These filter papers are made of 100% cotton linters. They are guaranteed to be free of any residual acids and they have an extremely low percentage of ash content. As a result, these filters are virtually ash-free. All Sartorius ashless filter papers are characterised by high wet strength and high purity and are therefore especially suitable for quantitative analysis, Büchner funnels, pressure or vacuum filtration.

388: 'Black dot filter' For coarse-flocculent and voluminous precipitates, especially iron, aluminium and chromium hydroxides; copper, bismuth, cobalt and iron sulphides; various organic, coloured metal deposits; determination of silicon in analysis of steel and pig iron; for acidic and slightly alkaline solutions; pressure filtration.

389: 'White dot filter' The most used grade for analyses; for relatively coarse precipitates such as silver, arsenic, antimony, cadmium, lead, iron and manganese sulphides; lead chromate; ammonium phosphorous molybdate; alkaline earth carbonates '...' for acidic and slightly alkaline solutions; pressure filtration.

390: 'Green dot filter' Filtration of fine precipitates; barium sulphate; lead molybdate; lead dioxide; calcium hydroxide; calcium fluoride; nickel, zinc and stannic sulphides; for acidic and slightly alkaline solutions; pressure filtration.

393: 'Purple dot filter' Ideal for particularly difficult filtration conditions and especially fine-grained precipitates; barium sulphate; copper oxide.