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An optical fiber-based sensor array for the monitoring of zinc and copper ions in aqueous environments.

Kopitzke S, Geissinger P - Sensors (Basel) (2014)

Bottom Line: In this work, a new optical fiber-based platform capable of providing fast and accurate results when performing solution analysis for these metals is described.These sensors demonstrated sub-part-per-million detection limits, 30-second response times, and the ability to analyze samples with an average error of under 10%.Finally, after developing sensors capable of monitoring zinc and copper individually, these sensors are combined to form a single optical fiber sensor array capable of simultaneously monitoring concentration changes in zinc and copper in aqueous environments.

View Article: PubMed Central - PubMed

Affiliation: Chemistry and Biochemistry Department, University of Wisconsin-Milwaukee, 3210 N. Cramer Ave. Milwaukee, WI 53201, USA. kopitzke@uwm.edu.

ABSTRACT
Copper and zinc are elements commonly used in industrial applications as aqueous solutions. Before the solutions can be discharged into civil or native waterways, waste treatment processes must be undertaken to ensure compliance with government guidelines restricting the concentration of ions discharged in solution. While currently there are methods of analysis available to monitor these solutions, each method has disadvantages, be it high costs, inaccuracy, and/or being time-consuming. In this work, a new optical fiber-based platform capable of providing fast and accurate results when performing solution analysis for these metals is described. Fluorescent compounds that exhibit a high sensitivity and selectivity for either zinc or copper have been employed for fabricating the sensors. These sensors demonstrated sub-part-per-million detection limits, 30-second response times, and the ability to analyze samples with an average error of under 10%. The inclusion of a fluorescent compound as a reference material to compensate for fluctuations from pulsed excitation sources has further increased the reliability and accuracy of each sensor. Finally, after developing sensors capable of monitoring zinc and copper individually, these sensors are combined to form a single optical fiber sensor array capable of simultaneously monitoring concentration changes in zinc and copper in aqueous environments.

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Related in: MedlinePlus

Calibration curves collected over multiple days (a) utilizing a fast photodiode as the excitation intensity reference, (b) utilizing a second cross-fiber sensor as the excitation intensity reference.
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f4-sensors-14-03077: Calibration curves collected over multiple days (a) utilizing a fast photodiode as the excitation intensity reference, (b) utilizing a second cross-fiber sensor as the excitation intensity reference.

Mentions: Up to this point, a single sensor region was employed to analyze solutions for zinc. However, the issue of source pulse energy fluctuations still needed to be addressed. First, the fast photodiode located at the excitation source, which measured back-scattered radiation from the front face of the optical fiber when a pulse was injected, was employed for this purpose. For both detectors, 100–300 signals were averaged to provide one trace on the oscilloscope. The area under each peak in a trace was integrated and a ratio between the integrated fluorescence and the integrated back-reflected signal was determined. This provided a means of correcting for fluctuations in laser pulse intensity discussed in Section 2.1. The second approach was to employ a fluorescent reference sensor in close proximity to the site of the primary measurement (i.e., at the site of the zinc sensor). This method was expected to yield further improved figures of merit, because this method should also account for additional excitation-pulse-energy fluctuations that may arise as these pulses travel from the laser source to the sensor sites. The two principal requirements for fluorophores that are to be used as reference sensors are (1) that the fluorophore must have an identical or similar spectral profile and (2) that these must be resistant to chemical changes in solution such as a change in pH or a change in the concentration of metals present. Dragon Green, the trade name for commercially available polymer microspheres doped with a fluorescent photostable dye, was determined to meet these characteristics (λex/λem = 495 nm/515 nm). These fluorescent microspheres were included within the replacement-cladding polymer in a manner identical to FZ-1. While none of the figures of merit showed significant improvement when compared to the fast photodiode reference, a marked increase in the reliability between day to day measurements was observed for the experimental setup which utilized FZ-1 and Dragon Green in the crossed-fiber array. Over a period of four days, calibration curves were collected using both methods of referencing (Figure 4). Using Dragon Green as a reference sensor in the crossed-fiber array provided linear calibration curves over multiple days, thus maintaining the linear relationship between the concentration of zinc and fluorescence intensity. When examining the calibration curves generated using the fast photodiode, it was noticed that a linear relationship was only obtained 50% of the time. Data analysis utilizing no reference signal (photodiode or optical fiber-based) revealed similar trends to those seen in Figure 4a, but the non-referenced data exhibited larger variances for each data point. This further supports the need for a second optical-fiber based sensor to serve as an intensity reference.


