NIST’s Most Popular Reference Materials and What They Tell Us About the Science of Measurement

Measurement, in its most basic form, is about comparing the thing you want to measure with a reference. To measure the length of a table, you compare it to a tape measure. To measure flour for a birthday cake, you compare it to a measuring cup. Better references mean better measurements.

If you're baking a cake, it doesn't matter much if your measuring cup is a little off, but sometimes millions of dollars or even people's lives depend on precise measurements.

That's why NIST develops and sells more than 1,300 standard reference materials (SRMs) that are critical for supporting American industry, enforcing laws and conducting research.

This post details our 10 most popular SRMs. Although you may have never heard of them, they have been used to ensure the safety of the water you drink, the bed you sleep in and the buildings you live and work in.

1. Metal Toughness

"Strength" and "toughness" might sound like synonyms, but for a civil engineer, the difference between these two words could mean life or death. In 1967, the Silver Bridge collapsed over the Ohio River during rush hour traffic, killing 46 people. The bridge was built from a new type of steel that was very strong because it was hard to bend or stretch. But the bridge's steel was not very tough - a small imperfection suddenly caused it to break apart.

NIST's investigation of the Silver Bridge disaster found that a crack just three millimeters long was enough to cause the entire bridge to collapse. When it was built in the 1920s, there was no standard way to measure toughness. But today, this measurement is an important part of making sure buildings, bridges and other structures are safe.

The Charpy [SHARP-ee] impact test is the most common way to measure toughness. A pendulum with a heavy weight on the end is dropped in the direction of a sample. The pendulum swings through the sample, typically breaking it in half, and continues rising up on the opposite side. The higher the pendulum swings, the less tough the sample. But for this test to be meaningful, the Charpy machine needs to be verified with reference specimens - samples with a toughness that is known with good precision.

NIST's Charpy SRMs are small steel bars about the size of your pinkie finger, with a V-shaped notch in the middle of one surface.

"The notch concentrates the stress into one line," explained Enrico Lucon, who runs NIST's Charpy program. "If you don't have a notch, the material would bend, not break, and then you wouldn't be able to measure toughness, which is the resistance of a material to applied stress in the presence of a crack or defect."

This SRM calibrates over 2,000 machines worldwide every year, helping ensure a sufficient level of toughness for the bridges you drive on and other steels all around you.

2. Engineered Antibodies

One of the key challenges for designing a new drug is making sure it can find and interact with the specific cause of the disease and nothing else. It just so happens that the body's immune system naturally makes seek-and-destroy tools called antibodies that do just that. When you become immune to a virus, it's because your body has made antibodies that can recognize that specific virus.

Researchers can design antibodies to recognize a specific disease target. Then, many copies of that antibody can be made in the lab or specialized manufacturing facilities. These are known as "monoclonal antibodies." By tweaking these antibodies in the lab, scientists can engineer them to treat all kinds of diseases, especially autoimmune disorders and cancers. Monoclonal antibodies are one of the fastest-growing segments of the pharmaceutical industry, making more than $200 billion in 2025 and expected to exceed $600 billion in 2031.

Developing and manufacturing monoclonal antibodies to do what you want is really challenging. Researchers need to develop numerous sophisticated tests to measure different characteristics of the antibody that can impact its safety and how well it works as a drug. A good reference antibody is critical for ensuring that these tests work and for designing better tests.

The NIST monoclonal antibody reference material (NISTmAb) is used by nearly every major biopharmaceutical company and many U.S. startup biotech companies. It's an important tool for studying antibodies that is used worldwide.

"The NISTmAb has made a huge impact on the global biopharmaceutical industry," said NIST researcher Kat Yandrofski. "We've distributed thousands of vials that have been used across the industry to develop the test methods to ensure that manufactured monoclonal antibody drugs are safe and effective. The NISTmAb has also been used in more than 140 patent applications and 100 scientific publications."

A sheet of SRM labels in the SRM warehouse in Gaithersburg, Maryland.

3. Sugar

If you want to bake a cake, you can borrow sugar from your neighbor. But if you want to know exactly how much sugar is in your food, you'll need carefully certified sugar like NIST's sucrose optical rotation SRM.

Sugar dissolved in water can rotate light. And the amount of rotation changes with concentration - as the concentration increases, the light rotates more. So, by shining light through sugar water and measuring the angle of rotation of the light using a device called a polarimeter, you can determine how much sugar you have.

Food producers regularly need to measure the sugar content of their foods, which is crucial for nutrition labeling, quality control and product consistency. And using the NIST sugar SRM as a baseline ensures that they make those measurements accurately.

