Technical A-Z

By accuracy we mean corresponding to the average value of a series of measurements adjusted for temperature and pressure with the desired value.

Borosilicate glass differs from soda lime glass by using a higher proportion of sand (SiO2). The composition of this glass contains 70-80% silicon dioxide (SiO2), 7-13% boron trioxide (B2O3), 4-8% Na2O and K2O, as well as 2-7% aluminia oxide (Al2O3). Glass with such composition is characterised by a high resistance against acidic attack, low thermal expansion and excellent temperature stability. This glass is particularly suitable for laboratories and chemical use where contact with aggressive materials is likely to be prolonged.

Volumetric glassware is either calibrated to deliver (EX) or to contain (IN).

• EX calibrated to deliver. The delivered liquid corresponds with the volume indication. The liquid that remains on the wall or in the tip of the glassware is taken into consideration.

 EX + s calibrated to deliver after a waiting time (for pipettes 5 or 15 seconds, for burettes 30 seconds).

Keeping to the waiting time is important to avoid mistakes in measurement.

• IN calibrated to contain. The contained liquid corresponds with the volume indication. Example: flasks and cylinders.

• 20°C The calibration has been done at 20°C. Volumetric glassware changes volume about 0,1 % each degree Celsius.

The coefficient of variation is the % value of the precision.

The colour markings on VOLAC FORTUNA® volumetric glassware are applied by silk screen printing. We only use diffusion or enamel colours. The diffusion colour – using amber stain – is completely absorbed into the glass surface during the firing process. It cannot be removed except by processes which remove the glass surface itself. It is therefore resistant to cleansing and even to very aggressive chemicals. The other colours blue and white are enamel or melting colours, which are melted onto the glass surface at high temperature.

Since January 01, 2015, new German Metrology and Verification Regulations have come into force. They replace the previous German Weights and Measures Regulations. For Class A and Class AS Volumetric Glassware which are produced in Germany, a new conformity sign is being used. The H-sign is now replaced by the DE-M -sign. As before, the manufacturer is allowed to certify the conformity on basis of the PTB-regulations (National Metrology Institute). Government institutions will ensure that the regulations are being followed. Therefore, nothing has changed in the production and testing methods. If required, a manufacturer’s declaration of conformity can be enclosed with class A and AS volumetric products.

Laboratory equipment that has been in contact with infectious material should be disinfected before use, for the protection of laboratory workers. It can be washed by hand with a cleaner-disinfectant. Further it can be cleaned by using physical or thermal methods (for 10 minutes at 93°C as required by the BGA). If necessary the glassware can be steam sterilized.

We distinguish between two different graduation types:

• for Class A or AS products: complete ring marks
• for Class B products: short graduations

We read value at the lowest point of the surface, which means when the lowest point of the meniscus touches the upper line of the graduation mark.

For burettes with Schellbach stripes the reading has to be made at the level where the wedge-shaped two points are touching (see picture 2). When reading the scales it is important that one‘s eyes are at height of the fluid level. Otherwise it results in reading errors (parallax errors).

PP – Polypropylene When polymerizing, propylene develops a product which contains methyl side groups of monomers of the paraffin chain. The volume requirement due to the regular methyl side chains is relatively large. For this reason polypropylene is the plastic with the lowest specific weight in compact form. It is similar to polyethylene, and may be used instead of polyethylene, where it particularly depends on good heat resistance, high impact strength, inherent stability during stress or particularly low specific weight. Polypropylene also has a good resistance to many inorganic reagents as well as the less aggressive organic solvents.

Precision is a measure of the variation from the nominal value achieved through a series of measurements at one setting.

To define the different classes (Class A, Class AS, Class B) the following terms are used: ‘accuracy’ and ‘coefficient of variation’ (precision). Sometimes we also speak about ‘tolerances’ which are specified in the ISO- or DIN standards.

Precision Class A: tolerance according to ISO. Class A is the most precise class. Glassware of class A is suitable for official calibration, that means it can be tested by the German Weights and Measures Offices. This is useful for the control of the measuring instruments according to DIN ISO 9001.

Precision Class AS: The waiting time is much shorter than for class A as class A, but for pipettes and burettes fast delivery.

Precision Class B: The tolerances of class B are about twice of the class A and AS. Volumetric glassware of class B is for routine work in the laboratory.

