Analytical Balances

An analytical balance, also known as an analytical scale or sometimes as a semi-analytical balance, is a type of laboratory instrument that measures mass to a high degree of accuracy, typically having a readability of 0.1 mg (four decimal places) or smaller. An analytical balance or analytical scale has a highly sensitive weighing cell and hence is built with a draft shield to protect the sample and the container from air movements which can cause instability and inaccurate results. Analytical balances from METTLER TOLEDO offer weighing capacity from 52 g to 520 g and readability ranging from 0.1 mg to 0.002 mg.

Nowadays, electronic analytical balances and analytical scales are often equipped with various functions and features to help maintain accuracy and improve weighing ergonomics, such as internal testing and adjustment, intuitive touchscreen operation, quality assurance, and motorized doors. METTLER TOLEDO's analytical balances also make it possible to connect to dedicated data management software such as EasyDirect and LabX. Our XPR analytical balances also feature StaticDetect™, which automatically assesses the weighing error due to static charges on samples and containers and provides a warning if the error exceeds predefined limits. XPR analytical balances can also be upgraded easily for automatic powder and liquid dispensing. Analytical balances and analytical scales provide connectivity options, such as USB, RS232 and LAN, to enable results to be transferred digitally, as well as facilitate balance connection to various peripherals, accessories and data systems.

The weighing principle of METTLER TOLEDO analytical balances is based on electromagnetic force compensation. The weighing cell inside the balance housing creates a counteracting electromagnetic force to the object that has been placed on the weighing pan. The analytical balance interprets the magnitude of this compensating electromagnetic force as the weight of the object. The result is displayed on the balance terminal in the appropriate unit (grams, milligrams, micrograms, etc.). 

The weighing pan of an analytical laboratory balance (0.1 mg readability or smaller) is placed inside a draft shield, which protects the sample and container from external environmental influences, like air drafts, hence helping to improve general weighing performance. This is particularly important in analytical weighing, when accuracy of results is of utmost importance.

Analytical balances are used for simple weighing applications, as well as for standard and sample preparation, formulation, density measurement, filter weighing, etc. 

Before weighing, first check that the balance is level. If your standard operating procedure (SOP) requires it, you may need to perform a balance adjustment.

• To start your weighing procedure, first press the zero button. This gives you a zero point as the start of your weighing process.
• Open the draft shield door and place your target container, sometimes referred to as the tare container, on the weighing pan. Remember to wear gloves or use tweezers, if necessary.
• Close the draft shield door and wait until the weight value of the container stabilizes. The weight of your tare container is now shown on the display.
• Now press the tare button. The balance records the weight of your tare container, and the display will now show zero again (note that this is not the same as the zero point).
• Start adding your sample until the desired target weight is reached.
• Close the draft shield door. Once the balance has stabilized, it will release the weight result.
• The balance has now recorded the weight of your tare container and the weight of your sample. If you print out the results, the weight values will be shown with T for tare, N for net, and G for gross.
• After you have finished weighing, make sure you clean the balance and the bench around the balance according to your SOPs. If the instrument is unplugged for cleaning, allow time for it to warm up again before reuse.

If you are weighing an item, rather than dosing a sample into a container, simply zero the balance and place your item in the center of the weighing pan. Then close the draft shield door and wait for the balance to release the weight result. Read more in our free guide: Weighing the Right Way

The zero function gives you a zero point from which to start your weighing process. If you are using a heavier weighing pan (with an ErgoClip for example) or perhaps have a protective mat on the weighing pan, the zero function effectively ignores this as any weight that is already recognized by the weighing cell is not included as part of your weighing process. However, any weight on the balance still contributes towards the maximum load you are able to place on the balance (i.e. the balance capacity).

When using the tare function, the balance internally records the weight that is already on the weighing pan and resets the display to zero, ready for something further to be added to the balance. When the results are recorded electronically, they will be shown with T for tare weight, N for net weight, and G for gross weight.

An analytical balance or analytical scale, often referred to simply as a "lab balance", enables the analysis of a wide variety of samples. Customer specific applications of where the use of an electronic analytical balance is required include:

• Sample/standard preparation
• Formulation
• Differential weighing
• Density determination
• Interval weighing
• Pipette routine testing
• Elemental analysis
• HPLC (high performance liquid chromatography)
• GCMS (gas chromatography – mass spectrometry)

Analytical balances are used in general laboratories, R&D and quality control laboratories across industries such as pharma and biotechnology, chemical, food, academia, metals and plastics, etc.

