The Solo-VPE variable pathlength extension enables UV/Vis measurements of varying solution concentrations without the need for dilutions. The closed-loop system dynamically changes the measurement pathlength based on operator-specified thresholds and criteria. The device automatically adjusts the optical pathlength from 0 millimeter to 10 millimeters in 10-micrometer increments, allowing the operator to determine the peak wavelengths, absorbance or required dilution ratios for any given solution. The disposable tip provides for quick changes without the risk of carryover.