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Are you struggling to separate synthetic cathinone isomers? Click here!

3 Oct 2023

Synthetic cathinones have been a popular recreational drug for a number of years. These compounds, commonly known as “bath salts”, are known to produce stimulant-like effects when abused. While there have been many synthetic cathinones detected, new compounds frequently emerge on the illicit drug market.

α-Pyrrolidinohexiophenone (α-PHP) and α-Pyrrolidinoisohexanophenone (α-PiHP) are two synthetic cathinones that have increased in popularity in the last few years. α-PiHP is a positional isomer of α-PHP, meaning they share a nearly identical structure, differing only in the position of a methyl group. Despite their similar structures, the toxicological and pharmacological properties can differ greatly between isomers. It is important that analytical techniques are able to distinguish α-PHP from α-PiHP to prevent false identifications in casework.

Chemical Structure of α-PHP Chemical Structure of α-PiHP
Figure 1. Chemical Structure of α-PHP Figure 2. Chemical Structure of α-PiHP

When it comes to LC-MS/MS analysis, isomers like α-PHP and α-PiHP can be a pain. Because they have the same molecular weight and almost identical chemical structures, these analytes will ionize similarly and cannot be differentiated by traditional mass spectrometry. However, under the correct chromatographic conditions, these isomers can be resolved and easily distinguished from each other. The following LC-MS/MS method was developed to separate α-PHP and α-PiHP.

Table 1. Method Parameters

Column: Raptor Biphenyl 50 x 2.1, 2.7 µm
Mobile Phase A: 0.1% formic acid in H2O
Mobile Phase B: 0.1% formic acid in MeOH
Flow: 1.0 mL/min
Time (min) %B
0.0 26
4.0  26
Column Temp: 30°C
Injection Volume: 3 µL
Sample Concentration: 100 ng/mL
Diluent: 0.1% formic acid in H2O (MPA)


α-PHP and α-PiHP chromatogram

Figure 3. α-PHP and α-PiHP chromatogram

Table 2. Analyte transitions

Peak TR (min) Ion Mode Precursor Product Ion Product Ion
α-PiHP 2.75 + 246.00 91.20 140.15
α-PHP 3.07 + 246.00 91.20 140.15


This 4-minute isocratic method separates α-PHP and α-PiHP for quick and straightforward isomer confirmation. While a traditional C18 phase column might be the first choice for many method developers, the use of the biphenyl phase is the key to this separation. The biphenyl stationary phase offers superior selectivity due to its enhanced pi-pi interactions, which are further intensified when used in conjunction with a methanolic mobile phase. If separating α-PHP/PiHP or other structurally similar synthetic cathinones is giving your lab a headache, give the Raptor Biphenyl column a try!