Polarimeters are used for more than just sugar. Many organic molecules are "optically active," meaning they rotate light like sugar. That makes this SRM a valuable tool for measuring the purity and identity of different chemicals, including pharmaceuticals, plastics and narcotics.

"We have a long reputation for establishing materials like this. Everyone knows it's a very reliable standard," said NIST's Aaron Urbas. "The meticulous effort we invest in certifying the sugar's purity is a hallmark of NIST's exceptional standards."

4. X-Ray Powder Diffraction

If you found a mysterious powder and wanted to know what it was, how would you find out? It's a question thousands of chemists need to answer every day. One way to do it is with a technique known as X-ray diffraction.

It works by shooting X-rays at a sample at an angle. The sample absorbs the X-rays and emits them at a new angle on the other side. It's like the way a billiard ball bounces off the rail of a pool table. Different materials will cause the rays to bounce off at different angles. By measuring those angles, you can figure out what the material is made of.

This measurement technique is used to identify and better understand drugs, metals, ceramics, electronics and many other materials. Nearly anyone who works with crystalline solids might need to use X-ray diffraction. There are around 40,000 machines worldwide, and they are invariably calibrated using NIST's SRMs to ensure that they are working properly.

The SRM itself is a white ceramic disk about the size of a nickel. To make it, NIST researchers need to measure the angle of X-rays very precisely with a machine called a goniometer. As far as we know, NIST has the most accurate goniometer in the world.

The goniometer is operated in an insulated underground room designed to carefully control the temperature. Even body heat will ruin the measurement, so the operator must use the machine from another room. NIST is the only lab in the United States that can make these measurements.

5. Drinking Water

Think about the last time you took a sip of water. Did you pause to wonder whether it was safe? Luckily, there are many regulations in place in the U.S. to keep our water supply generally OK to drink. That's important because even small amounts of some contaminants, such as arsenic, can make you seriously ill.

The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) set maximum limits for many toxic elements that can be in drinking water. But effective laws require effective measurements. These regulations would be unenforceable without an accurate way to measure drinking water safety.

"Let's say you manage a municipal water supply," explained NIST researcher John Molloy. "You run a test, and it says the lead levels are low enough to be considered safe. That could mean one of two things: Either there actually is no [detectable] lead, or the testing equipment isn't working properly and gave you a false answer. That would be very bad. You need a reference sample to know the test is working and that the water is safe to drink."

The NIST SRM for trace elements in water contains an accurate concentration value for each of the elements that the FDA and the EPA regulate. (NIST is a nonregulatory agency that provides measurements.)

To get those precise concentrations, NIST technicians start with distilled, deionized water - water that's as pure as possible. Then, they add the different elements one at a time.

It sounds simple, but mixing all those elements together is a tricky chemistry puzzle. You have to add them in the right order and in the right way. Otherwise, the chemicals will start reacting with each other. You could get solid clumps in the water or new molecules that you don't want.

Partly because combining all the elements into one sample is so tricky, NIST is the only entity that produces this reference material.

Some SRMs must be stored at precise and very cold temperatures. This freezer stores temperature-sensitive SRMs at around minus 80 degrees Celsius (minus 120 degrees Fahrenheit).

6. Cigarettes

A forgotten cigarette can smolder for several minutes, igniting a pillow or mattress after the resident has fallen asleep. Most fires caused by smoking start in the bedroom, and they are particularly deadly. Even though only 2% of house fires are started by smoking, they cause more total deaths than house fires that start any other way.

In the 1970s, NIST developed a test for manufacturers to see how likely a cigarette is to ignite a mattress. The test involves lighting nine standardized cigarettes and letting them smolder at specific spots on the mattress with and without sheets to see whether the cigarette leads to a fire. Originally, the test used a specific commercial cigarette. But in 2010, the test switched to a standard NIST cigarette, SRM 1196, to increase confidence in the test results.

After that test was developed and implemented, fires started by cigarettes have become significantly less deadly. Part of that decrease is due to large social changes, such as the introduction of smoke alarms and the decrease in indoor smoking. Ignition-resistant mattresses also play an important role in keeping people safe from fire.

All mattresses and mattress toppers in the U.S. are required to pass this ignition test. So, the bed you sleep on at night has almost certainly been tested using this SRM. (Well, your specific mattress wasn't tested, but a copy set aside by the manufacturer was.)

