Volumetric Material Calibration

November 3, 2021

Volumetric material calibration is an operation typical of a quality system. Bulk materials are typically glass items to facilitate proper dosage or formulation. It is a material widely used in physical-chemical, clinical and R&D laboratories. The volumetric material quantifies a certain volume by means of a printed scale, or by means of dosing mechanisms. In glass elements such as (*) flasks, burettes or other volumes, both the ambient temperature and a correct interpretation of the “meniscus” are essential for a good repeatability of the measurements. In measuring elements such as pipettes, ambient temperature and other sources of error are those that must be considered in order to make a correct estimation of the uncertainty.

In microbiology laboratories, volumetric tools such as pipettes, test tubes, beakers, tubes are commonly used. This material can be both single-use and reusable and is used for measuring volumes that can then directly affect the results of the tests. essays.

Obviously, this material must be cleaned and, if necessary, sterilized in a correct and documented way. Sterilization is normally carried out using the autoclave, which must generally be kept at 121ºC for a minimum time of 15 minutes. Dry heat sterilization (1 hour at 170ºC) or even the use of suitable chemicals is also appropriate.

In the case of using disposable materials, it must be guaranteed that the needs of sterility and the absence of substances that inhibit the growth of microorganisms are met.

To ensure the suitability of this equipment, it is not enough to acquire the best brands on the market, it is not even enough to use controls systematically, it is only possible to know in depth the operation of the equipment if each of its metrological characteristics is studied, for this reason, its calibration is necessary.

Table of Contents

Volumetric material

The exact measurement of volumes and their control in chemical laboratories is the objective of the use of volumetric materials. Therein lies its importance in knowing the errors provided by these types of volumetric materials applied in their routine uses, for this reason they require continuous calibration to ensure the reported results of their applications.

Remember that calibration consists of comparing a traceable reference standard with the measure of the measurand. When volumetric materials are calibrated, the reliability of their measurements is ensured within the control of the processes in which these measuring instruments intervene.

A variety of laboratory materials are used in a chemistry laboratory. Those used to measure volumes are classified as volumetric material.

Most are made of glass to allow viewing of the liquid or liquids to be measured. Although in some cases transparent plastic is used, either because of its low price, or to avoid a reaction between the liquid and the glass (for example when measuring hydrofluoric acid). But it should be noted that, in general, they have a lower precision.

Calibration process

The calibration is carried out by the gravimetric method, weighing the liquid taken by the tool and calculating the errors associated with the measurement, the method is based on the determination of the volume of water contained or discharged by the container. This volume of water is determined through the measured mass and the density expressed in the instruction as a function of temperature.

The entire process that involves handling the volumetric material must be carried out with clean cotton gloves to prevent fat or other substances from adhering to the instruments.

At least three capacity points shall be taken on volumetric tools with various reading capacities. In the case of tools with only one capacity, this will be taken for this purpose.

For each volume to be calibrated, 10 weighings must be carried out but, before starting the weighing, it must be ensured that the tool is completely dry (drying it if necessary). This value is constant for the following iterations.

In the case of pipettes and burettes, the measurement of the contained volume is carried out by discharging the desired content into a container, using the pouring method. In this case, the vacuum weighing is replaced by the value 0 and the dry container is tared into which the content of the volumetric tool to be calibrated is poured. A dry container must be used before tare for each iteration.

gravimetric method

The gravimetric method is the standard method used by both the National Institutes of Metrology (INM) and accredited laboratories to calibrate volume instruments. The method consists of weighing the instrument under calibration when it is empty and again when it is full.

The procedures adopted the use of the reference lines or marks in order to provide an accurate measurement of the liquid volume and the drainage or drying procedures must be followed carefully because they all affect the measurement.

The difference obtained in the weighing measurements of the mass of liquid contained or delivered. The Liquid used is generally pure water (distilled, bi-distilled or deionized) with a conductivity lower than 5 μS / cm [2] and chosen to suit the level of accuracy required in relation to the amount of water used.

 

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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