Refractometric Determination of Nonvolatile Matter in Floor Polishes

Relevant for: Industries dealing with floor polishes, resin solutions and wax emulsions

1. Total solids in floor polishes, resin solutions and wax emulsions

Scope

Refractometric method to determine the nonvolatile matter (total solids) in floor polishes, resin solutions and wax emulsions.

Analyte

Floor polishes (components and end products)

Standard

ASTM D 4095 - 97 (reapproved 2008)

Terminology of Refractive Index

The ratio of the velocity of light in air, to its velocity in the substance.

Application

This method is useful for quality control and in process control for the production of polishes and their components.

2. Procedure

2.1 Safety precautions

It is the responsibility of the user of this method to establish appropriate health and safety practices and determine the applicability of regulatory limitations prior to its use.

2.2 Apparatus

Abbemat refractometer from Anton Paar.

The measuring prism of Abbemat must be kept clean. The instrument should be calibrated against a refractive index standard provided by Anton Paar.

The temperature control of the liquid being examined and the cleanliness of the prism should be checked frequently by determining the refractive index of distilled water, which is 1.332986±, the accuracy of the used Abbemat at 20 °C and 589 nm wavelength.

All the data which are required by the ASTM standard can be recorded. This includes the type of floor polish, resin solution or wax emulsion (needs to be manually input), refractive index, wavelength and temperature of analysis.

The required resolution of four decimals is fulfilled by all Abbemat refractometers. Moreover, They all have internal Peltier elements, cooling the sample to the measurement temperature with high accuracy. Therefore, no water bath is needed.

2.3 Sample volume

A sample of approximately 0.5 mL is required.

2.4 Procedure

• Determine the nonvolatile matter of the sample according to ASTM method D 2834. Alternatively, the customer’s reference method can be used.
• Select the refractive index scale.
• Set the measuring temperature to 20.00 °C, or alternatively to 25.00 °C.
• Determine the refractive index of the process water used for preparation of the sample.
• Determine the refractive index of the sample(s). Wait until temperature has stabilized before taking the reading. Take multiple readings and record the arithmetic average.
• Plot a curve of refractive index (RI) versus total solids (%TS) with e.g. MS Excel:

• Use zero (0 %) solids and refractive index and the RI value of the process water as the origin.

• Plot the solid from ASTM D 2834 / reference method and the RI of the sample as the second point.

• Calculate the linear equation giving %TS as a function of the RI, %TS = f(RI)

• Verify the curve by careful dilution of the sample with the process water.

• If the curve is verified, use the linear equation to create a customized scale.

3. Notes

• Curves of polishes, resin solutions and wax emulsions are usually straight lines.
• Extrapolation of curves to significantly higher solids (more than 3 % total solids) is not recommended.

4. Advantage of Automatic Refractometers

Hand-held and Abbe-type refractometers can only be used with a considerable sacrifice in accuracy. The Abbemat will give a better repeatability and accuracy than handhelds and Abbe refractometers. Due to its measuring principle, the Abbemat operates independently of the operator.