[ActivationEnergy]

OK, so I know I will end up annoying everyone with my questions, but this is actually for my AH Biology investigation. I am titrating kiwis against iodade to get the Vitamin C content.

Today, I realised I had some problems concerning the preparation of the kiwi- I blended a kiwi with 50ml distilled water, then filtered the liquid off, to use the filtrate for pipetting.

However, the filtration was too slow and I couldn't get a water pump to work.
Also, the liquid had to be filtered twice, as some of the bigger pieces got through the filter paper and ended up stuck in the pippette.
Finally, when I titrated against 0.002M potassium iodate, the titre was very small (about 2ml). Maybe that wasn't the end-point, but...

Any ideas how to solve any of these problems?  

my original method: http://www.outreach.canterbury.ac.nz/chemistry/documents/vitaminc_iodate.pdf

[fledarmus]

There are a lot of proteins and lignins in fruit juice that can make it very difficult to filter, especially by vacuum filtration. There isn't much you can do about it. Filtering through cheesecloth two or three times may actually work better than trying to vacuum filter through paper, because the interactions with the cheesecloth tend to collect even many of the particles actually small enough to get through the pores. On a manufacturing level, these are usually filtered under pressure rather than under vacuum, and fining agents are added to coagulate the smallest particles and slimes into particles large enough to filter.

If you have access to a small centrifuge, that makes the process much easier - you can spin all the pulp down into the bottom of the tubes and just pour off the supernatant.

[ActivationEnergy]

I doubt I could get a centrifuge, any idea how to make the filtration quicker?

[fledarmus]

One thing you can do is add some diatomaceous earth to your sample and let it stir gently for a while before filtering it, or just filter it through a packed bed of diatomaceous earth in your funnel. Diatomaceous earth comes under a variety of different trade names - I have used it as Celite and as Filter-aid. That may help if the reason your filter is clogging is because your solid particles are too small.

If your filter is clogging because it contains a lot of proteins, semi-solids, or gels, you may need to try adding fining agents or flocculants to get them to precipitate. If you do a wiki search for water purification or for clarification of wines, you will find a number of suggestions. If you have a wine hobbyist anywhere in the area that you could talk to, you might be able to get some better suggestions.

[ActivationEnergy]

I am now sieving before filtering.
And (trying) to use fluted filter paper (I don't know exactly how to make it).

Thanks anyways guys.