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Q: Klett-Unit???

Rafael Maldonado rafael at howard.genetics.utah.edu
Tue Nov 14 23:21:37 EST 1995

There are too many misconceptions with Klett Units and spectophotometer 
units about mesuring the age of a culture. 

On 14 Nov 1995, Doerner Wolfgang wrote:

> Hi Netters,
> anyone out there who knows what a Klett-Unit is? We guess that it might be
> a unit for spectroscopical measurements, but we have not yet been able to
> find it in the respective literature! Any hints are appreciated, please
> mail to:
>                    appel at mailer.uni-marburg.de

The complete name is Klett-Summerson photoelectric colorimeter. It is an 
old fashioned spectophotometer. To mesure OD in a given wavelength, a 
filter should be used. So mesurements in Klett units should include the 
filter used, as we do with the OD in a spec: OD600 nm, or filter D30 of 
the Klett colorimeter. Since the colorimeter includes two filters, D10 ( 
420 nm) and D35 (540 nm), the mesurements of cultures were made at 540 
nm, more or less...

On Tue, 14 Nov 1995, Ned Mantei wrote:
> I used a Klett spectrophotometer as a student in the 1960's, and even then
> had the impression that the instrument was an old design (1940's?). The
> absorbance was indeed measured in "Klett units", but I don't know how many
> correspond to an O.D. unit

Yes, Klett unit were arbitrary units, and only are valid in Klett 
apparatus. But around the 40's, almost every bacteria lab had that 
machine, so the units were interchangeable among them. It was very useful.

But you can still buy a Klett-Summerson colorimeter. Thomas sells them 
(pag. 357 94-95 catalog). No relation with the company...

On 14 Nov 1995 leverone at CHUMA.CAS.USF.EDU wrote:
> Doerner Wolfgang:  Yes!  A Klett unit is a measurement of optical
> density.  20 klett units are equal to 0.1 optical density at a wavelength
> of 540 nm.  Marianne Leverone, Biology, University of South Florida,
> Tampa, FL

On 14 Nov 1995, Hiranya Roychowdhury wrote:
> Klett unit is mesured in a specially designed flask with a slanted blind
> side arm. The spectrophotometer used for this purpose is also an
> old-fashioned one specially designed for reading off the Klett flask, and
> is called "Klett meter' (I think). The OD may be read at varying ranges
> but is normally at the 550nm for bacterial cultures and the read out is in
> 'Kletts'. I may be slightly off, but I think 1 Klett = 0.004 O.D.
> (Absorbance/turbidity) units at the above wavelength as measured in a
> regular machine.

Wrong! Klett units are only valid in Klett colorimeters. Klett units were 
interchangeable among diferent Klett machines, because all of them were 
the same make and the same model.. But OD IS NOT 
interchangeable among spectrophotometers, because the disposition of the 
lamp and the cuvette and the reader make all numbers change. You are not 
mesuring light absorbance, but light scatering, in a culture. That makes 
the OD unit as arbitrary as Klett units, and OD units are only reliable 
in your own machine and on your own strain, after counting how many cells 
correspond to OD in your machine.

By the way, those flasks which Hiranya talked about are really useful. 
You can measure the turbidity without open the flask; of course, you 
could use some tubes for mesuring, as we use cuvettes in modern spec.


Rafael Maldonado                             |  La cita ha sido
room 6160 Eccles Institute of Human Genetics |  
Department of Human Genetics		     |  retirada por respeto
University of Utah			     |
Salt Lake City, Utah 84112. USA.	     |  a la propiedad 
Rafael.Maldonado at genetics.utah.edu           |
Rafael at howard.genetics.utah.edu	             |  intelectual.
Tel: 801-581-4429			     |
Fax: 801-585-3910			     |

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