Happy New Year

Happy New Year!!

 

P&R Labpak are open for business on Monday 5th January but would like to wish all it's customers and contacts a very Happy New Year for 2015.

 

Normal blog posts will commence 9th January.

 

 

Christmas Closure

P&R Labpak closes on Tuesday 24th December 2013 and re-opens on 2nd January 2014. There will be no deliveries during this period.

P&R Labpak would like to take this opportunity now to thank you for your custom this year, and look forward to continuing our relationships in 2014.

We hope you've enjoyed our blog posts over the last year and hope you will continue to read them in future.  If you want us to feature anything or try and answer a question for you then let us know.

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The amazing properties of Borosilicate Glass

Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion (~3 × 10⁻⁶ /°C at 20°C), making them resistant to thermal shock, more so than any other common glass. Such glass is less subject to thermal stress and is commonly used for the construction of reagent bottles, flasks, beakers and many other laboratory glassware items. Borosilicate glass is sold under such trade names as Pyrex, Schott & Simax.

 

Borosilicate glass was first developed by German glassmaker Otto Schott in the late 19th century and sold under the brand name "Duran" in 1893. After Corning Glass Works introduced Pyrex in 1915, the name became a synonym for borosilicate glass in the English-speaking world.

Chemical Properties
Borosilicate glass has a very high resistance to attack from water, acids, salt solutions, halogens and organic solvents. Only hydrofluoric acid, hot concentrated phosphoric acid and strong alkaline solutions cause appreciable corrosion of the glass.

Hydrolytic resistance For many applications, it is important that laboratory glassware has excellent hydrolytic resistance; e.g. during steam sterilisation procedures, where repeated exposure to water vapour at high temperature can leach out alkali (Na+) ions. Pyrex borosilicate glass for example has a relatively low alkali metal oxide content and consequently a high resistance to attack from water. Pyrex fits into Class 1 of glasses for hydrolytic resistance according to ISO 719 (98°C) and ISO 720 (121°C).

Acid resistance
Glasses with a high percentage weight of silica (SiO2) are less likely to be attacked by acids. Pyrex borosilicate glass is over 80% silica and therefore remarkably resistant to acids (with the exception of hot concentrated phosphoric acid and hydrofluoric acid). Glass is separated into 4 acid resistance classes and Pyrex corresponds to Class 1 in accordance with DIN 12116 and meets the requirements of ISO 1776.

Alkali resistance
Alkaline solutions attack all glasses and Pyrex can be classified as moderately resistant. The alkali resistance of Pyrex borosilicate glass meets Class 2 requirements as defined by ISO 695 and DIN 52322.

High usage temperature

           

The maximum permissible operating temperature for DURAN® borosilicate glass is 500 °C. Above a temperature of 525 °C the glass begins to soften and above a temperature of 860 °C it changes to the liquid state.

DURAN® can be cooled down to the maximum possible negative temperature and is therefore suitable for use with liquid nitrogen (approx. – 196 °C). During such use/ freezing. In general DURAN® products are recommended for use down to – 70 °C. During thawing ensure that the temperature difference does not exceed 100 K.

 

The link below shows how Duran glass is made
http://www.duran-group.com/en/about-duran/how-duran-is-made.html

For more information visit
http://www.scilabware.com/Glass_technical/
http://www.duran-group.com/en/about-duran/duran-properties.html
http://en.wikipedia.org/wiki/Borosilicate_glass

Safe Handling of Liquid Nitrogen

Handling Liquid Nitrogen

 

Hazards

Liquid nitrogen has two main properties that are potentially hazardous:-

• It’s extremely cold. At atmospheric pressure, liquid nitrogen boils at -196°C.

• Small amounts of liquid vaporise into large amounts of gas. Roughly 700 times expansion.

Cold Burns

Extremely low temperatures can freeze flesh very rapidly. When spilled on a surface the liquid tends to cover it completely and intimately, cooling a large area. The gas issuing from the liquid is also extremely cold. Delicate tissue like eyes can be damaged by exposure to cold gas alone which would be too brief to affect skin.

Unprotected body parts contacting objects cooled by liquid nitrogen may stick fast. This may result in flesh injuries whilst attempting to withdraw from the object.

It is often stated that small splashes of Liquid Nitrogen will run off bare skin due to a vapour layer forming between the skin and the liquid. This must never be relied upon.

Asphyxiation

Liquid Nitrogen rapidly vaporises to gas.  The gas may has the potential to kill by asphyxiation. When the Oxygen concentration in air is sufficiently low, a person can become unconscious without any warning symptoms.

Over Pressure

Because Liquid Nitrogen boils rapidly users must ensure that it is never used in a closed system.  Tape exposed glass parts to minimise the hazard of flying glass shards. Therefore do not use thermos flasks, and it may be necessary to punch holes in cryovials.

