Perchlorate in Wastewater
Photometric Determination with Methylene Blue after Extraction with Chloroform

Introduction

Perchlorate is a strong oxidizing agent that is found in a number of products including missile fuel, fireworks, vehicle airbags, and fertilizers, among others.¹ It is very water soluble and stable, persisting in the environment in water, soil, and plants.

Exposure to high levels of perchlorate can lead to adverse health effects in humans. The major toxic effect is on thyroid gland function: perchlorate blocks iodide uptake into the thyroid, decreasing production of thyroid hormone. This can lead to issues with metabolism, neurodevelopment, and other functions.² As a result, close monitoring of wastewater can be important to safe manufacturing of perchlorate-containing products. Here, we describe a method to measure perchlorate in wastewater after chloroform extraction using photometry.

Experimental Method

The mixture of reagents prepared as described below is determined photometrically at 665 nm.

Reagents, Instruments and Materials

Test Kits

One of the following test kits is necessary for this analysis:

• Chloroform for analysis EMSURE^® ACS, ISO, Reag. Ph Eur (1.02445)
• Methylene blue (C.I. 52015) Reag. Ph Eur (1.59270)
• Water for analysis EMSURE^® (1.16754)

Instruments

One of the following instruments is necessary for this analysis:

• Spectroquant^® VIS Spectrophotometer Prove 100 (173016)
• Spectroquant^® UV/VIS Spectrophotometer Prove 300 (173017)
• Spectroquant^® UV/VIS Spectrophotometer Prove 600 (173018)
• Spectroquant^® Photometer NOVA 60A (1.09752)

Materials

• Empty cells 16 mm with screw caps Spectroquant^® (1.14724)
• Folded filter, Whatman^® prepleated qualitative filter paper, Grade 1573 ½ (WHA10314745) or
• Membrane filter 0.45 μm pore diameter
• Separating funnels with ground glass stoppers 100 ml
• Cotton wool

Analytical Approach

Measurement range

10.0 mg/l ClO₄ at path length 14 mm (16 mm round cells) and 665 nm

Preparation of Reagent 1

Dissolve 0.10 g methylene blue in 100 ml of water for analysis.

Sample Preparation

The sample solution must be clear; if not, filter through a folded filter or membrane filter.

Analysis

1. Mix 10.0 ml clear sample, 0.20 ml reagent 1, and 8.0 ml chloroform in a separating funnel
2. Close the funnel and shake for 30 seconds
3. Allow to settle for 15 minutes and then separate off the lower organic phase through cotton wool directly into a 16-mm round cell with screw cap
4. Close off the cell. Measure at 665 nm against pure chloroform

Programming of the Spectroquant^® photometers

The parameter lists for the programming of the Spectroquant^® photometers can be found below. Due to batch-specific variations, it is recommended to check the calibration function by measuring a standard solution. In case of deviations, perform a recalibration of the method.

Calculation

When measuring the absorbance value at 665 nm using the Spectroquant^® photometers without programming the method in the memory of the instrument:

• Perchlorate in mg/l = Measured absorbance of sample * 8.73