I have a question about the meaning of ambient temperature for my HPLC method. In the method, the temperature is quoted as "ambient" however my colleague told me the column heater should be set at 40°C as this temperature constituted as ambient.

Could anone tell me a definitive answer?

We've had a bit of debate about the definition of ambient around here as well. I've found some references to "standard laboratory temperature" being 21 Celsius but I think more common for ambient temperature is 22 Celsius, so that's what we use here as "ambient". In no way can one consider 40 degrees Celsius as ambient.

Ambient implies that temperature is not controlled.

Agreed, ambient implies the temperature is not controlled but it also implies that it is at the temperature of the surrounding laboratory environment. Since 40 Celsius is equivalent to 104 degrees Fahrenheit, it's doubtful that 40 Celsius could ever be considered "ambient" unless a laboratory was some sort of torture chamber.

The USP has some definitions for controlled room temperature, etc. Most pharmaceutical labs have an SOP allowing ambient methods to be run temperature controlled in the range of controlled room temperature, or something like that.

Another thought. I guess it could depend on the type of column heater you have. Some of the older heaters couldn't really stabilize the temperature unless you set them about 10C above room temp. If the upper end of room temp is about 30C, then this could be the source of the recommendation to set your temp to 40C. Probably not applicable to the newer peltier heaters.

In the past we had the same discussion.

Ones takes 22 ºC as an "ambient" temperature and others takes 25 ºC, depending on what you can consider as a normal temperature.

When we saw that problem we just began to compare what could be considered as an "ambient" temperature if you worked in Finland or in Italy or Mexico.

Since then in our HPLC methods is not allowed to develop a new method at "ambient" temperature and we controled it. We have gained on reproductibility on retention times

You can dfine ambient in many ways. However, the BP defines room temp as between 15C to 25C. If you use this definition you would need some robust methods. I always prefer themostatted methods.

40°C is difficult to accept as 'Ambient'.
As Basil mentioned it depends on WHERE one is working. Normally laboratory Air Cond.. keeps the temperature at about 22-25°C. We prefer to keep the column at controlled temp. ie a minimum 30°C.

In Abuja Nigeria, ambient is 45 deg. C

A good assay is not affected by a temperature change of +- 5°C.

We have a peltier type column temp controller and we set ambient at 25C. While a good method should be robust, there are acceptable methods that can be sensitive (as some companies don't maintain the same temps throughout the day and some labs can have fluctuations greater than 5C in a lab during a day).

While 25 won't give you ideal control, its better than none as your day to day reproducibility may be affected.

What is Peltier type column Temp controller? Recently I downloaded one of the methods which specified that the columm temperature should be 50° C and the Peltier Temp should be 25° C . What purpose may it serve and what does it imply ?

Thanks

A Peltier chip is a solid state device that heats or cools based on the direction of current flowing through it. You can google on the word "Peltier" for more technical info. A Peltier temperature controler can heat or cool a column, without using a resistance heater/compresser driven refriderator. The chips are expensive, and can burn out if abused. I don't know which vendors in particular use the Peltier heater/cooler.

Perkin Elmer has a peltier in one line of Autosamplers. I beleive Agilent does as well.

Hello, I have one query. I have a Varian Nucleosil C18 column, and the pressure has become excessively high (~ 4700 psi) with a flow of 1mL/min; MeOH/H2O solvent mixture.

Since I have been analyzing analytes in high alkalinity (pH10), I tried flushing with high % of water, but it was no use. When I increased the column temperature from 25 to 45 degC, I noticed the pressure dropped to a minimum at 30 degC before rising again by 45 degC. Why is this? Is the temporary drop in pressure due to column expansion, while the vapour pressure of the solvent increases with temperature as well?

Thank you for anyone willing to drop one comment or two.

My opinion is that the column is dead. The remainder are random events not worth thinking about.