What is the difference in calibration between USP and Ph.Eur

1. CONTROL OF WAVELENGTH ACCURACY

to date:

For checking the wavelength accuracy, the following filters are recommended for each wavelength range:

240 – 650 nm: Holmium filter

above 650 nm (730 nm to 870 nm): Didymium filter

below 240 nm (200 nm to 255 nm): Cerium filter

Note:

For UV/Vis spectrophotometers (non-diode array technology), wavelength accuracy and precision must be verified over the operational range

using at least six replicate measurements. The following acceptance criteria apply:

Wavelength Accuracy:

The difference of the calculated mean and the certified value of the reference material (CRM) must be within the following acceptance criteria:

UV range 200 – 400 nm: ±1 nm

Vis/NIR range 400 – 900 nm: ±2 nm

Wavelength Precision:

The calculated standard deviation of the six measured values must not exceed the following acceptance criteria:

UV range 200 – 400 nm: ≤0.5 nm

Vis/NIR range 400 – 900 nm: ≤0.5 nm

 New supplement in USP <857>:

The wavelengths selected for qualification must bracket the intended range for use.

2. CONTROL OF ABSORBANCE ACCURACY

to date:

It is necessary to verify the absorbance accuracy of a system over its intended operational range.

UV range 0 – 1 Abs:

Potassium dichromate solutions with concentrations of 20 – 60 mg/l,

or nicotinic acid solutions with concentrations of 6 – 24 mg/l can be used.

UV range 1 – 3 Abs:

Potassium dichromate solutions with concentrations of 80 – 200 mg/l can be used for checking.

Vis range:
Neutral-density glass filters can be used over the intended application range up to 3 Abs for checking.

New supplements in USP 857

UV range 1 – 3 Abs:
To check the UV range, nicotinic acid solutions with concentrations of 36 – 60 mg/l can be used.

The procedure for control of absorbance is newly regulated in the updated USP:
The absorbance accuracy and precision performance of a UV/Vis spectrophotometer can be determined from the calculated mean and the
standard deviation of six replicate absorbance measurements at specified wavelength.

The verification of the absorbance accuracy and precision should be performed at the upper and lower absorbance of the operational range.

Acceptance criteria for the control of absorbance per reference material:

Potassium dichromate solutions and nicotinic acid solutions for the UV range:

Absorbance Accuracy:
The calculated mean of the six values must not deviate from the certified value of the reference material (CRM) by more than:
0 – 1 Abs: ±0.010 Abs
1 – 3 Abs: ±1.0%

Absorbance Precision:
The calculated standard deviation of the six values must not exceed the following acceptance criteria:
0 – 1 Abs: ≤0.005 Abs
1 – 3 Abs: ≤0.50%

Neutral density glass filter for the Vis range:

Absorbance Accuracy:
The calculated mean of the six values must not deviate from the certified value of the reference material (CRM) by more than:
0 – 1 Abs: ±0.008 Abs
1 – 3 Abs: ≤0.8%

Absorption Precision:
The calculated standard deviation of the six measured values must not exceed the following acceptance criteria:
0 – 1 Abs: ≤0.005 Abs
1 – 3 Abs: ≤0.50%

3. CONTROL OF PHOTOMETRIC LINEARITY

to date:
The control of photometric linearity was required.

New in USP 857, update Dec. 2022:
Checking the photometric linearity is no longer necessary!

The USP writes:
“Demonstrating absorbance accuracy over the system’s intended operational range assures proper photometric response.”

Note:
The control of the photometric linearity is still required in the European Pharmacopoeia (EP 11).

4. LIMIT OF STRAY LIGHT

to date:
Stray light levels have to be monitored at one or more UV wavelengths in the range: 200 – 400 nm.

Procedure A: Measuring stray light in accordance with USP <857> procedure A, requires a 5 mm reference filter and a 10 mm filter, both filled
with the same solution.

Procedure B: The analysts can measure the stray light filter with a path length of 10 mm against the reference filter filled with an appropriate
reference (10 mm path length). The measured absorbance value per filter should be greater than 2.0 at the recommended wavelength listed in
the table: