Experimental Considerations in Headspace Gas Chromatography - Pharmaceutical Technology

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Experimental Considerations in Headspace Gas Chromatography
In this case study of amines, the authors discuss several parameters to be considered in developing a headspace GC method.


Pharmaceutical Technology
Volume 34, Issue 5, pp. 76-79

Methods and materials

Instrumentation and sample materials. A gas chromatograph (Agilent 6890, Santa Clara, CA) with a G1888 (Agilent) headspace autosampler and 20-mL sample vials were used for the experiments. The column used for these amine analyses was a Restek RTX-5 AMINE (Bellefonte, PA), 30 m x 530 m x 5 m film thickness. Triethylamine (TEA) was purchased from FisherScientific (Division of Thermo Fisher Scientific, Waltham, MA); DMSO, n-butylamine, and allylamine were purchased from Sigma-Aldrich (St. Louis, MO); Water (high-performance liquid chromatography grade) was purchased from J.T. Baker (Phillipsburg, NJ); and dimethylformamide (DMF) was purchased from EMD Science (Darmstadt, Germany).


Table I: Headspace parameters
Stock TEA samples were prepared by diluting 138 L into 100 mL of diluent, where the diluent was different ratios of either DMSO:water or DMSO:0.01M sodium hydroxide (NaOH). Analysis samples were further diluted 1 mL into 100 mL with the appropriate diluent for the experiment. This dilution resulted in a final TEA concentration of 0.0100 mg/mL. Stock n-butylamine samples were prepared by diluting 213 L into 250 mL of diluent, where the diluent was either water, 0.1M NaOH, or DMSO. Analysis samples were further diluted 1 mL into 25 mL with the appropriate diluent for the experiment (different ratios of DMSO:0.1M NaOH or water). This dilution resulted in a final n-butylamine concentration of 0.0252 mg/mL. Stock allylamine samples were prepared by diluting 300 L into 100 mL of diluent, where the diluent was either 0.001M NaOH, 0.01M NaOH, DMF (or DMSO), or ratios of DMF (or DMSO):base. Analysis samples were further diluted 1 mL into 100 mL with the appropriate diluent for the experiment. This dilution resulted in a final allylamine concentration of 0.0228 mg/mL.


Figure 2
GC method for TEA and n-butylamine: Three minutes isothermal at 50 C, followed by a programmed temperature ramp at 20 C/min to 130 C, a hold period for 2 min, followed by a programmed ramp at 20 C/m into 170 C, a hold period for 3 min, followed by a ramp at 30 C/min to 240 C, with a four-minute hold period at the end of the temperature ramp. The injector temperature was 200 C, and the detector (i.e., FID) temperature was 300 C with a constant column flow of 3.8 mL/min of helium.


Figure 3
GC method for allylamine: Eight minutes isothermal at 45C, followed by a programmed temperature ramp at 40 C/min to 240 C, with a four-minute hold period at the end of the temperature ramp. The injector temperature was 180 C, and the detector (i.e., FID) temperature was 300 C with a constant column flow of 3.8 mL/min of helium. Headspace parameters are shown in Table I.


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