Обозначение марки фильтра, оставить как есть. См расшифровку ниже
https://www.spectrumchemical.com/OA_HTML/ibeCCtpItmDspRte.js...
WHATMAN(R) BINDER-FREE GLASS MICROFIBER GF SERIES FILTERS
Grade GF/A: 1.6 µm
Highly efficient general filter. Suitable for suspended solids in all types of water and effluent and filtration of particulates in water, algae and bacterial cultures. Also widely used for air pollution monitoring.
Grade GF/B: 1.0 µm
Thicker than GF/A with higher wet strength and increased loading capacity. Recommended for concentrated suspensions and retention of small particles. Suitable for suspended solids in industrial effluents, especially at high loading.
Grade GF/C: 1.2 µm
Combines fine particle retention with good flow rate. Used in many parts of the world for collection of suspended solids in potable water and natural and industrial waste. Widely used in biochemistry for cell harvesting, liquid scintillation counting and binding assays.
Grade GF/D: 2.7 µm
General purpose membrane prefilter with high loading capacity.

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Note added at 35 мин (2012-06-25 12:39:41 GMT)
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Конечно, марка фильтра должна быть GF/D (Фирмы Ватман или аналогичная).
Опечатка!