Which porosity grade of sintered glass filter should I choose?

Match the grade to the smallest particle you must retain. Coarse grade 1 pores are 100 to 160 micrometres and suit coarse precipitates and gas sparging. Grade 2 at 40 to 100 micrometres handles general gravimetric work. Grade 3 at 16 to 40 micrometres is the usual choice for fine precipitates and sample cleanup. Grade 4 at 10 to 16 micrometres retains very fine material but clogs quickly, so use it only when the method demands it.

Can sintered glass crucibles be used in a muffle furnace?

Standard borosilicate sintered discs are not designed for muffle furnace ashing. The sintered matrix has a large surface area and is far more sensitive to thermal shock and to flux attack than solid glassware, and repeated heating above about 200 degrees Celsius shortens its life. For ignition gravimetry at 500 to 900 degrees Celsius, use a porcelain or quartz Gooch crucible with a separate filter disc, or a platinum filter crucible.

How do I clean a clogged fritted filter?

Back-flush first with clean solvent in the reverse direction, then soak. For organic residues use a warm laboratory detergent, for protein use a dilute enzyme cleaner, and for inorganic scale use a short soak in dilute acid compatible with the precipitate you are measuring. Never poke the disc with a wire or scrape it, and never use hydrofluoric acid. Rinse with deionised water and dry in an oven at 100 to 120 degrees Celsius before weighing.

Does JWRESEARCH supply sintered glass filters and filter crucibles in Singapore?

Yes. JWRESEARCH supplies sintered glass filter crucibles with and without lids, fritted filter funnels, vacuum filter assemblies with fritted discs, glass filter discs and support screens in porosities 1 to 4 and disc diameters from 20 to 90 millimetres, together with vacuum flasks and adapters, delivered across Singapore.

Sintered Glass Filters and Filter Crucibles Singapore

Published: {{NEW_ARTICLE_DATE}} | By JWRESEARCH | Category: Laboratory Glassware and Filtration

A sintered glass filter is a disc of borosilicate glass particles fused into a rigid porous matrix. Unlike filter paper, it does not shed fibres, does not absorb the filtrate, and can be weighed, dried and reused. That makes it the standard tool for gravimetric analysis, for clarifying small volumes of solvent, and for holding a bed of adsorbent in a vacuum manifold.

At JW RESEARCH SUPPLY, we supply sintered glass filter crucibles, fritted funnels, vacuum filter assemblies and replacement discs to analytical, pharmaceutical, environmental and teaching laboratories across Singapore. This guide covers porosity selection, format choice and the handling rules that decide whether a frit lasts years or weeks.

Porosity Grades

Grade	Pore Size	Retains	Typical Use
1 — Coarse	100 – 160 µm	Coarse crystals, fibrous solids	Gas sparging, coarse precipitates, pre-filters
2 — Medium	40 – 100 µm	Medium precipitates	General gravimetric filtration, catalyst recovery
3 — Fine	16 – 40 µm	Fine precipitates	Sample cleanup, HPLC solvent filtration, barium sulfate
4 — Very fine	10 – 16 µm	Very fine precipitates	Fine gravimetry, clarifying turbid extracts
5 — Fine capillary	2 – 5 µm	Bacteria, fine colloids	Specialist work only; slow and easily blocked

Specification Reference

Parameter	Typical Value	What It Affects
Disc diameter	20, 30, 40, 60, 90 mm	Filtration area and hold-up volume
Nominal capacity	5 – 300 mL	Batch size the crucible can hold
Body material	Borosilicate 3.3	Chemical resistance and thermal expansion
Joint size	14/23 to 45/40 taper, or rubber adapter	Fit to vacuum flask or filtration assembly
Max operating pressure	Vacuum only, no positive pressure	Positive pressure can fracture the disc
Max drying temperature	110 – 150 °C	Higher temperatures degrade the sinter bond
Thermal shock limit	About 30 °C step	Hot crucible onto a cold bench cracks the disc
Chemical limits	No HF, no hot concentrated alkali	Both dissolve the sintered matrix

Choosing a Format

The filter crucible, or Gooch crucible, is a cylinder with the frit fused into the base. It is the right form when you need to dry and weigh the residue together with the crucible, and when the precipitate must be washed without transferring it. Crucibles with a lid allow a slower, controlled filtration and reduce dust pickup during weighing.

A fritted funnel puts the same disc in a conical body. It is easier to load with a spatula or with a bed of silica, alumina or charcoal, and it is the usual choice for solvent filtration and for short chromatography columns. The vacuum filter assembly combines a fritted support with a borosilicate flask and a clip, which is the most practical setup for routine membrane filtration where the frit acts as the support rather than the filter.

Disc diameter should match the volume, not the glassware you happen to own. A 20 mm disc on a 250 mL sample blocks long before the batch is finished; a 90 mm disc on a 10 mL sample wastes material and increases hold-up. As a working rule, keep the loaded solids below about one third of the disc area.

Working Under Vacuum

Sintered discs are strong in compression and weak in tension. Vacuum pulls the disc into its seat, which is safe; positive pressure from above pushes it out, which is not. Never pressurise a fritted funnel from the top, and never use a frit as a support for a pressurised line.

Apply vacuum gradually. A sudden full vacuum on a hot or dry disc is the second most common cause of cracking after thermal shock. Where the method allows, wet the disc with the filtrate solvent first, then apply vacuum, then add the sample. This also prevents fine particles from being driven into the pores before a cake has formed.

Cleaning and Re-use

Clean immediately. A frit that dries with residue in the pores is far harder to recover than one rinsed while still wet.

Back-flush with clean solvent in the reverse direction before any soaking.
Soak in warm laboratory detergent for organic residues; use an enzyme cleaner for protein.
Use a short dilute acid soak for inorganic scale, choosing the acid that will not dissolve your analyte.
Rinse with deionised water, then acetone, then dry at 110 to 120 °C.
Never scrape or poke the disc, never use hydrofluoric acid, and never clean with hot concentrated alkali.
Store crucibles in a dust-free cabinet; a covered crucible weighs more consistently.

Weighing Practice for Gravimetry

Bring the crucible to constant weight before use: dry, cool in a desiccator, weigh, and repeat until two consecutive weighings agree within 0.2 mg. Use the same desiccator time for the empty and the loaded crucible, because the glass holds a film of moisture that changes with cooling time and bench humidity.

Handle with tongs or lint-free gloves, never fingers. Singapore bench humidity is high enough that a warm crucible picked up bare-handed will gain measurable mass while it cools.

Ordering Checklist

Porosity grade, based on the smallest particle to be retained
Format: crucible with lid, crucible without lid, funnel or vacuum assembly
Disc diameter and nominal capacity
Joint size or adapter requirement for your vacuum flask
Whether the residue will be ignited, which rules out a sintered disc
Number of units and a spare disc or two for critical methods

Send us the method, the precipitate and the volume per batch, and we will recommend a porosity, format and disc size, delivered across Singapore.

Contact JWRESEARCH

JW RESEARCH SUPPLY — laboratory equipment and consumables, Singapore.
Telephone / WhatsApp: +65 8039 3660
Email: SINGAPORE@JWSHY.COM
Website: www.jwresearch.cn