Hi all,

 

I have a very stupid question. I have an overnight culture and I want to measure its absorbance at spectrophotometer. Since I want to adjust the density of the culture to a specific value of absorbance, I need to diluite or concentrate my samples with water depending on which absorbance value I get. My question is: do I need to change the cuvette everytime even if it is the same sample diluited or concentrated? If no, how do I wash the cuvette? I use the plastic cuvettes.

 

Thanks in advance.

 

Silvia

Concentrating cultures typically increases the error, so measurements below the detection limit typically are not terribly useful. For other measurements it depends largely on how precise your measurements need to be. Again, cultures are typically not that accurate so that re-using the cuvette is normally not an issue, if you go from the low to the high concentrated sample.

 

That all being said, typically labs are using standard methods in order to ensure reproducibility and I would advise you to talk to your supervisor what the standard protocol is.

So, you say that if I use a more concentrated sample I can even re-use the same cuvette...cant' I?

 

Thanks,

 

Silvia

Think about the following conditions:

- measure low concentrated sample then one with high concentration

- measure samples with relatively close concentrations

- measure high then low concentrated samples.

 

How would you rank these situations in terms of potential measurement errors?

well,

 

I think that the third condition you mentioned is that affecting the measurements most because of some residuals possibly left in the cuvette by the other higher concentrated sample.

then the second condition and lastly the first you mentioned..this latter should be that affecting the higher concentrated sample least..

 

so, the ranking in terms of potential measurement errors should be like this

-measure high then low concentrated samples

- measure samples with relatively close concentrations

- measure low concentrated sample then one with high concentration

 

Is it right?

That is correct. And again, it will depend on how precise your measurements need to be.