You can measure total and dissolve forme, the digestive method with mixed acid give you total concentrations, and without digestive you can measure the dissolve form. ASTM part 30 and 31 handbook or APHA give you the method to measure.good luck.
You can determine heavy metal concentration using ICP-OES/ICP-MS. In the case of Hg, you can use CVAFS (Cold Vapor Atomic Absorption Fluorescence Spectrometry). Remember that your samples need to be acidified immediately after they are collected.
There are various analytical techniques available for heavy metal analysis, including atomic absorption spectroscopy (AAS), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and inductively coupled plasma-mass spectrometry (ICP-MS). The appropriate technique should be selected based on the sample nature, detection limits, accuracy, precision, and cost considerations.
To determine the most suitable technique, it is recommended to refer to the guidelines provided by the Central Pollution Control Board (CPCB) and the American Public Health Association (APHA) for the required analysis. These guidelines can be found at the following sources: https://cpcb.nic.in/NABL/nabl_scope_jan21.pdf
Determination of heavy metals such as Flame emission spectroscopy and UV / Vis spectroscopy, but Atomic Absorption Spectroscopy (AAS) is the preferred analytical technique due to its cost effectiveness, sensitivity and its applicability.