6 mpdp routine maintenance guide EN

Maintenance Guide

Performance
Verification

Day-to-Day Routine Maintenance
of Melting & Dropping Point Instruments


Content

Content

1

Introduction

3

2

Tips & Hints for Accurate Melting Point Determination

4

3

Tips & Hints for Accurate Dropping & Softening Point Determination

7

4

How to Clean the Dropping Point Furnace

11

5

Performance Verification with MP VPac

13

6

More Information

14

™



Disclaimer
The information contained in this guide is based on the current knowledge and experience of the authors. The
guide represents selected, possible application examples. The experiments were conducted and the resulting data
evaluated in our lab with the utmost care using the instruments specified in the description of each application.
The experiments were conducted and the resulting data evaluated based on our current state of knowledge.
However, this guide does not absolve you from personally testing its suitability for your intended methods,
instruments and purposes. As the use and transfer of an application example are beyond our control, we cannot
accept responsibility therefore.

When chemicals, solvents and gases are used, the general safety rules and the instructions given by the
manufacturer or supplier must be observed.
® ™ All names of commercial products can be registered trademarks, even if they are not denoted as such.

2

METTLER TOLEDO

Automated Melting & Dropping Point Analysis


Introduction

1. Introduction
For almost 5 decades METTLER TOLEDO has provided instrumental solutions for the automatic determination
of the thermal values melting point, dropping and softening point. The MP and DP Excellence lines, METTLER
TOLEDO’s latest release of compact instruments for thermal characterization, support the complete analytical
workflow with innovative solutions.
In order to characterize a material aside from chemical analysis, primarily physical methods allow us to
differentiate between, identify and classify substances or to describe quality aspects. Thermal characteristics,
such as melting and dropping point provide valuable and accessible information in this respect.
This guideline provides advice and tips for the routine maintenance of the melting point and dropping point
instruments in the daily use.
The MP and DP Excellence lines consist of the following instruments:
•Melting point: MP50, MP70, MP90
•Dropping and softening point: DP70, DP90

METTLER TOLEDO

Automated Melting & Dropping Point Analysis

3


Melting Point Determination

2. Tips & Hints for Accurate Melting Point Determination


A practical and rather easy way to check the performance of a melting point instrument is the comparison
with standard reference samples. A periodically repeated comparison reveals immediately if instruments deviate
from the regular and required performance, if calibration is requested or even if service has to be done. For
comparison purposes several sets of standard reference materials are available.

2.1 Melting Point Standards Overview
The following table provides an overview of the melting point standards that are important for melting point
determination. The individual standards specify the measurement parameters, the experimental setup (e.g.
heating medium; oil bath or furnace), the capillary dimensions and the detection of the melting point event.
Some of the pharmacopeias offer their own reference substances that are recommended for use in the
calibration/adjustment of the instrument. The instruments of the MP Excellence line fully comply with these
standards.
Name

Detection point

Heating rate
[°C/min]

Own references
substances

US Pharmacopeia
USP 37-NF32 <741>

Melting range: Evaluation
of collapse and clear point

1

Yes, 6,
range 83–237 °C

British Pharmacopeia

Meniscus point

1

No

Japanese Industrial Standard K 0064
Japanese Pharmacopeia 16th edition

Clear point

1

No

Chinese Pharmacopeia

Clear point

0.2 °C/min and
1 °C/min

Yes, 12,
range 60 –280 °C

International Pharmacopeia (WHO)

Melting point:
Evaluation of clear point

1

Yes, 12,
range 69–263 °C

European Pharmacopeia 8th edition 8.2
chapter 2.2.60

Clear point

1

No

ASTM D1519-95 (2004)

Clear point

1 ± 0.2 °C/min

No

Table 1: Melting point standards overview

2.2

Melting Point Measurement Results

The following tables include melting point test results
of reference substances from two different suppliers,
USP and WHO, that were measured with an MP90.
For each reference substance, the measurement was
obtained by taking the mean value of six capillaries. The
results reveal the excellent measurement accuracy and
repeatability that can be achieved with MP Excellence
instruments. The basis of these measurements is careful
sample preparation which can easily be achieved using
the capillary filling tool.

