dilution calculation

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Hello, I have to check this calculation in the paper already published!.

I think dilution of 0.40 mg in 10 mL will give you 0.04 mg/mL. Then to make 1/5, 1/10, 1/25, 1/100 dilution this will give you 0.008, 0.0044, 0.0018, and 0.00044 mg/mL

So I feel they forgot to add zero

Am I right?


Kindly see the statements below:



Standard Preparation and Calibration Curve. Commercially
available standards of cyanidin-3-rutinoside chloride
(keracyanin chloride, 0.40 mg) and cyanidin-3-glucoside chloride
(kuromanin chloride, 0.35 mg) were separately dissolved
in 2% HCl/MeOH solution (v/v) (10 mL), and used as standard
stock solutions for generating calibration curves. The stock
solutions were diluted 1/5, 1/10, 1/25, and 1/100 times in 2%
HCl/MeOH (v/v) to afford 0.08, 0.044, 0.018, and 0.0044 mg/
mL solutions of cyanidin-3-rutinoside chloride and 0.07, 0.035,
0.014, and 0.0035 mg/mL solutions of cyanidin-3-glucoside
chloride, respectively. These four standard solutions and the
stock solution were injected to generate a five point calibration
curve for the two standard compounds separately, using
Millennium chromatography manager. Standard curve was
linear with R2 ) 0.9998. Peak areas of the target compounds
were within the linear range of the curve. Relative standard
deviations for two injections per standard (for set of five
standard solutions) were less than 2.0%.
It certainly looks as if they made an error, but in your calculations the significant figures fluctuate between 1 and 2, and you generate a mysterious extra 4 somewhere along the way.

It is good practise with SI units to use units that do not require long rows of leading zeroes. In this instance, change mg to ug and you will be working with whole numbers most of the time.

Peter
Peter Apps
Strewth! The 1/25th is wrong too... 40/25 = 1.6, not 1.8.

That could have been me, so I shouldn't be critical (we all have our bad days), but basically "we made up some solutions. We think we know their concentrations to within an order of magnitude. We made some dilutions and miscalculated what they are. We did a calibration curve, and because R-squared is a really awful measure of fit (or because we actually did something quite different to what we wrote in the paper) the R-squared value is quite nice. The peak areas of our samples were somewhere in the region of the peak areas of our standards, so if we knew what our standards actually contained, we could do a valid calibration. We can repeat our mistakes to within 2%.
Fortunately we knew that the chances of a reviewer spotting this were pretty small, so we published it anyway."

It's things like this that make me angry when people get over-enthusiastic about the quality of peer review.
Thanks a lot I learned from your reply all.
Peter Apps wrote:
It certainly looks as if they made an error, but in your calculations the significant figures fluctuate between 1 and 2, and you generate a mysterious extra 4 somewhere along the way.

It is good practise with SI units to use units that do not require long rows of leading zeroes. In this instance, change mg to ug and you will be working with whole numbers most of the time.

Peter


Peter,

I think I know where the extra 4 comes from and it is something the drives me crazy, and is usually done in biology settings instead of chemistry settings. Some people do the 1/10 dilution (or written 1:10) by taking 1ml standard and adding 10ml of solvent, which becomes a 1/11 dilution factor.

We even have a piece of equipment here in the lab that if you want it to multiply your results for a 10x sample dilution correctly you have to put in the dilution factor as 1:9 not 1:10. Drives me crazy!
The past is there to guide us into the future, not to dwell in.
Hi James

That's a new one on me, yet another entry in the catalogue of bizarre practices.

Peter
Peter Apps
James Ball wrote

I think I know where the extra 4 comes from and it is something the drives me crazy, and is usually done in biology settings instead of chemistry settings. Some people do the 1/10 dilution (or written 1:10) by taking 1ml standard and adding 10ml of solvent, which becomes a 1/11 dilution factor.


That is a very interesting and disturbing observation and true if we had 1ml of 0.44% diluted with, rather than to 10ml), which would give a 0.040% solution.

However in this case (unless I am missing something ) a 0.40g/ml diluted in this way would actually give a lower concentration.

I still think that you are possibly onto something there with that calculation factor.

Regards

Ralph
Regards

Ralph
James wrote

I think I know where the extra 4 comes from and it is something the drives me crazy, and is usually done in biology settings instead of chemistry settings. Some people do the 1/10 dilution (or written 1:10) by taking 1ml standard and adding 10ml of solvent, which becomes a 1/11 dilution factor.

That is an interesting and disturbing observation.

A 0.040% solution would be achieved by diluting a 0.44% solution by adding 1ml to 10 mls, rather than making up to 10mls.

in this particular case the figures seem the wrong way around, I would expect a more dilute solution if this were the case.

However I still think that you are onto something with those factors, which seem more than a coincident

Regards

Ralph
Regards

Ralph
I was thinking about that even after I posted and it would be more like multiplying with an 11 instead of 10, which just didn't work out. Unless they multiplied by 0.11 instead of 0.1 . I think the 1/10 and 1/100 was just a fumble on the calculator and got propagated by moving the decimal point and was never caught in review.

Or maybe it is just some New New Math that is being taught in the schools now days :)
The past is there to guide us into the future, not to dwell in.
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