Bushwalk Australia

has anyone come across a source for Picaridin spray in Aus? Apparently needs to be at least 20 percent to be effective. Found an online site for Sawyer brand here but expensive.
phil

'Off!' Available in your local Coles supermarket.

Yes I saw that but couldn't find what percentage of Picaridin it contained.
phil

191g/L = 19.1%

Thanks fellas, should work fine for Kokoda at half the price plus postage. Your maths is better than mine Strider!
phil

Strider the chemist!

My maths is appalling but that's pretty easy to work out.

If 1mL = 1g.

Then 191g/1000mL*100 = 19.1%

well here is a challenge beyond me. if it contains 19.1 ml per litre, how much Picaridin would be in 175ml?
phil

175ml x 19.1% = 33.425ml.
191ml per litre, not 19.1ml.

Wait, was that how you guys did the calculation? Thought you'll need to know the molecular weight of picaridin to calculate.

229.3g/mol

GPSGuided wrote:Wait, was that how you guys did the calculation? Thought you'll need to know the molecular weight of picaridin to calculate.

229.3g/mol

I think you just need the density.
If it's given in g/l and you want to convert to %vol/vol

Your right. It's been a while since I had to do one of these calcs. Given the nature of it, it'll have a density greater than water, therefore...

Maybe the '20%' refers to ml/l?

The msds that I found has this:

Thought I would add to this as I wasted time in the shop as the Off! product doesn't print the percentage on the label

The density of Picaridin is 1.07g/ml (at 20°C) according to http://www.drugfuture.com/chemdata/picaridin.html

Off! Tropical Strength at 191g/L has a percentage of 20.4% (191 x 1.07 = 204.37ml/L).

Off! Familycare version at 92.8g/L has a percentage of only 9.9% (92.8 * 1.07 = 99.296ml/L)

Anyone know if Picaridin is stable over time? I leave mine in the car through all seasons and wondered if it'll go off after a while?

You're looking at simple concentration expressed as a percentage of weight per volume.

Pharmaceutical solutions are expressed as weight per volume i.e. a 0.1% adrenaline solution is 1mg/ml (or 1g/L). You don't need the molecular weight for this calculation - it is an expression of weight of solute to solvent in grams/L.

The OFF! Tropical strength at 191g/L is a 19.1% solution. A 20% solution ought to be 200g/L. If you buy the Off tropical strength you will not achieve the 20% the OP is after but it is pretty close. That wouldn't worry me at all. I would just wear long sleeves, soak my clothes in permethrin and spray my exposed skin with the 19.1% solution.

Once it is prepared in the factory the molecular weight, temperature, latitude or angle of your tongue does not effect the concentration of the solution. I am not sure of the stability of the picaridin compound though - so long as you use it before the use by date it should be fine.