Determination of heavy metals in milk by potentiometric stripping analysis using a home-made flow cell

A method is described for sensitive and reliable determination of trace concentrations of cadmium, lead and copper in real samples by stripping potentiometry with a home-made flow cell. The selection of the experimental conditions was made using experimental design methodology. The optimum conditions for the method include an acetic acid–acetate buffer mixture (pH 3.4) as supporting electrolyte, an electrolysis potential of −1.1 V and a flow rate of 3 ml min⁻¹. The detection limits were 6.51 × 10⁻¹⁰ mol l⁻¹ for cadmium, 4.60 × 10⁻¹⁰ mol l⁻¹ for lead and 8.59 × 10⁻¹⁰ mol l⁻¹ for copper, with an electrolysis time of 900 s. The relative standard deviations at this concentration level were 0.038, 0.086 and 0.095, respectively. In order to check the analytical accuracy, standard solutions have been used and recoveries close to 100% were obtained. The method was successfully applied to the determination of cadmium, lead and copper in powdered milk, using the method of standard additions.     

Determination of cadmium and lead in fruit juices by stripping chronopotentiometry and comparison of two sample pretreatment procedures

A method for the determination of cadmium and lead in apple and pear fruit juices by stripping chronopotentiometry (SCP) is described. The results obtained after previous digestion of the sample with concentrated sulphuric acid and dry-ashing (sample pretreatment procedure “A”) and after a treatment with concentrated hydrochloric acid followed by heating in hot water bath (sample pretreatment procedure “B”) were compared. The sample pretreatment procedures were tested on real fruit juice samples and all data confirmed that the efficiency of procedure A was greater than procedure B. In particular, for samples treated with procedure A, good linearity was obtained in the range of examined concentration as is shown by the determination coefficients that were 0.998 (n = 4) for cadmium and 0.996 (n = 4) for lead. Recoveries of 86–104% for cadmium and of 87–102% for lead were obtained from a sample spiked at different levels. The accuracy was also evaluated by means of a matching reference sample of spiked skim milk powder (BCR 150—Community Bureau of Reference) to prove the reliability of the method. The detection limits were 2.0 ng g⁻¹ for cadmium and 4.8 ng g⁻¹ for lead. The relative standard deviations (mean of nine determinations), evaluated on a real sample, were 7.8% and 6.5% respectively. The average content was in the range not detectable–3.0 ng g⁻¹ for cadmium and 8.2–21.3 ng g⁻¹ for lead.     

Characteristics of Bacillus cereus isolates from legume-based Indian fermented foods

An antibiogram of 48 strains of Bacillus cereus isolated from 6 different kinds of legume-based Indian fermented foods (amriti, dhokla, dosa, idli, papad and wadi) was generated against 18 different antibiotics that are commonly used against foodborne diseases, mainly gastroenteritis. Each of the isolates was found to be resistant against at least nine different antibiotics. Production of extracellular enzymes, namely protease, lipase and amylase by 33%, 27% and 46%, respectively, of the isolates indicates their potentiality for food spoilage. In brain–heart infusion broth supplemented with glucose, the D_100 °C-values for the tested 12 strains ranged from 3.0 to 9.2 min. In nutrient broth, the minimum and maximum pHs permitting growth of B. cereus were 5.3 and 11.6, respectively. The minimum inhibitory concentrations of sodium chloride, benzoic acid and sorbic acid for the growth of the isolates were 65–85 mg ml⁻¹, 400–700 μg ml⁻¹ (pH 5.0–4.2) and 500–600 μg ml⁻¹ (pH 5.0–4.8), respectively. Of the tested 10 strains, eight were resistant to 300 μg nisin ml⁻¹ (pH 5.0). While studying the combined effect of selected hurdles on the growth of an isolate, the judicious combination considered was 20 mg sodium chloride, 300 μg benzoic acid and 25 μg nisin ml⁻¹ at pH 5.6. The whole-cell protein fingerprinting (WCPF) analysis using SDS–PAGE revealed a high level of diversity among the isolates. At 60% similarity level, the WCPF profiles could be grouped into four major clusters which were divided into 34 subclusters. Most of the subclusters were source-wise homogeneous.     

