Resolution of Biparametric Mixtures Using Bead Injection Spectroscopic Flow-through Renewable Surface Sensors

Use of a Polymer Inclusion Membrane and a Chelating Resin for the Flow-Based Sequential Determination of Copper(II) and Zinc(II) in Natural Waters and Soil Leachates

A bi-parametric sequential injection method for the determination of copper(II) and zinc(II) when present together in aqueous samples was developed. This was achieved by using a non-specific colorimetric reagent (4-(2-pyridylazo)resorcinol, PAR) together with two ion-exchange polymeric materials to discriminate between the two metal ions. A polymer inclusion membrane (PIM) and a chelating resin (Chelex 100) were the chosen materials to retain zinc(II) and copper(II), respectively. The influence of the flow system parameters, such as composition of the reagent solutions, flow rates and standard/sample volume, on the method sensitivity were studied. The interference of several common metal ions was assessed, and no significant interferences were observed (<10% signal deviation). The limits of detection were 3.1 and 5.6 µg L⁻¹ for copper(II) and zinc(II), respectively; the dynamic working range was from 10 to 40 µg L⁻¹ for both analytes. The newly developed sequential injection analysis (SIA) system was applied to natural waters and soil leachates, and the results were in agreement with those obtained with the reference procedure.

Molar absorption coefficients and stability constants of Zincon metal complexes for determination of metal ions and bioinorganic applications

Zincon (ZI) is one of the most common chromophoric chelating probes for the determination of Zn²⁺ and Cu²⁺ ions. It is also known to bind other metal ions. However, literature data on its binding properties and molar absorption coefficients are rather poor, varying among publications or determined only in certain conditions. There are no systematic studies on Zn²⁺ and Cu²⁺ affinities towards ZI performed under various conditions. However, this widely commercially available and inexpensive agent is frequently the first choice probe for the measurement of metal binding and release as well as determination of affinity constants of other ligands/macromolecules of interest. Here, we establish the spectral properties and the stability of ZI and its complexes with Zn²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Co²⁺, Ni²⁺ and Pb²⁺ at multiple pH values from 6 to 9.9. The obtained results show that in water solution the MZI complex is predominant, but in the case of Co²⁺ and Ni²⁺, M(ZI)₂ complexes are also formed. The molar absorption coefficient at 618 nm for ZnZI and 599nm for CuZI complexes at pH7.4 in buffered (I=0.1M) water solutions are 24,200 and 26,100M^-1cm^-1, respectively. Dissociation constants of those complexes are 2.09×10^-6 and 4.68×10^-17M. We also characterized the metal-assisted Zincon decomposition. Our results provide new and reassessed optical and stability data that are applicable to a wide range of chemical and bioinorganic applications including metal ion detection, and quantification and affinity studies of ligands of interest.

SYNOPSIS

Accurate values of molar absorption coefficients of Zincon complex with Zn²⁺, Cd²⁺, Hg²⁺, Co²⁺, Ni²⁺, Cu²⁺, and Pb²⁺ for rapid metal ion quantification are provided. Zincon stability constants with Zn²⁺ and Cu²⁺ in a wide pH range were determined.

State-of-the-art of (bio)chemical sensor developments in analytical Spanish groups

(Bio)chemical sensors are one of the most exciting fields in analytical chemistry today. The development of these analytical devices simplifies and miniaturizes the whole analytical process. Although the initial expectation of the massive incorporation of sensors in routine analytical work has been truncated to some extent, in many other cases analytical methods based on sensor technology have solved important analytical problems. Many research groups are working in this field world-wide, reporting interesting results so far. Modestly, Spanish researchers have contributed to these recent developments. In this review, we summarize the more representative achievements carried out for these groups. They cover a wide variety of sensors, including optical, electrochemical, piezoelectric or electro-mechanical devices, used for laboratory or field analyses. The capabilities to be used in different applied areas are also critically discussed.

A spectrophotometric method for the determination of zinc, copper, and cobalt ions in metalloproteins using Zincon

Zincon (2-carboxy-2'-hydroxy-5'-sulfoformazylbenzene) has long been known as an excellent colorimetric reagent for the detection of zinc and copper ions in aqueous solution. To extend the chelator's versatility to the quantification of metal ions in metalloproteins, the spectral properties of Zincon and its complexes with Zn(2+), Cu(2+), and Co(2+) were investigated in the presence of guanidine hydrochloride and urea, two common denaturants used to labilize metal ions in proteins. These studies revealed the detection of metals to be generally more sensitive with urea. In addition, pH profiles recorded for these metals indicated the optimal pH for complex formation and stability to be 9.0. As a consequence, an optimized method that allows the facile determination of Zn(2+), Cu(2+), and Co(2+) with detection limits in the high nanomolar range is presented. Furthermore, a simple two-step procedure for the quantification of both Zn(2+) and Cu(2+) within the same sample is described. Using the prototypical Cu(2+)/Zn(2+)-protein superoxide dismutase as an example, the effectiveness of this method of dual metal quantification in metalloproteins is demonstrated. Thus, the spectrophotometric determination of metal ions with Zincon can be exploited as a rapid and inexpensive means of assessing the metal contents of zinc-, copper-, cobalt-, and zinc/copper-containing proteins.

Flow-through fluorescence-based optosensor for the screening of zinc in drinking water

A single and rapid solid surface fluorescence-based flow-through optosensor has been developed for the screening of trace amounts of Zn(II) in drinking water samples. The proposed method is based on the transient immobilization of the target species: the complex formed between Zn(II) and the fluorogenic reagent p-(tosylamino)quinoline (p-TAQ) on an appropriate solid support (C(18) silica gel). The fluorescence of the complex was continuously monitored at an emission wavelength of 495 nm upon excitation at 377 nm. The instrumental, chemical and flow-injection variables were carefully investigated and optimized. The sensor was calibrated over the range of 5 - 125 ng mL(-1), obtaining a limit of detection of 0.9 ng mL(-1), a RSD of 1.8%, with a sampling frequency of 20 h(-1). The proposed method was successfully applied to different drinking water samples with recoveries between 98 and 104%.