Gc ms

Volatile compounds in the concentrated extract were separated and detected by using a gas chromatography-mass spectrophotometer (GC-MS) (Perkin Elmer, Waltham, USA). The separation of volatiles was carried out in an ELITE 1 non-polar capillary column (30 m X 0.25 mm (ID); 0.25 μm film thickness). One microliter of extract was injected (split ratio 1:10) into the injection port and carried along the capillary column by helium gas (99.9%) at a flow rate of 1 mL min⁻¹. The oven temperature was held at 100 °C for 6 min, heated at 4 °C min⁻¹ to 150 °C, then at 8 °C min⁻¹ to 220 °C and held at 220 °C until an approximate run time of 40 min.
The mass spectrophotometer was operated in the electron impact mode and mass spectra were taken using an ionization voltage of 70 eV. The mass scan range was 40–400 AMU, with a scanning speed of 0.2 s. Data acquisition and generation of chromatograms and mass spectra were done with the TurboMass software [29 (link)].
The identification of volatile compounds was performed by comparing the mass spectra with the standard spectra database from the NIST Ver. 2.1 2009 Mass Spectra Library. The proportion of each compound was calculated by comparing the peak area with the total area.

A 100 mL rainwater or other aqueous sample was poured into a glass bottle (200 mL size) and 1 mL PFBHA solution (1 mg/mL) was added simultaneously. The aqueous solution in the bottle was adjusted to pH 6.0 by 3 mL NaH₂PO₄‐HCl buffer solution and left overnight (14 h) for the completeness of derivatization reaction between carbonyls and PFBHA 21. The stir bar was put into the glass bottle containing 105 mL sample solution after the addition of 1 mL NaCl solution, which was located on a magnetic stirring plate. The stir bar was employed to extract carbonyl derivatives at speed of 500 rpm for 1 h. After extraction the stir bar was removed from the sample solution and dried by a tissue paper to clean the solution adhering to its surface. The stir bar was transferred into 2.0 mL acetonitrile as desorption solvent a 10 mL vial and desorbed by ultrasonic bath for 30 min. One microliter of the remaining acetonitrile solution was directly injected into a Perkin Elmer GC–MS (Waltham, USA) for analysis. The stir bar was cleaned as described above and stored in acetonitrile for future use. During the optimization process, several important SBSE parameters such as extraction time (30 min to 16 h), ultrasonic desorption time (10 min to 3 h), desorption solvents (acetonitrile, ethanol, methanol) and the temperatures of extraction solution were optimized.

Compound 3 (4 mg) was dissolved in five mL of 3% KOH/MeOH solution and kept undisturbed for 15 min at ambient temperature. After 15 min, 1 N HCl/MeOH was added to the solution for the neutralization. The solution was then partitioned with CHCl3, CHCl3 layer was separated, evaporated and the obtained residue was taken up for column chromatography on SiO2 (mesh 60–120) using as eluent hexane: EtOAc gradient to provide methyl ester of dotriacontanoic acid, which was verified by GC/MS (Ibrahim, Mohamed & Ross, 2016 (link); El-Shanawany et al., 2015 (link); Al-Musayeib et al., 2013 (link)). A 500-Clarus Perkin-Elmer GC/MS (Waltham, MA, USA) was applied for GC/MS analysis. The integrator combined with software (4.5.0.007 version) controller was turbo mass. A 5 MS/GC elite capillary (30 × 0.25 mm × 0.5 µm) column and helium (He) a carrier gas at 2 ml/min flow rate (55.8 cm/s flow initial with 32 p.s.i., split; 1:40) were applied. Temperature conditions including; source temperature, inlet line temperature, emission trap and electron energy were adjusted at 150 °C, 200 °C, 100 °C and 70 eV, respectively. The injector temperature at 220 °C was maintained. Whereas, the temperature of the column was set at 50 °C for 5 min, raised to 220 °C at the 20 C/min rate. MS was scanned from 50 to 650 m/z.

Separation and detection of the carbonyl‐PFBHA derivatives were performed on a Perkin Elmer GC–MS incorporating an Auto system XLGC and a quardrupole MS equipped with a DB5 column (30 m × 0.25 mm × 1.0 μm) (Agilent Technologies, Santa Clara, USA). GC conditions were as follows: the GC oven temperature was initially set at 80°C for 1 min, programmatically increased to 260°C with a ramp of 30°C min⁻¹. The solvent delay was set at 2 min. Helium (CP Grade (N5.0) 99.999%, BOC, Guildford, UK) was chosen as the carrier gas at a flow rate of 1 mL/min. The GC injection mode was set as splitless. The temperatures of GC inlet and GC–MS transfer line were kept at 250°C. The mass spectrometer was operated in scan mode with a mass range of 100–500 Da to identify the most abundant ions of carbonyl derivatives. The chromatograms at the most abundant ion were used to quantify the concentration of derivatives in solution. In this study the most abundant ions of all carbonyl‐PFBHA derivatives are the same as ([C₆F₅CH₂•]⁺) with m/z = 181 Da.