Method Statement Phenols

• Introduction
• Principle
• Performance Characteristics
• Range of Application
• Limit of Detection
• Analytical Quality Control
• References

Introduction

The performance of this method is validated in accordance with internationally recognised procedures.

This procedure describes a method for the determination of Total Monohydric Phenols in soils and waters. Non volatile impurities are removed by steam distillation and the total monhydric phenol is measured spectrophotometrically in the form of the 4-aminoantipyrine complex.

Principle

Phenols are extracted from soil samples with sodium hydroxide. The sodium hydroxide extract is acidified and steam distilled in order to separate phenol from non volatile impurities. The phenols in the distillate react with 4-aminoantipyrine at a pH of 10.0+/-0.2 in the presence of potassium ferricyanide to form a coloured antipyrine dye, the absorbance of which is measured at a wavelength of 510 nm.

For water samples, the sodium hydroxide extraction step is omitted and a suitable aliquot of the raw sample is distilled.

Performance Characteristics

The analytical procedure described herein uses 4-aminoantipyrine as a reagent which forms a coloured complex with certain phenols. It is important to note that some phenols do not react with 4-aminoantipyrine; these include para substituted phenols where the substitution is an alkyl, aryl, nitro, benzoyl, nitroso, or aldehyde group. Paracresol (4-MethylHydroxyBenzene), which may be present in certain industrial waste waters, is an example of a phenol which does not react with 4-aminoantipyrine.

However, 4-aminoantipyrine does react with phenol, ortho and meta substituted phenols. Furthermore, phenols in which a carboxyl, halogen, methoxyl or sulphonic acid group is located in the para position will react under appropriate pH conditions. Because the relative amounts of various phenolic compounds in a given sample are unpredictable, it is not possible to provide a universal standard containing a mixture of phenols. Hence, phenol (C6H5OH) has been selected as a standard for colorimetric procedures and all colour produced by the reaction of other phenolic compounds is reported as phenol. In general, functional groups on the aromatic ring reduce the response, thus, this value represents the minimum concentration of phenolic compounds.

Range of Application

• Solid samples 1 to 40 mg / kg

• Aqueous samples 0.1 to 4.0 mg / l

Limit of Detection

• Solid samples 1 mg / kg

• Aqueous samples 0.1 mg / l

Analytical Quality Control

Analytical quality control for phenols analysis is maintained by a number of measures:

• Multi-point calibration with authentic standards (with defined minimum performance characteristics)

• Analysis of control samples within each analytical batch, such as independent standards, matrix spikes or reference materials

• Analysis of reagent/method blanks within each analytical batch

• Ongoing quality assured by the use of control charts in conjunction with warning and action limits for the QC sample data

• Participation in external proficiency testing and interlaboratory schemes such as LGC CONTEST, HSE WASP, CSL FAPAS

References

Phenols in Waters and Effluents by Gas - Liquid Chromatography, 4-aminoantipyrine or 3-methyl-2-benzothiazolinone hydrazone. DOE Methods For The Examination of Waters and Associated Materials, published by HMSO. 1981.

Phenols, Part 5530. Standard Methods For The Examination Of Water and waste water. 1992. 18^th Edition. APHA - AWWA - WEF.