Abstract: A continuous sample detector includes a sample chamber, a cell body and one or more standard sources of radiation. Mounted in the sample chamber, the cell body has a cell, a coil of transparent tubing through which the sample solution continuously passes during the measurement. The standard source of radiation is mounted adjacent to the cell body. The detector also includes a sensor mounted and arranged proximate the cell and the standard source to encounter relative reciprocation for allowing the sensor to alternately sense radiation of the cell and the standard source. The detector is operated by connecting sample lines to the cell body. The sensor and cell are then positioned to detect radiation from the cell with the sensor, while a sample flow is pumped through the cell. The system is calibrated by disposing the sensor and the standard source to detect radiation from the standard source with the sensor, without disconnecting the sample lines from the cell body.