Litterless Litter Box for Cat Urine
The easiest way to collect feline urine is to get a litterless litter box. You can find these at a pet store. Immediately after your cat has urinated, go to the box and extract the urine using a syringe. Empty the syringe into the container and you're done.
However, your cat may notice that you've changed the regular litter box and he might avoid it.
Collect the Cat Urine on the Spot
If the before-mentioned technique is unsuccessful, you will have to collect the urine right when your cat urinates. Detect when your cat wants to urinate and be ready to collect. You can determine when your cat urinates by giving him a lot of liquids. When you notice that he assumes the urinating position, lift up his tail and place the container under the cat. Get some rubber gloves to avoid direct contact with cat urine.