On-demand in-line-blending and supply of chemicals

A method of providing a blended mixture to a point of use comprising:

• providing a flow of a first species to a blending unit;
• providing a flow of a second species to the blending unit;
• blending the first species and the second species in the blending unit to produce a mixture;
• distributing the mixture to a point of use via an output in fluid communication with the blending unit;
• measuring a concentration of the first species in the flow of the first species with a first metrology system;
• measuring a concentration of the second species in the flow of the second species with a second metrology system;
• and
• maintaining, using a controller in electronic communication with the first metrology system and second metrology system, a concentration in the mixture within 0.1% of a concentration range based on a mass balance, wherein the maintaining includes determining the mass balance to maintain the concentration in the mixture within 0.1% of the concentration range using information from the first metrology system, the second metrology system, and a flow in the output to the at least one point of use.