Choosing the right analytical balance is important. Accurate weighing is about more than just the digits on the balance display. Only by knowing your process risks, tolerances, the required quality, and the relevant regulations can you select the balance that offers you the right level of accuracy. The performance of the balance must meet both your internal accuracy requirements as well as any external regulations. Your analytical balance must be fit for its intended purpose, otherwise all weighing results and any subsequent processes making use of those weighing results will be deemed invalid.

METTLER TOLEDO's free GWP^® Recommendation service is designed to help you choose the instrument that is right for your specific process and accuracy requirements. It considers the following key factors:

• Maximum weight: The maximum load you weigh (including the tare container)
• Smallest net weight: The smallest load you weigh (excluding the tare container)
• Weighing tolerance: The weighing error that is acceptable, specified as ± percentage
• Safety factor: This factor is applied to the balance minimum weight to compensate for external influences such as vibrations, drafts, different operators, etc.

GWP^® Recommendation can also be used to ascertain if your installed balance is fit for purpose.

METTLER TOLEDO analytical balances and analytical scales can support you with simple data transfer without the need for additional software. First, connect your analytical balance to your PC using a USB cable.

• On our Excellence level analytical balances, activate the HID (drop-to-cursor) function. Now, simply press 'Add result' on the balance display, your weighing result will be transferred directly to an Excel spreadsheet or Word document.
• On our Advanced and Standard level analytical balances, activate PC Direct and press 'Print' to transfer your weighing result to an Excel spreadsheet or Word document.

Using dedicated software increases the data management possibilities:

• For our Advanced and Standard level analytical balances, our EasyDirect software provides extended result management capabilities, including csv file exporting, statistical calculations, and review of results.
• For our Excellence level analytical balances, LabX laboratory software offers advanced data management and results analysis. LabX is a powerful solution for the centralized management of data, tasks, instruments and users. LabX also assists with compliance with 21 CFR part 11 and ALCOA+ data integrity requirements.

A top loading balance has a weighing pan directly above the weighing cell. Furthermore, the term 'top loading' indicates that the load is applied to the top of the weighing cell. Many of METTLER TOLEDO's analytical balances and analytical scales and all precision balances are top loading balances. However, METTLER TOLEDO's Excellence level analytical balances and analytical scales that feature the patented SmartGrid hanging weighing pan are not top loading balances. In analytical balances with SmartGrid, the weighing cell and the associated electronics are positioned at the back of the balance, behind the weighing chamber. These analytical balances are sometimes referred to as 'front loading' balances because the load is applied to the front of the weighing cell. This construction enables active temperature control technology to efficiently remove heat from the electronics at the back of the balance, providing high temperature stability within the weighing chamber. The pictures below show a top loading Advanced level analytical balance and an Excellence level analytical balance with the hanging weighing pan.

One of the notable differences between an analytical balance and a microbalance is the number of decimal places of readability. Analytical balances and analytical scales are laboratory balances with readability of four decimal places or more. METTLER TOLEDO analytical balances offer readability in the range from 0.1 mg to 0.002 mg. Typical applications include sample and standard preparation, differential weighing, density determination, etc.

METTLER TOLEDO's microbalances and ultra-microbalances deliver the highest accuracy of all laboratory balances, offering readability of 1 µg (six decimal places) and 0.1 µg (seven decimal places). Typical applications include particulate matter (filter) weighing, pipette calibration, pesticide residue testing, and stent weighing. 

Further differences can be seen in the higher repeatability and in the construction. Microbalances have a small cylindrical weighing chamber and an additional balance display that helps with ergonomics when weighing very small samples.

Calibration is an assessment of the performance of the balance. The need to calibrate your analytical balance depends on where it is being used and whether there are any applicable regulations. It is also important to consider the risk and the cost implications of having an incorrect weight result compared to the cost of calibration.

In regulated environments, calibration is a requirement as it provides the certainty that the balance is performing according to expectations. Analytical balance calibration ensures that weighing equipment satisfies standards such as ISO, GLP/GMP, IFS, and BRC.

When it is essential to have highly accurate weighing results, choosing not to calibrate your analytical balance can be a high-risk strategy. In such environments, using non-calibrated equipment can lead to production problems such as:

• Unscheduled downtime
• Inferior product quality
• Process and audit issues
• Product rework and recalls

Analytical balance calibration should not be confused with routine testing. While calibration is performed by authorized service technicians, routine testing is executed by the instrument user. If performed frequently enough, routine testing helps with the early identification of potential out-of-tolerance results.

Read more on balance calibration by clicking here.

