Calibrating precision digital scales, analytical balances and moisture analyzers that rely on accurate weight measurement requires periodic tests using a scale weight closely matching the maximum capacity of the instrument being tested.
Why Testing with Scale Weights is Important
Daily we depend on weighing accuracy – such as visits to the deli counter in the supermarket. We want assurance that the weight shown on the scale is accurate. The U.S. Government’s Weights and Measures Division sets the guidelines.
But in research labs and in food, drug and other production facilities, weighing accuracy assumes a highly critical criterion. This applies to weighing and measuring instruments where readout (the smallest weight difference displayed) and linearity (the ± deviation from the actual weight) are governed by GLP, ISO and other standards.
Adding to challenges, the accuracy of precision weighing and measuring instruments can be … Read the rest
University and industrial laboratory researchers requiring extremely accurate measurements of extremely small quantities rely on a precision instrument called an analytical balance. Shopping for an analytical balance requires being familiar with some of the advanced features available today as well as the proper use of these precision instruments. It is on the second point that we focus this post on how to use an analytical balance.
Here you will learn
- How to set up an analytical balance
- The effect of environment on weighing accuracy
- How samples can introduce errors
- The importance of personal practices
- Important maintenance tips
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 actual sample weight over the weighing range of the … Read the rest
The 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 have
A lot goes into selecting a laboratory balance. Let’s start with weight. You’ll need to select a balance that displays sample weight to the resolution desired. This is described as readout. Readout can be to several decimal places presented in grams or milligrams.
Select a balance with a weighing capacity in excess of the samples you plan to weigh. Some balances also specify the minimum load that can be placed on the weighing plate.
Why is this you ask? If the sample weight is not much larger than the expected weighing error, the measured value will be neither accurate nor repeatable. For this reason the spec sheet for laboratory balances may specify a minimum load. For the Kern ABT 0.1 mg readout balances available with maximum loads of 120, 220 and 320 grams the minimum load is 10 mg. But if you want to weigh samples less than 10 mg … Read the rest
Determining the density of a solid or liquid is easier and more accurate when using a density determination kit with an analytical balance. Analytical balances such as the Kern ABS, AES and ABT models available from Tovatech can be programmed to work in concert with density determination sets, showing the density directly on the analytical balance liquid crystal display.
These density determination kits work on the buoyancy method, based on Archimedes’ Principle and recognized for a high degree of accuracy. As an example, 10 cm3 glass plummet is used for measuring the density liquids, giving a resolution of 0.0001 g/cm3. The density is determined from the weight of the plummet in air and its weight in the liquid being measured.
For solids, the density is the ratio of the object’s weight in air and its volume. Volume is determined by the buoyancy of the sample when immersed … Read the rest
As described by the FDA, stability testing provides evidence of the effect of time and environmental factors on the quality of pharmaceuticals and medicinal products. Such factors include light, humidity and temperature. Stability tests also establish a re-test period for the drug substance or a shelf life for the medicinal product along with recommended storage conditions.
Stability tests are conducted in validated stability chambers such as manufactured by Norlake for pharmaceutical (ICH), biological (BOD), scientific and laboratory applications. These tests, which subject the product samples to variations in temperature and humidity, are conducted during drug product development as well as once a candidate drug reaches use and are governed by current good manufacturing practices (cGMPs). They are regulated in the U.S. by 21 CFR Part 211 Section 166. (www.gmp1st.com/drreg.htm#211.166)
While these tests are conducted in stability test chambers, it is not simply a matter of buying a chamber and plugging … Read the rest