Issues regarding the determination of lead content in naphtha by graphite furnace method

The matrix is a lead standard solution at 1000 ug/ml

It changed after it was placed there. How should I understand this? How much time has passed since it was placed? It changed, by how much? This requires detailed explanation in order to determine where the problem likely lies. If you leave it for a year or it only changes by 1%, then there’s no need to discuss it. Analytical chemistry requires using data to communicate.

For the concentrations of 2.5 ug/ml, 5.0 ug/ml, and 10.0 ug/ml, the absorbance values were 0.03, 0.06, and 0.12 respectively; the regression value was 0.9998 with a slope of 0.004. After 48 hours, the absorbance values changed to 0.01, 0.04, and 0.10 respectively, with a regression value of 0.9800 and a slope of 0.01. The matrix used was a lead standard solution with a concentration of 1000 ug/ml, and 1% *ao acid was used as the solvent. The volumetric flasks were soaked in this acid solution and then rinsed thoroughly beforehand. Why is the properties of this prepared standard solution so unstable?

This is microanalysis; the standard solutions used to prepare the standard curve should not be stored. The adsorption of trace metals by containers is already quite significant, and the lower the concentration, the more pronounced this adsorption becomes. It is recommended that standard curves be prepared fresh as needed. Additionally, volumetric flasks should not be frequently cleaned with highly acidic solutions, as this can cause strong adsorption on the glass surface. It is recommended that under experimental conditions, a complete set of data calculations for the standard curve be performed daily using standard samples. After collecting data over a period of time, comprehensive data for the standard curve will be available; in subsequent experiments, only verification calibrations at specific concentration points of the standard samples will be necessary. However, the standard curve needs to be re-validated from time to time.

I’m not worthy of being called a senior. In micro and trace analysis, standard samples cannot be stored; they must be prepared just before use. It is also important to use containers for preparing standard samples in a manner that maintains a constant concentration, and it is not advisable to use strong acids or bases for prolonged soaking or cleaning. The abnormal phenomena observed in some experiments need to be considered comprehensively, and a judgment must be made based on the actual circumstances.