How much Phosphorus is actually in STPP & TSP?

[mich]

Anyone actually know?

 

I was reading a box of Finish Tabs and something hit me -

 

"The formula for this automatic dish detergent averages nor more than 8.7 phosphorus by weight, in the form of phosphates, which is equivalent to 2.2 grams per use level."

 

That's barely even half of a teaspoon. Is that actually the amount of STPP, or the by product of phosphorus contained in the amount added?

 

 

Laundress, do you know anything? I'd kinda like to know what is the proper ratio is. I mean, a teaspoon, sorta sounds right, looking at a tablet, but the same wording is on Old Laundry Boxes, and I KNOW, there was more than a teaspoon of phosphates in those formulas. I'd just love any sort of calculator, or any information any of you guys have. 

 

Thanks, 

 

Mich

 

[sudsmaster]

Some years ago I calculated the weight by percent of Phosphorus in STPP. I used the atomic weights of the various elements (H, O, P, Na) and the molecular weight and formula for STPP. I don't know where those calcs are now, but I do recall posting them here. I didn't do any calcs for TSP because it's basically inappropriate for laundry use.

I recall that what I found was that basically 8% by weight P works out to about 30% STPP by weight in the powdered detergent. And that is generally considered to be the optimum average dosing for STPP in a powdered laundry detergent.

What I do is to premix an off-the-shelf phosphate free powder with STPP to a weight ratio of 2 parts detergent and 1 part STPP. So if I have 20 lbs of detergent, I'll add 10 lbs STPP and then mix well. Then use whatever amounts of the mix in the washer give the best results.

 

[kenmoreguy89]

Michael, how did you determine the amount of stpp in each dose by knowing the phosphorus content?
Most dishwashing products over here do state 15% to 30%.Phosphates...not for long though as we know
Taking in exam finish:
Measure for heavy soil is 45 ml, package state 40 ml is 40 grams..
So 15x40/100=6 grams phosphates per 40 grams...which makes sense, and keep in mind that percentages goes from 15% to 30% ! And for this calculation I took in consideration the lowest (15%) So content per measure may be even higher and probably nearer 30% than 15%......
Not sure about tablets or pacs anyways......

However, regarding phosporus content...

I assume, that there are different types of phosphates much or less rich of phosphorus...
Finish dishwasher powder includes 15 to 30% of phosphates, and a maximum level of 6% of phosphorus...
Others dishwashing product I know do state 6.5%...usually..
I recall in sone older formular you could read even 7% or 8% phosphorus...
But, again, I assume that there are different types of stpp...and now they use types leaving less dispersible phosphorus.

[this post was last edited: 5/2/2014-18:25]

 

[mich]

The reason I asked..

Is I'm planning on doing writeups, on proper mixing ratios of STPP to Dishwasher Detergent. 

 

I've been finding ingredient disclosure & MSDS sheets, and comparing new formulas, from old, to see what's best to mix up. Only bad thing so far, is at $5-7 a pound for STPP, a $4 box of Cascade rings up to close to $15-20, after Phosphates are properly mixed. 

 

I'm still doing a lot of research, but, it's helpful to know that. Thank You