converting ppm to psu

[Eyore]

From an icp test. Ppm to ppt is obvious

Here is what I hope is correct, but would like confirmation or correction.

So I need to convert the cations and anions to sodium and chloride?

No need to bother with the minor stuff, but ca, k, mg, so4 are a big factor

So converting the following according to molar mass means I reduce the following accordingly (to sodium)
Calcium by 42.64% leaving 57.36% (or divide result by 1.7433)
Potassium by 41.2% leaving 58.8% (or divide result by 1.7007)
Magnesium by 5.41% leaving 94.59% (or divide result by 1.0572)
Sulphur by 23.53% leaving 76.47 % (or divide result by 1.3077)

While sulphur has a number finding value for sulphate has me a bit perplexed tbh. Sulphate is 33.38% sulphur, 66.62 oxygen, so sulphur to sulphate is pretty much multiply by 3.
The problem I have is how to factor the 4 oxygen into salinity or psu.
(A) do I calculate it's value before converting sulphur to sulphate and add this on to the converted sulphur?
(B) convert it as well to chlorine? In which case the conversation factor increases salinity (divide result by 0.4513)
(C) covert the 4 oxygen that are with 1 sulphur, which then gives a molar mass of nearly 64 for the oxygen to convert to 35.453 cl
Giving
Oxygen by 44.6% leaving 55.4% (or divide by 1.8052)

Or am I completely wrong??

 

[Galvanized]

Following with interest.

 

[disc1]

I have absolutely no clue what exactly you are trying to do. You want to figure the PSU of a seawater sample by knowing the amounts of its constituents? Can you link a brother to the math you're trying to do? I thought PSU was based on conductivity.

 

[bertoni]

PSU is defined in terms of conductivity. I'm confused as to what you're trying to do, too. For our purposes, 35 psu is close enough to 35 ppt at reef conditions, if my memory is correct.

 

[Eyore]

Trying to state salinity from the sum if it's parts shown in an icp test by converting the numbers to salinity as nacl

I think maybe my terminology is wrong then? Determining true salinity from a sum of the parts is the aim, i was unsure how to express this in a title, I think I realise my error, perhaps "determining salinity as nacl from icp" ?

 

[Eyore]

Could the title be changed bertoni? Might help people see what I am looking for?

 

[dkeller_nc]

Perhaps I'm not understanding what you're trying to do, but if I'm interpreting correctly and the output of your ICP analysis is in mass concentration units (such as ppm), then all you have to do to convert to a common salinity measurement unit (specific gravity) is add up the mass of all of the elements.

And in theory, you could get an estimate of the conductivity of a simple ion solution by converting the constituents to milliequivalents and reading from a chart or table.

But that would going around the world to take one step - why wouldn't you just measure the specific gravity or conductivity of your sample?

 

[Eyore]

Ie from ppm to ppt? (35000 ppm being 35ppt)
Or are we talking adding up all molar mass?

The tester says this is not acceptable, he would measure salinity via conductivity, and I need to convert (possibly why the title is what it is, and shouldn't be)

Inessense I am trying to gauge the accuracy of the test by comparing the sum of it's parts against what I know to be true (salinity)

Now true my salinity readings won't be 100% accurate, however I know how much salt is in there etc, so in reality I know it's close enough for my purpose

 

[disc1]

Ie from ppm to ppt? (35000 ppm being 35ppt)
Or are we talking adding up all molar mass?

The tester says this is not acceptable, he would measure salinity via conductivity, and I need to convert (possibly why the title is what it is, and shouldn't be)

Inessense I am trying to gauge the accuracy of the test by comparing the sum of it's parts against what I know to be true (salinity)

Now true my salinity readings won't be 100% accurate, however I know how much salt is in there etc, so in reality I know it's close enough for my purpose

That's not how you gauge the accuracy of an ICP. You should be checking against a standard or doing standard additions if you want to tell how accurate the reading is.

For example you measure sulfate at 10mM so you add an additional 5mM and remeasure. From there it's just math with the 2 measurements.

