An analytical system for the detection, measurement and recording of the concentration of any aqueous aldehyde-based biocidal compounds present in an aqueous solution flowing in a conduit at a sampling point, the system comprising: a mixing vessel; a delivery pump having an inlet in fluid communication with the conduit sampling point and an outlet for delivering a sample of the aqueous solution to the mixing vessel at a predetermined flow rate; a reagent metering pump having an inlet in fluid communication with a reagent storage vessel and an outlet in fluid communication with the mixing vessel for delivering a predetermined volume of reagent to the mixing vessel; the reagent storage vessel containing a dimedone reagent having a pH in the range of 4.0 to 5.0 that produces a fluorescent reaction product when contacted with an aldehyde or aldehyde functional group; the mixing vessel having means for mixing the aqueous sample and reagent; a heating vessel in fluid communication with the mixing vessel for receiving and heating the reaction mixture to a predetermined temperature; an optical detection cell in fluid communication with the heating vessel for receiving and circulating the heated reaction product, the cell comprising a closed circulation loop of predetermined volume, the loop including a chamber formed with a transparent wall, a light source of predetermined wavelength positioned proximate the transparent wall selected to produce a visible fluorescence in an aldehyde-containing reaction product, an optical device for receiving light emitted by any fluorescing reaction product and to produce an electrical signal corresponding to the intensity of the fluorescence; and a microprocessor connected to the optical device for receiving the electrical signal and having means for recording and storing data corresponding to calibration sample concentrations and to the electrical signals corresponding to the intensity of any fluorescence of a reaction product, the microprocessor being configured to compare the measured value of the intensity of any fluorescence produced to the measured values of calibrations samples, and produce a graphic and/or data display corresponding to the intensity of the fluorescence emission. a mixing vessel; a delivery pump having an inlet in fluid communication with the conduit sampling point and an outlet for delivering a sample of the aqueous solution to the mixing vessel at a predetermined flow rate; a reagent metering pump having an inlet in fluid communication with a reagent storage vessel and an outlet in fluid communication with the mixing vessel for delivering a predetermined volume of reagent to the mixing vessel; the reagent storage vessel containing a dimedone reagent having a pH in the range of 4.0 to 5.0 that produces a fluorescent reaction product when contacted with an aldehyde or aldehyde functional group; the mixing vessel having means for mixing the aqueous sample and reagent; a heating vessel in fluid communication with the mixing vessel for receiving and heating the reaction mixture to a predetermined temperature; an optical detection cell in fluid communication with the heating vessel for receiving and circulating the heated reaction product, the cell comprising a closed circulation loop of predetermined volume, the loop including a chamber formed with a transparent wall, a light source of predetermined wavelength positioned proximate the transparent wall selected to produce a visible fluorescence in an aldehyde-containing reaction product, an optical device for receiving light emitted by any fluorescing reaction product and to produce an electrical signal corresponding to the intensity of the fluorescence; and a microprocessor connected to the optical device for receiving the electrical signal and having means for recording and storing data corresponding to calibration sample concentrations and to the electrical signals corresponding to the intensity of any fluorescence of a reaction product, the microprocessor being configured to compare the measured value of the intensity of any fluorescence produced to the measured values of calibrations samples, and produce a graphic and/or data display corresponding to the intensity of the fluorescence emission.