# How Mass Measurement Is Used in Engineering and Science

While many kids are naturally inquisitive, it’s important to fuel this curiosity early on so they effortlessly grasp concepts like mass. Mass is a quantitative measure of an object’s inertia, or resistance to change in speed and direction when a force is applied.

Mass is usually measured with a balance or scale. A balance measures the mass of an object by comparing it to a standard weight.

## Physical

In physics, mass is a quantitative measure of inertia—the resistance that matter offers to change in velocity when a force acts on it. It is a property of all matter, and it determines the strength of gravitational attraction between bodies.

A physical object’s mass remains constant regardless of shape, location or size. For example, a 15-gram bird has the same weight on Earth as it does on Mars. Weight is determined by the magnitude of the gravitational force acting on that matter, measured in Newtons.

With the discovery of atomic and particle physics, however, the notion of mass underwent a radical revision. It is now considered to be completely equivalent to and interchangeable with energy, and it increases when an object reaches speeds near the speed of light.

## Chemical

Mass spectrometry measures the mass of particles and can provide information about molecular structure. This information is useful for determining chemical composition in quality control and process development laboratories.

For macroscopic samples the measured mass error decreases with increasing number of measurements (n) because the magnitude of positive and negative errors partially cancels out. However, this does not guarantee that the average measured mass will be equal to the calculated exact mass.

Therefore, it is advisable that accurate mass data should be reported to several decimal places, e.g., to four (or seven for masses between 100 and 999 Da). This will help avoid rounding errors when calculations using the accuracy data are performed.

## Electrical

Whether you steer electron beams at the National Synchrotron Light Source to probe next-generation nanomaterials, build a Smart Grid to enable greater efficiencies and renewable energy resources in the Nation’s electric power system, or weigh every container entering and leaving the United States to establish shipping costs, electrical metrology is at the heart of your work. NIST scientists have developed chip-scale instruments for measuring extremely small masses and forces, such as the radiation pressure a laser exerts on an attached mirror.

All physical quantities are measured in one of seven base or fundamental units. Other units are derived by mathematically combining these fundamental ones.

## Magnetic

Unwanted magnetic effects must be minimized and quantified for precision weighing and mass metrology. This involves comparisons between weights made of ferromagnetic and weakly magnetic materials as well as modelling the forces between the weight and the balance.

This paper studies a model for errors in the measurement of small masses and forces, particularly in relation to the permanent magnetization and susceptibility of the sample. Although the nonmagnetic basalt used for primary 1 kg standards has a volume susceptibility of only 7 mT, accidental magnetization can bias the balance reading with serious consequences.

This can be eliminated by positioning the balance away from a laboratory variable field source and demagnetizing the sample before measuring it. The results obtained show that this method is a suitable alternative for obtaining accurate masses and forces at the submilligram level.

## Thermal

Sierra offers a range of industrial thermal mass flow meters (also known as immersible or thermal dispersion flow sensors) that provide direct mass measurement for gases flowing laminarly in closed conduits. They can be used in a broad range of applications including process control, metering of gas supplies and consumption, detecting leaks, and monitoring distribution networks.

A material’s ability to absorb and release heat is known as its specific heat capacity or thermal lag. Materials with long thermal lag times are said to have high thermal mass, while those with short lag times are considered low-thermal-mass materials. In addition to insertion and bypass versions, SmartMeasurement’s thermal mass flowmeters can be configured with large diameter averaging tubes to reduce straight-run requirements in non-cylindrical ducts.

## Optical

Optical mass measurement uses techniques such as optical scattering or laser absorption. These measurements provide information about concentration of solutes, shapes and sizes of particles, as well as biological activities.

Many mass measurements use micro- and nanomechanical resonator devices such as graphene drums or clamped carbon nanotubes. These are usually controlled via feedback loops with electrostatic, magnetic or optical actuation and detection.

Detectors such as photodiodes and complementary metal-oxide semiconductor (CMOS) sensors typically have a linear signal response, but their maximum resolution is limited by the magnification and numerical aperture of the objective used for imaging. This limit has recently been pushed to the limits by reduced-dimensionality and resonance enhancement technologies.

# How to Design a Weighing Process to Reduce Errors in the Pharmaceutical Manufacturing Process

Weighing is an essential part of any laboratory procedure. It can be done either directly or indirectly using a variety of methods.

The most important factor in weighing is to follow proper laboratory techniques and standards. This will eliminate many of the errors that might occur during weighing. The other factors include the type of balance, the accuracy required and the manipulation skills of the operator.

## Weighing Procedure

Weighing is the most critical step in the pharmaceutical manufacturing process. Errors during this phase can cost time, money, and reputation as well as compromise human health. Fortunately, a weighing process designed to improve accuracy and efficiency can help reduce error in the production of pharmaceutical products.

The first step in the weighing procedure is planning the work to be done and assembling the necessary equipment. Use a weighing pan or receiver of an appropriate size for the sample, as well as forceps, pipets, and spatulas that are clean and properly sized to handle the material. Select a weighing paper of an appropriate size and chemical resistance to prevent contamination with reagents and other chemicals.

In addition, make sure the temperature of the sample and the balance are in thermal equilibrium. This will reduce the effects of air currents that may affect the weighing results. If possible, perform comparison weighing (also known as substitution weighing) when measuring liquids to eliminate built-in balance calibration errors.

## Preparation of the Sample

Many analytical techniques require that the sample be in a certain physical form. This can cause a great deal of preparation to get the sample into the required shape for analysis.

Care must be taken to ensure that the sample container is clean and dry. Similarly, if the chemicals being used are corrosive or oxidize rapidly, it is important to ensure that they do not react with the container. For example, metallic sodium may react with a cellulose paper container (which can be avoided by using a glass watch or Petri dish) or other materials.

If the chemical is a solid, it is sometimes possible to use special glazed paper as a weighing vessel. This can be useful if the substance is not toxic or allergenic and does not react with the paper. However, for more serious chemicals it is often necessary to transfer the solid into a volumetric flask or beaker. In this case, the weighing vessel must be carefully added to the balance pan and locked by pressing the bar or button and weighed.

## Weighing the Sample

The weighed sample can now be transferred into a container. Depending on the type of substance you are measuring, you may need to use special equipment. For example, a microspatula is useful for manipulating small quantities of liquids. A scoopula may also be needed for large amounts of powdered solids.

Once the weighing instrument is ready to be used, it is important to make sure that the draft shield is closed and the balance readout reads zero. If necessary, clean the weighing pan with a soft brush before adding your sample.

For analytical balances, it is best to use a weighing boat or sample tube so that you can avoid fingerprints on the weighing pan. For general-purpose two decimal place balances, you can also use a plastic disposable beaker to hold the solid. This allows you to omit the solution preparation stage of transferring the chemical into a volumetric flask. However, this is only recommended when the chemical is completely soluble in a particular solvent.