Analytical balance calibration should be performed by an authorized service technician following a standard procedure. The service technician will typically use dedicated software to support the process and provide a calibration certificate. Documented analytical balance calibration is essential in regulated environments such as pharmaceuticals and biotechnology.

Calibration involves assessing the performance of the analytical balance against measurement standards. This involves several tests, including comparing the indication on the balance to the known value of a calibrated weight placed on the weighing pan. The technician can confirm whether the balance meets requirements with clear pass/fail statements.

Balance calibration should be carried out according to the process risk (i.e. how high the negative impact of an incorrect weighing result). In the intervals between calibrations, analytical balances should be tested regularly by the user to ensure ongoing accurate results and provide early identification of any potential issues.

METTLER TOLEDO's Good Weighing Practice™, or GWP^®, is a global scientific standard for the secure selection, operation, and calibration of weighing equipment.

Every measurement is subject to a degree of uncertainty. The measurement uncertainty is due to random errors, e.g. from the user or the environment, and systematic errors, e.g. from the inherent tiny variations in the performance of the instrument every time it is used.

Every time you weigh something on your analytical balance, there is a degree of uncertainty in the result. This uncertainty should be declared together with the result. If the uncertainty is too high, you may not be able to trust the result. The relative measurement uncertainty is much greater at the lower end of the weighing range and care must be taken when weighing small quantities.

This guide explains the safe weighing range of your balance.

The measurement uncertainty of an analytical balance or analytical scale is determined from the assessment of the balance sensitivity, non-linearity, eccentricity, and repeatability. It is good practice to determine the measurement uncertainty at the time and place of installation and it will be reassessed during each balance service/calibration. Any measurement on an analytical balance or analytical scale cannot be considered to be accurate without a declaration of the measurement uncertainty.

The minimum weight of every analytical balance is different, and depends on the performance of the load cell, its location, the ambient conditions and the required weighing accuracy. The minimum weight is the accuracy limit of the instrument below this minimum weight, the relative measurement uncertainty is larger than the required weighing accuracy, and the weighing result cannot be trusted. The relative measurement uncertainty is determined by dividing the absolute weighing uncertainty by the load and is usually expressed as a percentage.

In order to determine the minimum weight for a balance, measurement uncertainty needs to be assessed in the working environment. Alternatively, repeatability, as the dominant source of error in the lower balance range, can be assessed to determine the minimum weight, carried out using a small weight, below 5% of balance capacity.

The MinWeigh function on METTLER TOLEDO analytical balances, implemented by a certified technician, monitors the weight of the sample being added to the balance. If the weight of a sample is below the determined acceptable minimum weight value, the balance display turns red and the weight value is not released.

Precision describes the closeness of two or more measurement values obtained under the same measurement conditions. A balance repeatability test, which determines the standard deviation of a measurement series, can be used to assess precision.

Trueness describes the closeness between a measured value the accepted true value. In the case of an analytical balance, the weight value shown on the balance display is compared to the accepted true value of a calibrated test weight (balance sensitivity test).

For an analytical balance to be accurate, the weighing results must be close to the true value of the applied weight and repeated weighings of the same object must have little scatter. Accuracy requires trueness and precision.

Electrostatic charges can lead to unstable, non-repeatable weighing results. Static electricity causes a force to be exerted on the weighing pan, which directly affects analytical balance results. Electrostatic charging is one of the biggest hidden sources of weighing errors and it is important to be able to recognize when your weighing process may be affected. Signs that electrostatic charges are influencing the weighing cell are unstable balance readings and readings that drift in one direction. In both cases, the balance may be unable to settle or you may have to wait longer than normal for the weight result to be released. You may have also experienced having to add more and more powder to a container to reach the target weight. However, if your sample or container does not dissipate the charge relatively quickly, your results may be subject to error without you being aware. Errors can be from a few milligrams to 100 mg.

METTLER TOLEDO XPR analytical balances incorporate the unique StaticDetect™ function that automatically assesses error in the weighing result due to electrostatic charges on the sample or the container. StaticDetect™ provides a warning if the error exceeds the pre-defined limit.

