Hexadecane, first analysis

The first practical example of an on-line SFC-1 NMR separation was recorded by Dorn and co-workers [16] (Figure 7.2.14). Since up to 90% of a fuel is aliphatic, SFC-NMR on-line analysis is the matter of choice for separation and identification. Figure 7.2.14 shows a fuel mixture of isooctane, n-hexane, -nonane, dodecane, and n-hexadecane, separated by SFC and detected by on-line NMR spectroscopy. The SFC separation was accomplished with a flow rate of 2.0ml/min, a C18 250 x 4.6 mm column, operated at an isobaric pressure of 100 bar and a temperature of 323 K, using CO2 with 1% (w/w) CD3CN as solvent. Each NMR spectrum consists of 20 co-added transients at an acquisition time of 1 s per transient. The total separation occurred within 5 min. The first eluting isooctane can be easily identified by the methylene-to-... 

The stressed samples were analyzed by two techniques, both based on gas chromatography. In the first, the solution with internal standard was injected into a 10 ft, 1/8 inch o.d., 5% OV-101 column which was programmed to 260°C at 12°/min after a 5.0 min initial hold at 60°C. The JP-5 cut was integrated as a single sum and compared to the internal standard to determine the yield of JP-5 from the pyrolysis experiment. The initial gc cut point for the JP-5 was set midway between n-octane and n-nonane and the final point midway between n-hexadecane and n-heptadecane. The gc baseline did not rise during this portion of the analysis, hence reliable integration was obtained. 

In a first step the VOC analysis are determined with a thermal desorption at 90 °C for 30 min. The emitted compounds are analyzed and calibrated using a toluene standard. The VOC concentration is expressed as toluene equivalent. The SVOC analysis (FOG) is run from the same sample in a second desorption at 120 °C for 60 min. The emitted substances are calibrated using a C16 alkane standard. The FOG result is expressed as hexadecane equivalent (VDA 278, 2011 ... 

Assign the area corresponding to the first peak (terminating at the bottom of the lowest valley between the retention times of hexadecane and toluene from the analysis of the performance mix) to the nonaromatics. 

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