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1 Determining dwell volume of gradient HPLC systems

With some instruments the gradient dwell volume can be quite significant, even a few milliliters. At the start of the gradient, the volume in the instrument is filled with the mobile phase corresponding…

2 How can I purge metals from my HPLC system using EDTA?

In LC-MS, metal ions can be responsible for distorted analyte peak shapes via chelating. If you determine that this is the cause of a peak issue, here is what you can do to eliminate metals from the system…

3 How can I separate phenylephrine HCl, acetaminophen, and dextromethorphan?

The Cogent Phenyl Hydride™ would be recommended for these compounds because of the dextromethorphan. It has a strong tendency to tail on most columns but the Phenyl Hydride™ column and can produce…

4 How do I calculate assay of lisinopril dihydrate based on the anhydrous form?

When you weigh your reference standard and use the mass in the assay calculations of your formulation, you must correct for the water since the reference standard is the dihydrate form. You know the molecular…

5 How do I choose a suitable mobile phase additive for Negative Ionization mode when using LC-MS?

For negative ionization we usually use: · Solvent A: 10 mM ammonium formate or acetate in DI water · Solvent B: 90% acetonitrile/10% DI water (v/v) /10 mM ammonium formate or acetate Solvent B has to…

6 How do I choose an appropriate guard column for my method using Cogent TYPE-C HPLC columns?

Two sizes of guard columns are available: 2.0 and 4.0 mm internal diameter (ID). Both sizes are 20mm in length and are used with a guard column holder. The 2.0mm ID guard columns are for use with the…

7 How do I choose an appropriate re-equilibration time in gradient methods?

When using gradient methods in HPLC or LCMS, the mobile phase and column must be allowed to equilibrate back to its inital conditions before starting the next run in order to ensure consistent chromatography.…

8 How do I condition Diamond Hydride columns when I use them for serum samples?

For serum (and other biological samples) we recommend using: Solvent A: 50% DI water/50% methanol (or 2-propanol) + 0.1% formic acid (for positive mode) or +10 mM ammonium acetate or formate (for negative…

9 How do I know if a crimped vial has a good seal?

The best way to know if you have a good seal is to take the vial and tightly hold it in your left hand. With your right hand, try to spin the crimped cap on the vial. If it moves, you should remove the…

10 How to Calibrate UV-vis and HPLC Detectors with NIST Traceable Solutions Below 230nm

Holmium Oxide is an internationally recognized wavelength calibration primary standard, supported by NIST and other standards organizations. It provides 14 official absorbance bands ranging from 241 nm…

11 How to change columns from reversed phase to normal phase mode and vice versa

Just as a reminder, all Cogent TYPE-C™ columns are filled with water containing solvents during shipping. To start work in normal phase mode, a simple switching procedure is recommended. A simple 30…

12 How to change ferrules on HPLC column connectors

HPLC Column Connectors So Easy... Anyone Can Use It! Ferrule Replacement Instructions for the HPLC Column Connectors Change ferrule after approximately every 50 insertions or when excessive ferrule wear…

13 How to clean sparging stones and inline SS filters.

Inlet stainless steel filters or sparging stones can be cleaned by ultra-sonication in 30% phosphoric acid, clean afterwards with DI water (ultra-sonication) and Methanol (ultra-sonication). Same would…

14 How To Condition 47mm Nylon Membranes for Use with the Mobile Phase Filter Degasser...

Filter membranes with smaller pores sizes such as 0.45µm have higher bubble points (the differential pressure required to draw air through a wet membrane). The bubble point is a function of the pore…

15 How to Condition a CEC Column

It is very important that you condition the capillary properly before using it. DO NOT CONDITION YOUR COLUMN LIKE A CE COLUMN: IT WILL BE DESTROYED. Instructions for Conditioning and Installation of Milli-phase…

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