Reduce Acetonitrile use by Analysing PAHs with Methanol-Based Mobile Phase

By Michelle Misselwitz, Innovations Chemist

• Save £30 per litre using methanol instead of acetonitrile.
• Resolve PAHs to baseline using a Pinnacle® II PAH column.

The recent acetonitrile shortage has resulted in limited availability and significantly increased solvent costs. In response, many labs are interested in alternate mobile phases for HPLC methods. Here we present an effective method for analyzing polycyclic aromatic hydrocarbons (PAHs) using methanol, instead of acetonitrile, resulting in a significant cost savings while maintaining baseline resolution of all target compounds.

Strategies to Reduce Acetonitrile Dependency

Save money by switching to a methanolic mobile phase.

Acetonitrile use can be reduced several ways, including decreasing column inner diameter, scaling down methods to ultra-high pressure liquid chromatography (UHPLC), or using an alternate mobile phase. While analysis times can be cut in half by using UHPLC, this technique creates significant backpressure and high pressure capacity pumps are required. For labs that do not have UHPLC equipment, using alternative solvents can be an effective way to reduce acetonitrile use without having to purchase new equipment.

Methanol-Based PAH Method Saves Labs Money

Analysis of PAHs often is done by HPLC, because it provides greater selectivity between structural isomers than GC. Chromatographic separation of these isomers is critical, because they cannot be distinguished by a mass spectrometer. Acetonitrile is commonly used in the mobile phase when analyzing PAHs, but excellent results can be obtained using methanol.

Here we switched the mobile phase solvent to methanol, instead of acetonitrile, and analyzed 16 target polycyclic aromatic hydrocarbons. All PAHs were baseline resolved on the Pinnacle® II PAH column using a methanolic mobile phase (Figure 1). One elution order change was noted: when using acetonitrile, dibenzo(ah)anthracene elutes before benzo(ghi)perylene, however the opposite elution order is observed when using methanol. Total analysis time was approximately 23 minutes, which is slightly longer, but comparable, to common acetonitrile-based methods.

Since acetonitrile is currently much more expensive than methanol (up to US$40 more per liter), this methanol-based procedure offers labs an opportunity to considerably reduce solvent costs, while maintaining complete resolution of all target compounds.

Figure 1: Reduce acetonitrile costs by analyzing PAHs on Pinnacle® II PAH columns with a methanolic mobile phase.

naphthalene acenaphthylene acenaphthene fluorene phenanthrene anthracene fluoranthene pyrene benzo(a)anthracene chrysene benzo(b)fluoranthene benzo(k)fluoranthene benzo(a)pyrene benzo(ghi)perylene dibenzo(a,h)anthracene indeno(1,2,3-cd)pyrene *contaminant Column: Pinnacle® II PAH Cat. #: 9219463 Dimensions: 150mm x 3.2mm Particle size: 4µm Pore size: 110Å Sample: Inj.: 10µL Conc.: 10µg/mL each component Sample diluent: methanol Conditions: Instrument: Shimadzu Prominence® Mobile phase: A: water B: methanol Time (min.) %B 0.0 75 10.0 90 22.0 100 Flow: 1.0mL/min. Temp.: 30ºC Det.: UV @ 254nm