Chelate formation of zirconium with xylenol orange and semi-xylenol orange

A frugal implementation of Surface Enhanced Raman Scattering for sensing Zn2+ in freshwaters - In depth investigation of the analytical performances

Surface Enhanced Raman Scattering (SERS) has been widely praised for its extreme sensitivity but has not so far been put to use in routine analytical applications, with the accessible scale of measurements a limiting factor. We report here on a frugal implementation of SERS dedicated to the quantitative detection of Zn²⁺ in water, Zn being an element that can serve as an indicator of contamination by heavy metals in aquatic bodies. The method consists in randomly aggregating simple silver colloids in the analyte solution in the presence of a complexometric indicator of Zn²⁺, recording the SERS spectrum with a portable Raman spectrometer and analysing the data using multivariate calibration models. The frugality of the sensing procedure enables us to acquire a dataset much larger than conventionally done in the field of SERS, which in turn allows for an in-depth statistical analysis of the analytical performances that matter to end-users. In pure water, the proposed sensor is sensitive and accurate in the 160-2230 nM range, with a trueness of 96% and a precision of 4%. Although its limit of detection is one order of magnitude higher than those of golden standard techniques for quantifying metals, its sensitivity range matches Zn levels that are relevant to the health of aquatic bodies. Moreover, its frugality positions it as an interesting alternative to monitor water quality. Critically, the combination of the simple procedure for sample preparation, abundant SERS material and affordable portable instrument paves the way for a realistic deployment to the water site, with each Zn reading three to five times cheaper than through conventional techniques. It could therefore complement current monitoring methods in a bid to solve the pressing needs for large scale water quality data.

Development of a colorimetric colony-screening assay for detection of defluorination by micro-organisms

AIMS

To develop a colorimetric colony-screening assay to facilitate the isolation of micro-organisms capable of defluorination.

METHODS AND RESULTS

A metal-dye chelate, zirconium-xylenol orange was used to detect fluoride ions released from a fluorinated substrate through microbial metabolism. Depolymerised zirconium reagent gave the greatest visual contrast for the presence of fluoride compared to more polymerised forms of zirconium reagent. The sensitivity of the assay was greatest when the molar ratio of depolymerised zirconium to xylenol orange was 1:2. Using depolymerised zirconium and xylenol orange (150 and 300 nmol l(-1) respectively), the assay could detect a fluoride application spot (5 mmol l(-1)) containing 50 nmoles of fluoride ions. Most media constituents were well tolerated by the assay, although phosphate ions needed to be restricted to 0.1 g l(-1) and some proteins digest to between 1 and 5 g l(-1). A microbial enrichment culture growing on solidified medium containing 20 mmol l(-1) fluoroacetate was screened using the assay, and defluorinating bacteria belonging to the genus Burkholderia isolated.

CONCLUSIONS

A method was developed that is sensitive, rapid and reliable for detecting defluorination by micro-organisms growing on solidified medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

This method can be used to facilitate the isolation of micro-organisms capable of defluorination.