The dissipation rates of cyprodinil, fludioxonil, procymidone and vinclozoline during storage of grape juice

The disappearance of the fungicides cyprodinil, fludioxonil, procymidone and vinclozoline, which are widely used to control grey mold in vineyards, from commercially sterilized white grape juice was studied. Fungicide losses from white grape juice stored at 40 °C were monitored for about 2 months in order to simulate in a fast way the shelf-life of the product at room temperature (about 1 year). The fungicides were determined by using a simple method based on a liquid–liquid extraction (LLE) and gas chromatographic separation, followed by mass spectrometric detection (GC–MSD). Fortified white grape juice subsamples were taken three times a week from the oven and the degradation of the fungicides monitored for 56 days. The half-lives at 40 °C for vinclozoline and procymidone were found to be 11 and 20 days, respectively. Those for the more recently introduced fungicides fludioxonil and cyprodinil were somewhat longer (33 and 44 days, respectively). Based on the first-order rate constants obtained, the fungicides dissipated in the following sequence: vinclozoline (0.062 d⁻¹) > procymidone (0.035 d⁻¹) > fludioxonil (0.021 d⁻¹) > cyprodinil (0.016 d⁻¹).     

Effects of some Chinese medicinal plant extracts on five different fungi

Chinese medicinal plant extracts were screened against some fungal strains, such as Aspergillus niger, Botrytis cinerea, Fusarium moniliforme, Glomerella cingulata, and Phyllosticta caricae. Plants were extracted with hot water, 80% methanol or acetone. Aliquots of the extracts at variable concentrations were then incubated with different fungal strains, and the minimum inhibitory concentrations (MICs) of each plant extract determined. In this study, the methanol extracts of Cinnamomum cassia had MIC values of 13.3 mg ml⁻¹, when tested against F. moniliforme and P. caricae. The acetone extracts of C. cassia had MIC values of 8.3 mg ml⁻¹ and 10 mg ml⁻¹ respectively, when tested against B. cinerea and G. cingulata. The hot water extracts of C. cassia inhibited significantly the growth of A. niger, B. cinerea, F. moniliforme, and P. caricae with MIC values at 10, 11.7, 5, and 6.7 mg ml⁻¹ respectively. The acetone extracts of Curcuma longa inhibited effectively P. caricae with the MIC value at 6.7 mg ml⁻¹. To determine the stability, various plant extracts were stored at 4 and 25 °C over a period of one month and their effects on fungal growth examined. Results show that the acetone extracts of Cu. longa and Coptidis rhizoma maintained their activity against fungal strains when stored at 4 °C, but not at 25 °C. The methanol extracts of C. cassia lost a great portion of inhibitory activities but not all, after stored at 4 °C and 25 °C for one month. The effect of various combinations of these extracts on antimicrobial activity has also been examined. The combinations of herb extracts showed higher inhibitory effect towards tested fungi than that of individual extract. Results from these findings suggest that these herbal extracts may be used as natural antifungal agents to inhibit growth of foodborne pathogen.     

Computer modelling for the control of particulate sterilization under dynamic flow conditions

A finite difference model was used for predicting the centre temperature of particulates during ultra-high temperature processing under continuous flow conditions. This model compared favourably with the analytical solutions. A sensitivity analysis was carried out on the input parameters to the numerical model, which indicated that particulate size and thermal diffusivity were the most critical parameters influencing process lethality and cook value. For example, a spherical particulate (thermal properties defined) of 20 mm diameter required a holding time greater than 5 min at 135°C to achieve a minimum safe cook (F₀ of 3.0 min for Clostridium botulinum), compared to a 10 mm spherical particulate which would have received an F₀ value of 68 min after 5 min processing at 135°C. The centre temperatures predicted using the model were sensitive to changes in the convective surface heat transfer coefficient in the range 100–300 W m⁻² K⁻¹, but became less sensitive as the values increased up to 500 W m⁻² K⁻¹. An initial product temperature change from 20 to 60°C resulted in an 8 min increase in process lethality for a 15 mm spherical particulate processed for 5 min at 135°C. The determination of experimental results in particulates of less than 20 mm (the critical dimension) was found to be significantly affected by conduction errors through the thermocouple wires, and therefore the model presented will be a useful prediction tool in situations of experimental uncertainty.     

Rapid gas-chromatographic method for the determination of diacetyl in milk, fermented milk and butter

In this work, a simple and fast method for the determination of diacetyl by gas-chromatographic technique coupled with flame ionisation detector (GLC-FID) was developed. Diacetyl is the typical butter flavour, but it is also commonly present in others fermented dairy products. Recently, diacetyl determination has also attracted interest because it is one of the parameters on which lactic acid bacteria (L.A.B.) are characterized and valued. Only acetone and 2,3-pentanedione were used as chemicals. After centrifugation of acetone–milk mixture, supernatant was filtered and directly injected into gas-chromatographic apparatus, without a further purification procedure step.

This method was accurate and precise; diacetyl recovery on milk was 97% and the detection limit was 1 mg L⁻¹. Finally, by using this method, diacetyl was easily determined in fresh and high-temperature treated milk, commercial butter, yoghurt and also in a series of L.A.B. performance tests.     

