What is w/w?..or w/w %?..what context can you use it in?

[seamoro]

so how do i make a w/w solution? bascially i am writing validation protocol and i want to explain the make up of a solution....is it correct to write.... 100% solution is 50mg/100l w/w...is this correct?....or should i just write a 100% solution is 50mg/100ml?
I understand what w/v % is...i just want to understand the context in which w/w can be used.

[shaun78]

% w/w is something you are more likely to see from your manufacturing folks. Labs are generally going to use a % v/v or a % w/v.

An example of w/w would be 1 gram of acid in 1 kg of water; something where you have a weight on both the part and the whole.

An example of v/v is 1 mL of acid in 1 L of water as you know volume amounts of both the part and the whole.

An example of w/v would be 5 g of potassium acetate dissolved in 1 L of water as you have a weight on the component and a volume on the whole. w/v is common in a lab for buffer preparations.

Hope this helps with the context in which all are used ... I am not so sure if it will.

[lmh]

Do you mean that you are preparing a standard solution at 50mg/100mL and you want to describe this solution as "100%" in the context that you will then prepare other dilutions from it?

If so, I would avoid stating it's 100% as this is potentially misleading, and instead describe it as a "concentrated standard" or some such neutral term, and then describe what dilutions to prepare from it.

[tom jupille]

Murphy's Law: If anything can go wrong, it will.

Method Development Corollary to Murphy's Law: No matter what you write, someone, somewhere will find a way to misinterpret it.

It is your job to make that misinterpretation as difficult as possible!

1. Minimize ambiguity by specifying the *exact* procedure for weighing/preparing/diluting the stadards

2. Specify exactly what they are (e.g., "dimethylchickenwire, 10 mg/mL)

[lmh]

Tom, ah, now would that be 10mg/mL of dimethyl chickenwire.3H2O potassium salt 99% based on 2.7% solvent from Sigma, or would it be 10mg.mL dimethyl chickenwire lithium salt, anhydrous 98% from Fluka?

You are absolutely right: particularly with mg/mL solutions, it is absolutely essential to state exactly what product you are using, as the weight of stuff in bottle per mole is likely to vary enormously.