Development of portable determinator for fast detection of lead ions

Abstract: With the growing deterioration of water environment, heavy metal pollution has become increasingly prominent, and causes a matter of concern. Heavy metals have a strong interaction with a variety of enzymes and proteins in the human body, where the protein and enzymes lose activity. Heavy metals maybe enrich in certain organs of the body, and if its content exceeds the limits of the content that human body can tolerate, it will cause human acute poisoning, subacute poisoning, and chronic poisoning. Development of portable rapid detection equipment of heavy metal becomes necessary. In this study, heavy metal lead ions (Pb2+) are the research object, and the research is based on colorimetry theory, Lambert-Beer's law and spectrometry to develop a portable detector for Pb2+. According to the analysis of the physical and chemical properties of Pb2+ and the research of colorimetric reaction between Pb2+ and dithizone, existing colorimetric detection method of Pb2+ is improved, and complex and cumbersome pre-process of detector is simplified. Under suitable conditions of room temperature, pH value of 9.0 and certain volume, Pb2+ reacts with dithizone solution whose color is blue-green, which can generate orange complex, so that the measured value of Pb2+ can be converted to easily measured mathematic data to build detection model for the determinator, and other metal ions do not interfere in the determination by adding the masking agents. The determinator designed includes the optical circuit part and electric circuit part. The optical circuit part consists of light source, optical fiber, and silicon detector, which is used to collect the optical signal. Optical module uses the 510 nm wavelength LED (light- emitting diode) with narrow band filter as the active light source, and optical fiber is the transmission channel to make sure the monochromatic light source gives the parallel and vertical light striking the detector. Additionally, a silicon photodetector is the optical detector. The optical part is aimed to detect the band transmittance. Electric circuit is designed to convert the light signal to electrical digital signal, amplify the signal, decrease the noises, data process and store, and real-time display and communication. The electric circuit includes microcontroller, LED drive circuit, detection circuit, communication circuit, keyboard circuit, and liquid crystal display circuit, and lithium-ion battery is used as power supply. PS0308 type photodiode with spectral response range 300-1 100 nm converts the optical signal to electric signal and also effectively guarantees the linearity of the instrument. The system software is used to detect electric quantity, measure and manage data, and so on. All the connection parts are fixed together through the metal pieces to prevent deviation by the movement of light path. When the device has been installed, system performance is analyzed to assure the accuracy. Power consumption and anti-interference of the software and hardware are tested, also repetitive testing is done to verify the accuracy of the measurement. Experimental results show that decision coefficient of the predicted and the real concentration values in training set is 0.934, and the value is 0.822 2 in prediction set, and the detection range of determinator is 0.01-0.2 mg/L, indicating it can detect the Pb2+ with lower concentration. Relative standard deviation of Pb2+ concentration is less than 1.0%. The test results indicate that this determinator is simple to operate with satisfactory precision, accuracy, and repeatability, realizing the miniaturization of instrument and on-site rapid detection. At the same time, the determinator has simple and stable structure with low consumption. Based on the instrument, in the future work, the portable rapid detection of Pb2+ can be adapted to a variety of heavy metals in aqueous media with a low cost, low detection limits, and simple pre-treatment.