstrated a close relationship between the two methods (r2 = 0.9324) employed in this study. In order to evaluate the potential health risks of AFB₁ on Koreans consuming meju, we calculated the estimated probable daily intake (PDI) based on the average contamination levels and compared it with the estimated tolerable daily intake (TDI). The PDIs of AFB₁ from kanjang and dwenjang were determined to be 0.04 and 0.21ng/kg bw/day, respectively, and were higher than TDIs.     

氮硼共掺杂碳量子点的制备及其对六价铬的检测

目的 建立一种基于荧光碳量子点的快速检测方法,定量检测饮用水和食品中的六价铬[hexavalent chromium, Cr(Ⅵ)]。方法 以无水柠檬酸和3-氨基苯硼酸分别作为碳、氮和硼源,通过一步水热法合成氮硼共掺杂碳量子点(nitrogen-boron-doped carbon quantum dots, N,B-CQDs),基于荧光内滤效应对Cr(Ⅵ)进行检测。结果 在优化后的最佳检测条件下, N,B-CQDs对Cr(Ⅵ)在0.01～10.00 mg/L内呈现良好的线性关系,检出限低至3.81μg/L,表现出选择性好、灵敏度高等特点。将此方法应用于饮用水、白醋和虾皮中Cr(Ⅵ)含量的测定,加标回收率在85.8%～112.3%之间,相对标准偏差低于5%。结论 本研究制备的N,B-CQDs在Cr(Ⅵ)检测方面具有检出限低、灵敏度高、选择性好等优点,可以为Cr(Ⅵ)快速检测提供一定的理论和技术参考。