Melting Point Instruments | METTLER TOLEDO

Melting Point Apparatus

Automatic Melting Point, Boiling Point, Cloud Point, and Slip Melting Point

A melting point system is an analytical instrument used to determine the melting point of solid crystalline substances. At the melting point, there is a change in light transmission through the sample, which is automatically detected with the METTLER TOLEDO Excellence Melting Point Systems. In addition to melting point, the versatile MP80 Excellence Melting Point System offers automatic determination of further physical properties, such as boiling point, cloud point and slip melting point.

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FAQs

What is a digital melting point apparatus?

A digital melting point instrument uses a furnace and video camera. The change in light transmission in relation to furnace temperature is measured for melting point detection. This melting point measurement is done digitally, reducing operator influence considerably. Up to 6 samples can be measured simultaneously with an accuracy of down to 0.2 °C using short heating and cooling times. With its compact size, the METTLER TOLEDO melting point meter fits well on every lab bench.

Learn more about melting point measurements

How does a digital melting point apparatus work?

A METTLER TOLEDO melting point system is represented in the schematic diagram below.

This system is a combination of a furnace and a video camera.
Melting point is determined by heating the sample. The furnace is used to control the temperature during an analysis. Temperature control and recording is performed by a digital platinum sensor.
The sample sits inside a glass capillary which is inserted into the furnace. During heating, when melting occurs, light transmission through the sample changes: When the material is solid and opaque, less light is transmitted through the substance. When a material is liquid and more transparent, more light is transmitted. This change in light transmission can easily be determined with a video camera, making this a reliable way to detect the melting point of a substance for a fully automatic melting point determination.
All results, measurement data and video files are stored on the melting point device and a lab report can be generated fully automatically.

Which samples can be measured with a digital melting point apparatus?

The determination of the melting point can be performed for powdered crystalline samples. The sample being investigated must be fully dry, homogeneous and in powdered form. Moist samples must be dried first. Coarse crystalline sample and non-homogeneous samples need to be finely ground in a mortar.

What does a melting point accessory box consist of?

For sample preparation, a dry powdery substance is ground in a mortar and filled into the capillaries, which are then inserted into the furnace. The melting point accessories box by METTLER TOLEDO contains everything needed for accurate and reproducible sample preparation.

The melting point accessory box is part of the standard delivery of the MP90 and is a highly recommended optional accessory for MP55, MP70 and MP80 instruments.

The melting point accessory boxes are available with standard or USP reference substances. The melting point accessories box contains two sets of 150 melting point capillaries each, three METTLER TOLEDO melting point reference substances or USP melting point reference standards, an agate pestle and mortar, tweezers, a spatula, and 5 capillary filling tools.

How do you calibrate and adjust a digital melting point apparatus?

If we want to make sure that the melting point analyzer is providing the correct results, we need to verify its measurement accuracy. As it is not possible to measure the sample temperature directly using a certified thermometer, the temperature accuracy is checked using reference substances, ideally with certified temperature values. Thus, we can compare nominal values including tolerances with actual measured values.

If calibration fails, which means if the measured temperature values do not match the range of the certified nominal values of the respective reference substances, the instrument needs to be adjusted.

The instrument should be adjusted with at least two reference substances that encompass the whole melting range required. The calibration should be performed with at least one reference substance melting point lying within the required temperature range. The new adjustment should be checked with a different reference substance than the one used for adjustment.

We highly recommended that you use METTLER TOLEDO melting point standards for calibration and adjustment purposes of METTLER TOLEDO melting point instruments. Each melting point reference substance comes with a certificate and both nominal pharmacopeia and thermodynamic melting points written on the label. The substances are securely identified with two barcodes showing the filling code and lot number.

Furthermore, METTLER TOLEDO offers a melting point performance verification package, called the MP VPac™, which contains prefilled and sealed capillaries for use in instrument verification.

How much substance do I have to fill in the capillary? How can I check the filling height?

The key to good results is careful and exact sample preparation. Prepare your samples so that the amount of substance is the same across all capillaries. Slight differences in the amounts could cause deviations in the measured melting point temperatures.

Check the capillary fill height using the lines marked on the melting point sample preparation tool. For accurate measurements, the optimum fill height of 3 mm should be observed.

The sample preparation tool offers many possibilities for checking the fill height of your substance. See Fig. 1 for an example of estimating various fill heights. For best results, it is important that the melted substance covers the holes for transmission light detection.

