Archive for the ‘Tips & Tricks’ Category

Can I use a 100% aqueous mobile phase with my LC column?

You might be asking this because you have read that not all columns are OK to use with highly aqueous content (>95%) in the mobile phase.  Or maybe the caption caught your eye because you have recently encountered some difficulty with using highly aqueous mobile phase. There is a phenomenon called “phase dewetting” that can […]

General (very general) guidelines to help meet GC detection limits.

Sometimes we (tech service) receive requests from customers who cannot meet detection limits when developing a new method or when trying to follow a current method. They ask for advice on how to meet these limits.  As a result, I decided to provide some (very) general guidelines that I would follow back-in-the-day when I would […]

How (Not) To Cut Your Capillary Column

There are numerous ways to cut a capillary column. Restek has several tools to accomplish this job. There are sapphire scribes, ceramic scoring wafers, wafers with a handle, and diamond blade column cutters. There are also some tools manufactured by other companies that will cut a capillary column. The choice is typically personal preference. No […]

Should I use LC or GC for my analysis?

Although most analysts already know which approach they need to use for analysis, this is occasionally a topic of discussion.  While this blog post is not meant to give an absolute answer for each specific application, I hope to provide some tips to steer you in the general direction towards a solution, if this is […]

Is the column shown on the COA for a chemical reference standard the best column for these compounds?

  In some cases the answer is “yes”. In most cases the answer is “no”.   So why would we choose a column that is not the optimal for a specific standard? It’s because of the large number of reference standards we sell. Each mix needs to have its own validated method. If we were […]

A little extra information for installing/conditioning a new packed/micropacked column

Even though we include instruction sheets with most of our packed/micropacked columns which contain enough information for most customers, some customers (many who are new to using packed columns) contact us routinely asking for some additional assistance. As a result, I decided to add some additional information to our current instruction sheets hoping it helps those […]

Troubleshooting Injection Volume Variation in the Concurrent Solvent Recondensation – Large Volume Sample Injection Technique

I’ve started receiving a number of questions about the large volume injection technique called Concurrent Solvent Recondensation – Large Volume Sample Injection. Most recently, a question came through the Tech Service group about injection volume variation. I had encountered a similar problem when working on the 50 µL injection for the combined 1,4-Dioxane and Nitrosamines (EPA […]

How can I use Raptor columns and the EXP Direct connect holder with stainless steel fittings?

Some customers may find themselves with this scenario. You have an HPLC instrument with existing stainless steel tubing and fittings and you are getting ready to install a Raptor column. The end of your tubing may very well look like the one shown above. Here are some questions you might have.   Can I attach […]

Utilizing Restek Reference Standards for Residual Solvent Testing

Restek manufactures several different residual solvent standards.  These can be used for testing according to USP <467>, the EP monograph, or other residual solvent assays, such as medical cannabis testing.   The calculations involved for the use of these standards has led to questions for our technical team.  This post should help provide guidance for their […]

Fluorophenyl LC Phases- what you should know

They may be called PFP, PFPP, pentafluorophenyl, fluorophenyl or F5 phases. What they all have in common is the structure shown above (the pentafluorophenyl  group) attached to the silica particles. Most modern phases contain a propyl spacer between the above group and the silica, so that the phase looks something like this:     A […]