Determination of Cr(VI) concentration in diluted samples based on the paper test strip method

At present, there are many methods for Cr(VI) concentration determination in diluted samples, however, these methods have their own inherent drawbacks, such as long response time, complicated pretreatment, expensive equipment etc. In this paper, a paper-based test strip method specific for determination of diluted Cr(VI) samples was developed. In this method, Aliquat 336, as an anion exchanger was loaded into filter paper to form a test strip. This test strip was used to pre-concentrate Cr(VI) when contacting with the diluted Cr(VI)-containing solution. The Cr(VI)-containing test strip was then immersed into a diphenylcarbazide (DPC) solution (a color forming solution), and the color intensity was correlated to the Cr(VI) concentration. The detection range of the present method was found to be 0.02–1.50 mg/L. The results also showed that the method gave a high selectivity for Cr(VI) in the diluted samples to be tested. The method was applied to synthesized samples and the results, which were compared to those from a reference method, showed that the developed method is an effective, reliable way for Cr(VI) determination in diluted samples.

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Bacteriophage-Based Enrichment Coupled to Immunochromatographic Strip–Based Detection for the Determination of Salmonella in Meat and Poultry

Journal of Food Protection ◽

10.4315/0362-028x-70.10.2235 ◽

2007 ◽

Vol 70 (10) ◽

pp. 2235-2242 ◽

Cited By ~ 17

Author(s):

MARK T. MULDOON ◽

GEORGE TEANEY ◽

JINGKUN LI ◽

DALE V. ONISK ◽

JAMES W. STAVE

Keyword(s):

Reference Method ◽

Test Strip ◽

False Positives ◽

Food Sources ◽

Detection Methods ◽

Immunochromatographic Strip ◽

Conventional Culture ◽

Sample Enrichment ◽

Enrichment Step

Immunochemical-based methods for the detection of Salmonella in food can be complicated by the presence of closely related, immunocrossreactive non-Salmonella species in the sample that may cause false-positive results. To circumvent this problem, specific bacteriophages against immunocrossreactive, non-Salmonella bacteria were used in the sample enrichment step to suppress their growth and improve the performance of an immunochromatographic strip–based detection method for Salmonella. Cross-reactive bacteria were isolated from various food sources and were characterized with a panel of Salmonella somatic O antigen–specific monoclonal antibodies. These cross-reactive bacteria were primarily Citrobacter spp. and Escherichia coli with serology shared with Salmonella serogroups B, D, and F. These bacteria were used as hosts for the isolation of specific lytic bacteriophages. When formulated with the primary enrichment, the bacteriophage cocktail significantly reduced false positives with a broadly reactive immunochromatographic test strip. This was demonstrated in both artificially and naturally contaminated meat. False positives in naturally contaminated beef samples were reduced from 32 of 115 samples tested to zero. In raw meat and poultry with a relatively high bioburden (>105 CFU/g), the use of the bacteriophage-based enrichment procedure gave improved recovery of Salmonella compared with the conventional culture-based reference method. This was observed when coupled to either test strip–based or selective agar–based detection. The use of specific bacteriophages for the control of immunocrossreactive and competitive microflora during the food sample enrichment step provides a new approach for enhancing the performance of both immunological- and cultural-based detection methods.

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Concentration determination of chromatin in unstained resin-embedded sections by means of Z-contrast in STEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100134521 ◽

1990 ◽

Vol 48 (2) ◽

pp. 186-187

Author(s):

M. Haider ◽

B. Bohrmann

Keyword(s):

Energy Loss ◽

Freeze Substitution ◽

Biological Macromolecules ◽

Local Concentration ◽

E Coli ◽

Concentration Determination ◽

Phosphorous Content ◽

Z Contrast ◽

Electron Energy Loss

The technique of Z-contrast in STEM offers the possibility to determine the local concentration of macromolecules like lipids, proteins or DNA. Contrast formation depends on the atomic composition of the particular structure. In the case of DNA, its phosphorous content discriminates it from other biological macromolecules. In our studies, sections of E. coli, the dinoflagellate Amphidinium carterae and Euglena spec. cells were used which were obtained by cryofixation followed by freeze-substitution into acetone with 3% glutaraldehyde. The samples were then embedded either in Lowicryl HM20 at low temperature or in Epon at high temperature. Sections were coated on both sides with 30Å carbon.The DF- and the inelastic image have been recorded simultaneously with a Cryo-STEM. This Cryo-STEM is equipped with a highly dispersive Electron Energy Loss Spectrometer. With this instrument pure Z-contrast can be achieved either with a Filtered DF-image divided by the inelastic image or, as is used in this paper, by dividing the conventional DF-image by an inelastic image which has been recorded with an inelastic detector whose response is dependent on the total energy loss of the inelastically scattered electrons.

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