How to test the lead level

Although plasma mass spectrometry ICP-MS can accurately determine the blood lead level, it is not suitable for daily analysis because of its high cost, and only some professional laboratories have this equipment. Anodic dissolution voltammetry (ASV), as a successful test method for determining blood lead concentration, has been applied in foreign countries for more than 30 years. The analysis of blood lead by anodic dissolution voltammetry was proposed in 1971, and since then it has shown its unique advantages in microdetermination. The lead ions in the blood, treated with reagents, are released as free lead ions. When a certain negative voltage is applied to the electrode, all the lead ions will be reduced to lead and attached to the electrode, and then a more positive voltage is applied to the electrode, and the lead on the electrode is ionized into lead ions, and a certain number of electrons are released, generating a current signal. This current signal is proportional to the concentration of lead in the solution, and the concentration of lead ions is determined. The Model 3010B blood lead analyzer manufactured by ESA in the U.S. uses the conversion method, in which the 2-valent lead ions in blood proteins are replaced with lead ions containing (CH3COO)2Ca, CrCl3, and Hg2+, and its main advantage is the increase in the speed of the analysis and the possibility of obtaining more reliable results. Several comparisons from the CDC program have shown good agreement between ASV and GFAAS. Graphite Furnace Atomic Absorption Spectrometry (GFAAS) is one of the internationally recognized standard methods for the detection of blood lead. However, graphite furnace atomic absorption spectroscopy is greatly affected by light scattering and molecular absorption, and this method stipulates that a Seeman background correction system must be used and the wavelength used to analyze lead must be stabilized at 283.3 nm. Moreover, this method is very demanding in terms of sample handling and working environment, and the following should be noted in the operation: 1. During blood collection and blood sample handling, since the blood samples are completely exposed to the environment, it is important to pay attention to the lead contamination in the environment. Therefore, we must pay attention to lead contamination of blood samples in the environment (such as lead contamination brought by particles in the air, the use of contaminated appliances). 2. Nitrification of blood samples after blood collection, the role of nitrification is to remove the cellulose in the blood, so that the lead in the form of free form exists in the solution. The lead content of nitric acid used in the process is very high, even higher than the lead content of the blood sample, so it is necessary to test the lead content of nitric acid and take measures to reduce the lead content of nitric acid before using nitric acid to nitrify blood samples, to avoid the secondary contamination of the blood sample and the emergence of false positives. 3. In the use of the Seeman Effect Graphite Furnace Atomic Absorption Spectrometry for the determination of blood lead, it is necessary to have a professional and technical personnel to complete this process. complete this procedure. Flame Atomic Absorption Spectrometry (AAS) is an old technique to analyze the blood lead content in human body by flame AAS. Since the blood lead that affects human body is in trace amount, using flame AAS, the atomization rate of lead is very low, i.e., the baseline drift is very serious in practical operation. Therefore, its sensitivity is not up to the detection range of human blood lead, and false-negative results are possible. Flame atomic absorption is more seriously affected by external factors in operation, especially the influence of human factors, and different people operating may get different results. At the same time, because blood samples are completely exposed to the environment (e.g., lead contamination from airborne particles, use of contaminated instruments) and the nitric acid used in the nitrification of blood samples is too high in lead, secondary contamination of blood samples is possible, which may result in the occurrence of a false-positive phenomenon in which the actual blood lead level of children is low while the measurement result is high. This method has basically been replaced by the graphite furnace atomic absorption method. The erythrocyte protoporphyrin (EP) method, also known as the zinc protoporphyrin (ZPP) method, was once used as a lead screening tool for asymptomatic children and other high-risk groups. Data suggest that the zinc protoporphyrin method (EP/ZPP) does not have sufficient sensitivity and accuracy to determine blood lead levels at low concentrations and is no longer used for blood lead screening. The zinc protoporphyrin assay is a method used to account for the increased levels of protoporphyrin due to the replacement of iron in the porphyrin ring by zinc (and the inhibition of iron complexing enzymes in the mitochondria by lead). Protoporphyrins reach a stable level only after all circulating red blood cells are completely renewed, which takes 120 days, and the half-life of protoporphyrins (68 days) is longer than that of lead in the blood (28-36 days). The zinc protoporphyrin method does not indicate the level of blood lead at the time of testing, but is only an indirect estimate of moderate blood lead levels. Based on numerous studies, it has been shown that zinc porphyrin levels are usually less than 35 μg/dL, and that the concentration of new protoporphyrin in the body is only proportional to blood lead levels in the range of 30-80 μg/dL (PorruAlessio 1996). At blood lead concentrations of 10 μg/dL-30 μg/dL, the diagnostic sensitivity and precision of the test by the EP method are very low. And this blood lead level is clearly harmful to children's health. Therefore, the sensitivity of the zinc protoporphyrin method is not sufficient to determine lead exposure in low blood lead levels, so testing by the EP method will result in children with higher actual blood lead levels and lower measurements, which is prone to false-negative results. In patients with jaundice and iron-deficiency anemia, sickle cell and other hemolytic anemias, EP values are elevated and can lead to false-positive diagnostic results.