Abstract: The present invention provides systems and methods of determining the concentration of chemicals in a wet processing stream where the wet processing stream is formed from two or more liquid streams having known chemical concentrations. The concentration of chemicals in the wet processing stream are monitored by measuring the flow rates of the liquid streams during combination to form the wet processing stream, and calculating the concentrations of chemicals in the wet processing stream based on the flow rates and known chemical concentrations of the liquid streams. The present invention also provides systems and methods for controlling the wet processing of semiconductor substrates using the calculated concentrations in the wet processing stream. The methods and systems of the present invention are particularly useful when the semiconductor substrates are contacted with the wet processing stream in a single pass.