I really fail to understand why you are interested in FAU and FTU units and their interconversion to absorbance. I would recommend a very simple method and that is you measure the Absorbance and then using the conventional (tried and tested) MacFarlands method to get the number of cells/ml in the required absorbance. 

Thank you for your reply. Its because the protocol I am trying to replicate prescribes that bacterial suspension has turbidity of 10 FAU, and it doesn't say which absorbance corresponds to that FAU value. So I first need to figure out  what absorbance bacterial suspension of 10 FAU has, so I could simply measure absorbance as you said.  Hope I explained it properly now. 

Formazin was established as the first calibration standard for turbidity meters in the 1950's. A variety of probes are available to measure turbidity; the degree to which light is scattered by particles suspended in a liquid. It depends on the wavelength of light and the angle at which the detector is positioned. The available turbidity probes do not use the same light sources, angles of measurement of scattered light, and signal processing criteria varies for various reasons. To overcome these problem new units of measurement were established in 2004.

 Formazin Nephelometric Unit (FNU) is similar to a Nephelometric Turbidity Unit (NTU) in which both measure scattered light at 90 degrees from the incident light beam. The FNU is measured with an infrared light source according to the ISO 7027 method whereas the NTU is measured with a white light according to EPA method 180.1.

Dear Dragana Čučak,

I am also facing the same problem now as you were in converting FAU to NTU units. Could you figure out how to measure turbidity in FAU units? And how it can be related to NTU?

Thanks

Prasenjit

Dear Prasenjit Ghosh,

I didn't need conversion of FAU to NTU. I had a problem of not knowing what absorbance correlates to 10 FAU (this value is prescribed in one standard method I am doing). In the end I established that suspension of 10 FTU has an absorbance of about 0.06-0.08, so I used this as a guidlines.  

As I understand from this document on the link, FAU is eqivalent to NTU (" One FAU is

equivalent to one Nephelometric Turbidity Unit (NTU) of

Formazin. However, the optical method of measurement for FAU

is very different than the NTU method (1 NTU =

1 FTU = 1 FAU when traced to formazin primary standards.)" 

Hope it helps.

All best,

Dragana

http://www.hach.com/asset-get.download.jsa?id=7639983664

why i determinated different values to elderberry juice concentrate in FNU and NTU? For example in NTU i have 1400 and in FNU 700. 

Dear Dragana,

I am sorry to reply you after so long time. Actually I didn't a notification of your reply. What you are saying is correct. I got to know  from some other sources also that, if we use Formazin as calibration standards in Turbidity measurement, then even if we use Nephelometer for turbidity measurement, FAU and NTu will be same. 

Regards

Prasenjit

Dear Dragana

You mentioned that you established that suspension of 10 FTU at 578 nm has an absorbance of about 0.06-0.08.   Did you measure it with Vibrio fischeri?  Which wavelength and optical length (1 cm cuvette?) did you use?.

Regards, Marina

I think what Marina has pointed out and asking you to reply is very pertinent.

I also encounter the same problem with the relationship of NTU with FAU or AU units, because when I measure turbidity with my prepared suspension, it has different values with NTU and AU. I think AU unit has bigger values than NTU, I still figure out their relationship.

Dear Marina L Nievas ,

sorry for the veeery late reply, I missed the notification.

Yes, I did measure with Vibrio fischeri.

I used 578 nm wavelength in Multiskan GO (Thermo Fisher) microplate reader.

I didn't use cuvette, but flat bottom optically clear microplates.

Under these conditions Vibrio fisheri suspension with 0.06-0.08 apsorbance corresponded to 10 FTU measured on turbidimeter.

I used such suspension with good results for the method I was performing. The method prescribed suspension of V. fischeri of 10 FAU. It is not exactly as prescribed but it worked for me.

All best,

Dragana

One FAU is equivalent to one NTU. Both are same but measurement process is different. In FAU infrared red light is source whereas in NTU white light.

any body here know about the relationship between NTU , temperature of the fluid collected sample and injection rate of the pomp which drive the fluid sample in dynamic condition with time?

So many great info here,

FAU and NTU are unit used to measure scattering by suspended materials. The link to absorption is complicated. For example, if you had only absorbing dissolved material in your sample (e.g. tea) you will measure 0NTU. The number of NTU will go up if you added a white scatterer (e.g. plastic beads) particularly for non-absorbing beads. I hope the above makes sense to you. If the measurement setup is one of attenuation - both scattering and absorption cause attenuation, issues such as wavelength of measurement, acceptance angle of detector etc' could cause large variation between what you assume to be NTU reading and absorption.

Best, Emmanuel