Cryotube Explosions

Cryotubes used to contain samples stored under liquid nitrogen may explode without warning. Tube explosions are thought to be caused by liquid nitrogen entering the tube through minute cracks and then expanding rapidly as the tube thaws

When thawing Cryotubes take the following precautions :

• Wear a face shield, or at least safety goggles.

• Wear heavy gloves.
• Wear a lab coat and trousers or long skirt.
• Place the Cryotube in a heavy-walled container (e.g., a desiccator) or behind a safety shield while it is thawing.

Embrittlement.

Many ordinary materials cannot withstand cryogenic temperatures. Never dispose of cryogenic liquids down the drain. Materials exposed to cryogenic temperatures for long periods or which have undergone periodic warming and freezing should be examined for cracks and crazing.

Lifts

It is unlikely that a Dewar will spill its contents whilst in a lift thus putting the handler at risk of injury or death. It’s also unlikely a lift will breakdown whilst one is being transported. There is a small risk that should a person remain in a closed lift for a prolonged time the venting gases may reduce the Oxygen level sufficiently to cause harm. However to eliminate these risks the following practice should be followed when transporting Dewars.

• No one should accompany the Dewar.

• One person should send and another should receive the Dewar from the lift.

Precautions

Storage of Dewars
Dewars should not be stored in sealed rooms (e.g. walk in refrigerated rooms) because the reduced ventilation may be inadequate to mitigate against spillage and general evaporation.

Containers

Use only containers designed for low-temperature liquids.

Cryogenic containers (eg Dewars) are designed to withstand the rapid changes and extreme temperature differences encountered in working with Liquid Nitrogen. However, these special containers should be filled SLOWLY to minimise the internal stresses that occur when any material is cooled. Excessive internal stresses can damage the container.

• Do not cover or plug the entrance opening of any Liquid Nitrogen refrigerator or Dewar.

• Do not use any stopper or other device that would interfere with venting of gas.

Cryogenic liquid containers are generally designed to operate with little or no internal pressure. Inadequate venting can result in excessive gas pressure which could damage or burst the container. Check the unit periodically to be sure that venting is not restricted by accumulated ice or frost.

Protective Clothing

When using or decanting Liquid Nitrogen a face shield or safety goggles must be used.

Always wear appropriate cryogenic gloves when handling anything that is, or may have been, in immediate contact with Liquid Nitrogen. Use tongs to withdraw objects immersed in the liquid, and handle the object carefully. Do not put hands (even in the best gloves) into Liquid Nitrogen.

Inadequate protective clothing can absorb the Liquid Nitrogen and result in even more severe burns than would otherwise have resulted.

Training

Safety precautions must be followed to avoid potential injury or damage. Do not attempt to handle liquid nitrogen until you fully understand the potential hazards, their consequences, and the related safety precautions.

Decanting of Liquid Nitrogen

Never overfill Dewars. Spillage damages flooring and may cause injury. Insert pipes and funnels slowly to avoid splashing. Great care should be exercised to ensure that space is left to replace lids/tops on Dewars especially those that insert a considerable distance into the vessel. Spills and splashes can set off oxygen monitors

Maintenance of Dewars

Condensed moisture or frost on the outer shell of a refrigerator or Dewar and abnormally rapid evaporation of the liquid nitrogen are indications of vacuum loss. If vacuum loss is evident or suspected, transfer the materials stored in the unit to another refrigerator as soon as possible and remove the unit from service.

Use correct equipment

Use a phase separator or special filling funnel to prevent splashing and spilling when transferring Liquid Nitrogen into or from a Dewar or refrigerator. The top of the funnel should be partly covered to reduce splashing. Use only small, easily handled Dewars for pouring liquid. When liquid cylinders or other large storage containers are used for filling, follow the instructions supplied with those units and their accessories.

Never use hollow rods or tubes as dipsticks. When a warm tube is inserted into liquid nitrogen, liquid will spout from the bottom of the tube due to vaporisation and rapid expansion of liquid inside the tube. Wooden or solid metal dipsticks are recommended.

Transport

Keep Dewars upright at all times.

Rough handling can cause serious damage to Dewars and refrigerators. To protect the vacuum insulation system, handle containers carefully.

Do not place Liquid Nitrogen containers in closed vehicles where the nitrogen gas that is continuously vented can accumulate.

Disposal

Never dispose of cryogenic liquids down the drain. Allow waste Liquid Nitrogen to evaporate naturally in a fume hood or, preferably, pour the liquid slowly on gravel or bare earth, from which other people are excluded, where it can evaporate without causing damage.

