List of Articles in the Category Analytical Balance

Avoiding Errors with Analytical Balances

Avoiding Errors with Analytical Balances

Avoiding errors when using analytical balances – or for that matter any weighing instrument – involves the coming together of several practices on the part of the user.  This post focuses on assuring accurate weighing results when using analytical balances with readouts (what is displayed on the instrument) to milligrams.    For an analytical balance such as the KERN ABT 120-4M available from Tovatech it is 0.1 milligram.   Semi-micro balances can display to micrograms or 0.01 milligram.

Accuracy is paramount when weighing to these levels with analytical balances and is often subject to regulation by organizations such as the FDA and professional trade associations.  Technicians must institute practices and procedures to avoid weighing errors and to insure that the displayed weight precisely reflects the weight of the sample.

Selecting and Using Precision Scale Test Weights

Calibrating Scales with Test Weights

Weighing accuracy is a primary criterion for precision scales, analytical balances and moisture analyzers where readout (the smallest weight difference displayed) and linearity (the ± deviation from the actual weight) are governed by GLP, ISO and other standards.  Test weights have a critical role to play when scales  with capacities from milligrams to tons are not automatically internally (see below) calibrated . The type of calibration, whether internal or external, is indicated on scales’ spec sheets.

Analytical Balance Recalibration – A Critical Exercise

analytical balance calibration

Accuracy and precision (there is a difference) in the performance of analytical balances are crucial when weighing extremely small masses such as to 0.1 or 0.01 mg.  Even the smallest deviation in accuracy can throw off critical measurements when compounding, for example, pharmaceuticals and weighing active pharmaceutical ingredients (API).  For this reason analytical balance recalibration exercises and procedures should be carefully spelled out in a company’s standard operating procedures.

The Effect of Gravity on an Analytical Balance

Manufacturers of analytical balances such as the Kern line available from Tovatech call attention to the importance of calibration and recalibration early in their instruction manuals.  Kern points out, for example, that gravitational pull varies throughout the world due to the fact that the world is not a perfect sphere.  This was demonstrated a few years ago by shipping the Kern Gnome to many locations around the world.  The Kern Gnome was accompanied … Read the rest

Selecting Calibration Weights

Test weights can be purchased individually or in sets.

Test weights can be purchased individually or in sets.

Our posts on precision scales, analytical balances and moisture analyzers frequently refer to the importance calibrating these instruments to ensure weighing accuracy.  Some balances such as the Kern ABJ models offered by Tovatech provide automatic internal calibration based on ambient temperature changes or a regular timed basis.  The companion ABS series require external calibration using calibration weights that must be purchased separately.

External calibration, by the way, is not that complex.  Operators do not have to perform adjustments during the exercise.  Procedures are spelled out in operation manuals and usually consist of selecting the “calibration” mode, placing the correct test weight (more below) on the weighing plate and activating the procedure.  The scale will adjust itself.

Why Calibration is Important

It does not take much to throw off the accuracy of an analytical balance.  We cover this in our post on … Read the rest

5 Tips for Using Analytical Balances

The Kern ABT Analytical Balance

The Kern ABT Analytical Balance

Milligram analytical balances such as the Kern models available from Tovatech are among the most sensitive instruments in the laboratory.  In order to comply with good manufacturing practices (GMP) lab personnel must follow specific procedures to ensure weighing accuracy.  Recommend procedures are generally spelled out in analytical balance operations manuals.  Because these brochures go into detail on all aspects of using an analytical balance we offer this brief as a ready reference for new lab personnel and as a reference for the seasoned pro.

Tip No. 1: Start Right

Gravitational pull varies from place to place throughout the world.  Before using an analytical balance it must be calibrated at the location where it will be used.  It must be re-calibrated any time it is moved and it should be re-calibrated on a regular basis.  Some balances are internally calibrated, others externally calibrated.  User manuals provide … Read the rest

Why Calibrating Analytical Balances is Crucial

The Kern Gnome visits Japan where he weighs 307.9 g

The Kern Gnome visits Japan where he weighs 307.9 g

Strong emphasis is placed on the importance of calibrating analytical balances in laboratories, universities and other areas where accurate and precise weighing to 0.1 or 0.01 mg is required. Even though a balance has been calibrated by the manufacturer it must be recalibrated locally.

