19
Figure 2: Selectivivity Comparison of Watercol Phases using Water as an Analyte Conditions
column: WatercolTM column: WatercolTM column: WatercolTM
1460, 30 m x 0.25 mm I.D., 0.20 µm (29695-U) 1900, 30 m x 0.25 mm I.D., 0.20 µm (29761-U) 1910, 30 m x 0.25 mm I.D., 0.20 µm (29711-U)
oven temp: 96°C inj. temp.: 250°C detector: TCD, 200°C carrier gas: helium, 26 cm/sec injection: 1 µL, 100:1 split
liner: 4 mm I.D., split type, cup design sample: 6 analytes in acetone
selectivity difference. All three phases contain trifluoromethanesulfonate as the anion. The descriptive numbers for each phase (1460, 1900, and 1910) indicates the Kovats Retention Index (KRI) value of water determined on each at 100°C isothermal oven temperature.
Selectivity Comparison
To show the sharp peak shape obtained for water, and also highlight selectivity differences, a QC test mix containing water was analysed on each column under identical run conditions. The resulting chromatograms are presented in Figure 2. As shown, each column is capable of producing a water peak that is sharp enough to be properly integrated. The retention of water (peak 2) is lowest on Watercol 1460 and greatest on Watercol 1910. Conversely, retention of the tridecane, an n-alkane (peak
Figure 3: Water as the Injection Solvent Conditions
column: WatercolTM column: WatercolTM column: WatercolTM
1460, 30 m x 0.25 mm I.D., 0.20 µm (29695-U) 1900, 30 m x 0.25 mm I.D., 0.20 µm (29761-U) 1910, 30 m x 0.25 mm I.D., 0.20 µm (29711-U)
oven temp: 35°C, 4 °C/min to 125°C (2 min) inj. temp.: 250°C detector: TCD, 300°C carrier gas: helium, 25 cm/sec injection: 1 µL, 100:1 split
liner: 4 mm I.D., split type, cup design sample: 8-component solvent mix in water
1), and naphthalene, an aromatic (peak 6) is greatest on Watercol 1460 and lowest on Watercol 1910.
Selectivity Comparison 2
Differences in selectivity are also revealed when water is the injection solvent. To demonstrate this, an 8-component solvent mix in water was analysed on each column under identical run conditions. Figure 3 shows the resulting chromatograms. A low initial oven temperature of 35°C allowed the small polar analytes to partition into the stationary phase. A final oven temperature of 125°C ensured that the water was completely eluted from the column.
Calibration for Water
A 5-point calibration curve for water using standards prepared in absolute ethanol
was generated on Watercol 1460. Both FID and TCD were used, which allowed the calibration curve to be subsequently used to quantify water in gasoline. The concentration range covered 0.05% to 1% (v/v). Concentration was plotted against TCD response of the water peak (as area counts). A blank ethanol sample was also analysed, which was used to blank correct each calibration point. The resulting chart is displayed in Figure 4. The r2
value of 0.9961 indicates good linearity across this range. Water in Gasoline
Residual moisture in fuel is very undesirable because it reduces the heat of combustion which increases engine stress. It can also corrode fuel system components, permit gelling of fuel in cold temperatures through ice crystal formation/nucleation, and accelerate the growth of microbial colonies
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