- What is the difference between soda glass and neutral glass?
Soda glass contains more soda ash (Na2O) and less boron and silica than neutral glass. Glasses with a high percentage of boron and silica are known as borosilicate glass. Soda glass is less tolerant of rapid temperature changes and has an active surface chemistry rather than an inert or neutral glass. The surface chemistry is assessed by measuring the hydrolytic activity of the glass with water, i.e. is it affected by water? Water has a far greater reaction than most acids. Soda glass is cheaper and easier to form and cut, it is correspondingly less expensive and is adequate for many purposes. Customers using glass vials for diagnostic purposes or as dropper bottles will need to use neutral glass.
- Why does a freeze dry stopper have a groove near the base but an injection stopper does not?
During freeze drying moisture needs to be extracted or released from the bottle, as this is happening the stopper is partially inserted allowing the water vapour to escape via the groove. When freeze drying is complete the stopper is pushed fully home to seal the vial and therefore prevent the ingress of moisture as vacuum is removed and the vials warms up. An injection stopper is used to seal the vial but the top can be pierced by a needle, when the needle is withdrawn the rubber ‘heals’ itself by closing up and re-sealing the vial.
- What is the difference between moulded and tubular vials?
Moulded vials are hot formed by injecting a ‘gob’ of molten glass into a mould, this gob is then pre-formed then blown out with compressed air to fill the mould, when cooled the mould is opened and the vial or bottle is removed. Tubular vials are converted from long sections of glass tube known as cane, we use machinery to cut this cane into shorter lengths then manipulate the glass into vials or glass dropper pipettes. Large glass melting companies such as Schott draw this tube from their furnaces and sell it to glass converters. Moulded vials tend to be heavier and more durable, being intended for multi use or long term storage, tubular vials aregenerally used as laboratory disposals, i.e. one use only. However tubular vials have their advantages as they are lighter to store and more tolerant of rapid temperature changes (particularly if made from neutral glass).
- Why does glass need annealing?
To make it stable and prevent it breaking spontaneously. As the vials are formed the outer skin of the glass cools faster then its core, this affects the alignment of the molecules within the glass and creates tension and compression internally within the same piece of glass, this is know as strain and can be assessed using a strain gauge. A strain gauge uses polarised light to show the different refractive indices within a piece of glass, this causes the light to split into primary colours in the same manner as a prism.
Tubular vials with their thin sidewalls and thick threads exacerbate this situation, the solution is to anneal the glass, to do this we must heat it to above its strain point, at which point the molecules re-align, the glass is then cooled slowly rather than rapidly and the skin cools at a closer rate to the core and reduces the strain, extended annealing can remove strain totally but this takes a long time or requires expensive plant and space. Glass can be batch annealed in a kiln or can be cooled on a moving belt through an oven known as a lehr.
- I have been asked to obtain 5ml vials with a crimp neck that have been "clean room packed". Do I need to make sure that any company I buy these from has ‘10,000’ certification?
Possibly, “10,000” certification is one of the classifications used for clean rooms. In simple terms it relates to the number of airborne particles in a cubic metre of air, those particles being 0.1 um or less in size, a 1,000 standard would be cleaner and a 100,000 less clean. It is important to know that ISO 14644-1 superseded this standard in November of 2002; the table shown below illustrates the comparisons between the standards. There are two options when selecting vials, you can seek vials packed in such a clean room provided they were sterile before being packed, such an environment is expensive with the costs invariably being passed on to the customer. At Wheaton UK we pack in a clean room with staff adhering to strict dress code and hygiene procedures, but we cannot guarantee sterility, if a customer needs sterile vials then this is best achieved as a secondary process. Sterilisation can be achieved more economically in this way with the choice of method being chosen by the customer according to product type and application, irradiation and autoclaving are the two most used methods with certification being available from either. Many customers choose to autoclave the product themselves prior to use but we can provide irradiated product if requested.
Airborne Particulate Cleanliness Class ComparisonISO 14644-1FED STD 209E1231M1.5410M2.55100M3.561,000M4.5710,000M5.58100,000M6.59
- I have been told that storage conditions can cause deterioration of glass, is this true and does it apply to microscope slides?
Yes, all glass starts to deteriorate as soon as it has cooled! The type and rate of deterioration varies with the glass type, but in our industry we need only be concerned with soda glass. All soda glass, including microscope slides, suffers deterioration to its surface, but if it is kept dry then the effect is rarely seen. If the glass is regularly washed, as in window or container glass then the effects can be removed. The reasons for this are the active surface chemistry of the glass, because of the high content of soda ash (NA2O) in the mix the glass has free sodium ions available at its surface, calcium and potassium can also be available dependent on the glass type). If moisture is available then it can react with the sodium to form calcium hydroxide, this in turn can react with sulphur in the atmosphere to form calcium sulphate, this shows as a greasy bloom on the glass surface. The sulphates in particular can cause smearing and poor wettability on microscope slides. The moisture can be made available by storing glass in damp conditions or by allowing the storage temperature to rise and fall around the ‘dew point’ of the atmosphere, this results in condensation. At LSL we keep all our glassware in dry and heated storage areas to prevent such damage, microscope slides are stored in a dehumidified atmosphere to maximise their shelf life.
- What is different about EPA vials?
The vials are quite straightforward, but there is a classification system to denote their level of cleanliness. The Environmental Protection Agency (EPA) is responsible for the monitoring of analytical standards used for environmental analysis in the UK, much of this dealing with the testing of water supplies. For this purpose the vials used for this type of analysis must be free of the chemicals and volatiles that samples are being tested for. For this reason the vials are also referred to as Volatile Organic Analysis (VOA). The vials are defined by their size, volume, and degree of cleanliness.
Class 100, as made and sold by Wheaton UK are supplied pre-assembled and shrink wrapped in clean room packaging after initial cleaning (annealing at up to 600°C for 20 minutes). This is sufficient for most users.
Class 200 are used for identifying trace amounts and are subjected to a controlled washing procedure, they are supplied with certification of the washing process.
Class 300 have a certification of batch analysis for the vials supplied.