Read our free white paper: Electrostatic Charges During Weighing

Wherever possible, preventive action should be taken to reduce or eliminate the build-up of static charges on samples and weighing containers, to avoid any errors, instability or the frustratingly slow release of weighing results. Some of the precautions to mitigate static charges include:

• Ensuring adequate air humidity (≥ 45%)
• Using antistatic weighing containers (metal is ideal)
• Avoiding rubbing containers
• Using a metal dish with high sides to help shield the sample from electric fields
• Discharging the sample and container with an ionizer before weighing

METTLER TOLEDO XPR analytical balances incorporate the patented StaticDetect™ sensor, which automatically detects electrostatic charge on a sample and/or its container. The balance measures the weighing error and provides a warning if the user-defined limit is exceeded. Synchronized operation of an ionizer with StaticDetect automatically removes electrostatic charge on the object being weighed.

Click here to read additional information on electrostatic charges and the physics behind it.

METTLER TOLEDO's XPR analytical balances and analytical scales can be fitted with the optional liquid dispensing module. This laboratory liquid dispenser doses liquid directly into a container on the XPR analytical balance weighing pan. By using the density of the liquid and the ambient temperature, the weight of the liquid is interpreted as a volume. The advantage of the XPR automatic laboratory liquid dispenser is that when making a solution of a desired concentration, the precise amount of liquid can be added according to the actual dosed quantity of substance to create highly accurate solutions.

The range of an analytical balance or analytical scale is the maximum amount that can be weighed on that balance, i.e. the weighing range, otherwise known as the balance capacity. When selecting an analytical balance, careful consideration should be given to the maximum amount that you may want to weigh, including the weight of the tare container. A 200 g analytical balance is a common choice, enabling small samples to be weighed in relatively large containers. For more information, please refer to the question below.

The most common capacity of an analytical balance or analytical scale is 200 g, although there are many models available with a capacity of 100 g and 300 g. METTLER TOLEDO analytical balances actually offer capacities from 52 g up to 520 g. The extra grams of capacity are to account for the use of a tare container. However, an analytical balance is defined according to its readability, which must be 4 decimal places (0.1 mg) or more. On METTLER TOLEDO analytical balances, the numbers in the model name provide an indication of the capacity, with the last number specifying the number of decimal places of readability. For example, the XPR205 is a 200 g analytical balance (220 g in practice) with 5 decimal place readability (0.01 mg) and the MS104TS is a 100 g analytical balance (120 g in practice) with 4 decimal place readability (0.1 mg).

The C in the model's name XPR226CDR indicates that it is a comparator analytical balance. The XPR226CDR is a high-performance analytical balance, specially selected for its extremely high accuracy. It is the instrument of choice for high-precision mass measurement applications by mass determination laboratories and weight calibration service providers. In these applications, weights are compared to reference weights, hence the name comparator balance. However, they can also be used for analytical balance applications where a high degree of accuracy is required.

A 5 digit scale is an analytical balance or analytical scale with a readability of 5 decimal places. The term '5 place balance' is also often used. Five decimal places is 0.00001 g, which equates to 0.01 mg, and is known as the scale division, d. This is the smallest difference in mass that can be determined, but this should not be confused with the smallest amount that can be weighed accurately (for this, please see the question "What is the analytical balance minimum weight?"). It should also be noted that every weight measurement is subject to a degree of uncertainty, which is typically greater than the scale division. A 5 digit scale, or 5 place balance, can be used for the same applications as any analytical balance, but particularly where even smaller samples are to be weighed and a high degree of accuracy is required.

The maximum amount that can be weighed on an analytical balance or analytical scale is limited by the capacity of the balance. METTLER TOLEDO analytical balances offer capacities from 52 g up to 520 g. All our analytical balances are built with overload protection to protect the sensitive weighing cell from damage in case something is dropped on the balance, or an excess load is applied. A warning is provided if the maximum load is exceeded. The smallest amount that can be weighed on an analytical balance depends on a variety of factors, including the desired process tolerance/accuracy. Please refer to the question "What is the analytical balance's minimum weight?"

The analytical balance bubble is typically a small glass dome positioned somewhere on your balance that contains liquid and an air bubble. The analytical balance bubble is used for levelling the balance. It is important to level your analytical balance to ensure your results are accurate. Your analytical balance is precisely engineered to operate in the level position so that the weighing cell registers the full weight of any item placed on it. If your analytical balance is not level, the weight value will deviate from the true value in proportion to the square of the angle of tilt. When looking down on the balance bubble, the bubble should be in the center. If the bubble is not centered, the level can be adjusted by rotating the balance feet until the bubble returns to the central position.

METTLER TOLEDO Excellence and Advanced level analytical balances incorporate graphical levelling guidance that displays which foot needs to be turned in which direction and by how much, making it easy to level the balance perfectly in just a few seconds. Many of our analytical balances no longer even feature the physical balance bubble.

