Fixed-Path Length Laser-Induced Sound Pinging: A Streamlined Method for Sound Speed Determination in Arbitrary Liquids

• Published in: Journal of chemical and engineering data Vol. 64; no. 11; pp. 4924 - 4931
• Main Authors: Adhikari, Laxmi, Larm, Nathaniel E, Bhawawet, Nakara, Dhingra, Divya, Pandey, Siddharth, Polo-Parada, Luis, Gutiérrez-Juárez, Gerardo, Baker, Gary A
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.11.2019
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/acs.jced.9b00436

Recently, we introduced laser-induced sound pinging (LISP) as a simple photoacoustic technique for the expedient and fairly rapid (2–3 min) measurement of the speed of sound traversing low-volume samples (25–1000 μL), built around an inexpensive tattoo-removal laser source (Sens. Actuators B-Chem. 2019, 291, 401–410). In this report, we expand on the utility of this technique by improving the facility of measurement and speed of analysis by adopting a fixed-path length (FPL) architecture which allows for much faster analysis (1–5 s) of similar sample volumes. The FPL-LISP setup was employed to determine the speeds of sound at temperatures from 293 to 333 K for four popular hydrophilic deep eutectic solvents (DESs) containing choline chloride (i.e., reline, ethaline, glyceline, and maline), plus several representative decanoic acid–based (i.e., hydrophobic) DESs. The temperature-dependent speeds of sound were used alongside the corresponding experimental densities to calculate the bulk modulus for these illustrative DESs. Interestingly, the bulk modulus was in the 4000–5000 MPa range for choline chloride-derived DESs, essentially twice the value of a hydrophobic DES (typified by 1:2 tetraoctylammonium bromide/decanoic acid), suggesting unique potential for hydraulic applications, for example. The modest volume requirements of FPL-LISP make it suitable for determining the speed of sound in scarce, precious, or hazardous liquids, and the speed of analysis enables integration into a continuous-flow platform for real-time analytics (e.g., beverage quality control).