Depends on sensitivity of the balance, amount of lead in solution, and the volume of solution assayed. As a back of the envelope calculation, let's say you have 1 gram (1 mL) of solution. A concentration of lead at 1 ppm (1 g lead/1 million g water), would have a mass of lead of 1 ug. Granted, it'd be coordinated with something else that will have mass, so let's be generous and call it 2 ug of precipitate. If your sample volume were 100 mL, and assuming 100% recovery, now we're talking 200 ug mass of precipitate. Do you have a balance that can discriminate 200 ug from background? If not, method isn't feasible for 1 ppm level detection. Moreover if you know the sensitivity of your balance, you can back-calculate the expected approximate detection limit for a gravimetric detection of lead using your balance. 10-100 ug pushes the sensitivity of even high quality analytical balances, so, the method isn't ideal for trace analysis, and this doesn't even get into possible interferences by other metals that can precipitate. But if your concentrations are in the 100s or ppm so that your precipitate mass is a few mg, then maybe you could get a semi-reliable value.