On most METTLER TOLEDO analytical balances, you can find the level bubble at the front of the balance, near the display. On older analytical balance models, the level bubble is located at the right-hand side, towards the rear of the balance. However, many of our newer models of analytical balances feature electronic levelling with an onscreen levelling guide and so the physical levelling bubble is no longer needed.

Analytical balances and analytical scales may be subdivided into analytical balances and micro-analytical balances. By definition, an analytical balance must have at least 4 decimal places of readability or more (0.1 mg or smaller). Analytical balances enable small quantities to be weighed in relatively large containers. METTLER TOLEDO's micro-analytical balances offer 6 decimal place readability (0.001 mg or 1 µg), and due to the higher sensitivity of the weighing cell they have a second inner draft shield and hence a smaller hanging weighing pan. At 32 g and 52 g, the balance capacity is lower than that of an analytical balance.

Occasionally, microbalances are grouped together with analytical balances. However, METTLER TOLEDO classes these separately due to the combination of the higher readability of at least 6 decimal places (1 µg), capacity of just a few grams, and the different balance construction. These balances are typically used for very high accuracy applications where the amount being weighed is extremely small, such as weighing particulate matter on filters and precious metal assays.

METTLER TOLEDO offers a wide range of balances:

1. Ultra-microbalance
   • Readability: 0.5 µg – 0.1 µg (0.0005 mg – 0.0001 mg, 0.0000005 g – 0.0000001 g)
   • Decimal places: 7
   • Minimum weight (5% load, k=2, U=1%): Down to 30 µg (0.03 mg)
   • Draft shield type: Round
   • Capacity range: 2.1 g – 6.1 g
2. Microbalance
   • Readability: 1 µg (0.0001 mg, 0.000001 g)
   • Decimal places: 6
   • Minimum weight (5% load, k=2, U=1%): Down to 82 µg (0.082 mg)
   • Draft shield type: Round
   • Capacity range: 2.1 g – 10.1 g
3. Micro-analytical balance
   • Readability: 1 µg (0.0001 mg, 0.000001 g)
   • Decimal places: 6
   • Minimum weight (5% load, k=2, U=1%): Down to 120 µg (0.12 mg)
   • Draft shield type: Rectangular outer + second rectangular inner
   • Capacity range: 32 g – 52 g
4. Analytical balance
   • Readability: 100 µg – 2 µg (0.1 mg – 0.002 mg, 0.0001 g – 0.000002 g)
   • Decimal places: 4-6
   • Minimum weight (5% load, k=2, U=1%): Down to 600 µg (0.6 mg)
   • Draft shield type: Rectangular
   • Capacity range: 52 g – 520 g
5. Precision balance
   • Readability: 1,000,000 µg – 100 µg (1,000 mg – 0.1 mg, 1 g – 0.0001 g)
   • Decimal places: 0-4
   • Minimum weight (5% load, k=2, U=1%): Down to 12,000 µg (12 mg)
   • Draft shield type: None/ Rectangular for 3 and 4 decimal place readability
   • Capacity range: 120 g – 64 kg

To ensure you select the correct balance for your application, METTLER TOLEDO established the global weighing standard, Good Weighing Practice™ (GWP^®). Our free GWP^® Recommendation service can help you select the right balance that meets your particular application needs and process accuracy requirements.

A digital analytical balance is a modern electronic instrument that processes the weight measurement signal by digital/electronic methods. Digital analytical balances have a digital display where the result is displayed in numbers, in contrast to an analog balance where the result is read from the position of a pointer against a scale. The result on a digital display is unambiguous, whereas reading off an analog scale can give rise to subjective reading errors. However, with an analog scale, it is possible to determine measurement values in fractions of the scale intervals. The smallest possible increment on a digital analytical balance or an analog scale is known as the scale division, d.

The scale division, d, is the smallest possible increment on a measurement scale. On an analytical balance, d equates to the readability of the balance, which is the smallest difference is weight that can be determined. This should not be confused with the minimum weight of the balance. The verification scale division, e, is relevant for Legal for Trade analytical balances and relates to the maximum number of decimal places that can be used for weight results in direct sales transactions. For example, in the case e = d, the weight in a direct sales transaction can be given using the readability of the balance. So if d is 0.001 g, all weight results can be given to 3 decimal places. In the case where e = 10d and d = 0.001 g, weight results can only be given to 2 decimal places, i.e. 0.001 g x 10. In this case, on the display of your analytical balance, you may see the third decimal place of the weight result enclosed in brackets, e.g. 2.67(3) g.