4

METTLER TOLEDO

Automated Melting & Dropping Point Analysis

Figure 1: USP reference substances

2.2.1 USP References
USP specifies that the measured melting range must
a) lie within the specified minimum and maximum temperatures (e.g. 81–83 °C for vanillin), and
b) must not be broader than the specified admissible values (e.g. 1.5 °C for vanillin). So, the permitted measured
melting range for vanillin could be 81.0–82.5, 81.3–82.8 °C etc.
Name of USP
reference substance
Vanillin

Assigned MR [°C]
min/max

Measured MR [°C]

admissible range

min/max

range

Repeatability
[°C]

81.0–83.0

1.5

82.0–82.6

0.6

TA: 0.13
TC: 0.05

Phenacetin

134.3–136.0

1.5

135.0–135.5

0.5

TA: 0.05
TC: 0.00

Sulfanilamide

164.0–165.7

1

164.1–165.0

0.9

TA: 0.23

TC: 0.05

Sulfapyridine

190.0–192.0

1.5

191.1–191.9

0.9

TA: 0.05
TC: 0.04

Caffeine

235.6–237.5

1

235.6–236.1

0.5

TA: 0.07
TC: 0.07

Table 2: USP references (MR: melting range, Repeatability: 6 capillaries)

Six capillaries of each USP reference substance were measured simultaneously and the respective transmission
curves were evaluated in the melting range mode, meaning the default parameters of points A and C were used.
Conclusions
The accuracy and repeatability of the results obtained from the MP90 are excellent. With each of the tested
reference substances a melting range smaller than the admissible reference value was reached. The absolute
melting range values were all within the specification temperatures. Hence, the MP90 instrument is ideally suited
to determine melting points according to USP.

METTLER TOLEDO

Automated Melting & Dropping Point Analysis

5


Melting Point Determination

2.2.2 WHO References
WHO reference substances are specified with a
maximum permissible temperature range, in the same
way as the METTLER TOLEDO reference substances.
The melting point criterion is the clear point C, when
all solid material has been transformed into the liquid
state.

Figure 2: WHO reference substances

Name of WHO reference
substance

Assigned MR [°C]

Measured MR [°C]

Repeatability
[°C]

Azobenzene

69.0 (± 0.4)

69.0

TC: 0.22

Vanillin

83.2 (± 0.6)

83.3

TC: 0.17

Acetanilide

116.0 (± 0.3)

116.1

TC: 0.09

Phenacetin

136.0 (± 0.3)

135.7

TC: 0.15

Sulfapyridine

192.7 (± 1.2)

192.9

TC: 0.10

Saccharin

230.0 (± 0.5)

230.3

TC: 0.09

Table 3: WHO references (MR: melting range, Repeatability: 6 capillaries)

Conclusions
The MP90 achieved excellent results also with the WHO reference substances. The melting points of all tested
references were within specifications. The achieved repeatability was far better than the assigned values. Thus, the

MP90 is best suitable to measure melting points following WHO guidelines.

6

METTLER TOLEDO

Automated Melting & Dropping Point Analysis


Dropping & Softening Point Determination

3. Tips & Hints for Accurate Dropping & Softening Point Determination
The procedure to check the performance of dropping and softening point instruments is similar to the melting
point instrument check. However, more strict rules apply in terms of suitable reference materials measurement
parameters.
3.1

Instrument Performance Verification
If we want to make sure that our dropping point instrument
functions correctly, we need to verify its measurement
accuracy. The following section gives valuable tips and
hints to help execute the performance verification correctly.
In order to check temperature accuracy we use reference
substances and compare their nominal values, including
tolerances, with the measured values ("calibration"). If the
measured temperature values are outside the values of the
certified reference substance, the instrument needs to be
adjusted ("adjustment").
METTLER TOLEDO reference substances such as

Figure 3: METTLER TOLEDO reference substances

benzophenone, vanillin, benzoic acid and potassium nitrate provide certified temperature values that can be
used for temperature calibration of the DP70 and DP90 furnaces. It is highly recommended that METTLER
TOLEDO reference substances are used for calibration and adjustment purposes of DP Excellence instruments.
The substances are securely identified with two barcodes showing the filling code and lot number. The quality of
the substances is guaranteed and is monitored by DSC measurement.
The DP70 and DP90 Excellence instruments include an
automatic procedure that compares the measured value
with the nominal value. The basis for comparison is the
thermodynamic melting point of the reference substance
(referred to as calibration substance) that is detailed on
the corresponding certificate and includes measurement
uncertainty. The thermodynamic melting point is the
physically correct melting point temperature of the actual
sample, not the furnace temperature, and is independent
of the experimental setup.
The dropping point of a reference substance is not equal
to the thermodynamic melting point as the measured
temperature is actually the furnace temperature and
not the sample temperature. Therefore, the furnace
temperature value needs to be adjusted using a
correction value, which is stored for each reference
substance in the instrument.
The correction factor is substance-specific and heatingrate dependent. It corrects the measured furnace
temperature to the thermodynamic melting point of the
relevant substance. The correction factors in the table are
valid for a heating rate of 0.2 °C/min.

