Various authors(1-8) have reported highly sensitive spectrophotometric determinations of a number of metals utilizing water soluble red complexes formed by metal ions and 4-(2pyridylazo)resorcinol(PAR). However, because of the poor selective nature of PAR, the application of the above procedures to practical samples is limited to special cases where interfering metals were separated by preliminary treatments such as solvent extraction and ion-exchange chromatography.Takeuchi and Shijo (9,10) reported that cobaltand nickel-PAR chelates are not decomposed by a large excess of EDTA at room temperature. We also have reported a similar behavior of PAR chelates of iron(II) (11) and chromium(III) (12). Based on these findings, a selective spectrophotometric method for Fe, Co, Ni, and Cr was proposed in which the interference by other metals can be readily screened out with EDTA (9-12). However, intense mutual interference among Fe, Co, Ni, and Cr which can not be masked by EDTA, makes it difficult to establish a selective PAR method for these metals.We have found that the PAR chelates of Fe2+, Co3+, and Pd2+ alone are stable for at least for two hours in boiling aqueous borate buffer solution (pH 9.0) containing a large excess of EDTA, whereas Fe(III)-, Co(II)-, and all other metal-PAR chelates are decomposed by EDTA within 30 min. Thus, except for palladium(II) ion, the color of PAR chelate is stable only for iron under reducing conditions and for cobalt under oxidizing conditions.This finding makes it possible to develop a highly selective and sensitive spectrophotometric method for iron and cobalt.
EXPERIMENTALApparatus. The absorbance measurements were made with a Hitachi 124 Model double-beam spectrophotometer.Toa Electronics Ltd. HM-5A Model pH meter equipped with a glass electrode was used to measure pH.Reagents. A standard iron(II) solution was prepared by dissolving 0.702 gram of ferrous ammonium sulfate in 50 ml of 0.01A hydrochloric acid solution and diluting to 100 ml (1 ml = 1.0 mg of Fe). A standard cobalt(II) solution was prepared by dissolving 5.95 grams of cobaltous chloride in (1) F.
An
abnormal growth of cyanobacteria in eutrophicated freshwaters
can cause various environmental problems. In particular, Microcystis producing hepatotoxic cyclic heptapeptides
microcystins (MCs) has been globally observed. Recent studies have
demonstrated that matrix-assisted laser desorption/ionization time-of-flight
mass spectrometry (MALDI-TOF MS) offers a rapid classification of
cyanobacteria; however, they have not fully considered the toxicity
yet. In this study, we have performed MALDI-TOF MS for intact cyanobacterial
cells using Biotyper software and optimized their conditions to achieve
cyanobacterial classification with the toxicity. The detection mass
range used for Biotyper was extended to cover small molecules, but
their intense ions were suppressed as a function of the used instrument
Autoflex Speed, which enabled simultaneous observations of large molecular
fingerprints and small MCs with comparable ion intensity. Hierarchical
clustering of mass spectra obtained under the optimized conditions
differentiated toxic and non-toxic clusters of Microcystis strains and furthermore formed a tight cluster of non-toxic strains
possessing the MC biosynthesis gene mcyG. Spectral
libraries were expanded to >30 genera (>80 strains) under the
default
and optimized conditions to improve the confidence of cyanobacterial
classification. Consequently, spectral library searching allowed for
characterization of cyanobacteria from a field sample as mixed toxic
and non-toxic Microcystis cells, without
isolating those cells.
The purpose of the present study was to demonstrate that the lysis with the blue color formation was caused by densification of the cyanobacteria, and related events of the species change in the cyanobacteria were induced by the resulting volatile organic compounds (VOCs), particularly β-cyclocitral. In order to obtain a high cell density of cyanobacteria in the laboratory, a concentration technique (graduated cylinder method) using the buoyancy of the gas vesicles was successfully used. The collected scum contained mainly Dolichospermum spp. and Microcystis, and the dispersed cyanobacteria were concentrated in the surface layer after several hours and the concentration ratio became approximately 10. The concentrated cyanobacteria were gradually lysed, while some of the cyanobacteria sank to the bottom, which finally died and disappeared. This method has the additional advantage that it is possible to visualize the entire lysis process. During the concentration process, β-cyclocitral and its oxidation products together with β-ionone were significantly detected. Because β-cyclocitral was easily oxidized to the corresponding carboxylic acid, the pH of the water in the graduated cylinder decreased to approximately 6. Under favorable conditions, lysis with the blue color from phycocyanin could be observed due to the acid stress. Overall, the results of the present study were consistent with the hypothesis that VOCs were produced when the cyanobacteria are highly dense, and that the lysis with the blue color formation occurs due to the higher density.
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