Hi Akshaya, I have colleagues that do dissolved metal measurement regularily in the Gironde estuary. You may be interested in one of their paper where they use ICP MS for this purpose.

Mario

Dabrin, A., Schäfer, J., Blanc, G., Strady, E., Masson, M., Bossy, C., Castelle, S., Girardot, N. and Coynel, A., 2009. Improving estuarine net flux estimates for dissolved cadmium export at the annual timescale: Application to the Gironde Estuary. Estuarine, Coastal and Shelf Science 84, 429-439.

you can follow APHA guidelines. Using atomic absorption spectrophotometer, you can analyse the samples.

Thank you