Portable instrument employing a surface acoustic wave sensor with a regenerable reagent coating for direct measurement of 1,3‐butadiene and styrene

The design and preliminary laboratory testing of a prototype portable instrument capable of near‐real‐time measurement of selected airborne olefins and dienes at low‐ and sub‐ppm concentrations is described. The sensor employed is a 60‐MHz surface‐acoustic‐wave (SAW) oscillator coated with a Pt‐olefin coordination compound having the formula trans‐PtCl2(olefin)(pyridine) (olefin=1‐hexene or ethylene). The continual mass change that occurs upon replacement of the initially coordinated olefin by the olefin or diene analyte leads to a commensurate change in the output frequency of the SAW sensor. Analyte air concentrations can be determined therefore by measuring the rate of frequency change. In tests with 1,3‐butadiene and styrene the instrument provided linear response isotherms from 0.050 to 3.0 and 0.60 to 50 ppm, respectively, and calculated detection limits of 0.043 and 0.28 ppm, respectively, based on a 10 s measurement interval. Repeated regeneration of the reagent sensor coating is accomplished automatically by brief exposure to a high concentration of the initially coordinated olefin generated from a reservoir that can be housed within the instrument. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70595/2/RSINAK-66-1-239-1.pd

Microfabricated optofluidic ring resonator structures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98683/1/ApplPhysLett_99_141108.pd

Influence of substituent and ligand electronic factors on the measurement of gas phase olefins using a surface acoustic wave oscillator coated with trans-PtCl2(olefin)(amine) complexes

Certain olefin gases and vapors can be measured selectively at low concentrations using surface acoustic wave (SAW) sensors coated with reagents of the general formula trans-PtCl2(olefin)(amine). The sensor response depends on the steady-state rate of mass change associated with substitution of the initially complexed olefin by the free olefin analyte. This paper examines the effects of changes in the electronic nature of substituents on the free olefin and the olefin and amine ligands in the complex on the sensitivity and selectivity obtained with this class of SAW sensor coatings. For a given reagent, higher reaction rates are generally observed with electron-donating substituents on the double bond of the free olefin. For a given free olefin, varying the 4-substituent of the pyridine ligand in PtCl2(ethylene)(4-X-pyridine) gives a maximum response at an intermediate degree of amine basicity. Replacing pyridine by aniline, pyridine N-oxide or the 4-substituted derivatives of these ligands results in reduced responses for the olefins tested. Changing the initially complexed olefin leads to large changes in response, the pattern of which varies with the nature of the free olefin. Results demonstrate the potential for controlling the response of SAW sensors through subtle structural modifications of these coating reagents.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30642/1/0000284.pd

Microfabricated gas chromatograph for Sub-ppb determinations of TCE in vapor intrusion investigations

AbstractA microfabricated gas chromatograph (μGC) is described and its application to the analysis of sub-parts-per-billion (ppb) concentrations of trichloroethylene (TCE) in mixtures, relevant to the problem of TCE vapor intrusion (VI) into homes and offices, is demonstrated. The system employs a MEMS focuser, dual MEMS separation columns, and MEMS interconnects along with a microsensor array. These are interfaced to a (non-MEMS) front-end pre-trap and high-volume sampler module to reduce analysis time. The response patterns generated from the sensor array for each vapor are combined with the chromatographic retention time to identify and differentiate the components of VOC mixtures. All functions are controlled by a LabView routine written in house. A chemometric method based on multivariate curve resolution has also been developed for analyzing partially resolved mixture components. First results are presented of the capture, separation, recognition, and quantification of TCE in a mixture. TCE is measured at 0.185 ppb, with a projected detection limit of 0.030 ppb (20-L sample)

Organic vapor discrimination with chemiresistor arrays of temperature modulated tin-oxide nanowires and thiolate-monolayer-protected gold nanoparticles

This paper explores the discrimination of organic vapors with arrays of chemiresistors (CRs) employing interface layers of tin-oxide nanowires (NWs) and thiolate-monolayer-protected gold nanoparticles (MPNs). The former devices use contact-printed mats of NWs on micro-hotplate membranes to bridge a pair of metal electrodes. Oxidation at the NW surface causes changes in charge transport, the temperature dependence of which differs among different vapors, permitting vapor discrimination. The latter devices use solvent cast films of MPNs on interdigital electrodes operated at room temperature. Sorption into the organic monolayers causes changes in film tunneling resistance that differ among different vapors and MPN structures, permitting vapor discrimination. Here, we compare the performance and assess the 'complementarity' of these two types of sensors. Calibrated responses from an NW CR operated at two different temperatures and from a set of four different MPN CRs were generated for three test vapors: n-hexane, toluene, and nitromethane. This pooled data set was then analyzed using principal components regression classification models with varying degrees of random error superimposed on the responses via Monte Carlo simulation in order to estimate the rates of recognition/discrimination for arrays comprising different combinations of sensors. Results indicate that the diversity of most of the dual MPN-CR arrays exceeds that of the dual NW-CR array. Additionally, in assessing all possible arrays of 4–6 CR sensors, the recognition rates of the hybrid arrays(i.e. MPN + NW) were no better than that of the 4-sensor array containing only MPN CRs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90786/1/0957-4484_22_12_125501.pd

