Calibration check issues

[senecabot]

Hi,

I am a new user to IC and I'm currently trying to commission a metrohm 930 IC compact. Using a Metrosep A Supp 5 - 150/4.0 with guard & suppression & ultrafiltration.

I have had a bespoke mix made by two different manufacturers which contain 1000ppm of F, Cl, NO2, Br, NO3, PO3 & SO4.
I have created a Hi-lo cal the lo range comprises 0.1, 0.25, 0.5, 0.75 & 1pmm stds.
The hi range comprises 1, 5, 15, 30 & 50 ppm stds.
All are made up to 100ml in grade a volumetrics.
For the 50ppm std l take 5ml of the 1000ppm mix upto 100ml for my 50ppm using a calibrated 5ml rainin electronic pipette, the 3ml for the 30ppm std, 1.5ml for the 15ppm std etc.
For my lo range I take appropriate dilutions upto 100ml in grade A volumetrics using my 50ppm std prepared earlier.

I repeat this for my std checks.

I can get what I have been told are good calibration slope. RSD 0.5-2% with an r value of 0.9999

The issue is the accuracy I see on the std checks is poor 80-120%. PO3 NO2 & NO3 being the worst.

Can anyone advise if this is normal. Am I expecting too much. Is my cal range to wide, too many points, too many analytes?

I use fresh demin water each preparation and I'm following metrohms mainatenance schedule closely.

Any help gratefully received.

[Markus Laeubli, Metrohm]

Dear senecabot

First of all I do not see a problem in your calibration range. This is as we do it quite often.

The problem with recovery values is more difficult.
Do I understand correctly, you are using one standard set (from one manufacturer) for calibration and the other for recovery tests?
If this is the case: did you try to re-inject calibration standards for recovery? Rre these recoveries in the same range (80...120%)?
What are the results when switching calibration and recovery standard solutions?

Could you export your determinations to *.idet and send them to me by e-mail (lae@metrohm.com). I then could have a look to them.