Hi Danielle

You can order syringe filter separetly by sigma. Here is the link

http://www.sigmaaldrich.com/catalog/product/sigma/z359904?lang=en®ion=US

Use 0.22um it can be also from Millipore or othe company.

Good luck

I think, @ Buchs,  Danielle is talking about the kind of filter using in plasmid isolation (midi prep), not the 0.22um syringe filter which is often used for 'sterilization' of solutions.

From this booklet about GenElute™ Plasmid Miniprep Kit, on page 2 (see yellow highlight), it lists the Cat. No. G8917 for the GenElute HP Midiprep Filter Syringes alone.

Do you mean, this product (G8917) has been discontinued by the company?

Sigma does have a "catalog number" for the syringes, but they are not available for purchase separate from the kit. My question is about the syringe filter, not the plasmid isolating column. I do think Buchs answered my question about a substitute filter; however, I did want to leave the question open a little longer to see if anyone else had already tried using substitute filters and which ones worked best. But also, if anyone has any ideas for substitute midi-prep columns (plasmid isolating traps) I'd love to hear them! I tried the HCl method for cleaning and regenerating used columns, but that didn't for us as the old template was still intact after PCR.

1. Yes, I understood that your question is about the 'syringe filter', not the DNA binding column. I use Qiagen® Midiprep kit myself, and only one column is needed for purification (See attachment page 7). After lysis, we just centrifuge to remove the bacterial debris. The centrifuged clear lysate is then directly pour into the column. And that's it. All later wash, elute is done on the column.

Your kit has 2 steps, first use syringe to filter and get clear lysate, then let lysate drop into a DNA-binding column. I am wondering, can you just centrifuge the lysis product and then pour the clean lysate into the column without going through the syringe filter step??

2. The 0.22 um filter unit (see attachment) is usually used for sterilization of a 'lighter' solution. Such as antibiotic solution used in tissue-culturing medium, which cannot be autoclaved sterilization. The bacterial lysate is viscous and fill with debris; I am afraid that they can easily clog the 0.22 um filter.  

Update: we now centirfuge the lysis product and then filter whats left through a .45um filter since there still seems to be some debris that still floats around after spinning for 10min. We find that spinning before filtering prevents the filter from getting clogged, and the filtering is essential for us or else the DNA column gets clogged from the leftover debris.

Danielle: have you found that this reduces yield at all? Have you tried using 0.22um filters? I'm considering trying this, but am worried about the potential of losing plasmid during the filtration step. Thanks!