Protein Measurement -- Sources of Error


(See Also Colorimeter Troubleshooting Section)

Low Values:

Reagent Dye Concentration too high.

Check Concentration.

Reference Dye Concentration too low.

Check Concentration by comparing to Reference Dye freshly prepared from Reference Dye Concentrate or a new bottle of Prepared Reference Dye Solution.

Not enough sample.

Check Balance at Zero and with the 1000 mg weight or other appropriate calibration weight.

Commodities values set incorrectly.

Consult UDY Corporation.

Temperature correction not applied correctly.

More than 40.00 ml Reagent Dye dispensed.

To check dispensor, weigh the dispensed Reagent. Weight should be 40.37 "0.08 grams. If the weight is incorrect, consult UDY Corporation for recalibration.

Insufficient reaction time.

Incomplete reaction due to worn out React-R-Tube.

Filtration of sample not giving clear solution.

Protein degraded (deteriorated) or natural protein to non-protein nitrogen ratio altered by environment or processing.

High Values:

Reagent Dye Concentration too low.

Check concentration.

Reference Dye Concentration too high.

Check as in above section.

Too much sample.

Check as in above section.

Commodity values set incorrectly.

Check setting of Zero, K1 and K2 values.

Temperature correction not applied correctly.

Less than 40.00 ml Reagent Dye dispensed.

Check as in above section.

Ten or more minutes elapsed before filtering sample from React-R-Tube.

Interference caused by potassium dichromate preservative. USE UDY-Pol Preservative

Inconsistent Values:

Inconsistent Reagent or Sample amounts.

Check dispensors and balance

Incomplete reaction

Air Bubble(s) in cuvet

Solid particles in cuvet from poor filtering.

Room light and shadows causing varying readings.

Slow drift of reading: Too much sample filtered through filter.

Sample/Reagent Dye mixture filtrate not clear.


Procedures for Commodities Not Listed

Occasionally, instrument settings and procedure values for other Protein Systems are needed. These values and settings can be determined at UDY Corporation See Sheet for Procedure for new sample Set-ups Using UDY Colorimeter.

Moisture Correction

If the percent of moisture of a sample is known, results may be corrected to the percent protein on a dry basis, or other moisture content basis. For moisture on a dry basis, use M = O in the following equation. For moisture on another basis, use the appropriate value for M.

% Protein (%M basis) = (100 - M) x (% Protein measured)/(100 - % H2O sample)

For example, if % Protein measured = 13.4 and %Moisture measured 10.6, then %P (dry basis) = (100 - 0) x (13.4)/(100 - 10.6) = 15.0

Weight Correction

When actual weight of aliquot(s) varies more than -.01 g from that specified, multiply % protein reading by specified weight and divide by actual weight.

For example, Actual reading = 15.00% x 2.75%g (specified sample weight)

2.69% (actual sample weight)

= 15.33% corrected protein

10-Fold Dilutions

During sample preparation, when samples are diluted 10-fold, the amount of diluent to use is nine times the actual sample weight. Place diluent into Blender first, then add the sample.

Sample Volume and Weight

Sample volume and weight, as well as Reagent Dye Volume and weight, may vary when other dispensing systems are used. However, the ratio of Reagent dye weight to sample weight must remain the same if the specified A and CI values are used.

Shaking Times or Reacting Times

Longer shaking times or reacting times may be needed by some products when not reconstituted (i.e. dairy powders or ground material), depending on solubility. To verify adequate time, retest using a longer shaking time.

Factory Calibrations

The UDY Colorimeter is set up at the factory using primary standard dyes at different c concentrations. After one year=s time, it is recommended that you verify the linearity of the Colorimeter by purchasing a Calibration Test Solution Kit(PN 30-0522). This can be purchased from UDY Corporation.

UDY Cuvet and Lamp

If the cuvet is broke, the Colorimeter unit will have to be sent to the UDY Corporation. UDY Corporation will match a new cuvet to the unit and a factory alignment will be performed. Contact the UDY Corporation for more details, pricing, etc.

If the lamp goes out on the Colorimeter, a new LED will have to be installed. UDY Corporation will install a new LED lamp and perform a factory alignment. Contact UDY Corporation for more details, pricing etc.