How do boiling, cloud, and slip melting points reveal the hidden qualities of materials? Explore the methods and innovations behind these critical measurements and their impact on food, cosmetics, and industrial manufacturing.
 |
Cracking the Thermal Code: Precision in Quality Control
In the world of modern science, the properties of materials often hold the key to their quality, safety, and performance. From the boiling point of liquids to the slip melting point of fats, thermal properties offer invaluable insights into the purity and behavior of substances under different conditions.
In this detailed exploration, E. Ziółkowska unpacks the critical role of thermal analysis in today’s industries, ranging from food and cosmetics to industrial manufacturing. This article delves into three essential determinations: boiling point, cloud point, and slip melting point, highlighting their significance in processes like quality control, regulatory compliance, and product development.
Thanks to state-of-the-art instruments like the Excellence MP55 and MP80, these traditionally labor-intensive measurements are now more accessible, automated, and precise. Discover how these innovations are setting new standards for material analysis while streamlining workflows for researchers and quality control teams alike.
Dive into the science and learn how mastering thermal properties can empower both innovation and consistency in your field.
Boiling Point, Cloud Point, and Slip Melting Point Determinations
How can we test the purity of products? What methods can be used to assess the quality of materials? Various techniques, including melting point, boiling point, cloud point, and slip melting point, can be employed to characterize a substance and evaluate its properties.
In many modern production processes, it is important to know the thermal behavior of a substance under different conditions. A number of physical methods, such as melting, boiling, cloud, and slip melting points, can be used to characterize a substance and analyze its properties.
The MP55 and MP80 instruments automatically determine these parameters. Thermal values are essential regardless of your workplace or field of work, from quality control to research and development, or whether or not you adhere to a given standard or norm. In this article, we make use of selected examples to illustrate each technique.
Boiling point measurements over a wide temperature range
The boiling point (BP) of a pure substance is the temperature at which the liquid-to-gas phase transition occurs under normal conditions. It is a substance-specific property that is often used to select an optimal process temperature, suggesting a storage condition and identifying products. It is also required for Material Safety Data Sheets (MSDS).
Procedure
The Excellence MP80 System is used to automatically determine the BP of liquids. Samples are pipetted into a glass tube and a boiling point capillary is inserted into the tube. The sample is then introduced into the instrument and the method is started. As the temperature rises, gas bubbles are formed within the liquid and escape to the surface (Figure 1).
Boiling occurs when the vapor pressure of the substance in the liquid is equal to the vapor pressure exerted by its surroundings. The principle of BP detection is based on counting the ascending bubbles and is thus univocally defined. This clear definition allows the evaluation to be automatized without any ambiguity regarding the temperature at the boiling point. With the MP80, very little sample is required; the recommended liquid volume is in the range of 100 μL, which also makes this technique very safe.
 |
Figure 2. Boiling point in °C of common substances at sea level. |
Results
Boiling point experiments can be carried out across a wide temperature range, from ambient temperature up to 350 °C, covering many substances. Figure 2 shows the results for a selection of chemicals commonly found in laboratories. Boiling temperature is a pressure-dependent parameter. Because most determinations of the boiling temperature are made at ambient pressure, a calculation is necessary to derive the normal pressure-corrected BP from the measurement. An example of measurement without correction for ethanol:
- Measure at sea level (normal pressure): boiling point = 78.4 °C
- Measure at 400 m altitude: boiling temperature = 77.3 °C
With the Excellence MP80, ambient pressure is measured with a built-in calibrated pressure sensor, and compensation to sea-level pressure is automatically calculated and applied to the results.
Conclusions
The Excellence MP80 is suitable for the boiling point determination of samples of a diverse nature and temperature range. The typical liquid volume required is ca. 100 µL. The built-in barometer is used to scale the measured temperatures at ambient pressure to normal pressure. Together with accurate temperature and heating rate control, experiments can be performed simultaneously, allowing precise statistics to be obtained for duplicate results.
Cloud point: quality control monitoring
Conducting quality control (QC) verifications is the basis for ensuring a high level of production and technical performance. As vast as it may seem, QC efforts are often concentrated on monitoring a few key properties. These may be a process degree of conversion, a temperature, or a separation step. Often it concentrates on a single indicator at the end of a workflow.
Cloud point (CP) is a reliable QC parameter for water-soluble surfactants, be they emulsions or dispersions. Nonionic surfactants (typically used as detergents) are known to show optimal effectiveness when used near or below their cloud point. Low-foam surfactants, however, should be used at temperatures slightly above their cloud point. These two examples demonstrate the pivotal importance of CP monitoring of processed materials.
