Dilute! Dilute! OK!
May 14, 2019 4:47 AM   Subscribe

My dilution abilities are not great, and I need someone to help me with what is basic math but I can't seem to figure it out right now.

You are not my vet or my chemist or my poultry whisperer.
A post on chicken forums says "Elector PSP is 44.2% = 442 mg spinosad per one ml
Captain Jack's 0.5% = 50 mg spinosad per 1 ml...
Elector says to mix 8.9 ml to one gallon. 8.9 x 442 mg = 3933 mg per gallon"

From the Elector product sheet for northern fowl mites is says "dilute 3 oz of the product with 10 gallons of water" which does seem to work out to about 8.9 ml per gallon. My question is: DILUTED, what is the final concentration of the Spinosad in that Elector dilution and how does that compare to the NON-DILUTED Captain Jack's Deadbug concentrate (0.5% spinosad in the bottle). In other words, is there any way I can dilute Captain Jack's to get the same spinosad percentage dilution as the DILUTE Elector product. This is probably a really basic chemistry question but I am having trouble figuring it out, thanks for any help someone can give me!

(Yes I know about permethrin and DTE which apparently doesn't work as well as people would like to hope, and I know I have some other things I can (will) do to alleviate the situation a little bit, but I am specifically asking about the spinosad concentrates and uses. I am not asking for general mite fighting ideas. Thanks. )
posted by Rufous-headed Towhee heehee to Home & Garden (8 answers total) 3 users marked this as a favorite
Figure out the total mass of spinosad (in mg) that went into the solution. Then, separately, figure out the total volume of the solution (I’d convert gallons to liters and just work in SI units). Divide mass by volume and Bob’s your uncle, you’ve got concentration in mg/L.
posted by snowmentality at 4:53 AM on May 14, 2019

So please check my understanding and math, but it looks like the encore is 1.04 mg per ml in the dilution (3933 mg in 3785 ml). Approx 1 to 1? So would I mix the Deadbug with 50 ml water to get a similar percent dilution? I really don't want to mess this up, while spinosad is relatively safe as a pesticide, one doesn't want to play around with them anyway. Thanks!
posted by Rufous-headed Towhee heehee at 5:13 AM on May 14, 2019

You need to do the mass and volume calculations separately for Elector and Captain Jack’s. The ratio will be different because the starting concentration is different.

Elector is 442 mg/mL. If you put 8.9 mL in, you get a mass of 442 mg/mL x 8.9 mL = 3933.8 mg. The volume is 1 gallon + 8.9 mL = 3785.4 mL + 8.9 mL = 3794.3 mL. That means you have 3933.8 mg per 3794.3 mL, or 1.03 mg/mL final concentration.

Captain Jack’s is 0.5%, or 50 mg/mL to start. If you want a final volume of 1 gallon, or 3785.4 mL, at a concentration of 1.03 mg/mL, then you have to solve the following algebra problem to figure out what mass you need:

X mg/3785.4 mL = 1.03 mg/mL

Multiply both sides by 3785.4 mL to solve for X. This gives you 3898 mg.

Now, how much of the original 0.5% solution do you need to get 3898 mg? Again, algebra:

3898 mg = 50 mg/mL * V mL

Divide both sides by 50 mg/mL to solve for V

3898 mg / (50 mg/mL) = V mL
V = 77.96 mL

So, you would need to use 77.96 mL of Captain Jack’s to get a mass of 3898 mg spinosad.

To get a final total volume of 1 gallon, you need to take that 77.96 mL into account. So, dilute with (1 gallon - 77.96 mL) = (3785.4 mL - 77.96 mL) = 3707.4 mL water.

Someone else please check my math to make sure I haven’t made a stupid algebra or units error. But this is the basic idea.
posted by snowmentality at 5:38 AM on May 14, 2019 [2 favorites]

Captain Jack's 0.5% = 50 mg spinosad per 1 ml...

This doesn't add up. A 0.5% solution would be 5mg/mL. Verify the strength of Captain Jack's before doing snowmentality's math.
posted by Rock Steady at 7:06 AM on May 14, 2019 [3 favorites]

Still awaiting more answers but the front label of the Captain Jacks concentrate does say 0.5% . I think that's correct that that means 5mg/ml.
This might be an easier question: for the dilution of 3 oz per 10 gallons of the Elector, what would the final solution strength (in percent of Spinosad) be? That's the first rung of the ladder.
posted by Rufous-headed Towhee heehee at 3:16 PM on May 14, 2019

3 oz per 10 gal is 3/1280, or a factor of .0023. 44.2%*.0023 = 0.1%. So the concentration of Elector PSP after diluting is 0.1%.

The Captain Jack's at 0.5% must be diluted by a factor of 5, so to get an equal concentration by diluting Captain Jack's, for every 1 part Captain Jack's add 4 parts water (for a total of 5 parts solution).
posted by biogeo at 4:36 PM on May 14, 2019 [1 favorite]

Now that I'm not on my phone, strictly speaking the above is a slight fudge, but it doesn't affect the answer because 10 gallons is much larger than 3 ounces.

More verbosely to show my work better:

Elector PSP full concentration = 44.2% w/v

Elector PSP diluted concentration = (full concentration) * (volume of concentrate / volume of solution)

Volume of concentrate = 3 oz
Volume of solution = 10 gal + 3 oz = 1283 oz (this is where I fudged before)

Elector PSP diluted concentration = 44.2% w/v * (3 oz / 1283 oz) = 0.10% w/v

Captain Jack's concentration = 0.5% w/v
Elector PSP diluted concentration = (Captain Jack's concentration) * (X parts Captain Jack's / (X + Y parts solution))

Substituting in:
0.1% = 0.5% * X / (X + Y)
X + Y = 5X
Y = 4X
i.e., the volume of Y (the diluent, in this case water) is 4 times the volume of the concentrate (in this case, Captain Jack's).

Or in other words, 4 parts water per 1 part Captain Jack's equals the concentration of the Elector PSP diluted solution.
posted by biogeo at 5:10 PM on May 14, 2019 [1 favorite]

Fantastic, thanks!
posted by Rufous-headed Towhee heehee at 5:21 PM on May 14, 2019

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