Ok so my final year project is on validating the Dionex DX-500 Ion Chromatography instrument and its analytical method. I’m doing this with the environmental lab in Roche, and I have to repeat the validation for nitrate, phosphate and sulphate anions.
The first step in the validation is to determine the LOQ (limit of quantitation) of the anion. Now the LOQ must be below the RL (reporting limit) which is set by the EPA (environmental protection agency).
Initially, I had a huge problem, the LOQ for all three anions was above the RL. I then increased the injection loop of the instrument from 25 microlitres to 100 microlitres. This was successful in the case of nitrate and sulphate i.e. i managed to get the LOQ below the RL for these two anions.
Phosphate however is still failing 
Its LOQ still comes out as above the RL.
What more can I do??? Can I change any other parameters to imrpove the LOQ?? Or do I have to buy a new column thats more efficient??? Mind you, this particular column that im currently using is also very very sensitive, it can detect anions down to 0.01 ppm.
I’m so tired of this, I just wanna get started on the validation, but I must sort out the LOQ first.
Plzzzz help!!!