Trace-concentration detection of cobalt in a liquid flow cell by degenerate four-wave mixing using low-power off-resonant laser excitation

Abstract

Optical phase conjugation by degenerate four-wave mixing (D4WM) in an absorbing metal-ion solution using a low-power argon-ion laser as the excitation source is demonstrated. This nonlinear laser technique can be used as a sensitive analytical spectroscopic method for trace-concentration measurement of metal ions in a small-volume continuously flowing analyte cell. Several important characteristics are discussed, including the effects of solvent properties, excitation wave-length, laser intensity, and analyte absorptivity on signal intensity. Detection of 0.26 ng (4.4 pmol) of cobalt inside the laser probe volume of 0.14 microL is reported using an excitation wavelength that is 136 nm away from the maximum absorption wavelength of the analyte solution. The minimum absorbance measured in our D4WM experiment is 2.0 X 10(-5) without complex formation for cobalt. The D4WM detection sensitivity, in terms of the concentration-absorptivity product, is 4.05 X 10(-4) cm-1 for cobalt(II) in ethanol. Our preliminary detection sensitivity compares favorably with other laser-based spectrometric methods. This nonlinear laser technique is applicable to both fluorescing and nonfluorescing analytes.

Sensitive circular dichroism spectroscopy based on nonlinear degenerate four-wave mixing

“…Nonlinear D4WM detection methods offer many potential applications, since the detection sensitivity is excellent for both fluorescing and nonfluorescing analytes, as demonstrated previously. [29][30][31][32]…”

Circular Dichroism Spectroscopy Using Coherent Laser-Induced Thermal Gratings

“…Laser-induced grating spectroscopy (LIGS), four-wave mixing (FWM) spectroscopy, has proven to be a powerful tool for probing the chemical and physical properties of numerous chemical samples in many different environments. − In absorbing liquids, thermally induced nonlinear effects often dominate other types of nonlinearities in the generation of the signal, and FWM has been demonstrated to be an excellent technique for measuring weak absorbances in liquid analytes. − Unlike conventional absorption techniques which are “transmissive” in nature ( i.e. , the desired measurement is derived from a small difference in two large signals), FWM is a “dark background” technique.…”

Trace Analysis of Rubidium Hyperfine Structure in a Flame Atomizer Using Sub-Doppler Laser Wave-Mixing Spectroscopy

“…It is an unusually sensitive nonlinear laser method with a relatively easy multi-wave optical setup that is suitable for trace-concentration chemical analysis. 4,5 Since the signal is inherently sub-Doppler, resonant laser wave m ixing offers excellent spectral resolution that is suitable for isotope and hyper ne structure measurements 6,7 and many other applications, including atomic frequency locking. 8 Taking advantage of both excellent spectral resolution and detection sensitivity, one could employ this relatively simple nonlinear laser m ethod for trace-concentration elemental analysis 9 and for parts-pertrillion-level m easurement of isotope and hyper ne structures.…”