Measurement time distribution in referencing schemes

A method of determining a concentration and a type of substance in a sample at a sampling interface during a plurality of cycles, the plurality of cycles including a first cycle and a second cycle, the method comprising:

• during the first cycle:
• measuring one or more optical properties of the type of substance in the sampling interface during a first time period;
• measuring one or more optical properties of a reference during a second time period;
• measuring noise during a third time period;
• and
• dynamically changing a duration of at least one of the first time period, second time period, and third time period during the second cycle.

A system for determining a concentration and type of substance in a sample site including a sampling interface, the system comprising:

• a light source configured to emit a first light and a second light, the first light incident on the sampling interface and the second light incident on a reference, wherein the first light and the second light include a noise component;
• a first detector configured to measure incident light, the incident light being at least one of the first light and the second light, and configured to generate a first signal indicative of the incident light;
• a second detector configured to measure the noise component included in a range of frequencies, and configured to generate a second signal indicative of the measured noise component;
• and
• logic capable of scaling the second signal and compensating the first signal using the scaled second signal.