ASTM D5006 Test Method for Measurement of Fuel System Icing Inhibitors (Ether Type) in Aviation Fuels
8. Refractometer Calibration
8.1 All refractometers should be zero-set to water before use. The exact procedure for zero-setting a refractometer varies based on the type and make of instrument. Consult the user manual for specific instructions on zero-setting each make of refractometer.

8.2 The calibration step is incorporated into the procedure to minimize the effect of temperature changes between the time of calibration and measurement. (Warning - The extraction, calibration, and measurement steps should be done at ambient conditions. Avoid placing the refractometer on hot or cold surfaces, in pockets on your person, or other locations that would change the temperature of the instrument from ambient. When zero-setting or making a measurement, take care not to heat or cool the refractometer from ambient.)

8.3 For the most accurate possible readings, the refractometer, the calibration fluid, and the ambient temperature should all be in equilibrium within the temperature compensation range, or the operational temperature range, of the refractometer. If there is a temperature disparity, allow some time for the temperatures to equalize before taking a reading.

9. Sample Preparation and Extraction
9.1 Extraction Ratios for Both Analog and Digital Refractometers with Direct Reading DiEGME Scales:
9.1.1 Measure 160 mL of fuel to be tested into the extraction vessel.

9.1.2 Measure 2.0 mL of water into the extraction vessel.

9.2 Extraction Ratios for Analog Brix Refractometers With or Without Automatic Temperature Compensation :
9.2.1 Measure 80 mL of the fuel to be tested into the extraction vessel.

9.2.2 Measure 1.0 mL of water into the extraction vessel.

10. Sample Extraction
10.1 Shake the extraction vessel vigorously for a minimum of 5 min for all fuels, preferably with the cap facing down.

10.2 Mechanical shakers may be used, provided that thorough intermixing of the aqueous and fuel phases occurs, similar to that obtained by hand shaking. (Warning - Following the extraction procedures is most critical. Failure to extract for the specified time or failure to provide vigorous agitation can result in false readings. If lower than expected readings are obtained, a second test should be done with a longer extraction time.)

10.3 Allow the extraction vessel to sit undisturbed at ambient temperature for a period of at least 2 min to allow the water to settle to the bottom.

11. Sample Testing
11.1 Measurement ofSamples Using Digital Refractometers with DiEGME Scales:
11.1.1 Locate the thermometer and refractometer where they will remain at ambient temperature during the test.

11.1.2 Isolate several drops of the water extract from the extraction vessel, and transfer to the sample well of the digital refractometer.

11.1.3 If a separatory funnel is used, it may be necessary to collect some extract into a smaller container, and then transfer several drops to the prism face with a clean eyedropper, syringe or pipette.

11.1.4 If a dropping bottle is used as an extraction vessel, place it right side up, remove the cap, squeeze slightly, and replace the cap with the bottle under a slight vacuum. Invert the bottle and allow the water extract to settle to the bottom. Uncap the bottle and squeeze it gently until several drops of extract are collected on a tissue held in the same hand as the refractometer, and then allow several drops of the water extract to fall into the refractometer well.

11.1.5 If using the MISCO Jet Fuel Refractometer, close the evaporation cover to help prevent evaporation of the sample during testing.

11.1.6 Allow some time for the temperature of the refractometer, fluid, and ambient environment to equalize.

11.1.7 Initiate the reading by pressing the "GO" Button on the MISCO Jet Fuel Refractometer or the "READ" Button on the Gammon HB2D Refractometer.

11.1.8 Record the ambient temperature reading displayed on the thermometer to the nearest degree Celsius.

11.1.9 Make certain that the temperature displayed on the thermometer is within the temperature compensation range of the refractometer.

11.1.10 Record the reading on the refractometer digital display to two significant figures in volume percent DiEGME.

11.1.11 Take four more readings of the same sample, and average the results.

11.1.12 Properly dispose of test fluids, wash apparatus with soap and water, and dry all items. (Warning - Treat the refractometer as an optical instrument and avoid damage to the lens and window elements. Store the refractometer in a protective cover or case.)

11.2 Measurement ofSamples Using Analog HB or Analog Brix Refractometers:
11.2.1 Locate the thermometer and refractometer where they will remain at ambient temperature during the test.

11.2.2 Isolate several drops of the water extract from the extraction vessel, and place on the prism face.

11.2.3 If a separatory funnel is used, it may be necessary to collect some extract into a smaller container, and then transfer several drops to the prism face with a clean eyedropper, syringe, or pipette.

11.2.4 If a dropping bottle is used as an extraction vessel, place it right side up, remove the cap, squeeze slightly, and replace the cap with the bottle under a slight vacuum. Invert the bottle and allow the water extract to settle to the bottom. Uncap the bottle and squeeze it gently until several drops of extract are collected on a tissue held in the same hand as the refractometer, and then allow several drops of the water extract to fall onto the prism face.

11.2.5 Slowly lower the prism cover into place, point the refractometer at a light source, and look into the eyepiece. (Warning - Fuel entrained in the water may cause an indistinct refractometer reading. In most cases fuel residue on an analog refractometer can be eliminated by slowly lowering the refractometer cover. The surface tension of water should sweep fuel off the prism surface.)

11.2.6 Take the reading at the point the shadowline intersects the scale.

11.2.7 If using a HB refractometer, record the reading to two significant figures in volume percent DiEGME.

11.2.8 If using a Brix refractometer, record the Brix value and perform the conversion calculation in 12.2.

11.2.9 Record the ambient temperature to the nearest degree Centigrade using a thermometer.

11.2.10 Make certain that the temperature displayed on the thermometer is within the operational range, or the temperature compensation range, of the refractometer.

11.2.11 Properly dispose of test fluids, wash apparatus with soap and water, and dry all items. (Warning - Treat the refractometer as an optical instrument and avoid damage to the lens and window elements. Store the refractometer in a protective cover or case.)

12. Calculation
12.1 For both analog and digital refractometers with direct reading DiEGME scales, report the reading obtained to two significant figures as the final result in volume percent DiEGME. If multiple determinations are made, average the results that fall within the specified repeatability and reproducibility tolerances. For rounding off of significant figures, Practice E29 shall apply.

NOTE 2 - For analog HB refractometers produced prior to July 2003 that have both an EGME and DiEGME scale on the reticle, report the reading in volume percent from the left hand scale marked DiEGME or M. The scale is printed on the reticule in the eyepiece of the refractometer.

12.2 For a non-temperature compensated analog refractometer with a Brix scale, first apply the temperature correction factor from Table 1. No temperature correction is necessary for Brix refractometers with automatic temperature compensation, as long as the measurements are taken within the temperature compensation range of the refractometer.
12.2.1 Calculate the volume percent DiEGME as follows:
Vol % FSII = 2 x Temperature Corrected Scale Reading/100