Gaya APA

Helrich, K. (1990). Official Methods of Analysis 15 Edition 1990 : Association of Official Analytical Chemists Volume Two . USA: Association of Official Analytical Chemists.

Gaya MLA

Helrich, Kenneth. "Official Methods of Analysis 15 Edition 1990 : Association of Official Analytical Chemists Volume Two". USA: Association of Official Analytical Chemists, 1990. PRINTED BOOK.