Microbiological profile of helva sold at retail markets in Izmir city and the survival of Staphylococcus aureus in this product

The objective of this research was to determine the microbiological profile of tahin helva, a low moisture confectionery. A total of 63 tahin helva samples were collected from the retail markets in Izmir, Turkey. These samples were examined by standard procedures for aerobic plate count (APC) and counts of moulds and yeasts, Enterobacteriaceae, Staphylococcus aureus and Salmonella spp. APC of samples ranged from <10 to 1.6 × 10⁵ cfu/g. The counts for moulds, yeasts and Enterobacteriaceae ranged from <10 to 1.8 × 10³, <10 to 7 × 10², <10 to 8.5 × 10² cfu/g, respectively. None of the samples contained S. aureus or Salmonella. The potential for survival of S. aureus in the product stored at refrigeration (4 °C) and room (20 °C) temperatures was evaluated by artificial contamination. S. aureus cells were still recovered after 9 months of storage at both temperatures. The results of this investigation indicate that S. aureus contamination of tahin helva, (a_w of 0.172) may constitute a potential public health hazard, depending on the extent of contamination and mishandled exercise at the sale area and the kitchen.     

Incidence of aflatoxins, ochratoxin A and zearalenone in tunisian foods

A total of 209 samples of different groups of foods widely consumed by the Tunisian population were collected during 2004–2005 years. Samples were analyzed for contamination with aflatoxins, ochratoxin A and zearalenone, using competitive enzyme-linked immunosorbent assay (ELISA). The predominant mycotoxin was ochratoxin A with a mean level of 3.5 ± 5.3 ng g⁻¹ in 59.8% of studied samples. Furthermore, Aflatoxins were detected in all analyzed commodities with a contamination frequency of 50.5%. In addition, aflatoxin B1 was found in 37% of the samples. The zearalenone was detected around 15% with a mean level of 10.4 ± 11.8 ng g⁻¹. Species, dried fruits and sorghum were the most contaminated samples by aflatoxin and ochratoxin mycotoxins, whereas Rice was the least contaminated commodity. The most frequent mycotoxins co-occurrence included aflatoxins and ochratoxin A, which have been detected in 33.8% of analyzed samples. Furthermore, the simultaneous contamination by aflatoxins, ochratoxin A and zearalenone was observed in 7.2% of studied samples.     

Determination of biogenic amines in sucuk

The biogenic amines content of sucuk (Turkish dry fermented sausage) were determined on 30 samples obtained from retail markets and butchers in Turkey. Also, pH and a_w values, microbiological properties, and NPN levels of these samples were analyzed. The most important biogenic amines were tyramine (range 2.4–676 mg/kg), followed by putrescine varied from not detected to 364 mg/kg. Histamine content was under 50 mg/kg in 80% of the samples while it was over 100 mg/kg in only one sample. Tryptamine was detected in 16 of 30 samples in the range of 1.2–82.3 mg/kg.

Lactic acid bacteria, Micrococcus/Staphylococcus and Enterobacteriaceae counts of samples varied from 2.84 to 8.85 log cfu/g, <2.00 to 6.74 log cfu/g, and <2.00 to 5.04 log cfu/g, respectively. pH values were varied between 4.53 and 6.29 while water activity (a_w) were measured to be between 0.761 and 0.960. NPN values were determined to be between 1.47% and 4.10%. Generally, total amine content was high in samples that had high NPN levels.     

N2中SO2对S Zorb吸附剂活性组分的影响

S Zorb烟气中空纤维膜分离的尾气中含有大量N₂和少量的SO₂。为了考察膜分离尾气用于S Zorb装置再生和汽提的可行性,采用小型固定流化床装置,以含有少量SO2的普氮作为进料气,在S Zorb再生条件下分别考察了SO₂含量对S Zorb新鲜剂再生和再生剂汽提过程中活性组分 金属氧化物的影响。结果表明,N2中SO2质量分数低于0.5%时,只对新鲜剂再生略有影响而对再生剂汽提没有影响,因此膜分离尾气可以用于S Zorb吸附剂的再生或汽提;随着N2汽提时间延长,汽提产品气中硫含量提高,表明N₂汽提可以促进再生剂中已生成的硫酸盐、亚硫酸盐分解。     

Mixed Micelle Formation and Adsorption of Anionic/Nonionic Surfactant Mixture on Barite for Drilling Fluids