Why is this so crucial? The results displayed on the balance are impacted by gravity. If Earth were a perfect sphere of uniform density, then gravity would be consistent. But it’s not, which means gravity varies wherever you go. While a person’s weight may not noticeably vary whether in Japan, Germany, Australia or North America, when weighing in milligrams gravity does impact results. And that explains the title of this post.

A Calibration Point Proved by the Kern Gnome

Kern & Sohn, manufacturers of analytical balances and digital scales offered by Tovatech, conducted an interesting experiment … Read the rest

Tips for Analytical Balance Weighing Accuracy

The Kern ABT analytical balance with automatic internal calibration

The Kern ABT analytical balance with automatic internal calibration

Accuracy is a prime if not the prime criterion for analytical balances used in industries such as researching and compounding pharmaceuticals. Analytical balance weighing accuracy is a measure of how close the displayed weight is to the actual weight of samples on the weighing pan.

Two terms apply here. The first is readout, which is the smallest difference in weight that can be read and displayed by the unit. For an analytical balance it is typically 0.1 milligram or 0.001 g. Micro and ultra microbalances can weigh lighter samples.

Accuracy is sometimes confused with precision but it is an incorrect assumption. Precise means that results are consistent. However they may be consistently wrong, and therefore not accurate.

Instead, the second term or criterion to look for is linearity. Linearity is the maximum ± deviation of the displayed sample weight vs. the … Read the rest

Proper Use of Analytical Balances in University Laboratories

Analytical balances are among the most vital pieces of equipment in any modern university laboratory. These delicate instruments display the mass of materials with precision levels as fine as 0.0001 or 0.00001 grams. Students and researchers in fields such as materials analysis and pharmaceutical testing require high precision levels for their experiments. Analytical balances come equipped with transparent enclosures, as even the smallest dust mote or air current can adversely affect the measurements.

Analytical balances are so important to university laboratories that some facilities run daily zoomed-balance-weightscalibrations to be sure that their instruments are delivering accurate results. At the University of Connecticut, a staff member coordinates a verification routine for each balance used in advanced chemistry courses. The school’s chemistry department also arranges for a technical firm to conduct annual inspections of each balance to insure each instrument’s accuracy.

The department also arranges for an “Introductory Balance Talk”, which serves … Read the rest

Practice Makes Perfect: How the Pharmaceutical Industry Uses Precision Scales

kern-pcb-1000-2The primary measure of the effectiveness of a pharmaceutical product is how beneficial it is for the patient, while introducing minimal side effects. A vital part of the pharmaceutical manufacturing process occurs at the quality control stage. A variation of a few milligrams in a powerful drug can mean the difference between a nightmare of side effects, a harmless and ineffective placebo, or a valuable treatment method. The key to ensuring that a “wonder drug” achieves the goals that the developers set out for it is careful measurement via a laboratory scale.

Types of Laboratory Scales
Just as various types of microscopes offer the ability for researchers to see items ranging from bacteria down to molecules, different types of laboratory scales offer the ability to measure items to within very small masses. These scales carry specific names to differentiate their levels of readability:

  • Precision balances vary in resolution and some
Read the rest

Can an Analytical Balance Change Our Views on Mars?

curiosity-roverAs of this writing, the Mars Rover “Curiosity” rolls across the Red Planet at less than ten miles per hour. During the small craft’s journey across the surface of the alien world, its sensors encountered what have been described as “shiny particles” of an unknown origin. At first, NASA scientists assumed that the particles were debris left over from the lander that brought Curiosity to the Martian surface. After further examination, the researchers now believe that the shiny fragments are of Martian origin.

“Rocknest” Findings
When the craft cleared what was believed to be the debris field, its cameras caught more of the glittering crystals. Curiosity explored the rock samples near the site, which NASA researchers have named “Rocknest”, and has begun to examine the lustrous material. In previous missions, including “Sojourner” and “Pathfinder”, the sensors attached to the landers did not find any such glistening particles amongst the dull, … Read the rest