Procedure
Cloud point can be determined with the Excellence MP80 System. Often CP protocols ask for a 1% weight dilution in water. The samples in a volume of 100 µL are then pipetted into glass tubes and inserted into the instrument. The CP corresponds to the temperature above which the sample becomes turbid. The sequence of this transformation is represented in Figure 3.
Turbidity is monitored via transmitted light detection. In this respect, above the saturation temperature, the more turbid the solution and thus the less light is transmitted through the solution. This transition has an early onset that is difficult to detect with the human eye. That's why automatic detection is less biased and virtually error-free. The actual cloud point (the onset of clouding) was determined to be 62.8 °C. At higher temperatures, the solution clouds visibly (Figure 3, 63.5 °C).
 |
Figure 4. Control chart of a series of CP determinations of a 1% ethoxylated nonylphenol (aq). |
Results
Control charts are efficient tools for monitoring test method performance and maintaining the stability of test method bias and precision. The best-known and most commonly used control charts are Shewhart charts.
The results of a series of 50 measurements are plotted in Figure 4. The substance investigated is 1% ethoxylated nonylphenol (aq). The control chart of the 50 results illustrates the normal distribution around the center line (CL, marked in green). Variations in results are due to normal processes. Upper and lower control limits (UCL and LCL respectively, marked in red) are set at a 3-sigma limit, corresponding to +/-0.25 °C from the center line and denoting acceptable limits. As shown in Figure 4, the measurements fall well within control limits.
Conclusions
Camera detection of the decrease of the transmitted light intensity is the key to obtaining repeatable and reliable results. This procedure can be fully automatized, allowing unattended CP determination. The chosen example of the QC for surfactants illustrates how this property can reliably and robustly be used for in-control process monitoring. CP duplicate measurements provide added security of results, increasing the sampling number of a substance's specimen.
Slip melting point determination of fats and oils according to ISO 6321
Vegetable fats and oils find widespread use in many industries, including food, detergents, and cosmetics. The melting characteristic of fats and oils is an important parameter determining quality and suitability.
The slip melting point (SMP) is often used to characterize fats and oils. This method is also known as open tube or open capillary melting point and is described in detail in ISO 6321 [1]. The importance of the SMP is demonstrated with palm oil, a product derived from the flesh of oil palm fruits composed of various saturated fatty acids (see Table 1).
Depending on the composition of the palm oil and its corresponding SMP, it can be used in a variety of applications from low to high temperatures, from ice cream to confectionary products and bakery fillings.
 |
Table 1. Typical fatty acid composition of palm oil. |
Procedure
The slip melting point is measured in a capillary tube immersed in water. The capillary tube, containing a column of fat crystallized under controlled conditions, is heated at a pre-defined rate. The temperature at which the column starts rising in the capillary tube is recorded as the SMP (Figure 5).
The slip of the substance is evaluated via digital image analysis. As soon as the column of substance starts to move, the video processing algorithm automatically determines the SMP.
Results
Typical palm oil samples are a mixture of many ingredients (Table 1) that can be divided into solid (stearin) and liquid (olein) fractions. The main components of stearin, stearic, and palmitic acid melt at higher temperatures than oleic acid. Thus, by blending different amounts of stearin and olein, the melting point of the sample can be adjusted without increasing the trans-fatty acid content. The SMPs of two different blends (A and B) are presented in Figure 6.
The SMP of each blend was determined three times, with two simultaneous, duplicate measurements each. As can be seen, blend A is richer in the stearin fraction than blend B. This is reflected in the SMP of the two blends: The SMP of blend A is approximately 10 °C higher than blend B. The SMP can be adjusted by modifying the fraction composition.
 |
Figure 6. Averaged results for the slip melting point determination of blend A and blend B. Error bars indicate the standard deviations of the measurements. |
Conclusions
Slip melting point is generally used when conventional analysis techniques prove difficult to implement, as is the case with vegetable fats and oils. In this respect, SMP helps in product characterization, supporting international trade, which makes standardization and compliance pivotal.
Repeatable and reliable SMP results are ensured by video processing algorithms, which allow for fully automatized, unattended measurements. SMP norms and standards require an arithmetic mean of two readings; therefore simultaneous, duplicate measurements as performed with the MP80 system decrease measurement time.
References
[1] International Standard, ISO 6321:2002, Animal and vegetable fats and oils – Determination of melting point in open capillary tubes (slip point), second edition.
 |
Ewa Ziółkowska |
Ewa Ziółkowska is a Product Manager at METTLER TOLEDO, specializing in Physical Values.
With a degree in biotechnology engineering and over five years of experience spanning customer support, product management, and application development, Ewa collaborates with cross-functional teams to refine analytical solutions, ensuring they address evolving market needs.