Fig. 1: Sample preparation tool: fill height markings
Fig. 1: Sample preparation tool: fill height markings

 

 

Does the METTLER TOLEDO Excellence Melting Point Systems support compliance with regulations for melting point determination such as Ph.Eur 2.2.14, USP chapter <741>, Japanese Pharmacopeia 2.60?

METTLER TOLEDO melting point instruments fully comply with most official standards for melting point determination, including: 

  • US Pharmacopeia USP <741>
  •  Japanese Pharmacopeia JP 2.60
  • European Pharmacopeia Ph.Eur. 2.2.14 and 2.2.60
  • Chinese Pharmacopeia ChP 0612
  • International Pharmacopeia WHO 1.2.1
  • ASTM D1519
  • Japanese Industrial Standard JIS K0064 and K4101


For detailed information on Excellence Melting Point systems related to international norms and standards, visit www.mt.com/MPDP-norms

Does the METTLER TOLEDO melting point apparatus support compliance with to 21 CFR Part 11?

The Excellence Melting Point apparatus can be connected to METTLER TOLEDO's LabX laboratory PC software for analytical instruments and balances. This robust software powers the melting point system with automated data handling, high process security and full SOP guidance.
LabX enables full integration of analytical data into other laboratory systems such as LIMS and ERP, which can help your lab comply with regulations and be ready for audit. LabX fully supports you with software validation and compliance including 21CFR part 11, EU GMP annex 11 and ISO 17025.

What are the pharmacopeia requirements for melting point determination?

Pharmacopeia requirements for melting point determination at a glance include: 

Use capillaries with outer diameters ranging from 1.3–1.8 mm and wall thicknesses from 0.1– 0.2 mm. Apply a constant heating rate of 1°C/min. If not otherwise stated, the temperature is recorded point C when no solid substance is left (which corresponds to the clear point). Pharmacopeias such as the United States Pharmacopeia (USP) require the determination of the melting range, where points A (corresponds to collapse point) and C are used for temperature determination. The recorded temperature represents the temperature of the heating stand, which can be an oil bath or a metal block, in which the thermocouple is positioned.

Learn more about how to achieve compliance to local and international pharmacopoeias for melting point determination

Is it possible to perform measurements other than melting point determination on METTLER TOLEDO melting point instruments?

All melting point instruments can also measure the melting range. The instrument models MP55 and MP80 can be used for diverse tasks. With the MP55, melting and slip melting points can be determined. On the MP80, the melting point application is extended by boiling point, cloud point and slip melting point.

In detail, the METTLER TOLEDO MP55 and MP80 Melting Point Systems offer the possibility to perform the following applications:

Boiling Point Measurement:
The MP80 acts as an automatic boiling point apparatus according to the following measurement principle: To determine the boiling point, which is the temperature at which a phase transition from liquid to gas occurs, approximately 100 µL of sample is pipetted into a glass tube. A smaller boiling point capillary is then inserted into the filled tube to prevent superheating of the liquid, which would induce boiling retardation and give rise to inaccurate readings. The sample is then inserted into the boiling point instrument, and the method is started. The temperature rises, and gas bubbles are formed within the liquid and escape to the surface. These ascending bubbles reflect the light of the built-in light source and are detected individually. The frequency of the bubbles is measured and is used as the basis for boiling point determination. Ambient pressure is measured with a built-in calibrated barometer, and compensation to sea-level pressure is automatically calculated and applied to the results.  

Cloud Point Measurement:
The MP80 acts as an automatic cloud point apparatus according to the following measurement principle: The cloud point of a solution corresponds with the temperature above which a sample becomes turbid. Cloud point determination is typically performed with a 1% weight dilution of the substance of interest in water. Approximately 100 µL of sample is pipetted into a glass tube and inserted into the cloud point tester. The solution of interest is transparent at the beginning of the experiment, and when the cloud point is reached, the solution becomes turbid. This turbidity is monitored via transmitted light detection – the higher the temperature above the cloud point, the more turbid the solution, and thus less light is transmitted through the solution. Automatic video camera detection of the decrease in transmitted light intensity is the key to obtaining repeatable and reliable cloud point results.

Slip Melting Point Measurement:
The MP55 and MP80 act as automatic instruments for slip melting point determination according to the following measurement principle: To determine the slip point of e.g. fats, oils and waxes, an inner slip melting point capillary tube containing a column of sample is immersed in water, which is then heated at a specific rate. The temperature at which the column of fat is observed to start rising in the inner capillary tube – due to a combination of buoyancy and the molten outside surface of the column – is recorded as the slip melting point. The slip melting point of the substance is evaluated via digital image analysis. When the column of substance starts to move upwards, the image processing algorithm determines the slip melting point fully automatically.