Naphthenic Acids: Formation, Role in Emulsion Stability, and Recent Advances in Mass Spectrometry-Based Analytical Methods

Figure 4

NAs chromatograms in simulated produced water sample obtained by GC-MS (a) and GC×GC-MS (b). GC analyses were performed on a TRACE1310 gas chromatograph coupled to a fast-scanning ISQ single transmission quadrupole mass spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). For GC-MS, a 30 m × 0.25 mm-di (film thickness of 0.25 μm) Equity1701 capillary column was used. The carrier gas was helium at a constant flow of 1.0 mL·min⁻¹; 2.0 μl of the sample was injected into a 250°C spitless injector. The oven temperature was set from 50°C to 260°C at 2 min⁻¹. The ion source and transfer line were kept at 275°C and 260°C, respectively. Electron ionization (EI) was performed at 70 eV. Mass range was set from 35 to 350 Da at 6 scans s⁻¹. For GC × GC-MS, the first-dimension column was a 20 m × 0.18 mm-di (0.18 µm film thickness) SLB-1MS capillary column and the second-dimension column was a 5 m × 0.25 mm-di (0.25 μm film thickness) OV 1701 capillary column. The injector was operated in split mode with a 1 : 10 split ratio, at 250°C. Helium was used as carrier and auxiliary gas at constant flow rate of 0.5 and 20.0 mL·min⁻¹. Modulation period was set to 6 s with a 400 ms reinjection (flush) pulse. The oven temperature was set from 50°C to 265°C at 5°C·min⁻¹. Ion source and transfer line were kept at 275°C and 260°C, respectively. Mass range was set from 40 to 350 Da at 15 scans s⁻¹.

(a)

(b)