"Antiphase" peak at beginning of chromatogram

[timamos10]

Hello,

I am having the following issue: https://imgur.com/a/Z1yrV3m . I am currently trying to analyze the solvent NMP using an RI detector and C18 column. My mobile phase is acetonitrile/water/phos acid - 10/90/0.1. Samples were diluted to 300 ppm and 3000 ppm using 40:60 MeOH to Water.

I have noticed that I am getting a negative-positive peak in multiple chromatograms. I am trying to diagnose this problem and unsure where this could be coming from. Is it the RI detector, column issue, or a sample preparation issue?

Any help would be great! Thanks!

[Multidimensional]

Based on the minimal information and chromatograms provided, you have no retention, no chromatography at all. What you are observing is the injection pulse (normal) created when you inject your sample. This is not an instrument issue, it is an operator training issue. If you calculate (better yet, measure it) the Tzero for your proposed 'method' you will see that is where your peak elutes. As of now, you have no HPLC method and no data to review. For a method to be reviewed, you must first demonstrate selectivity for the sample (proper K prime), then show that good chromatography fundamentals have been followed. * Please, to move forward, contact someone LOCAL with many years of practical experience to assist you in using HPLC for your project. It takes the average scientist about five years of full-time, professional training to acheive a "basic" level of training in using this technique. This is not something that can be learned in a class, web forum or watching a video. Use without formal training will lead to irrational troubleshooting and invalid methods/data.