Figure 4: DP screen shot. Entry field for correction factor and reference substance

Reference substance

Correction factor [°C]

Benzophenone

-1.2

Vanillin

-1.5

Benzoic acid

-1.4

Potassium nitrate

-1.4

Table 4: Correction factors based on thermodynamic melting point
METTLER TOLEDO

Automated Melting & Dropping Point Analysis

7


Dropping & Softening Point Determination

Once this is done, the comparison between measured and nominal temperature values is given. Furthermore the
correction factor takes into account the viscosity of the molten reference sample that drops from the cup, which
has an influence on the dropping point temperature. The correction factors have been determined empirically by
comparing the furnace temperature dropping point with the known thermodynamic melting point of the reference
substance.
If the measured values of the reference substances are
(a) within the nominal temperature value ranges, the instrument performance is ok
(b) are outside of the nominal temperature value ranges, performance is not ok. In this case, the instrument
issues a warning. It then needs to be adjusted.
3.2

Sample Preparation
The basis for comparable and reliable results in dropping point and softening point analysis is repeatable
sample preparation. This is why we recommend to use the accessory box of the DP instruments including the
patented sample preparation tool.

3.2.1 Excellence Accessory Box
The DP accessory box is included in the standard delivery of the DP70 and DP90. It provides useful accessories
for reliable sample preparation:
•The DP sample preparation tool that enables efficient and clean filling of up to 4 dropping and softening point
cups with liquid or solid substances, including a handle to place or remove the tool's plate into an oven or a
refrigerator
•Two tamping rods to press ground solid samples into dropping or softening point cups
•2 softening and 2 dropping point cups made of chromium-plated brass
•2 stainless steel balls according to ASTM D6090
•2 cup lids with vent hole to close the sample-containing cup
•6 glass cups for collection of liquefied or softened samples during the respective tests
•Sample carrier that holds two dropping or softening point cups with glass collectors and cup lids
•A stand that holds two sample carriers

•A spatula to transfer the sample into a cup or to remove excessive sample
•A rod to remove excessive lubricant grease from a dropping point cup according to the procedure specified in
ASTM D556
Cup lids
Cups

Spatula and rod

Handle

Balls

Sample
preparation tool
Collector glass
Tamping rod

Reference substance
Benzoic acid
Stand

8

METTLER TOLEDO

Figure 5: DP accessory box

Automated Melting & Dropping Point Analysis

Sample carrier

3.2.2 Efficient and Reliable Sample Preparation: The Sample Preparation Tool
The basis for comparable and reliable results in dropping point and
softening point analysis is repeatable sample preparation. With the DP
Excellence sample preparation tool this crucial step is perfectly supported:
• Efficient sample preparation as four cups can be prepared at a time
•Handling errors are minimized and operational security maximized
•Contamination of the outer surface of the sample cup is avoided which
contributes to result reliability
The sample preparation tool consists of four pieces:
•A double-sided base plate that holds four dropping point cups on one
side and four softening point cups on the other
•A support disk with four holes
•A disk-like funnel for powdered samples
•A handle to carry the whole tool (not shown in the pictures)
Dropping point cups are positioned on the side of the base plate with the
deepest indentations. The shallower indentations on the other side of the
plate are used for positioning the softening point cups.
A support disk is used to fix the cups and to make the upper rim of the
cup level with the surface. The support disk therefore serves a threefold
purpose: first to prevent the sample from contaminating the outer surface
of the cups, second to facilitate the removal of excessive sample, and
third to facilitate the complete filling of the sample cup with powdered
samples.

