USP<857> (United States Pharmacopeia)

In the years 2019 to 2022, the chapter USP <857> was subjected to a further revision; the resulting USP <857> (43rd edition, update from Dec. 2022) is showing the following major changes:

New requirements in USP 43 NF 38, Chapter 857

The new USP <857> compliant control of the UV/Vis spectrophotometer depends on the operational range (absorption and wavelength range).

The requirements and specifications for the procedure for the "Control of Absorbance" have been newly regulated; from December 2022, six replicate absorbance measurements must be carried out for each wavelength. On the other hand, the requirement to check the photometric linearity, which was recently added in December 2019, is now being removed.

Important Statement in the USP <857>

„.. certified reference materials (CRMs) are to be used in preference to laboratory-prepared solutions“


Following parameters should be regularly controlled:

1. Wavelength accuracy
2. Absorbance accuracy
3. Photometric linearity - no longer required from Dec 2022
4. Limit of stray light
5. Resolution

New requirements of USP <857>

The changes in the new USP <857> updated in December 2022 compared to the previous version are briefly explained in the following context

 

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.
 

Here you can find more information about Wavelength Filters.

 

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%


Here you can find more information about Absorbance Filters.

 

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).
 

Here you can find more information about Photometric Linearity.

 

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 pure water (10 mm path length), with the exception of acetone, which is measured against air. The measured absorbance value per filter should be greater than 2.0 at the recommended wavelength listed in the table:

Filter / Solution
used for Procedure A or B
Spectral Range Recommended Wavelength
for Procedure B
Potassium chloride (12 g/L) 190 - 210 nm 198 nm
Sodium iodide (10 g/L) 210 - 270 nm 220 nm
Potassium iodide (10 g/L) 210 - 270 nm 220 nm
Acetone (pure) 250 - 330 nm 300 nm
Sodium nitrite (50 g/L) 300 - 400 nm 340 nm

 

New supplement in USP <857>:
When using acetone, measurements should be performed using air as a reference.

 

Here you can find more information about Stray Light Filters.

 

5. CONTROL OF RESOLUTION

to date:
A liquid filter of Toluene in Hexane and a Hexane reference filter are used to check the resolution of the spectrophotometer..

New USP <857>:
No changes!.

Here you can find more information about Control of Resolution.

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