Decreased response when mixed solution injected

[DrBeefloof]

Residual solvent method calls for mixed standard. Response is poor when even high concentration mixed solution is injected.
However when individual solutions of each solvent are injected, response is good, even at low concentration.
What is happening?!

[James_Ball]

Residual solvent method calls for mixed standard. Response is poor when even high concentration mixed solution is injected.
However when individual solutions of each solvent are injected, response is good, even at low concentration.
What is happening?!

What solvent is used for each individual analyte when injecting them separately? Are they being injected neat or as a dilution separately and in mixture?

[DrBeefloof]

Residual solvent method calls for mixed standard. Response is poor when even high concentration mixed solution is injected.
However when individual solutions of each solvent are injected, response is good, even at low concentration.
What is happening?!

What solvent is used for each individual analyte when injecting them separately? Are they being injected neat or as a dilution separately and in mixture?

The diluent for all injections is 90:10 1,3-Dimethyl-2-imidazolidinone:water.
I've injected all as a mixture as per the method,and each separately in diluent at LOQ concentration.
LOQ injections have higher responses than the highest concentration mixed solution .

[James_Ball]

Residual solvent method calls for mixed standard. Response is poor when even high concentration mixed solution is injected.
However when individual solutions of each solvent are injected, response is good, even at low concentration.
What is happening?!

What solvent is used for each individual analyte when injecting them separately? Are they being injected neat or as a dilution separately and in mixture?

The diluent for all injections is 90:10 1,3-Dimethyl-2-imidazolidinone:water.
I've injected all as a mixture as per the method,and each separately in diluent at LOQ concentration.
LOQ injections have higher responses than the highest concentration mixed solution .

What are the stock concentration of each before mixing and how are they mixed? What should the final concentration of the mixed solution be?