Filtration Sterilisation Flashcards
what is filtration?
passage of a fluid (liquid or gas) across a filter, removing any contaminating solutes. You may have the same size filters, but they will be made out of different materials. The composition of the filter may have an effect and the solution that you are filtering. Pore size needs to be smaller than the particles you are wanting to keep. Filters can also remove particles that are slightly smaller then the pore size.
what are the 4 important factors when it comes to filtering?
- ) The angle the particle approaches the pore is important as if it comes at the wrong angle it might not be able to pass through the pore
- ) A sudden rush of particles may mean that neither will be able to pass
- ) Large particle may block the pore so little particle are now unable to get through pore past the big particle
- ) Most bacterial cells are negatively charged, so you could produce a filter with a positive charge and this would cause an attraction.
what is filter voidage?
open area where the particles accumulate. If during the filtering process you see an accumulation of particles at the top of the filter, you have reached the filter voidage and this means the filter is at full capacity.
the capacity depends on number and size of particles
what is a depth filter?
– Non fixable pore size (variable)
– Inertial impaction particles run into it
– High retentive capacity
– Robust
– Cheap
– No sterility cannot guarantee a sterile product, these is no control over this
what is a screen (absolute) filter?
– Uniform pore size (0.8um, 0.45um)
– Direct interception
– Easily blocked
– Fragile
– Expensive (5x the price of a depth filter for a similar size)
– Sterility (only if you use the right porosity - 0.22um)
how can you carry out filter validation?
- bubble point pressure test
- challenge filter with brevundimonas diminuta
what is the bubble point pressure test?
put filter into apparatus with water on top and on the underside introduce some air/gas and gradually increase the amount of air that passes through the filter until you get bubbles forming. Relationship between porosity and the filter
how do you challenge filter with brevundimonas diminuta?
challenge the filter with the biological indicator, most resistant form is your smallest form
• Minimum requirement 107/cm2
• Working capacity 109-10 10cm2
what is moist heat sterilisation?
- death by protein coagulation and hydrolysis
- steam at elevated temperatures (>100 degrees)
- this is used for aqueous products, devices and dressings
what is dry heat sterilisation?
- death by oxidative processes due to absence to moisture/
- slow death process of bacteria
- used for drug powders, oil preparations or glassware
what technology is used for dry heat sterilisation?
- Dry heat ovens – used for batch cooking
* Sterilising tunnels – continuous process
what is the mechanism of heat transfer for dry heat sterilisation?
- Conduction
- Radiation
- Convection
what is the critical aspects of dry heat sterilisation?
- Product size
- Loading pattern – should allow free circulation of air around the products
- Air circulation
what is the dry heat sterilisation cycle?
- Drying – glassware you have washed the oven will warm up and remove any moistue
- Heating – to the heating temperature needed
- Exposure – sterilisation occurs in this part. You know what temperature is needed and you hold the over at this for the set period of time
- Cooling – longest part of the cycle. Could take up to 16 hours from start to finish
what is the technology for moist heat sterilisation?
• Autoclave
- self boiler
- mains stream, stainless steel to maintain the pressure, there will be an external pipe work that brings steam into the chamber
what is the mechanism of heat transfer in moist heat sterilisation?
• Latent heat of vaporisation – steam comes into contact with an object within the chamber, condenses around the object and as it does so there is a vaccum pool which sucks in more steam and the energy from the steam transfers to the product – continuous process until the product is in equilibrium with the steam and has reached the same temperature. As the vacuum pool is growing there is a production of liquid – damp process. Needs to be resistant to moisture (labelling and packagaing)
what are the critical aspects of moist heat sterilisation?
- Air removal – if any air present you are unlikely to get temperature exceeding 100 degrees, need to replace air with steam
- Saturated steam – has a defined moisture content
- Steam under pressure
what are the critical lethal parameters?
- Steam
- Dry saturated NOT wet or superheated (superheated has a much lower moisture content and you are moving more towards oxidative kill so there will be a difference between the amount of cells killed) - Temperature
- Maintained within +/- 5 kelvin of limit - Time of contact
- Sufficient to give >10-6 SAL - Bioburden level
- Nature, number and location of microorganisms.
what is the autoclave operation?
- ) air removal – downward displacement; evacuation. Usually drain at bottom of the autoclave. Bring about same function which is too remove air from chamber snd the product
- ) Heating
- ) Sterilisation / holding period – reach the agreed sterilising temperatures
- ) Cooling down – either natural decay, gradual reduction in temperature of product, or active by pumping in sterile cold air
- ) Drying – product may be damp so you need to dry off any moisture that is on the product
what are the types of autoclave cycles?
- Fluid cycle
- Porous load cycle
- Air ballasted cycle
what is the fluid cycle?
most common
used for aqueous fluid and heat resistant solids.
complete time of around 2 hours from start to finish
what is the porous load cycle?
porous materials like fabrics. Don’t take that long to heat up whole cycle in about 30 minutes but the major issue is because they are fabrics air can get trapped, so crucial part is the air removal, replace air with steam.
what is the air ballasted cycle?
hemephrically sealed products, molten plastic rapidly seals, sealed in sterilised in situe. Completely sealed
what is the master temp record?
a. test load, don’t know whether cycle will work or not so you can tweak your controls to make sure you get a result
b. thermocouples - probes you put in chamber and they measure temps
what is the temperature record chart?
drain probe temp
- drain should always be the coldest part of the chamber, when the drain reaches the right temperature it should mean by default everything else is the right temperature
how many thermcouples are needed in a chamber?
minimum of 12