PTFE – Polytetrafluorethylene PTFE has no thermoplastic characteristics although it consists of linear, chemical chain molecules which are not linked. It is not possible to handle or form PTFE in the usual thermoplastic way. Nevertheless PTFE is a thermoplast because it can be sintered. For the production of shaped parts from PTFE the polymer is cold pressed as powder under high pressure into the desired form and sintered at temperatures around 380°C. PTFE is attacked only by elemental fluorine and chlorine tri fluoride at higher temperatures and pressures as well as by melting alkali metals. Otherwise it is resistant to all chemicals. A further advantage of polytetrafluorethylene: it has got the lowest coefficient of friction of all solids. However above 350°C PTFE burns in air to form noxious gases.

What is understood by quality? In general usage the term ‘Quality’ has a number of meanings. Glass products of first class quality might be called this because the finish is good, the raw material used is good, the packaging is good, the appearance is good or the accuracy is good. Quality is defined as having all those characteristics and features of a product, which refers to its suitability for the fulfilment of given requirements, that is ‘fit for purpose’. So Quality is related to the need and the specification set

The Quality Management of Poulten & Graf Product quality is directly dependent on the quality of the production process. Quality assurance must begin in the very first phase of the creation process and cover all subsequent phases. Our global focus on quality assurance, involving all aspects of production, design, testing, packing and conformity with both internal standards and externally set specifications, is the basis of our quality management. This is reflected in the approvals of DIN EN ISO 9001/2015, which we have achieved and which we maintain.

Important safety instructions:

1. In the context of the inspection of incoming goods, users should check laboratory instruments before application to ensure proper functioning.

2. Within the daily laboratory routine, laboratory instruments should always be examined for damage in order to avoid risk of injury. Damaged laboratory instruments will be dangerous for the user due to the risk of cuts, burns and infection.

3. Damaged volumetric glassware such as volumetric flasks, pipettes and measuring cylinders should never be repaired. The effects of heat can leave stress in the glass (high risk of breakage!) and changes the volume.

4. Avoid sudden changes of temperature during handling of the glassware (especially, thick walled glassware has to be cooled down slowly).

5. Before using glass equipment in a vacuum or under pressure it must always be inspected visually. Damaged glassware (e.g. with scratches) should not be used for work under pressure or in a vacuum. Glass equipment that is under pressure or in a vacuum (e.g. filter flasks) must be handled with care to avoid damaging the surface.

7. Avoid sudden changes in pressure, that means vent items that are in a vacuum, smoothly. Laboratory glassware with flat bottoms, e.g. Erlenmeyer flasks, should not be used under pressure or in a vacuum.

Please note that we offer plastic coated volumetric glassware to minimize risks when using glass in the laboratory.

Soda Lime glass finds its use in the foodstuffs industry as bottle and preserve glass as well as in the laboratory industry. The chemical composition of this glass consists of 71-75 % sand (SiO2), 12-16 % soda and 10-15 % of lime. Soda lime glass is subject to acute stress under heat shock and has a relatively high coefficient of expansion. It is particularly resistant to alkaline liquids.

Steam sterilization refers to the DIN 58 900,Pt.1,1986 ‘the destruction or irreversible inactivation of all microorganisms of 120°C and 2 bar’. At a sterilization temperature of 121°C the glassware should be sterilized for 20 minutes minimum effective application time. Laboratory equipment should be always cleaned carefully before steam sterilization, otherwise any soiling will bake on during the steam sterilization. If there are any chemicals on the surface of the glassware during the sterilization they can damage the glass due to the high temperatures. Containers should be opened during the sterilization to avoid a build-up of pressure. The steam has to have unrestricted access to all contamined points to ensure an effective steam sterilization.

When manufacturing pharmaceutical products or intermediates which may either be exported into US markets or which are made by companies being audited by US authorities, such as the Food and Drug Administration (FDA), it is a written requirement of the FDA that volumetric glass used in laboratories for control purposes must conform to the standards laid down within the US Pharmacopoeia.

The standards of accuracy for volumetric glass laid down by the US Pharmacopoeia are not always the same as those laid down by ISO. DIN standards are never the same as USP. Each individual piece of USP Class A glass is individually tested and carries its own individual number. Not only does this offer full traceability, but it also permits all laboratory work to be done with identifiable and identified equipment. Accuracy to USP Class A standards is guaranteed. A calibration certificate is not normally supplied. Individual works certification can be provided at extra cost.

All VOLAC FORTUNA® conformity approved volumetric glassware is delivered with the VOLAC FORTUNA® Batch Certificate of Performance. A regular control of all testing equipment is claimed in the DIN EN ISO 9001. The demand for traceability is fulfilled with the lot number and the batch certificate. Beside the conformity sign all VOLAC FORTUNA® volumetric glassware is marked with the individual lot number that allows an exact classification back to the batch certificate. If your certificate is lost, you may ask for a copy by informing us about the product details and the batch number.