3.2.3 DP Excellence Sample Holder and Standard Compliant Cups
Standardized dropping and softening point cups from METTLER TOLEDO
are made of chromium-plated brass or aluminium. The experimental
setup required for an automatic dropping and softening point test consists

of the sample-containing cup, closed with a lid, and a collection glass
Figure 6: Work sequence with sample
preparation tool
underneath to collect the liquefied sample. The sample carrier allows the
efficient, simultaneous measurement of two samples, which are placed with
the sample carrier into the DP furnace. After test completion the sample carrier is removed from the furnace and
securely placed on the stand to cool down to ambient temperature.
It is then quickly disassembled and the collection glasses are put into the waste with the aluminium dropping
or softening point cups. Cup lids prevent discharge of expanding sample, which avoids contamination of the

Collection glass

Cup Lids

Stand
Cups

Figure 7: DP Sample holder and stand

Figure 8: Dropping point cups

Figure 9: Softening point cups

METTLER TOLEDO

Automated Melting & Dropping Point Analysis

9

Dropping & Softening Point Determination

furnace.

10

Tedious and time-consuming work in dropping and softening point analysis involves cleaning the components
after completion of the analysis. Unhealthy, nonpolar solvents may be required in order to dissolve the sample
residues. The DP Excellence system provides disposable aluminium sample cups and glass sample-collectors
that make cleaning unnecessary. The post-treatment process is therefore significantly accelerated and the
system is ready for the next measurements within a short time. The DP Excellence solution is therefore much
more efficient than other competitor systems that require complete cleaning of the sample holder prior to the next
analysis.

METTLER TOLEDO

Automated Melting & Dropping Point Analysis


How to Clean the Dropping Point Furnaceon

4

How to Clean the Dropping Point Furnaceon
Thermal treatment under pure oxygen atmosphere
or ambient air is recommended, if the furnace of a
DP70 or DP90 Excellence dropping point system
is contaminated with decomposition products that
originated from thermal decomposition of the samples
such as lubricant grease during dropping point tests.

However, best practice is to avoid having to clean
the furnace. This is achieved by preparing samples
carefully and making sure that the sample carrier,
cups and cup lids are free of residue. Nevertheless, the
area around the sample carrier can still become sticky
over time and request removal of such decomposed
materials.

4.1

Figure 10: Cross section view of a DP70. The furnace and the camera glass that may be contaminated with decomposition products

When is furnace cleaning due?
• The video image has darkened and may require adjustment of the brightness factor.
• During startup of the instrument the furnace position may not be accurately detected anymore. Then a
respective error message will appear to alert the user and to indicate that default parameters for furnace position
detection are being used.

4.2 Cleaning procedure
Please adhere to the general lab safety measures and instrument safety as described in the
operating instructions. If you are unsure about the cleaning procedure, please contact
METTLER TOLEDO first for service advice.
Instead of disassembling the furnace followed by thorough manual cleaning with solvents or abrasive materials,
a thermal treatment is recommended.
Apply pure oxygen gas and heat the furnace to 400 °C until clean. At this temperature the decomposed materials
are oxidized to carbon dioxide. Usually a one hour treatment is sufficient to clean the contaminated parts. If
necessary the procedure shall be repeated.

METTLER TOLEDO

Automated Melting & Dropping Point Analysis

11


How to Clean the Dropping Point Furnaceon

The instrument shall be placed preferentially in a hood
or alternatively in a well ventilated place. A slight
stream of oxygen (approximately 20 mL/min) from
a pressurized gas bomb applied during the whole
heating process is sufficient. The oxygen stream shall
be directed directly into the furnace.
Let the instrument cool off to room temperature. Now,
the furnace is clean and ready for the next analyses.
4.3 DP cleaning method
We recommend to program the following method.

Figure 11: Setup of dropping point instrument and oxygen gas
supply.

Temperature segments
Start temperature:
394 °C
Waiting time:
1000 s
Heating rate:
0.1 C/min
End temperature:
400 °C

Evaluation
Operation mode:
Dropping point
Set manually:
No
Temperature correction:
No
Brightness: 50%
Result round-off:
0.1
Calibration substance:
No
Termination and end behavior
Stop at event:
No
End behavior:
Remove temperature
Temperature:
50 °C

In order to save the furnace, a lower end temperature of 350 - 380 °C can be applied as long as the
decomposed materials are still oxidized. Set the start temperature 6 °C lower than the selected end temperature.