An optical fiber-based sensor array for the monitoring of zinc and copper ions in aqueous environments.

Kopitzke S, Geissinger P - Sensors (Basel) (2014)

Calibration curves collected over multiple days (a) utilizing a fast photodiode as the excitation intensity reference, (b) utilizing a second cross-fiber sensor as the excitation intensity reference.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3958230&req=5

f4-sensors-14-03077: Calibration curves collected over multiple days (a) utilizing a fast photodiode as the excitation intensity reference, (b) utilizing a second cross-fiber sensor as the excitation intensity reference.
Mentions: Up to this point, a single sensor region was employed to analyze solutions for zinc. However, the issue of source pulse energy fluctuations still needed to be addressed. First, the fast photodiode located at the excitation source, which measured back-scattered radiation from the front face of the optical fiber when a pulse was injected, was employed for this purpose. For both detectors, 100–300 signals were averaged to provide one trace on the oscilloscope. The area under each peak in a trace was integrated and a ratio between the integrated fluorescence and the integrated back-reflected signal was determined. This provided a means of correcting for fluctuations in laser pulse intensity discussed in Section 2.1. The second approach was to employ a fluorescent reference sensor in close proximity to the site of the primary measurement (i.e., at the site of the zinc sensor). This method was expected to yield further improved figures of merit, because this method should also account for additional excitation-pulse-energy fluctuations that may arise as these pulses travel from the laser source to the sensor sites. The two principal requirements for fluorophores that are to be used as reference sensors are (1) that the fluorophore must have an identical or similar spectral profile and (2) that these must be resistant to chemical changes in solution such as a change in pH or a change in the concentration of metals present. Dragon Green, the trade name for commercially available polymer microspheres doped with a fluorescent photostable dye, was determined to meet these characteristics (λex/λem = 495 nm/515 nm). These fluorescent microspheres were included within the replacement-cladding polymer in a manner identical to FZ-1. While none of the figures of merit showed significant improvement when compared to the fast photodiode reference, a marked increase in the reliability between day to day measurements was observed for the experimental setup which utilized FZ-1 and Dragon Green in the crossed-fiber array. Over a period of four days, calibration curves were collected using both methods of referencing (Figure 4). Using Dragon Green as a reference sensor in the crossed-fiber array provided linear calibration curves over multiple days, thus maintaining the linear relationship between the concentration of zinc and fluorescence intensity. When examining the calibration curves generated using the fast photodiode, it was noticed that a linear relationship was only obtained 50% of the time. Data analysis utilizing no reference signal (photodiode or optical fiber-based) revealed similar trends to those seen in Figure 4a, but the non-referenced data exhibited larger variances for each data point. This further supports the need for a second optical-fiber based sensor to serve as an intensity reference.

Bottom Line: In this work, a new optical fiber-based platform capable of providing fast and accurate results when performing solution analysis for these metals is described.These sensors demonstrated sub-part-per-million detection limits, 30-second response times, and the ability to analyze samples with an average error of under 10%.Finally, after developing sensors capable of monitoring zinc and copper individually, these sensors are combined to form a single optical fiber sensor array capable of simultaneously monitoring concentration changes in zinc and copper in aqueous environments.

View Article: PubMed Central - PubMed

Affiliation: Chemistry and Biochemistry Department, University of Wisconsin-Milwaukee, 3210 N. Cramer Ave. Milwaukee, WI 53201, USA. kopitzke@uwm.edu.

ABSTRACT
Copper and zinc are elements commonly used in industrial applications as aqueous solutions. Before the solutions can be discharged into civil or native waterways, waste treatment processes must be undertaken to ensure compliance with government guidelines restricting the concentration of ions discharged in solution. While currently there are methods of analysis available to monitor these solutions, each method has disadvantages, be it high costs, inaccuracy, and/or being time-consuming. In this work, a new optical fiber-based platform capable of providing fast and accurate results when performing solution analysis for these metals is described. Fluorescent compounds that exhibit a high sensitivity and selectivity for either zinc or copper have been employed for fabricating the sensors. These sensors demonstrated sub-part-per-million detection limits, 30-second response times, and the ability to analyze samples with an average error of under 10%. The inclusion of a fluorescent compound as a reference material to compensate for fluctuations from pulsed excitation sources has further increased the reliability and accuracy of each sensor. Finally, after developing sensors capable of monitoring zinc and copper individually, these sensors are combined to form a single optical fiber sensor array capable of simultaneously monitoring concentration changes in zinc and copper in aqueous environments.

Show MeSH
Related in: MedlinePlus