How Acetone Can Save Your Lab Time & Money

In most reversed phase HPLC separations today, acetonitrile is the organic solvent of choice. However, I found that use of acetone instead can have many advantages. In preparative chromatography, acetone is more volatile and therefore it is easier to obtain product from a collected fraction. In addition, its lower cost compared to acetonitrile translates to significant savings at the preparative scale. In analytical applications, it can be used as a means to change elution order in the case of some analytes. Sometimes the peak shape or efficiency may even be superior.

               I investigated the separation of a variety of test solutes using either acetonitrile or acetone. Due to the high UV cutoff of acetone, I selected analytes with strong absorption in the high UV/visible range. These analytes typically have a high degree of conjugation, such as dyes. If you’re not using a UV-based detection method though, acetone won’t be a problem for analysis of an analyte with little or no UV absorption. An example of this is our study of amino acids using acetone with LC-MS.

               In 2008–2009, there was a worldwide shortage of acetonitrile that prompted studies of alternative solvents. Often, methanol was found to be the next best choice, but it has its own drawbacks as well. In terms of safety, its toxicity is higher than acetone. Chemically, acetone is more similar to acetonitrile than methanol since both are polar aprotic solvents. For this reason, you could predict that in general retention using acetone would be comparable to acetonitrile in many instances. I found this to be the case for four of the five test solutes I tested, which showed very similar retention (Fig. 1).

               You can read about the full investigation here.

Fig. 1

 

Ferrule Removal Tool really works!

Every once in a while, a ferrule can become stuck inside a fitting in your HPLC system or your column. If this happens, don’t worry! Your HPLC system can be up and running again in no time. The ferrule can be easily removed with a special tool designed for this purpose. Called the Ferrule Removal Tool, it consists of a threaded portion like you would find in a drill bit. However, the threading goes the opposite way to allow for the stuck component to be extracted. Simply push against the ferrule with the tool while turning counter-clockwise. In some cases, you may need to give it a light tap with a hammer to get it to bore into the ferrule. As you turn, the ferrule will screw out from inside the fitting. That was easy!

Ferrule Removal Tool Product Page

Advantages of Mixed Mode HPLC for Polar Compounds

It was a relief when I used the brand new Cogent UDA™ columns for analysis of closely related polar compounds. I used them in the Aqueous Normal Phase (ANP) retention mode with additional selectivity of the Ion exchange chromatography capacity.
                With the Cogent UDA 2.o™ column, you can have the best of both worlds by using each retention mode together to obtain excellent separations. In the latest study from our laboratories, we demonstrated the ion exchange characteristics of the Cogent UDA 2.o™ column by separations of three test solutes. With a carboxylic acid group at one of the bonded ligand, ion exchange propertied can be either activated or inactivated by selection of the mobile phase pH.  Under acidic conditions, the carboxylic acid is protonated and neutral and no ion exchange occurs. At mild pH, the group becomes de-protonated and anionic. When the group was ionized, increased retention and separation of the three basic test analytes were observed.

                You can read about the full investigation here.

Separation of the three analytes under ion exchange conditions

An Interesting Compound found in Green Tea

Green tea is more than just a tasty beverage. It also has a number of compounds with potential health benefits. For example, catechins found in tea are known antioxidants. Another such interesting compound is L-theanine. It is a psychoactive compound and is believed to exhibit various beneficial effects on the brain. These may include increased alertness, decreased anxiety, and general sense of well-being.

                It is a polar compound though and may be difficult to analyze by reversed phase chromatography. With the Cogent Diamond Hydride 2.o™ column, it can be well-retained using an Aqueous Normal Phase approach. There are not many other polar compounds in green tea (catechins are fairly hydrophobic), so you can obtain a nice L-theanine peak which is well-separated from the others.

                We estimated L-theanine content in a typical home-brewed green tea sample using this column and found concentrations consistent with those reported in the literature (around 10 mg/L). See the full study for more information!

 

How much caffeine is in your coffee?

The amount of caffeine in various beverages can vary widely. Drip-brewed regular coffee has about 555–845 mg/L caffeine content but a shot of espresso can have about 1,691–2,254 mg/L. What some people may not know is that decaffeinated coffee has caffeine as well. The caffeine is chemically removed by a series of extraction procedures (solvents used can include benzene, supercritical CO₂, or others). However, even after 8–12 extractions there is still some caffeine remaining. Therefore, decaffeinated coffee has about 24–72 mg/L caffeine.
                This can be studied with HPLC methodology. Here a Cogent Bidentate C18 2.o™ column is used to separate caffeine from other matrix components in three types of common coffee products. The caffeine peak is the most prominent of all the peaks in the espresso sample but is only a minor peak with the decaf sample. Using a caffeine reference standard, a calibration curve could be made which allows for an estimation of the caffeine content in the samples. The calculated values were: espresso: 964 mg/L, regular: 539 mg/L, and decaf: 85 mg/L. These values were mostly close to the literature ranges for each coffee beverage, although the espresso sample had somewhat lower caffeine content than expected.
                Click the link for more info!