7. Cement

When manufacturers make cement, they need to grind it into a fine powder, about the same texture as flour. The exact size of the powder particles, the "cement fineness," controls how fast the concrete hardens after you add water. If the cement is too fine, it will start to solidify before you can pour it in place. If the particles are too large, the cement will take longer to harden, costing time during construction.

Cement is big business. In 2024, the U.S. manufactured about $17 billion worth of cement in 99 cement factories. And those manufacturers need good measurements for quality control.

In 1943, NIST invented the Blaine Permeability Test to easily measure cement fineness. The test involves pushing air through the cement, measuring the time it takes for a certain amount of air to pass through the sample. Then, you compare that time to a reference such as NIST's cement fineness SRM. Lasers and sieves offer more sophisticated ways to measure fineness, but the Blaine test continues to be one of the most common methods because it's fast, simple and easy.

"It's a perfect example of how a measurement science institute is proving a measurement method so that industry continues to be successful. We work hard to make sure that everyone is getting the same consistent, robust, trusted material," said NIST's Aron Newman.

8. Infant Formula

NIST has SRMs for many different types of food, from spinach to baking chocolate, that make sure nutrition labels are accurate, among other important uses.

"When you're at the grocery store, you should be able to compare the nutrition label on food from any shelf, even though those foods may have been made by different companies on different continents," said NIST's Melissa Phillips. "That kind of consistent, accurate measurement is only really possible with a reference material to know your test is working."

Infant formula is NIST's most popular food SRM because it's so widely used and carefully regulated. Formula is a complex mixture of fats, proteins and vitamins that babies need to survive, so it's important to get it right.

NIST's neutrality is an important part of the value of this SRM. There are only a handful of infant formula companies, and the market is very competitive. The companies need to use the same reference formula for making meaningful measurements. Businesses prefer not to depend on one of their competitors to make and sell the reference formula to them.

This SRM also helps with international commerce. Different countries have different regulations for infant formula. So, if formula is made in one country and needs to cross the border to another, those countries need to agree on how the contents should be measured. For the last 20 years, the NIST infant formula SRM has been the benchmark for comparing testing internationally.

NIST researcher Melissa Phillips and her colleagues help keep food safe by creating and maintaining standard reference materials (SRMs) to help those in the food industry measure toxic contaminants, so their levels can be minimized in our foods.

9. Extremely Pure Acid

Measuring acidity is critical to many industries. It helps food companies get the taste of their soda just right, helps farmers monitor the health of their soil, helps pharmaceutical manufacturers do the complex chemistry needed to make drugs, and much more.

NIST's SRM for potassium hydrogen phthalate (KHP) is an extremely pure acid that's used to measure other acids and their opposites, known as bases.

Acids and bases cancel each other out. By dissolving this acid SRM in water and then slowly adding an unknown base one drop at a time until it completely neutralizes the acid, you can very accurately measure how basic the unknown liquid is. That dripping process is called "titration."

No measurement is perfect. The uncertainty of a measurement is the amount of doubt about the true value of a quantity after making a measurement. Each of the titration steps adds a little uncertainty. It's important that the SRM, the first thing in that chain of measurements, is pure with as much certainty as possible. The KHP SRM's uncertainty is 0.0076%, meaning that we know how much KHP is in each sample with extreme accuracy.

"You can buy high-purity KHP from other vendors," explained NIST's John Molloy. "But their measurements have more uncertainty, and that can be extremely important if you're making a pharmaceutical, for example."

10. Blood Plasma

Urine and fecal matter are two of the bodily fluids that NIST provides as reference materials. But the most popular, however, is blood plasma, specifically SRM 1950, metabolites in frozen human plasma.

Metabolites are all the small molecules moving around your body and doing different jobs to help you live. They include things like amino acids, sugars, vitamins, hormones and many more. Over 1,000 different metabolites have been identified in this NIST SRM.

Whose plasma is it? The plasma is a mixture derived from 100 different blood donors who were carefully chosen to reflect the demographics of America. NIST keeps this batch of the SRM in a special freezer at minus 80 degrees Celsius (minus 112 degrees Fahrenheit).

This SRM is mainly used for research. Including this sample in a study allows blood researchers to directly compare data collected in labs around the world from different years. When manufacturing this SRM, NIST made a total of 20 liters of plasma. Each SRM package is only one milliliter.

The sample is also regularly used in designing and patenting new medical devices. This SRM has been used in 20 different patents.

"It's highly important to the medical community that NIST maintains these samples," said NIST researcher Tracey Schock. "They help people come up with new technologies or blood screenings used by doctors to keep people healthy."