 

Laboratory Plasticware-Physical properties and chemical resistance

The link below is a table showing the physical properties and chemical resistance of plastics including its care and maintenance. Click here.

Our new 2012-2014 catalogue is now available!! Copies are being distributed to customers but if you haven't got yours yet or would like a copy please get in touch.

The new catalogue features a wealth of products catering for all budgets laid out in application based chapters, bringing all of your needs together in one place.

Don't miss out!

All your laboratory consumables, laboratory equipment and more in one place.

What size glove do I need?

Glove Sizing Guide

1.      With hand extended flat, loosely loop measuring tape around the circumference at the knuckles (area indicated in picture)

2.      Keeping measuring tape around the knuckles, make a fist with your hand

3.      Adjust tension to match how you prefer your gloves to fit. (looser for a baggier fit, tighter for a snugger fit).

4.      Record circumference measurement in inches. Match size to chart below. The Sizing Charts below are a general approximation and can be used to assist in glove sizing. When trying on gloves, to be sure a glove fits properly it should:

a) Fit at the base of the fingers
b) Fit comfortable over the extended thumb
c) Fit comfortably at the base of the thumb
d) Not become baggy when you flex your hand

Inches	Women's Size	Men's Size
5-5.5	X-Small
5.5-6.5	Small	X-Small
6.5-7.5	Medium	Small
7.5-8.5	Large	Medium
8.5-9.5	X-Large	Large
9.5-10.5	XX-Large	X-Large
10.5-11.5		XX-Large

pH Measurement theory and Electrodes

pH Measurement

The measurement of pH using a pH Electrode is an age old method that centres around
the perception of a substance as acidic or alkaline and is dependent on the concentration
of the hydrogen Ion (H+) within the substance.

The use of a pH electrode allows this measurement to be expressed in a meaningful way.

Derived from the Sorensen Equation the pH value is defined as a negative logarithm of the H+ concentration in a given solution.

A high H+ Concentration equals: 1mol/L = 10o pH = 0 (ACIDIC)

A low H+ Concentration equals: 10-14 mol/L pH=14 (ALKALINE)

It is therefore simple to measure the pH of a substance and compare it with other substances. pH 0 is extremely acidic, pH 14 is extremely alkaline and pH 7 neutral.

Measuring pH Values

Measuring the pH of a substance requires the use of a pH Electrode and a Reference Electrode. The pH Glass at the end of the electrode acts as the sensing part of the circuit.

The second part of the circuit is the reference electrode. This is a stable point that has a defined potential and is independent of the solution to be measured. The reference electrode fig is made up of a reference element that is commonly a Silver/Silver Chloride wire encased in a known electrolyte. The reference electrode then has a junction, which is the contact between the stable internal reference electrode and the solution to be measured. This is commonly a porous ceramic pin.

The evolution of pH electrodes came with the joining of the two separate electrodes to produce the COMBINATION pH ELECTRODE. The formation of the combination electrode can be seen below. The formation of the combination electrode still has the pH Glass membrane acting in the same way. The reference electrode is continually encased around the pH electrode. As the pH Glass comes into contact with an aqueous substance to measure, a gel layer forms on the membrane. This also happens on the inside of the glass layer. The pH value of the aqueous solution will either force Hydrogen Ions out of the Gel layer or into this layer. The Internal buffer in the glass electrode has a constant pH value and this keeps the potential at the inner surface of the membrane constant. The membrane potential is therefore the difference between the inner and outer charge. If you then factor in the reference electrode with its stable potential you have a combination pH electrode that encapsulates the measuring electrode and reference electrode.

P&R Labpak are able to offer a huge range of electrodes and through it’s electrode supplier Sentek can offer their equivalents which are less expensive and yet are the same or better quality.  Contact us on 0870 034 2055 or e-mail us at sales@prlabs.co.uk with your electrode enquiries.

 

How the pH Electrode Works

As the pH Glass comes into contact with an aqueous substance to measure, a gel layer forms on the membrane.
This also happens on the inside of the glass layer.

The pH value of the aqueous solution will either force Hydrogen Ions out of the Gel layer or into this layer.
The Internal buffer in the glass electrode has a constant pH value and this keeps the potential at the inner
surface of the membrane constant.

The membrane potential is therefore the difference between the inner and outer charge.
If you then factor in the reference electrode with its stable potential you have a combination
pH electrode that encapsulates the measuring electrode and reference electrode.

Visit www.prlabs.co.uk for more information or to contact us.  Check out our news pages for special offers – www.prlabs.co.uk/news

Whatman filter papers - Which one to use?

The download link below is a pdf document detailing which Whatman filter papers to use for which application.  Just click on the link below.

PDF download

If you require any help with filtration just contact our sales desk - sales@prlabs.co.uk or call us on 0870 034 2055.