Chromatography Forum

Hello everyone! I turn to you again waiting your kind HELP!!!
This is my situation:
I have to analyze PO4, NO3, NO2, and NH3 in sea water, around 30 sample per day, I know I could do it by spectrophotometry, but i am thinkin that on my location is very very hard to get reagents, so I was thinking that I have a HPLC, so I could do my analysis ussing ion exchance, but I never has used this technic before, so I have a Doubt becuase also I have to do Total Nitrogen, and Total Phosphorous, so my question is:
There is any problem if I digest my samples and after I analyze the total nitrogen converted to NO3?, even though I have a HIGH hydroxi ions content, and the other ions used for digest? I think to use an ion conductivity detector.
I suppose this only depends of what column or method I would choose.

Other question is: There are a method to clean a sea water sample digested using potassium persulfate, and sodium hydroxide?

If could do this my life would be easy and could dedicate the time to improve my english.

Thank a lot.

Not the response you were expecting, but - there are numerous test kits that will tell you nitrite, nitrate, ammonia, phosphate etc. made by Hach and other vendors. They are generally designed for aquarium owners and work pretty well for seawater. I do not know how precise they are, but i think that they are pretty sensitive and reproducible within the ranges typically seen in seawater.

As for total nitrogen, this is more typically done with a LECO type N analyzer, but in your case, you may well be able to report total N as a sum of the ammonia, nitrite & nitrate contributions...

For 30/day, I would suggest 2 complete test kits and 1/2L bottles of reagents.

If this approach won't serve you well, I'd talk to someone (Dionex 1st) about buying an IC.

Thanks DR for you reply, but my problem is that I am in a place where to get anything is very dificult and expencive, I know this sound weird.
Hach is very practical but is expencive for us a long term, and we could think to extend our sample number in a mid term.

I have a HPLC pump that I am not using with autosapler. so I would like to know if there are a lab that work like that or similar?

Dear Oscar:

You can use your HPLC to analyze the NOx either with Conductivity or UV detection. I suggest starting with what you have - HPLC/UV I assume? I would start with the use of an anion column such as the Metrosep A Supp 8 with 1.7M NaCl eluent. This will allow you to 'see' the NO2 and NO3 without the chloride interference from the sea water. The application is available on the internet from the www.metrohm.com website or contact a local Metrohm distributor. Other anion columns may work but you would need to optimize the eluent. I know this column is created specifically for this application.

You can also use your HPLC with UV detection in a vacancy mode for anions although the sea water matrice may be a problem and require substantial dilution. A column specific for non-suppressed anion applications would be a good starting place. Transgenomic makes an excellent column for this type work.

You can add a conductivity detector capable of non-suppressed applications such as the Metrohm 732 or 819 Conductivity Detector but other manufacturers such as Alltech also offer a conductivity detector. This can be used in a non-suppressed mode using a Metrohm, Transgenomic or Alltech column for non-suppressed anions. The phosphate is a bit tricky by non-suppressed but I know Metrohm also has an application for phosphate by non-suppressed conductivity. If you have the money you can also add a suppressor to your system such as the Metrohm 753 MSM or the Alltech.

For ammonium, a conductivity in non-suppressed mode with a cation column such as a Metrohm, Alltech or Transgenomic cation column will work for you. I suggest visiting the Metrohm website for the application notes. Alltech and Transgenomic also have info available via their website. Hope this info helps you.

Jeff Brewer

Dear Jeff,
Thank you very much for your repley, I know it would be very usefull to me, just a last question, If I digest my sample with Sodium Hydroxide and Potassium Persulfate, finally I would have a high concentration of Hidroxide and Sulfate; Could be this a big problem than just look for the adecuate column and mobile phase?

Thanks Again.

Its me again I saw the information already, Now I dont have any doubt, Thank.