Adsorption of surfactants on barite from aqueous solution is of interest for flotation and purification processes. A study of the adsorption of the anionic/nonionic surfactant mixture C₁₀ H₂₁N₂ Φ SO₃(ANO)/C₉ Φ E - ₁₂ (ETH) on barite showed that the adsorption isotherm of the nonionic C₉ Φ E - ₁₂ (ETH) was altered by the anionic, C₁₀ H₂₁ N₂ Φ SO₃(ANO). Although the adsorption of the anionic was affected by the nonionic surfactant and enhanced its isotherm. The reason for this is associated with change in the micelle composition. Variations of the surface tension of the anionic/nonionic mixed surfactant systems against mole fractionchanges were studied. Physical parameters, particularly maximum adsorption density Γ_max, area occupied per molecules, activity coefficients, and free energy of micelle were also investigated. The adsorption isotherm was analyzed, these parameters confirm that the synergistic action of mixed micelle as collector for barite depends on its mole fraction. The optimum recovery of barite was obtained with 0.8 mol fraction. The results were discussed according to the obtained physical properties of the system at solution/air and barite/liquid interfaces.     

多元统计分析在油源对比中的应用

用聚类分析方法对松辽 盆地北部黑帝庙油层34块原油样品进行分析,结果表明,该层原油可以分成两大类,三亚类。I类原油饱和烃色谱在nC14-nC21范围峰强度最大,II类a次之,II类b最小。在ΣnC21-/ΣnC₂₂⁺ 范围内,I类b原油强度占优势, II类a次之,I类原油最小。I类原油的nC21+nC22比值和nC21+nC22占有优势。采用因子分析方法对黑帝庙原油和109块泥岩样品进行油源对比,结果表明,I类原油主要来源于青一段生油岩,I类原油主要来源于嫩一段生油岩,嫩二段亦有-定贡献。     

Si或P改性Pd/Al2O3催化剂的水热稳定性和耐磨性及其催化戊基蒽醌加氢性能

采用等体积浸渍法向γ-Al₂O₃中引入Pd,Si或P元素,制备了系列2%Pd/X-Al₂O₃ (X=Si或P)催化剂。采用XRD、NH₃-TPD、CO化学吸附、XRF、TEM、XPS等测试手段对催化剂进行表征,并评价了其催化戊基蒽醌加氢性能。结果表明,Si或P的掺杂未改变原始γ-Al₂O₃载体的晶型结构,Si或P嫁接在γ-Al₂O₃表面,减少了其四面体和八面体空穴,形成了Al—O—Si或Al—O—P键,使催化剂的表面酸性有所降低,金属与载体的锚固作用减弱从而分散性降低,Pd²⁺/Pd⁰的摩尔比增大。水热实验结果表明,由于γ-Al₂O₃表面空穴的减少,改性催化剂的水热稳定性和耐磨性均显著提高。在蒽醌加氢反应实验中,改性后催化剂的蒽醌加氢效率达到了17~20 g/L,选择性提高到了94%,这可能是因为Pd²⁺的比例增大使催化剂表面的缺电子吸附位增加,蒽醌分子更易活化,且催化剂表面强酸量的减少调节了蒽醌分子的吸附强度,从而加氢活性和选择性均有所提高。     

正己烷在Pt/HBeta催化剂上的异构化反应动力学模型

采用等体积浸渍法制备了Pt/HBeta催化剂,并在10 mL固定床反应装置上评价了反应温度和质量空速对Pt/HBeta催化正己烷临氢异构化反应的影响,在此基础上建立正己烷异构化反应动力学模型。结果表明：在 240~260  ℃内正己烷临氢异构化反应可以用拟一级动力学模型来描述,反应的活化能Ea=139.06 kJ/mol,指前因子A=7.3814×1013 h-1;建立了连串反应动力学模型,第一步反应活化能Ea=167.80 KJ·mol-1,A=7.2130×1016 h-1,第二步反应活化能Ea=118.34 KJ·mol-1,A=1.3053×1011 h-1;当反应温度大于260 ℃,拟一级动力学模型不再适合,修正后270 ℃时的反应级数为1.3,280  ℃时的反应级数为1.7。     

Analysis of 140 pesticides from conventional farming foodstuff samples after extraction with the modified QuECheRS method