An integrated vapor source with a porous silicon wick

A micro vapor source has been developed for calibrating micro gas chromatograph (ΜGC) systems. By utilizing a porous silicon wick in a micro diffusion system, vapor generation with excellent stability has been achieved. The source has shown uniform and repeatable vapor generation for n-decane with less than a 0.1% variation in 9 hours, and less than a 0.5% variation in rate over 7 days. The evolution rate follows the diffusion model as expected, although the room temperature rate is higher than theoretically predicted. Equipped with a refillable reservoir, this vapor source is suitable for extended ΜGC field deployment. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56056/1/1449_ftp.pd

Extended disjoint principal-components regression analysis of SAW vapor sensor-array responses

The application of a disjoint principal-components regression method to the analysis of sensor-array response patterns is demonstrated using published data from ten polymer-coated surface-acoustic-wave (SAW) sensors exposed to each of nine vapors. Use of the method for the identification and quantitation of the components of vapor mixtures is shown by simulating the 36 possible binary mixtures and 84 possible ternary mixtures under the assumption of additive responses. Retaining information on vapor concentrations in the classification models allows vapors to be accurately identified, while facilitating prediction of the concentrations of individual vapors and the vapors comprising the mixtures. The effects on the rates of correct classification of placing constraints on the maximum and minimum vapor concentrations and superimposing error on the sensor responses are investigated.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30857/1/0000520.pd

Three-dimensional solubility parameters and chemical protective clothing permeation. I. Modeling the solubility of organic solvents in Viton® golves

A model based on the polymer solution theory of Flory and Rehner is presented for estimating the solubility of organic solvents in chemical protective clothing (CPC) polymers using three-dimensional (3-D) solubility parameters. Immersion test solubility values of 40 organic solvents in commercial Viton® glove samples are used to develop and assess the performance of the model. It is found that the solvent-polymer 3-D solubility parameter differences must be weighted to obtain accurate solubility estimates. However, in most cases, a single weighting factor is sufficient to bring estimated values within a factor of two of experimental values for the members of a given chemical class. The effect of temperature on solubility from 25 to 37°C is predicated within 6%, on average, for the subset of 17 solvents examined. In the companion article that follows, solubility values estimated with this approach are combined with diffusion coefficients, also estimated using 3-D solubility parameters, to determine solvent-Viton breakthrough times and steady-state permeation rates. © 1993 John Wiley & Sons, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38613/1/070500315_ftp.pd

Three-dimensional solubility parameters and chemical protective clothing permeation. II. Modeling diffusion coefficients, breakthrough times, and steady-state permeation rates of organic solvents in Viton® gloves

Three-dimensional (3-D) solubility parameters are used in separate models of the solubility, S , and diffusion coefficient, D , of organic solvents in polymers. Modeled values of these variables are then combined in Fickian diffusion equations to estimate solvent breakthrough times (BT) and steady-state permeation rates (SSPR). Published data on the permeation of 18 solvents through commercial Viton® glove samples are used to test the accuracy of the approach. Estimates of S are determined based on the model described in the preceding article. Of several empirical correlations investigated to model D , best results are achieved using the product of the solvent molar volume, V 1 , and either the weighted solvent-Viton 3-D solubility parameter difference, A w , or the Flory interaction parameter, X , also calculated from 3-D solubility parameters. To account for the change in the value of D over the course of the permeation test, D values are evaluated at breakthrough and steady state. Modeled BT values within a factor of three of experimental values (typically within a factor of two) are obtained for the 15 solvents for which analytical detection limits were reported. Modeled SSPR values within a factor of six of experimental values (typically within a factor of four) are obtained for the 15 solvents with valid SSPR measurements. © 1993 John Wiley & Sons, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38614/1/070500316_ftp.pd

Investigation of nematic liquid crystals as surface acoustic wave sensor coatings for discrimination between isomeric aromatic organic vapors

The use of thermotropic nematic liquid crystals (LC) as surface acoustic wave (SAW) vapor sensor coatings were investigated. Responses to four pairs of isomeric aromatic organic vapors were measured using two LC coatings and four isotropic polymer coatings. In most cases, the LC coatings showed higher sensitivity toward the more rod-like isomer within a pair due to the anisotropic nature of the deposited LC films. However, the importance of vapor-coating functional-group interactions as mediating factors in the sensor responses was evident in several cases. Incorporation of an LC coating into a four-sensor array improved the discrimination between isomers relative to an array employing only isotropic coatings. A persistent decline in the sensor baseline signal and vapor sensitivity observed over time with both LC coatings could be attributed to evaporative loss and/or changes in the elastic stiffness of the coatings.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31640/1/0000574.pd