Evaluation of the lactose Tergitol-7, m-Endo LES, Colilert 18, Readycult Coliforms 100, Water-Check-100, 3M Petrifilm EC and DryCult Coliform test methods for detection of total coliforms and Escherichia coli in water samples

In this study we compared the reference membrane filtration (MF) lactose Tergitol-7 (LTTC) method ISO 9308-1:2000 with the MF m-Endo LES method SFS 3016:2001, the defined substrate chromogenic/fluorogenic Colilert 18, Readycult Coliforms and Water Check methods, and ready-made culture media, 3M Petrifilm EC and DryCult Coli methods for the detection of coliforms and Escherichia coli in various water samples. When the results of E. coli detection were compared between test methods, the highest agreement (both tests negative or positive) with the LTTC method was calculated for the m-Endo LES method (83.6%), followed by Colilert 18 (82.7%), Water-Check (81.8%) and Readycult (78.4%), whereas Petrifilm EC (70.6%) and DryCult Coli (68.9%) showed the weakest agreement. The m-Endo LES method was the only method showing no statistical difference in E. coli counts compared with the LTTC method, whereas the Colilert 18 and Readycult methods gave significantly higher counts for E. coli than the LTTC method. In general, those tests based on the analysis of a 1-ml sample (Petrifilm EC and DryCult Coli) showed weak sensitivity (39.5-52.5%) but high specificity (90.9-78.8%).     

Chromogenic signalling of water content in organic solvents by hydrazone-acetate complexes

New chromogenic probe systems for the signalling of the water content in representative water-miscible organic solvents (acetonitrile and tetrahydrofuran) were investigated. The effect of the water content in organic solvents on the complex formation of hydrazone dye with acetate ions was utilized for the signalling. The hydrazone-acetate system exhibited a pronounced chromogenic signalling behaviour that could be detected by eye in response to the changes in water content in such common water-miscible organic solvents as acetonitrile and tetrahydrofuran. Prominent colour changes were observed for up to 1 and 2% water content in acetonitrile and THF, respectively. Detection limits of the anthracene-based hydrazone-acetate system for determination of the water content in acetonitrile and tetrahydrofuran were 0.037 and 0.071%, respectively. The 7-hydroxycoumarin-based hydrazone-acetate system showed somewhat less sensitive signalling behaviour, with respective detection limits of 0.12 and 0.63% in acetonitrile and tetrahydrofuran. The designed hydrazone-acetate systems could be used as a simple and convenient chromogenic probes for the determination of the water content in representative organic solvents of acetonitrile and tetrahydrofuran.     

草酸-酸亚硅钼蓝光度法检测钢铁及合金中硅的含量

试样用稀酸溶解,在微酸性溶液中,硅酸与钼酸铵生成硅钼杂多酸,在草酸存在下,用硫酸亚铁铵还原成硅钼蓝,测其吸光度.与钼酸盐形成杂多酸的硅必须以正硅酸状态存在,所以在试样溶解过程中必须避免硅酸的聚合.在溶液中硅酸较易于聚合,其聚合程度与溶液的酸度、溶解时加热的程度和时间以及最终溶液中正硅酸离子的浓度有关     

Spectrophotometric Trace Determination of Iron in Food, Milk, and Tea Samples using a New Bis-azo Dye as Analytical Reagent

A newly synthesized bis-azo dye, 2,6-bis(1-hydroxy-2-naphthylazo)pyridine (PBN) was used as a sensitive reagent for iron. To determine the metal ion using a spectrophotometer in the concentration range between 0.3 and 2.76 ppm (molar absorptivity of 2.65 × 10⁴ l mol⁻¹ cm⁻¹ at 550 nm). In a phosphate-buffered medium, none of the transition metals, except Fe(II), Co(II), Ni(II), Cu(II), and Hg(II), produced color with the reagent; however, colors produced by Co(II), Ni(II), Cu(II), and Hg(II) could be masked using thiosemicarbazide, therefore, making the reagent highly selective for iron determination. The reagent was applied for the estimation of iron levels in milk, food grains, and tea samples and the results were compared with the iron levels found in those samples using AAS.     

显色剂在金的光度分析中的应用

综述了近年来各类显色剂在金的光度分析中的应用发展状况、测定体系及其条件，及相应光度分析方法的检出限、测定范围和干扰情况等。     

变色酸双偶氮稀土显色剂进展

介绍１９９０年以来变色酸双偶氮显色剂在稀土分析中应用的进展,着重介绍了新出现的显色剂。     

不同分离培养基检测食品中沙门氏菌效果的比较

目的基于GB 4789.4-2010沙门氏菌检验标准,比较2种沙门氏菌显色培养培养基、亚硫酸铋琼脂培养基(BS)、木糖赖氨酸脱氧胆盐琼脂培养基(XLD)等4种常用分离培养基对沙门氏菌的检测结果的影响。方法通过4种分离培养基对沙门氏菌的回收率和最低检出限的影响,添加柠檬酸杆菌和奇异变形杆菌对分离结果的影响,以及不同样品间检测效果的比较,对不同培养基的检测结果进行统计。结果 2种沙门氏菌显色培养基和XLD培养基的检测效果无差异,BS次之。结论在实际应用中,需要根据样品的污染程度选择单独或联合使用分离培养基,选择不同的前增菌培养时间,以提高检测的准确性。     

New developments in chromogenic and fluorogenic culture media

This review describes some recent developments in chromogenic and fluorogenic culture media in microbiological diagnostic. The detection of beta-D-glucuronidase (GUD) activity for enumeration of Escherichia coli is well known. E. coli O157:H7 strains are usually GUD-negative and do not ferment sorbitol. These characteristics are used in selective media for these organisms and new chromogenic media are available. Some of the new chromogenic media make the Salmonella diagnostic easier and faster. The use of chromogenic and fluorogenic substrates for detection of beta-D-glucosidase (beta-GLU) activity to differentiate enterococci has received considerable attention and new media are described. Rapid detection of Clostridium perfringens, Listeria monocytogenes, Bacillus cereus and Staphylococcus aureus are other application of enzyme detection methods in food and water microbiology.     

锰的光度试剂综述（上）

就锰的光度试剂作一综述。