Dear Mamdouh Alsayed Eissa; Here are few references attached, may be useful. Thanks

http://www.sciencedirect.com/science/article/pii/S0039914004005557

http://www.sciencedirect.com/science/article/pii/0048969795048308

Dear Mamdouh Alsayed Eissa,

You may try visit IRMM [https://ec.europa.eu/jrc/en/reference-materials] for information on reference materials production and quality control.

Reference: Stoeppler et al. (2001). Reference materials for chemical analysis. Wiley.

I purchased reference material from these two organizations, known to be the best reference material providers.

1: Institute for Reference Materials and Measurements (IRMM), European Reference Material (ERM) Belgium.

2: International Atomic Energy Agency (IAEA) standards.

To carry out QA/QC in a satisfactory way requires much more than just buying CRMs.

May I suggest that you start reading ISO 17025 - and then perhaps aim at obtaining official accreditation.

Good luck