Detection problm in Ibandronate while preparing with placebo

[dhru]

Hi every one

i am facing one problem in ibandronate sodium injection
while i am preparing phosphate(0.5%) phosphite(0.5%) and ibandronate(0.4%) in water i am getting all peaks.
but while i am preparing the same solution with the same limit in placebo i am unable to get any peaks. no response at all in RI detector.
my mobile phase is 1 ml Formic acid in 1 Lit water pH 3.0 with NaOH
Placebo is mixture of Acetic Acid, Sodium Acetate and sodium chlroide
Thanks in advanced

[Uwe Neue]

1. Have you injected phosphate/ibandronate solution again?
2. What is the column that you are using? Please be specific!

[dhru]

yes i am injected it so many times
i am using IC pak anion HC column
4.6*150