12

METTLER TOLEDO

Automated Melting & Dropping Point Analysis

Performance Verification with MP VPac™

5. Performance Verification with MP VPac™
5.1 Ready-to-use Kit of Traceable Reference Substances
Performance verification by temperature calibration is the recommended
workflow to ensure faultless routine operation of a melting point instrument
and to secure result reliability. The MP VPac provides 3 different certified
reference substances in prefilled, sealed capillaries for a simple method of
verifying instrument accuracy over the temperature range 40 to 230 °C.
No sample grinding and time-consuming manual upfront filling of melting
point capillaries is required. Just take the pre-filled capillaries and
insert them into the MP instrument furnace, as in a normal method. The preprogrammed performance verification (->calibration method) can be started
directly without any modification.
Each of the three reference substances included in the MP VPac comes
with a certificate that states the certified temperature value including
measurement uncertainty.

Figure 12: MP VPacTM contents

5.2 Do-it-yourself Service
This is a cost-effective and do-it-yourself service that can be performed on Melting Point Excellence instruments.
It allows you to:
• Have confidence in the accuracy of your results
• Control the performance of the melting point system
• Receive an unbiased and traceable analysis verification
Performance verification is recommended:
• After setting up an instrument
• In relation with operational qualification of an instrument
• For monthly periodic check of the instrument

5.3 Reference Substances
The MP VPac™ contains the following melting point reference substances, each in 50 sealed standard METTLER
TOLEDO melting point capillaries.
• Phenyl salicylate:
Thermodynamic melting point: 41.8 ±0.2 °C
Pharmacopeia melting point (1 °C/min heating rate): 43.8 ±0.2 °C
• Benzoic acid:
Thermodynamic melting point: 122.4 ± 0.2 °C
Pharmacopeia melting point (1 °C/min heating rate): 124.4 ±0.2 °C
• Saccharin:
Thermodynamic melting point: 228.3 ±0.3 °C
Pharmacopeia melting point (1 °C/min heating rate): 230.3 ±0.3 °C

METTLER TOLEDO

Automated Melting & Dropping Point Analysis

13


More Information

6. More Information
Find more information to the following topics:
Presentation of all instruments of the MP and DP Excellence instrument line, including technical information
(downloadable product brochures).
www.mt.com/MPDP

Comprehensive product movies showing the operation of the MP and DP Excellence line instruments.
www.mt.com/one-click-melting

www.mt.com/one-click-dropping

Good Melting and Dropping Point Practice GMDP™: Service product offering supporting the whole life cycle of the
MP and DP Excellence instruments, including risk check, downloadable data sheets and application literature.
www.mt.com/GMDP

Detailed information about the LabX PC Software for the MP 70 and MP90 Excellence instruments.
www.mt.com/LabXMP

Useful accessories which support secure and efficient sample preparation for melting , dropping and softening
point determination.
www.mt.com/MPDPaccessories

MPVPac™ performance verification: a unique self service for MP Excellence instrument performance verification
based on pre-filled, certified reference substances.
www.mt.com/MPVPac

Comprehensive on-demand webinars that introduce automatic melting, dropping and softening point
determination. A lot of useful application tips & hints and a concluding knowledge-testing quiz are included.
Go to

• Good Melting Point Practice

• Good Dropping Point Practice


14

METTLER TOLEDO

www.mt.com/webinar-analytical

Automated Melting & Dropping Point Analysis


Good Measuring Practices
Five Steps to Improved Measuring Results
The five steps of all Good Measuring Practices guidelines start with an evaluation
of the measuring needs of your processes and their associated risks.
With this information, Good Measuring Practices provide straight forward
­recommendations for selecting, installing, calibrating and operating laboratory
equipment and devices.
• Guaranteed quality
• Compliance with regulations, secure audits
• Increased productivity, reduced costs
• Professional qualification and training
5
Routine
Operation

4

Calibration /
Qualification

1
Evaluation

Good

Measuring
Practices

Learn more about Good Measuring Practices program
www.mt.com/gp

2
Selection

3
Installation /
Training

Good Melting and Dropping Point Practice™
Reliable thermal values – optimized by GMDP™
www.mt.com/GMDP

www.mt.com
For more information

Mettler-Toledo Laboratory Division
CH-8606 Greifensee, Switzerland
Tel. +41 44 944 22 11
Fax +41 44 944 30 60

Subject to technical changes
© 05/2015 Mettler-Toledo AG
Global MarCom Switzerland / MC