There is likely a lot more error in what you are trying to do with salinity than there is with the ICP.

 

[Eyore]

Not my results, but a fairly typical result

1 9.88 0.543 90.80 22823.641 Cl
2 13.48 0.482 0.03 0.000 system
3 14.63 0.236 0.14 66.335 Br
4 16.84 0.332 0.01 3.915 No3
5 19.81 0.000 0.00 0.000 system
6 25.72 0.394 9.05 3703.551 So4
_____________________________________________
6 45.01 0.331 100.02 26597.441
14.33 132.958 12236 426.820 K
27.50 281.543 4306 526.005 Ca
33.35 1464.906 1104 1360.597 Mg
__________________________________________
80.01 9342.089 4574 14395.294

Not actually in icp test (hplc) but I only seen cations on icp
However you see why I doubt the accuracy from the sum of the parts

 

[disc1]

I know those numbers make sense to you because you're looking at the test data. They're just numbers to me right now. Label them and put on some units.

How are you detecting ions by HPLC? What type of detector are we talking about? What was the column?

 

[Eyore]

I know those numbers make sense to you because you're looking at the test data. They're just numbers to me right now. Label them and put on some units.

How are you detecting ions by HPLC? What type of detector are we talking about? What was the column?

Lol, errr, hmmm tbh no idea. The end column is ppm of the various cation and anion tested. Total ppm of the sample is up near to 42000 ppm plus whatever is not tested.
Now nobody has pointed this out (bar me) and I have ended up in a view arguments on the forums in normally frequent (to understate possibly), so you understand I don't really want to name any names), but these tests are used in conjuction with a Classic balling method as a means of tighter control of the chemistry as water changes are not used, and it's fair to say I have doubts.
It was pointed out that I cannot just total the bits to conclude salinity (which given that nobody can or does run at 42ppt, and the majourity of reefers show comparable "sum totals" is not what I am getting at (accuracy is))...
So apparently I need to convert the anions and cations back to nacl (I believe) by doing so I can conclude salinity as it should be, and Therfore test inaccuracy to a point. (this is what I am trying to do in the opening post)
Though looking at rhf table of seawater, where he states done if the values in ppm, actually these do add up to about 35ppt, once you add on a few bits

Bit more background than I wanted to divulge tbh

 

[disc1]

So apparently I need to convert the anions and cations back to nacl (I believe) by doing so I can conclude salinity as it should be,

Here is the confusion. First of all, I know how to get accuracy from an instrument like that and this isn't how. You either need to run a standard or do standard additions. When the error margin on your check is larger than the error margin on the measurement then the check is meaningless.

Second, please explain what you mean by converting them to NaCl. I assume you don't mean that you will physically change calcium into sodium, so this must be math. Are you saying you want to know the molarity of calcium that would have the same mass? Or the mass of sodium that would be the same number of ions? Or what? What do you mean by convert to NaCl? I mean what exactly do you mean.

 

[Eyore]

Ok

What I am trying to do is take the ppm of the all the parts, add them up and conclude salinity
I believe I cannot add ( in the example above) 526 ppm calcium and conclude 0.526 ppt, likewise magnesium is not 1.36 ppt in terms of salinity.
So in these elements I need to convert them to the weight of the correct anion or cation, which would be sodium. This gives .301 calcium, 1.286 magnesium in respect of ppt to 've added to come to over all salinity
However these calculations are based on 2 conversations with chemists (one of whom is the man who does this testing ) whereby they do not actually tell me what to do, so I have made the rest up myself based on this and logic (the calculations in the first post)
I realise what you say regarding how to test accuracy, however I am not the person testing, I am basically trying to work out if it's even remotely accurate

 

[dkeller_nc]

Eyore - Whomever told you that you couldn't "add up the bits" to arrive at the total wasn't right, at least from the standpoint of salinity expressed as parts per million or parts per thousand.

