5 replies to this topic

[ERICinWV]

Hello,

 

  I am wanting to determine if a dry PCR PET material mix is within spec.

 

For example:  I take and weigh 500 gram sample from a bag of PCR mix. 

 

I then separate out contaminants such as colored PET and weigh the sorted color and record that it weighs .0405 grams.

 

I have a spec showing the limit for colored PET in PCR is 20 PPM.

 

I found one formula showing to use percentage and multiply by 10000.

So I used (.0405/500)*10000 = 0.81ppm

 

Then I find another reference saying to convert values and divide milligrams by kilograms.

So .0405 grams is 40.5 mg and 500 grams is .5kg (40.5/.5) = 81ppm

 

Can someone please explain which is right and hopefully why the other is wrong?

 

In advance, thank you for your time and help.

[Belmont2201]

What is your definition of distinguishing between the two?

[ERICinWV]

I am seeing the difference as two places with the decimal. 

If anyone is familiar with determining PPM in a similar loose product, I would appreciate your experience and method.

[redfox]

I found one formula showing to use percentage and multiply by 10000.

So I used (.0405/500)*10000 = 0.81ppm

 

Then I find another reference saying to convert values and divide milligrams by kilograms.

So .0405 grams is 40.5 mg and 500 grams is .5kg (40.5/.5) = 81ppm

 

Hello Eric,

 

It is true that 1 percent (part per hundred) is equal to 10,000 ppm (parts per million) or 1mg/1kg.

 

Some equations:

 

1 percent = 10⁴ ppm

ppm =(g solute/gsolvent)x10⁶

ppm=mg solute/kg solvent

ppm=ml solute/liter solvent

 

In your first computation you miss to multiply first the (0.0405g/500g) by 100 to get the percent value of 0.0081%. Then you have to multiply it by 10,000 to get 81ppm. Your second computation is right.

 

regards,

redfox

[usrreva]

If your sample size is always 500g, you will reject if contaminants are greater than 0.01g (that is 20ppm).

(500) * (0.00002) = 0.01

 

 

[Charles.C]

Hello,

 

  I am wanting to determine if a dry PCR PET material mix is within spec.

 

For example:  I take and weigh 500 gram sample from a bag of PCR mix. 

 

I then separate out contaminants such as colored PET and weigh the sorted color and record that it weighs .0405 grams.

 

I have a spec showing the limit for colored PET in PCR is 20 PPM.

 

I found one formula showing to use percentage and multiply by 10000.

So I used (.0405/500)*10000 = 0.81ppm

 

Then I find another reference saying to convert values and divide milligrams by kilograms.

So .0405 grams is 40.5 mg and 500 grams is .5kg (40.5/.5) = 81ppm

 

Can someone please explain which is right and hopefully why the other is wrong?

 

In advance, thank you for your time and help.

 

Hi Eric,

 

IMHO both methods are right and should give the same answer.  But only assuming you make no numerical errors.

(As proven in Post 4)

(IIRC there is often a hidden density assumption in some ppm figures but not in yr specific example).