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A fundamental step prior to sample injection is the "Auto-Zero" function. As outlined in the operational protocols, the detector measures the absorbance of the mobile phase continuously. Before the sample enters the flow cell, the instrument must establish a zero-absorbance baseline. The Auto-Zero command electronically sets the current absorbance to 0.000 mAU. This must be performed when the mobile phase composition is stable and the flow rate is constant. Failing to auto-zero can lead to inaccurate peak area calculations and integration errors.

: Outlines the 190–700 nm wavelength range and noise levels ( SHIMADZU CORPORATION Quick Setup & Operation shimadzu spd20a user manual