negative peak near the propionic acid

[marx]

the shimadzu scl-10A system
KC-811 column
column and cell temperature are 40
0.1% phosphoric acid as mobile phase
injectant is 0.5чl
RID as detector

Using this system detect actic acid, acetic acid, propionic acid, and butyric acid at same time. Before and near the propionic acid peak, appear the negative peak, the mobile phase and solition without sample appear too.
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[Chris Pohl]

marx,

This looks like an eluent purity problem. Buy a higher purity phosphoric acid (e.g. HPLC grade from Fluka)

[marx]

The phosphoric acid is purity, and same problem with Perchloric acid.

[unmgvar]

Maybe you should check the purity of your water, glass bottles or vials.

with all of them we encounterd that type of problem. with the MiliQ equipment we had to change the filters (it was almost needed anyway).
with the vials the company that sold them to us check it for impurities and saw that the specific batch we used was not washed properly.
with the glass bottles we repaired the dishwasher machine changed filters and changed the reagents used for cleaning.

anyway i agree with Chris Pohl that it looks like an eluent purity problem first.

[marx]

By the message of engineer for Shimadzo, the negative peak is CO3. He or She suggested that using 3mM HClO4 mobile phase and 50 Deg. I'll try on and send the result quickly.
Thank you for your reply!