Janire Saez

Application of multivariate analysis to the turbidimetric determination of sulphate in seawater

Spectroscopic techniques are widely used in the field of analytical chemistry for the determination of a huge number of analytes. The use of diode array spectrophotometers involves the possibility of collecting the whole UV-Vis spectrum, which provides an opportunity to perform a multivariate analysis of the samples. The effectiveness of the use of multivariate data analysis against the univariate counterpart (which is the most common for classic spectroscopic methods) is demonstrated through application in the sulphate determination in seawater samples using a modified turbidimetric method. The original method recommends performing the analysis at 420 nm, this being a univariate analysis. The modification presented uses multivariate methods for the calibration with the whole UV-Vis spectrum from 200 to 800 nm instead of the single measurement at 420 nm. The external calibration shows that there is a matrix effect which can compromise the accuracy of the measurements, so that an in-house Iterative Multivariate Standard Addition Method (IMSAM) was successfully tested in order to avoid this effect. As the spectrum interval was too wide, both Genetic Algorithm (GA) and interval Partial Least Square (iPLS) regression methods were used in order to select the best wavelengths for the regression and back prediction of the samples. The results obtained in this work show that the performance of the method at 420 nm, as the original method recommends, leads to a considerable error and also that the best segment of the spectra for the determination of the sulphate concentration in seawater is from 600 to 800 nm.

Ionogel-based nitrate sensor device

The increment of uncontrolled nitrate concentration in water could lead to an environmental disaster. In order to favour an easy and adequate monitoring of this environmental problem, we have developed an ionogel-based sensor for the colorimetric determination and image analysis detection of nitrate in water at the point of need.

Chemometrics for the classification and calibration of seawater using the H+ affinity spectrum.

In 1819 Alexander Marcet proposed that seawater contains small amounts of all soluble substances and that the relative abundances of some of them were constant. This hypothesis is nowadays known as Marcets Principle or the principle of constancy of the composition of seawater. Based on this principle, the present research tried to prove that it is possible to detect polluted seawater samples using the seawater H(+) affinity spectrum by the application of the possibilities provided by chemometric tools. Seawater samples were classified using the principal component analysis (PCA) of the HBound spectra of the samples. It was concluded that the sampling points location does not have any influence in the cluster formation, while the season in which they were collected is significant. On the other hand, the seawater composition was calibrated using estuary water samples of different salinities. Once the major constituents were measured, the data analysis concluded that it is possible to make a calibration of the HBound spectrum vs. any of these constituents by means of partial least square (PLS) regression. Thus, the experimental evidence collected in this work confirms that it is possible to detect polluted sea or estuary water samples using these chemometric tools and the H(+) affinity spectrum because with polluted samples these multivariate methods lead to incoherent results. So, suspect polluted zones may be monitored in a simple way with a low cost method and spending much less time.

Light-responsive polymers for microfluidic applications

While the microfluidic device itself may be small, often the equipment required to control fluidics in the chip unit is large e.g. pumps, valves and mixing units, which can severely limit practical use and functional scalability. In addition, components associated with fluidic control of the device, more specifically the valves and pumps, contribute significantly to the overall unit cost. Here we sketch the problem of a gap between high end accurate, but expensive sensor platforms, versus less accurate, but widely employable hand-held low-cost devices. Recent research has shown that the integration of light-responsive materials within microfluidic devices can provide the function of expensive fluidic components, and potentially enable sophisticated measurements to be made using much less expensive equipment. An overview of the most recent developments will be presented for valves, mixers, transport and sample handling inside microfluidic devices.

CHAPTER 9:Applications of Ionic Liquid Materials in Microfluidic Devices

“Lab-on-a-chip” (LOC) and microfluidics enable the manipulation of fluids at small length scales (from micrometers to millimeters). These systems often have well-defined fabrication processes and are capable of integrating multiple functional elements, to provide complete sample-in/answer-out systems. Nevertheless, the development of fully integrated microfluidic devices still faces some considerable obstacles, including fluidic control, miniaturisation and high costs. Due to their unique properties, ionic liquids have arisen as smart solutions to circumvent some of the hurdles facing current LOC technologies. They can directly benefit microfluidic devices by aiding miniaturised fabrication and passive microfluidic elements for fluid control, sensing and sample storage. Improved chemical reactions and separation, in addition to power generation, temperature control, and electrowetting show potential for reducing manufacturing costs and widening market possibilities. In this chapter we will review and discuss the fundamental applications of ionic liquids within microfluidic systems.

In-situ generated biocompatible alginate actuators for flow control in microfluidics

This abstract describes for the first time the use of alginate hydrogels as miniaturised valves in microfluidic devices. These biocompatible and biodegradable microvalves are in-situ generated, on demand, allowing for microfluidic flow control. The microfluidic devices were fabricated using the origami technique with seven layers of cyclic olefin copolymer (COP) and thermocompression bonding. They can be thermally actuated (ON/OFF) at mild temperatures, 37 °C, and chemically erased from the main channel using an ethylenediaminetetraacetic acid disodium salt dehydrated (EDTA) solution, ensuring the reusability of the whole device.