A system for detecting and quantifying an analyte in a liquid using a chemical assay, the system comprising: a single pre-dosed vial comprising one or more pre-dosed reagents disposed within the single pre-dosed vial, wherein the one or more pre-dosed reagents comprise pre-dosed freeze-dried solid reagents configured to conduct the assay, wherein the single pre-dosed vial is configured to receive and hold a volume of the liquid comprising the analyte, wherein the one or more pre-dosed reagents are dissolvable in the volume of the liquid so as to form a sample liquid solution comprising chromophores or fluorophores, wherein the one or more pre-dosed reagents are configured to react with the analyte to yield the chromophores or fluorophores; a detection device comprising an optical chamber configured to retain the single pre-dosed vial, the detection device comprising: a plurality of light sources, each light source being configured to direct light towards the sample liquid solution in the single pre-dosed vial and being modulated at a fixed frequency; two photosensitive detectors consisting of a first photosensitive detector (812, 220) positioned in the optical chamber opposite to at least one of the plurality of light sources and configured to detect light transmitted through the sample liquid solution and a second photosensitive detector (812, 222) positioned at a right angle to the first photosensitive detector (812, 220), and configured to detect fluorescence and scattering from the sample liquid solution; and a control system, wherein the control system is configured to quantify the analyte in the sample liquid solution. a single pre-dosed vial comprising one or more pre-dosed reagents disposed within the single pre-dosed vial, wherein the one or more pre-dosed reagents comprise pre-dosed freeze-dried solid reagents configured to conduct the assay, wherein the single pre-dosed vial is configured to receive and hold a volume of the liquid comprising the analyte, wherein the one or more pre-dosed reagents are dissolvable in the volume of the liquid so as to form a sample liquid solution comprising chromophores or fluorophores, wherein the one or more pre-dosed reagents are configured to react with the analyte to yield the chromophores or fluorophores; a detection device comprising an optical chamber configured to retain the single pre-dosed vial, the detection device comprising: a plurality of light sources, each light source being configured to direct light towards the sample liquid solution in the single pre-dosed vial and being modulated at a fixed frequency; two photosensitive detectors consisting of a first photosensitive detector (812, 220) positioned in the optical chamber opposite to at least one of the plurality of light sources and configured to detect light transmitted through the sample liquid solution and a second photosensitive detector (812, 222) positioned at a right angle to the first photosensitive detector (812, 220), and configured to detect fluorescence and scattering from the sample liquid solution; and a plurality of light sources, each light source being configured to direct light towards the sample liquid solution in the single pre-dosed vial and being modulated at a fixed frequency; two photosensitive detectors consisting of a first photosensitive detector (812, 220) positioned in the optical chamber opposite to at least one of the plurality of light sources and configured to detect light transmitted through the sample liquid solution and a second photosensitive detector (812, 222) positioned at a right angle to the first photosensitive detector (812, 220), and configured to detect fluorescence and scattering from the sample liquid solution; and a control system, wherein the control system is configured to quantify the analyte in the sample liquid solution.