ISO 3696:1987 - Water for analytical laboratory use

Water is an essential reagent for many analytical laboratory procedures. It is used as a solvent, a diluent, and a carrier for reagents and samples. The quality of water can have a significant impact on the accuracy and precision of analytical results.

ISO 3696:1987 - Water for analytical laboratory use

1. Introduction

ISO 3696:1987 is an international standard that specifies the requirements and corresponding test methods for three grades of water for laboratory use for the analysis of inorganic substances. The three grades are:

• Type 1: Water that is free from dissolved or colloidal ionic and organic contaminants. This grade is suitable for the most sensitive analytical purposes, such as atomic absorption spectrometry (AAS) and the determination of trace elements.
• Type 2: Water that contains very low inorganic, organic, or colloidal contaminants. This grade is suitable for general analytical purposes, such as titrations, gravimetric analysis, and spectroscopy.
• Type 3: Water that contains moderate levels of inorganic, organic, or colloidal contaminants. This grade is suitable for non-sensitive analytical purposes, such as washing glassware and preparing solutions for qualitative analysis.

2. Requirements

The requirements for each grade of water are specified in terms of the following parameters:

• Conductivity: The conductivity of water is a measure of its ability to conduct electricity. The conductivity of Type 1 water shall be less than 0.1 μS/cm at 25°C. The conductivity of Type 2 water shall be less than 1 μS/cm at 25°C. The conductivity of Type 3 water shall be less than 10 μS/cm at 25°C.
• pH: The pH of water is a measure of its acidity or alkalinity. The pH of Type 1 water shall be between 5.0 and 7.0. The pH of Type 2 water shall be between 5.0 and 9.0. The pH of Type 3 water shall be between 5.0 and 14.0.
• Oxidizable matter: Oxidizable matter is a measure of the amount of organic matter in water. The concentration of oxidizable matter in Type 1 water shall be less than 0.02 mg/L as oxygen. The concentration of oxidizable matter in Type 2 water shall be less than 0.05 mg/L as oxygen. The concentration of oxidizable matter in Type 3 water shall be less than 0.1 mg/L as oxygen.
• Reactive silica: Reactive silica is a measure of the amount of dissolved silica in water. The concentration of reactive silica in Type 1 water shall be less than 0.05 mg/L as SiO2. The concentration of reactive silica in Type 2 water shall be less than 0.1 mg/L as SiO2. The concentration of reactive silica in Type 3 water shall be less than 0.5 mg/L as SiO2.
• Absorbance: The absorbance of water is a measure of its ability to absorb light. The absorbance of water at 254 nm shall be less than 0.01.

3. Test methods

The test methods for determining the parameters listed above are specified in the standard. These methods are based on standard analytical procedures, such as:

• Conductivity: The conductivity of water is determined using a conductivity meter.
• pH: The pH of water is determined using a pH meter.
• Oxidizable matter: The concentration of oxidizable matter in water is determined using a chemical oxidation method, such as the potassium permanganate method.
• Reactive silica: The concentration of reactive silica in water is determined using a colorimetric method, such as the molybdenum blue method.
• Absorbance: The absorbance of water is determined using a spectrophotometer.

ISO 3696:1987 is an important standard for laboratories that perform analytical work. The standard specifies the requirements for three grades of water, each of which is suitable for different analytical purposes. The standard also specifies the test methods that can be used to determine whether water meets the required specifications.