Sintered discs are commonly used when carrying out filtration processes in the laboratory.
The discs are particularly effective when working with corrosive chemicals such as ammonia and sulphuric acid that would otherwise damage less resistant filter paper.
DWK Life Sciences provides a range of filtration products incorporating sintered discs in both the PYREX® and QUICKFIT® jointed glassware ranges – both of which are made from PYREX® 3.3 expansion borosilicate glass.
In this blog we will explain how to clean sintered discs safely and effectively.
Cleaning sintered discs
Before first using glass filters with sintered discs, the discs themselves should be cleaned with diluted, hot hydrochloric acid, followed by several rinses with distilled water.
As with all types of laboratory glassware, this is required to remove any potential residual contamination from the manufacturing process or the product packaging (such as cardboard fibres).
The glassware should also be washed as quickly as possible after use. During washing with water, all parts of the item should be scrubbed with a soft brush.
A gentle approach and a soft brush are essential to avoid any abrasion or scratching of the glassware. After cleaning, you should thoroughly rinse again with distilled water.
Drying of the cleaned filters can be undertaken either in air or in a dry oven at temperatures not exceeding 100°C.
If after this cleaning procedure the sintered disc pores remain clogged, a more thorough chemical cleaning process may be required.
The choice of solvent used in the cleaning process depends on the contamination on the discs. The following table indicates the correct solvent to use for common contaminants in the filtration process.
|Barium sulphate||Hot concentrated Sulphuric acid, Silver-chloride, Ammonia or Sodium hyposulfite|
|Copper/Iron Oxides||Hot Hydrochloride acid plus potassium chlorate|
|Mercury residue||Hot Nitric acid|
|Mercury sulphide||Hot aqua regia|
|Albumen||Hot hydrochloric acid or hot ammonia|
|Grease, Oil, fatty materials||Carbon tetrachloride|
|Organic matters||Hot concentrated cleaning solution, or hot concentrated sulfuric acid plus a few drops of sodium or potassium nitrite|
|Glucose||Carefully heat to approx. 200°C with mixed acid (5% sulfuric acid and 1% nitric acid)|
Extensive rinsing of the filter with water must follow any use of the above-mentioned solvents.
Hot, concentrated phosphoric acid and hot alkaline solutions attack the glass surface and are therefore unsuitable as cleaning agents. If they have to be used in the filtration process itself, an increase in sintered disc pore size and reduced life of the sintered disc is unavoidable.
Sintered discs provide a safer and more robust approach when carrying out filtration processes involving corrosive chemicals. Discs can be safely reused too, but their effectiveness and long-term sustainability depends on the correct cleaning processes outlined in this blog.