Chromatography Forum

Hi!,

I have posted again about this topic. I am having lots of trouble with method, since ballast waters are seawaters and method EPA 300.1 is about drinking waters mostly.

Anyway, first off, I would like to know what is the best way to spike. Let me explain: so my two analytes are chlorite anion and chlorate anion. My lowest standard is 4ppb and I am trying to spike my lowest sample at my ballast waters samples. (I am doing this in order to prove that I can indeed determine at such levels my analytes in a sample such as seawater). So what I do is I have a High Concentration Standard at 10ppm. I take 40uL of this and add it to a 100mL volumetric flask. I add 1mL of my sample and dilute to volume with HPLC grade water. When I do this I see no peaks. Is it something wrong with the way I spike or are there any interferences I need to evaluate?

Second of all the chromatogram in this analysis is not a perfect one. It has lots of broads peaks and my analytes are always next and almost on top of other nearby peaks. I do not use the column that is suggested (i use a metrosepp A supp 5 instead of a metrosepp A supp 7), because in drinking waters and in my standards the column I use seems to do fine, with great linearity and sharp peaks. It's on the samples of seawaters that I have the problem. Do you think that changing the column would help?

Thanks in advance!!

I would definitely use the recommended column. By no peaks you mean chlorate and chlorite? Or no peaks at all? What happens when you spike pure water? Have you tried changing the flow rate to see if helps narrow peaks?

I would definitely use the recommended column. By no peaks you mean chlorate and chlorite? Or no peaks at all? What happens when you spike pure water? Have you tried changing the flow rate to see if helps narrow peaks?

The thing is I don't know what difference could it make (since i detect my standards in the column I use). By no peaks I mean the peaks of my analytes which are chlorate and chlorite. I have spiked pure water, tap water and drinking water as well as deionized water and the results are great!. I have not tried changing the flow rate since the manual says that I should use the column at 0.7mL/min.

Thanks for your reply! Do you think that changing the column might make a difference? Do you have any relevant experience?

I don't know how a different column could help, but I have been doing IC long enough to know that sometimes things happen that you can't figure out. I've been running IC for drinking water for a decade. I ran ocean water once out of interest and chloride was so high that anything near it like nitrite was not visible. I actually saw drinking water with 5000 mg/L chloride once. I had to reject the nitrite and tell the customer to resample if he wanted a result. I would have to run it by method 353.2. The ocean also had 2400 mg/L sulfate which would probably be hard on a column. I see you are per-treating to remove the chloride.

Maybe you could try spiking some pure water with chloride and sulfate to simulate ballast water and see if you get peaks with that.

I don't know how a different column could help, but I have been doing IC long enough to know that sometimes things happen that you can't figure out. I've been running IC for drinking water for a decade. I ran ocean water once out of interest and chloride was so high that anything near it like nitrite was not visible. I actually saw drinking water with 5000 mg/L chloride once. I had to reject the nitrite and tell the customer to resample if he wanted a result. I would have to run it by method 353.2. The ocean also had 2400 mg/L sulfate which would probably be hard on a column. I see you are per-treating to remove the chloride.

Maybe you could try spiking some pure water with chloride and sulfate to simulate ballast water and see if you get peaks with that.

Thanks a lot!!

I will actually try to do that! You know there are cartridges for removing sulfates also. Do you think that high content of sulfates damages my column?

(We are talking about 35000 ppm and i usually dilute 100fold or 50fold)

Metrosep A Supp 7 has the better separation of oxyhalides then the Metrosep A Supp 5. This might be important in high chloride waters.
High chloride or sulfate concentratons will not damage the column directly. But they may act as internal eluent ions which can change the retention of other ions.
Therefore, checking artifitial samples, as anionman recommends, is definitely the experiment to start with.
Run several samples with increasing chloride concentration to see influence of it.