Standard sample/25 kinds of metal mixed standard/aluminum, arsenic, boron, barium, beryllium, calcium, cadmium, cobalt, chromium, copper, iron, mercury, potassium, magnesium, manganese, molybdenum, sodium, nickel, lead, antimony, selenium, titanium, thallium, vanadium, zinc/medium: nitric acid + hydrochloric acid + hydrofluoric acid