An in situ monitor for metallic contamination in dilute hydrofluoric acid (HF) was developed and demonstrated detection of 20 parts per trillion Cu in a 500:1 HF bath. The monitor is based on the contactless measurement of minority-carrier lifetime and is designed as part of a point-of-use dilute HF recycling system. Reducible ions in solution were detected as they deposit on the surface of a silicon monitor wafer. The sensitivity of the monitor is determined by (i) the signal-to-noise ratio of the surface coverage measurement, (ii) rate of metal deposition from the solution of interest, and (iii) the maximum time allowed for detecting contamination. Such an in situ monitoring system could simultaneously reduce cost of ownership, through limiting yield excursions, and reduce environmental impact by reducing chemical consumption.