Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Amber Chang on January 23, 2015, 12:07:36 AM
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Hi, guyes.
I want to know if the vicosity value depends on different viscometers.
My company anthorizes a product to H company.
However, H company and my company get the different viscosity values of the same product.
The instrument and spindle types are as follow.
My company,
Fungilab, visco basic plus R type
Sindle TR8
Stir speed: 10 rpm
viscosity value=3000
H company,
Brookfield DV-II+Pro, LV type
Spindle S34
Stir speed: 10 rpm
viscosity value=4500
Do these results make sense?
I want to know what makes this difference.
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If you want to know what makes the difference, then you need to compare procedure you used and they used. From top of my head it could be in temperature or sample concentration
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Are the two spindles you used (company H and Brookfield) the same size
and surface area?
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If you want to know what makes the difference, then you need to compare procedure you used and they used. From top of my head it could be in temperature or sample concentration
The temperature and sample concentratio are the same.
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Are the two spindles you used (company H and Brookfield) the same size
and surface area?
I know they're similar.
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Absolutely, the viscosity results can be different between two different models of viscometer/rheometer using the same spindle, same rpm, same material/concentration, measured at same temperature, and same exact sample preparation procedure used for each product being measured.
One reason is that the springs inside are not rated the same. For example, the Brookfield DVII+ viscometer/rheometer comes in LV (Low Viscosity) and RV models (Regular Viscosity) with the torque constant for the LV at 0.09373 and torque constant for RV being 1.0 so in effect the LV model is over 10 times more sensitive (1.0/0.09373) for use with lower viscosity samples. Even with same model, two viscometers could give slightly different results if one or both are out of calibration (but likely not 3000 vs 4500 cP unless one spring has been irreversibly strained and needs replacing).
Our QC department had similar issues between our viscosity results and an ingredient supplier and the investigation turned up that the instruments used to measure (both Brookfield LV models) were calibrated well, but temprature was a factor (one country cold and other tropical) but most significant factor affecting variability was the different sample preparation SOPs. So I would say try to find out your model's torque constant, run some silicone oil viscosity standards within (3000-4500 cP range) to test your instrument in conjunction with the other company's instrument. Then if instrument spring's are comparable, start comparing step-by-step the sample preparation procedures.