Sterilization temperature profile

The relationship between temperature and pressure holds true only in the presence of pure steam adulteration with air contributes to a partial pressure but not to the temperature of the steam. Thus, in the presence of air the temperature achieved will reflect the contribution made by the steam and will be lower than that normally attributed to the total pressure recorded. Addition of further steam will raise the temperature but residual air surrounding articles may delay heat penetration or, if a large amount of air is present, it may collect at the bottom of the sterilizer, completely altering the temperature profile of the sterilizer chamber. It is for these reasons that efficient air removal is a major aim in the design and operation of a boiler-fed steam sterilizer. 

The temperature profile is obtained by placing at least 10 thermocouples distributed in the empty tunnel or batch sterilizer in such a way as to determine heat profiles. In the flames sterilizer the thermocouples should be placed at the level of the ampules. The thermocouple tips should be suspended to avoid contacting any solid surfaces (wall, ceiling, support rods, etc.). A good profile should demonstrate uniform temperatures across the sterilizer. 

In subsequent loaded chamber heat penetration studies, penetration thermocouples should be positioned within the container at the previously determined cold spot. The temperature profile of the container should remain constant among different sterilizing chambers, utilizing steam heat as the sterilizing medium. 

The sterilization process time is determined from the design F value and the product heat transfer data. The sterilization cycle design must be based on the heating characteristics of the load and of containers located in the slowest heating zone of the load. The variation in the rate of heating of the slowest heating zone must be known, so this variation must be determined under fully loaded conditions. The effect of load-to-load variation on the time-temperature profile must also be determined. Then, the statistically worst-case conditions should be used in the final sterilization process design. 

In estimating the sterilization time for the medium, one must define the contamination, the desired degree of apparent sterility, and the time-temperature profile of the medium that is, T = f(t). For typical bacterial spore contaminants, the constants used in most designs have the following values. 

Fig. 20.4 Typical temperature profile of a heat sterilization process.

The Tjt profile of a continuous reactor must be taken into consideration in any practical calculation for a sterilization, since is temperature dependent (Equ. 5.3a). To determine the effective holding time at the sterilization temperature, the following equation is a basic consideration ... 

The initial testing is performed on an empty chamber to measure temperature distribution. The thermodynamic characteristics of the empty sterilizer are depicted in a temperature distribution profile, which will serve to locate hot or cold areas in the sterilizer by mapping the temperatures at various points in the chamber. 

A narrow range is required and is generally acceptable if the variation is less than 10°C ( 2°F) of the mean chamber temperature. Significant temperature deviations greater than 2.5°C ( 4.5°F) of the mean chamber temperature may indicate equipment malfunction. Stratified or entrapped air may also cause significant temperature variations within the sterilizer chamber. Initially, a temperature distribution profile should be established from studies conducted on the empty chamber. Confidence may be gained through repetition, and therefore empty chamber studies should be conducted in triplicate in order to obtain satisfactory assurance of consistent results. 

Subsequent to the empty chamber studies, maximum load temperature distribution studies should be conducted to determine if the load configuration influences the temperature distribution profile obtained from the empty chamber studies. The thermocouples utilized in the heat distribution studies are distributed geometrically in representative horizontal and vertical planes throughout the sterilizer. The geometric center and corners of the sterilizer should also be represented. An additional thermocouple should be placed in the exhaust drain adjacent to the sensor that controls vessel temperature, if possible. 

Where tunnel peak dwell temperature and time are to be used for routine production cycle control, or as back-up control, correlation of sterilizer peak dwell time and temperature with the hottest and coldest profile container must be shown for each run, where applicable. 

D.V. Kilpadl, J.J. Weimar and J.E. Lemons, Colloids Surf. A135 (1998) 89 SD. surface roughness analysis via AFM and mechcinical profile method (a) air-dried, (b) passivated in 30% (by volume) nitric acid for 20 min. at room temperature (c) ibid, heat-sterilized, ibid, (d) re-sterilized, ibid, (e). heat-sterilized. 

The temperature stability profile of imipenem effectively niles out cooling or evaporative crystallization. Antisolvent addition is the obvious choice. The preferred solvent is water because of the need for sterile filtration of the solution to be fed to the crystallizer. A good antisolvent is known to be acetone. In this case, the antisolvent has the important function of reducing the metastable zone width as well as the solubility. 

Multiprobe temperature and humidity distribution profiles should be obtained for empty preconditioning chambers, and temperature penetration profiles should be obtained with probes located within loads. The purpose of these studies is to demonstrate that the load is being uniformly equilibrated to the temperature (and by inference to the humidity) of the sterilizer within the proposed preconditioning time frame. Any serious lack of uniformity detected during validation studies should be investigated and corrected (even if Only by extending the time of the preconditioning cycle). 

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