A method of controlling flow of components separated from whole blood, the method comprising: opening a first valve to allow a flow of platelets separated from the whole blood into a first container ; emitting a beam of a first visible light at the flow of platelets; detecting , with a first sensor, a first amount of the first visible light; emitting a beam of a second visible light at the flow of platelets; detecting , with a second sensor, a first amount of the second visible light; determining , by at least one processor , a baseline ratio, wherein the baseline ratio comprises a ratio of the first amount of the first visible light to the first amount of the second visible light; after a period of time: emitting a second beam of the first visible light at the flow of platelets; detecting , with the first sensor, a second amount of the first visible light; emitting a second beam of the second visible light at the flow of platelets; detecting , with the second sensor, a second amount of the second visible light; determining , by the at least one processor , a current ratio, wherein the current ratio comprises a ratio of the second amount of the first visible light to the second amount of the second visible light; determining , by the at least one processor , whether a difference between the current ratio and the baseline ratio meets a predetermined threshold indicating the presence of white blood cells; and closing the first valve to stop the flow of platelets into the first container if the difference between the current ratio and the baseline ratio meets the predetermined threshold. opening a first valve to allow a flow of platelets separated from the whole blood into a first container ; emitting a beam of a first visible light at the flow of platelets; detecting , with a first sensor, a first amount of the first visible light; emitting a beam of a second visible light at the flow of platelets; detecting , with a second sensor, a first amount of the second visible light; determining , by at least one processor , a baseline ratio, wherein the baseline ratio comprises a ratio of the first amount of the first visible light to the first amount of the second visible light; after a period of time: emitting a second beam of the first visible light at the flow of platelets; detecting , with the first sensor, a second amount of the first visible light; emitting a second beam of the second visible light at the flow of platelets; detecting , with the second sensor, a second amount of the second visible light; determining , by the at least one processor , a current ratio, wherein the current ratio comprises a ratio of the second amount of the first visible light to the second amount of the second visible light; emitting a second beam of the first visible light at the flow of platelets; detecting , with the first sensor, a second amount of the first visible light; emitting a second beam of the second visible light at the flow of platelets; detecting , with the second sensor, a second amount of the second visible light; determining , by the at least one processor , a current ratio, wherein the current ratio comprises a ratio of the second amount of the first visible light to the second amount of the second visible light; determining , by the at least one processor , whether a difference between the current ratio and the baseline ratio meets a predetermined threshold indicating the presence of white blood cells; and closing the first valve to stop the flow of platelets into the first container if the difference between the current ratio and the baseline ratio meets the predetermined threshold. <EOS>