Measuring Purity of Acetonitrile


Application Summary

Analytes % Transmittance in acetonitrile
Detector OMA-300 Process Analyzer
Process Stream Acetonitrile
Measurement Range 80-100 %T
Path Length 1 cm


Generated as a by-product of acrylonitrile manufacture, acetonitrile is used as a solvent in butadiene purification and as a component in batteries. The purity of acetonitrile must be verified to ensure suitability for these industrial uses.

The traditional offline method for acetonitrile quality control relies on pulling samples for lab analysis. The lab system compares the sample’s UV transmittance at a few wavelengths (220 nm, 240 nm, 275 nm, 350 nm) to that of demineralized water at the same wavelengths. Since pure acetonitrile has zero absorbance in the UV range, a simple principle applies: higher transmittance = higher purity.

The OMA system applies the same principle but with enormous advantages, including: (1) continuous analysis updating every 1-5 seconds, as opposed to slow sample transport for discrete lab measurements; (2) fast response for immediately pinpointing changes in stream purity; (3) totally automated sampling system normalizes measurement by Auto Zero; (4) installation of system close to sampling point for convenience of process adjustment.

Transmittance Spectra of Different Acetonitrile Samples

The transmittance at 220 nm of various acetonitrile samples is shown below in spectra and table form.

measuring 0-0.5% BPA in a methylene chloride stream-analyzer

Accuracy in Terms of Transmittance

Some applications call for purity in the 99-100% transmittance range. Verification requires extremely accurate measurement.

Wavelength Accuracy and Reproducibility

Transmittance measurement requires extremely stable wavelength accuracy. If the diode drifts wavelength assignment, significant measurement error is introduced. Mechanical scanning instruments with filters have moving parts that wear over time and lose wavelength assignment. The solid state OMA uses a photodiode array for extremely stable accuracy.

Rich Trend Data

Since the OMA performs continuous analysis of acetonitrile purity, trend data is available to the operator with easily configured data storage to view process history.

analysis of acetonitrile purity software screen

Application Data

The specifications below represent performance of the OMA-300 Process Analyzer in a typical acetonitrile purity application.

For technical details about the OMA-300 Process Analyzer, see the data sheet:
DS-001A: OMA-300 Process Analyzer

All performance specifications are subject to the assumption that the sample conditioning system and unit installation are approved by Applied Analytics. For any other arrangement, please inquire directly with Sales.

Performance Specifications
Accuracy Acetonitrile Transmittance at 220 nm
@ 80-100 %T measurement range: ±0.3 %T

Note: Subject to modifications. Specified product characteristics and technical data do not serve as guarantee declarations.

Further Reading

OMA-300 Process AnalyzerData sheet
Advantage of Collateral DataTechnical Note