Metrohm Calibration Curve

[eja85]

Hello,

I am trying to build a calibration curve to run EPA 300.0. My analytes will be bromate, bromide, chlorate, chloride, chlorite, nitrate, nitrite, fluoride, phosphate, and sulfate. I am using a Metrohm 930 Compact IC Flex with sequential suppression, a Metrosep A Supp 7 250/4.0 column, Metrosep A Supp 16 Guard/4.0, and A Supp 7 eluent.

We analyze surface, ground, and drinking water. Our samples can sometimes range into the high 200s mg/L for chloride and sulfate. On our existing column (A Supp 5 150/4.0), the calibration ranges for chloride and sulfate max out at 100 mg/L, which seemed kind of low from what they can handle, but I have noticed matrix interference on nitrite when chloride gets above 200.

I'd appreciate any examples of curves others are running for EPA 300.0/300.1 that they've found success with using.

Thanks in advance for any guidance!

[dblux_]

Have you considered chloride anions removal with Ag cartridges ?

[eja85]

Have you considered chloride anions removal with Ag cartridges ?

We would still need to be able to analyze chloride for a chloride-sulfate mass ratio (CSMR) calculation we run quite often, is this something that could be easily bypassed when needed?

Edit: I'm not sure this would be permissible by EPA 300.x. Chloride is an analyte that needs to be quantified so we cannot remove it. I was looking for guidance on calibration points for analytes to preserve accuracy, if possible.

[dblux_]

...
We would still need to be able to analyze chloride for a chloride-sulfate mass ratio (CSMR) calculation we run quite often, is this something that could be easily bypassed when needed?

Edit: I'm not sure this would be permissible by EPA 300.x. Chloride is an analyte that needs to be quantified so we cannot remove it. I was looking for guidance on calibration points for analytes to preserve accuracy, if possible.

The solution is to execute two runs, one with chlorides removed and one with chlorides intact. The last is for chlorides determination. These cartridges are quite expensive.

[anionman]

We analyze surface, ground, and drinking water. Our samples can sometimes range into the high 200s mg/L for chloride and sulfate. On our existing column (A Supp 5 150/4.0), the calibration ranges for chloride and sulfate max out at 100 mg/L, which seemed kind of low from what they can handle, but I have noticed matrix interference on nitrite when chloride gets above 200.

I'd appreciate any examples of curves others are running for EPA 300.0/300.1 that they've found success with using.

Thanks in advance for any guidance!

I lobbied to keep the lab's old flow injection analyzer so I can run nitrites on that when the chloride is > 250 mg/L. I've never had to use Ag cartridges to remove Cl.

The other thing you could try is calibrating nitrite to a very low level far below the reporting limit so you can make dilutions of the high Cl water. How low do you want to go in reporting nitrite? How high does your Cl get? I've seen it as high as 5000 mg/L, and my lab only analyzes drinking water. But usually it's not > 1000 mg/L.

On the old FIA the lab reported nitrite down to 0.05 mg/L, but when we started running IC we raised it to 0.1 mg/L for that method because of interference problems. We rarely see nitrite > 0.1 mg/L.

[John Guajardo]

Hi eja85,

Are you open to trying a different column? The Dionex IonPac AS29-Fast-4µm column was designed to handle high ionic strength samples and may work better for your application. It operates with carb/bicarb eluent albeit at a higher pressure than your existing Metrosep A Supp 5 due to the smaller particle size. You can find out more using the links below (note especially the calibration curves on page 8 of application note AN73607).

• Thermo Scientific AN73607 - Determination of inorganic anions in drinking water, wastewater, and high ionic strength water
• Dionex IonPac AS29-Fast-4µm product page
• Dionex IonPac AS29-Fast-4µm specification sheet

I would be glad to send you a column to try if you'd like.

[dblux_]

Definitely none of above answears fullfiled her/his expectations.

[eja85]

We analyze surface, ground, and drinking water. Our samples can sometimes range into the high 200s mg/L for chloride and sulfate. On our existing column (A Supp 5 150/4.0), the calibration ranges for chloride and sulfate max out at 100 mg/L, which seemed kind of low from what they can handle, but I have noticed matrix interference on nitrite when chloride gets above 200.

I'd appreciate any examples of curves others are running for EPA 300.0/300.1 that they've found success with using.

Thanks in advance for any guidance!

I lobbied to keep the lab's old flow injection analyzer so I can run nitrites on that when the chloride is > 250 mg/L. I've never had to use Ag cartridges to remove Cl.

The other thing you could try is calibrating nitrite to a very low level far below the reporting limit so you can make dilutions of the high Cl water. How low do you want to go in reporting nitrite? How high does your Cl get? I've seen it as high as 5000 mg/L, and my lab only analyzes drinking water. But usually it's not > 1000 mg/L.

On the old FIA the lab reported nitrite down to 0.05 mg/L, but when we started running IC we raised it to 0.1 mg/L for that method because of interference problems. We rarely see nitrite > 0.1 mg/L.

We're in the southwest, so high sulfate and chloride are very common out here. Both reach ~250 mg/L in our drinking water samples, depending on the water source. I have yet to see it go over 300, even on our groundwater samples.

I took your suggestion and had success calibrating down to 0.05 mg/L on nitrite! I'm trying to avoid the use of cartridges, as those are quite costly, and we analyze both chloride and sulfate for chloride/sulfate mass ratio calculations.

The goal is to find a calibration range to reduce batch run times, most samples are having to be run twice, usually undiluted and 5x. With each determination taking upwards of 40 minutes on this column, it can push quite close to hold time limits for some analytes.

[eja85]

Hi eja85,

Are you open to trying a different column? The Dionex IonPac AS29-Fast-4µm column was designed to handle high ionic strength samples and may work better for your application. It operates with carb/bicarb eluent albeit at a higher pressure than your existing Metrosep A Supp 5 due to the smaller particle size. You can find out more using the links below (note especially the calibration curves on page 8 of application note AN73607).

• Thermo Scientific AN73607 - Determination of inorganic anions in drinking water, wastewater, and high ionic strength water
• Dionex IonPac AS29-Fast-4µm product page
• Dionex IonPac AS29-Fast-4µm specification sheet

I would be glad to send you a column to try if you'd like.

Hi John,

Thanks for the info! I'd be open to trying a new column.

[John Guajardo]

Hi eja85, please contact me at john.guajardo@thermofisher.com with your shipping details and I'll have one sent.