Pesticides in foodstuff are becoming a major issue due to their intensive use in agriculture. Thus an appropriate control of their residues in food samples has to be operated. In this study we analysed 105 pesticides with GC/SQ-MS and 46 pesticides with HPLC/IT-MS after extraction with the QuECheRS method in four matrices (grape, lemon, onion and tomatoes). For GC-amenable substances, the LOD and LOQ ranged from 0.4 to 48.2 μg/kg and from 1.2 to161 μg/kg, respectively. For HPLC-amenable substances, they varied from 1.0 to 115 μg/kg and from 3.3 to 382 μg/kg, respectively. With GC/MS, 61–82% of the substances showed a recovery in the range of 70–110% and 6–30 % presented a recovery higher than 110% at the 500 μg/kg fortification level. With HPLC/MS, 87–93% of the substances presented recoveries in the range of 70–110% at the 500 μg/kg fortification level compared to 78–85% at the 50 μg/kg fortification level. Lemon and onion showed poor recoveries but are known to be difficult matrices (high acidic and high sulfur content, respectively). The method was proved to be repeatable with RSD lower than 20% at 500 μg/kg and lower than 15% at 50 μg/kg with both devices.     

硫酸亚铁、硫酸高铁分离法及干酪根与黄铁矿结合形式的研究

对于干酪根样品的制备,目前方法较多,制备的纯度各不相同,甚至差异很大,直接影响了各项参数的测定。我们在制备干酪根过程中主要采用如下步骤:①有机溶剂除去可溶性有机质;②盐酸处理碳酸盐;③氢氟酸处理硅酸盐;④稀盐酸处理不溶性硅氟化物;⑤氯仿抽提进一步除净可溶性有机质;③溴化锌重液超声离心除去黄铁矿及其他杂质。      

催化裂化烟气脱硫脱硝装置废水COD超标原因分析及应对措施

针对中国石化海南炼油化工有限公司重油催化裂化烟气脱硫脱硝装置外排废水COD(化学需氧量)超标的问题,通过分析补充新鲜水COD、综合塔补水量、余热锅炉出口烟气中SO2浓度、燃料气中C5+组分浓度、余热锅炉操作条件、废水氧化时间等因素,并采用重整轻汽油加入浆液中试验考察其对亚硫酸盐和亚硫酸氢盐氧化反应的影响.通过综合判断,...     

Pt-SO42-/ZrO2-Al2O3固体超强酸催化剂的研究

采用共沉淀法制备ZrO₂-Al₂O₃,用硫酸溶液浸渍ZrO₂-Al₂O₃制备SO₄^2-/ZrO₂-Al₂O₃,采用等体积法浸渍氯化铂溶液制备Pt-SO₄^2-/ZrO₂-Al₂O₃固体超强酸催化剂。采用N₂吸附-脱附、X射线荧光、X射线衍射、NH₃ 程序升温脱附、吡啶吸附红外光谱等表征了不同Pt-SO₄^2-/ZrO₂-Al₂O₃催化剂的孔结构、晶相结构和酸性质,以正己烷为原料评价Pt-SO42-/ZrO₂-Al₂O₃催化剂上的反应转化率和异构化活性。结果表明：Al₂O₃质量分数为5%、SO₄^2-/ZrO₂-Al₂O₃焙烧温度为650 ℃、硫酸加入量（w）为15.0%时,Pt-SO₄^2-/ZrO₂-Al₂O₃催化剂四方晶相ZrO₂含量最高,总酸量和B酸量最多,正己烷转化率和异构化率最高。在反应温度240 ℃、反应压力2.0 MPa、体积空速1.0 h^-1、氢油体积比700的条件下,Pt-SO₄^2-/ZrO₂-Al₂O₃催化剂上的正己烷转化率为88.72%,异构化率为80.07%。     

噻吩脱硫过程中钒氧化物晶格氧的作用

以γ-Al₂O₃、VO₂和V₂O₅为催化剂,在连续固定床微反装置上、500℃下,考察了噻吩在常压下的脱硫反应过程,并进行了噻吩原位吸附红外光谱、XPS光电子能谱、XRD等表征。结果表明,在催化裂化反应条件下,采用具有单纯L酸中心的催化剂时,噻吩脱硫反应的转化率很低;采用具有单纯氧化-还原中心的催化剂时,噻吩可被氧化成CO、CO₂及SO₂,但转化率也较低;采用既具有酸中心又具有氧化 还原中心的V₂O₅时,由于酸中心和氧化-还原中心的协同作用,噻吩脱硫反应的转化率最高,H₂S和SO₂的产率也最高。催化裂化反应条件下,噻吩可以被钒氧化物的晶格氧氧化,同时V₂O₅与VO₂失去部分晶格氧被还原为V₂O₃等低价态产物;由于V₂O₅比VO₂活泼晶格氧数目多,较易被还原,因此噻吩脱硫反应的SO₂产率更高。V₂O₅表面存在的L酸中心Vⁿ⁺－O－V为噻吩的初始吸附中心,L酸中心与临近的V=O双键的作用促进了噻吩的氧化。