Quartz crystal impedance analysis has been developed as, with concentration varied using methanol, was tested and also found to provide a Newtonian response. In both cases, the values of the square root of the viscositydensity product deduced from the small-volume quartz crystal technique were consistent with those measured using a viscometer and density meter. The third harmonic of the crystal was found to provide the closest agreement between the two measurement methods; the pure ionic liquids had the largest difference of ∼10%. In addition, 18 pure ionic liquids were tested, and for 11 of these, good-quality frequency shift and bandwidth data were obtained; these 12 all had a Newtonian response. The frequency shift of the third harmonic was found to vary linearly with square root of viscosity-density product of the pure ionic liquids up to a value of (Gη) ≈ 18 kg m, but with a slope 10% smaller than that predicted by the Kanazawa and Gordon equation. It is envisaged that the quartz crystal technique could be used in a high-throughput microfluidic system for characterizing ionic liquids.Over the past decade, the drive toward cleaner industrial processes has led to the development of ionic liquids as alternative, environmentally friendly, solvents. 16 However, the data on their physical properties as a function of chemical composition are limited, and extending the range of known data is difficult due to the expense and difficulty of producing large volumes of pure liquids for characterization.Acoustic wave microsensors, such as the quartz crystal microbalance (QCM), are widely used for studying the properties of small-volume samples of liquids, the attachment of mass from the liquid phase and in situ determination of the properties of surface coatings, such as electrodeposited polymers, during the deposition process. [17][18][19] A QCM operates by creating a highfrequency, typically 5 MHz, shear mode oscillation of the surface. When operated in a liquid environment, this surface oscillation entrains liquid and creates an oscillation, which for a Newtonian liquid decays within a penetration depth of the interface δ ) (η/ *1/2 where F and η are the density and viscosity of the liquid and f s is the resonant frequency. 20 In impedance analysis, both the resonant frequency and bandwidth, B, of the crystal are measured and are functions of the liquid properties. Bandwidth is a measure of the loss of energy and of the damping of the shear mode oscillation of the liquid close to the solid-liquid interface, and so some authors prefer to define a dissipation D ) B/f s (also equal to Q -1 ). When the liquid is Newtonian, a frequency decrease, ∆f, and a bandwidth increase, ∆B, occur in proportion to the square root of the viscosity-density product,where the specific acoustic impedance of quartz is, f o is the fundamental frequency and f s ) nf o is the overtone frequency at which the response is measured. 21,22 Thus, by verifying that changes in resonant frequency and bandwidth are correlated, such that ∆f ) -∆B/2,...

A microfluidic glass chip system incorporating a quartz crystal microbalance (QCM) to measure the square root of the viscosity-density product of room temperature ionic liquids (RTILs) is presented. The QCM covers a central recess on a glass chip, with a seal formed by tightly clamping from above outside the sensing region. The change in resonant frequency of the QCM allows for the determination of the square root viscosity-density product of RTILs to a limit of approximately 10 kg m(-2) s(-0.5). This method has reduced the sample size needed for characterization from 1.5 ml to only 30 mul and allows the measurement to be made in an enclosed system.

A microfluidic device designed for electrochemical studies on a microliter scale has been utilized for the examination of impurity levels in ionic liquids (ILs). Halide impurities are common following IL synthesis, and this study demonstrates the ability to quantify low concentrations of halide in a range of ILs to levels of ∼5 ppm, even in ILs not currently measurable using other methods such as ion chromatography. To validate the mixer device, the electrochemistry of ferrocene was also examined and compared with spectroscopic and bulk electrochemistry measurements. An automated "sample preparation, delivery, and calibration" method was developed, and the chip successfully used for linear sweep, cyclic voltammetry (under both quiescent and steady-state flowing conditions), square wave voltammetry, and differential pulse voltammetry. An effective method of electrochemically cleaning the electrodes is also presented.In the past decade, the use of ionic liquids (ILs) as alternative solvents and media for a wide range of applications has expanded significantly in both academia, as well as in industry. [1][2][3][4][5] The importance of impurities in ILs has been recognized by many researchers in this area with water, halide, and metal impurities from the synthesis of the ILs being the most prevalent. These affect both physical and chemical properties of the media, for example, drastically increasing viscosity 6 and thermal conductivity, 7 while also poisoning catalytic reactions. 8 Additionally, Jacquemin et al. have quantified the effect of halide and water content on the density of a wide range of ILs as a function of pressure and temperature, highlighting the importance of being able to measure their concentration accurately. 9,10 It should be noted that typical commercial samples contain between 10 and 1000 ppm of halide from their synthesis. 11 The purity strongly determines their cost because of the loss of IL during multistage purification.With respect to halide content, although commonly used, the technique of using the "silver nitrate" is only qualitative and is insufficient to examine ILs for many applications. 12 However, a number of other methods have been demonstrated for the quantification of halide in ILs, although it is important to note that many have only been investigated for halide in water-miscible ILs with few studies aimed at more hydrophobic ILs, such as those based on tetraalkylphosphonium cations or trispentafluoroethyltrifluorophosphate ([FAP] -) anions. These techniques include Volhard (silver nitrate) and chloride-selective electrodes, 6,13 spectrophotometry using fluorescent indicators, 14 ion chromatography (IC), [15][16][17][18][19] 23 In general, the electrochemistry techniques employed to date require a significant volume of IL (at least ∼1000 µL) for each sample, and multiple samples are required to produce calibration curves. In addition, each sample takes a significant amount of time to measure, including electrode preparation, multiple sample preparation, cleaning and reass...