By definition, parts per million is milligrams per liter. In other words, mass per volume. Any analytical instrument will be measuring the ion of specific interest in terms of concentration. Assuming that the calibration curve that is required for each ion of interest is prepared and entered into the instrument's software as ppm (that's typical for water chemistry analytical instruments), then what you get back is the analyte (ion) of interest in parts per million.

Because mass is conserved, then yes, in theory if you add all of the ions in solution in terms of parts per million, you will get the total in terms of parts per million.

Note that this is not the same as adding x grams of an soluble material to y grams of pure water and interpreting that the total density is therefore (x+y)/(y/density of water). It doesn't work that way because of something called the partial molar volume, which means that if you take 10 mL of sodium chloride and add it to 90 mL of pure water, you will get something less than 100 mL.

 

[Eyore]

So my initial understanding is correct?

(not the opening post btw)

Eyore - Whomever told you that you couldn't "add up the bits" to arrive at the total wasn't right, at least from the standpoint of salinity expressed as parts per million or parts per thousand.

By definition, parts per million is milligrams per liter. In other words, mass per volume. Any analytical instrument will be measuring the ion of specific interest in terms of concentration. Assuming that the calibration curve that is required for each ion of interest is prepared and entered into the instrument's software as ppm (that's typical for water chemistry analytical instruments), then what you get back is the analyte (ion) of interest in parts per million.

Because mass is conserved, then yes, in theory if you add all of the ions in solution in terms of parts per million, you will get the total in terms of parts per million.

Note that this is not the same as adding x grams of an soluble material to y grams of pure water and interpreting that the total density is therefore (x+y)/(y/density of water). It doesn't work that way because of something called the partial molar volume, which means that if you take 10 mL of sodium chloride and add it to 90 mL of pure water, you will get something less than 100 mL.

 

[disc1]

Ok


So in these elements I need to convert them to the weight of the correct anion or cation, which would be sodium.

So you want to find out the equivalent mass of sodium for the same number of moles? That's not going to get you to salinity.

Please do be specific. Convert them to the weight doesn't make any sense chemically. 1g of calcium is 1g. The equivalent weight of sodium would be 1g. No conversion needed. So I'm surely not understanding what type of conversion you want to do and since I don't know of any conversion that will get you to salinity this way, you're really going to need to be specific.

 

[Eyore]

So you want to find out the equivalent mass of sodium for the same number of moles? That's not going to get you to salinity.

Please do be specific. Convert them to the weight doesn't make any sense chemically. 1g of calcium is 1g. The equivalent weight of sodium would be 1g. No conversion needed. So I'm surely not understanding what type of conversion you want to do and since I don't know of any conversion that will get you to salinity this way, you're really going to need to be specific.

It's ok
Seems like I am on a bit of a wild goose chase tbh

It's hard for me to state exactly what I mean, as tbh I don't know

The guy who did the test was not too happy I added up all the bits to conclude salinity or accuracy was out by 20%, and told me I could do not do this, I had to "convert", another chemist told me I must convert the relevant numbers to nacl to conclude this

Seems I am misinformed, and invented nonsense then! Lol

 

[E Rosewater]

I suppose my question is why? There are many easy ways to determine major and trace components, HPLC seems like a very convoluted method.

 

[dkeller_nc]

Well, here is what one of the folks might have been telling you. Concentration can be expressed in a number of ways, two of which are ppm and mmol/liter. One is a mass per volume unit (ppm) one is a molar volume unit (technically, a "number of molecules per volume" unit).

If, for example, your results were expressed as "30 mmol of X", then you would have to convert using the molecular weight of compound X to get ppm and therefore density.

There are a number of reasons why adding up all of the concentrations of the ions may not give you an accurate representation of the total density given your chosen method (ion chromatography). Most of these are inaccuracies in quantitation because of non-linear response factors, baseline determination, standard errors, etc...

But HPLC ion chromatography is a very good way to quantitate minor and trace elements so that you can "correct" the concentration in tank water. Not quite as good or as sensitive as ICAP, but a whole lot better than wet chemistry tests.