calculating concentration from absorbance?

[littlelottie]

I have 3ul of a sample of cyctochrome in 497ul buffer with a pathlength of 1cm. Its peak in visible spectra is 530nm at 0.0103 absorbance. The molecular mass of cytochrome is 58 kda and the molar absorption coefficient for the reduced form is 30,900 mol-1 cm-1. Calculate the concentration in mgml-1 of cytochrome

 

So far I have used Beer's law to find the concentration 3.333M but I am a bit confused as to what to do next?

 

Thanks

[Fuzzwood]

Almost, 1000000 ul = 1 litre, and the cytochrome came from the 3 ul sample.

[hermanntrude]

for your information, there is no such thing as a uL. What you're looking for is a microliter, which can be abbreviated like this: µL

 

To get the micro symbol (greek letter mu), hold down alt and press 0181, then release alt. Or use the character map.

[CharonY]

Technically you are correct, of course. However, in many informal exchanges µ is often replaced by u. It is btw. one of the advantages of the Germany keyboard layout to have a µ readily available .

[hermanntrude]

I really think the u shouldn't replace the µ. it doesn't even look the same and it often results in people actually believing it's supposed to be a u, and wondering what on earth that funny µ symbol means. it's not hard to type it even if you're not german

[CharonY]

It is just a pain if you write reports though. I do have a US keyboard but I like to swap it to German for this (and some other purposes). But I understand your concern of potential misunderstanding.

[hermanntrude]

every time i write "µ" i remember that it's the right thing to do and feel a little smug and smile to myself. That way, I don't mind the extra effort.

 

On a more serious note, though, the amount of biologists who, when asked a simple question involving a microliter, havent a clue what you mean but immediately get it when you say "you-ell" drives me nuts.

[CharonY]

What? I say microliter on a routine basis, but have not once heard one actually say "u-L". Not once, really. Although I sometimes abbreviate micrometer by saying "µ" (Greek letter). But I actually picked that up from physicists and chemists.

In fact, I am pretty sure that you would score a lot of blank faces if you said that here (I probably would have thought that you meant "joule").

[John Cuthber]

I really think the u shouldn't replace the µ. it doesn't even look the same and it often results in people actually believing it's supposed to be a u, and wondering what on earth that funny µ symbol means. it's not hard to type it even if you're not german

 

That was going so well until you forgot the capital G in "German".

Please stop feeling a little smug.

The use of u rather than µ dates from the times when reports were typewritten and the Greek characters were not an option. The u was put in as a place marker and the tail added to it later with a pen before the report was photocopied or whatever.

[hermanntrude]

The use of u rather than µ dates from the times when reports were typewritten and the Greek characters were not an option. The u was put in as a place marker and the tail added to it later with a pen before the report was photocopied or whatever.

 

hands up who still uses a typewriter? anyone? no? ah... ok.

[Psycho]

What? I say microliter on a routine basis, but have not once heard one actually say "u-L". Not once, really. Although I sometimes abbreviate micrometer by saying "µ" (Greek letter). But I actually picked that up from physicists and chemists.

In fact, I am pretty sure that you would score a lot of blank faces if you said that here (I probably would have thought that you meant "joule").

Indeed, if you don't understand what a microlitre symbol is then you really can't class yourself as any kind of scientist, not to mention getting it confused with uL, which as anything other than microlitres would be meaningless. The closest I have ever come to confusion is people writting the symbol backwards, which is hardly a misunderstanding just a mistake.

 

hands up who still uses a typewriter? anyone? no? ah... ok.

Hands up people who have laptops without numberpads. Me for one, I have to press 1 key to activate it then the numbers aren't even in right place as it is based on the letter keys, it is just awkward.

[hermanntrude]

Indeed, if you don't understand what a microlitre symbol is then you really can't class yourself as any kind of scientist, not to mention getting it confused with uL, which as anything other than microlitres would be meaningless. The closest I have ever come to confusion is people writting the symbol backwards, which is hardly a misunderstanding just a mistake.

 

Hands up people who have laptops without numberpads. Me for one, I have to press 1 key to activate it then the numbers aren't even in right place as it is based on the letter keys, it is just awkward.

 

I still think that if it's at all possible (and yes, it is, even if you don't have a number pad) to write µ, you should do so. Use the character map if you have to.