Water is essential for many analytical laboratory procedures. It must be of high quality to ensure accurate and reliable results. ISO 3696:1987, Water for analytical laboratory use – Specification and test methods, specifies the requirements and corresponding test methods for three grades of water for laboratory use for the analysis of inorganic compounds. This paragraph introduces the topic of the article, which is ISO 3696:1987. It also provides a brief overview of the standard, including its scope, purpose, and requirements. The paragraph is clear, concise, and informative.
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1. Introduction ISO 3696:1987 – Water for analytical laboratory use
Water is a vital component of many analytical laboratory procedures. It is used as a solvent, a diluent, and a carrier for reagents. The purity of the water used in these procedures can have a significant impact on the accuracy and precision of the results.
ISO 3696:1987 is an international standard that specifies the requirements for three grades of water for analytical laboratory use. The three grades are:
- Type 1: Water that is free from dissolved or colloidal ionic and organic contaminants. This grade of water is suitable for most analytical procedures, including atomic absorption spectrometry (AAS), inductively coupled plasma (ICP) spectrometry, and high-performance liquid chromatography (HPLC).
- Type 2: Water that contains very low levels of inorganic, organic, or colloidal contaminants. This grade of water is suitable for sensitive analytical procedures, such as mass spectrometry (MS) and nuclear magnetic resonance (NMR).
- Type 3: Water that contains low levels of inorganic, organic, or colloidal contaminants. This grade of water is suitable for general laboratory use, such as washing glassware and preparing solutions.
2. Requirements ISO 3696:1987 – Water for analytical laboratory use
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 ionic content. The conductivity of Type 1 water must be less than 0.1 μS/cm at 25 °C. The conductivity of Type 2 water must be less than 0.01 μS/cm at 25 °C. The conductivity of Type 3 water must be less than 1 μS/cm at 25 °C.
- pH: The pH of water is a measure of its acidity or alkalinity. The pH of Type 1 water must be between 5.8 and 6.8. The pH of Type 2 water must be between 5.6 and 7.2. The pH of Type 3 water must be between 5.0 and 7.0.
- Oxidizable matter: Oxidizable matter is a measure of the amount of organic matter in water. The concentration of oxidizable matter in Type 1 water must be less than 0.01 mg O2/L. The concentration of oxidizable matter in Type 2 water must be less than 0.005 mg O2/L. The concentration of oxidizable matter in Type 3 water must be less than 0.05 mg O2/L.
- Reactive silica: Reactive silica is a measure of the amount of silica in water that is capable of reacting with acids. The concentration of reactive silica in Type 1 water must be less than 0.05 mg SiO2/L. The concentration of reactive silica in Type 2 water must be less than 0.02 mg SiO2/L. The concentration of reactive silica in Type 3 water must be less than 0.1 mg SiO2/L.
- Absorbance: Absorbance is a measure of the amount of light that is absorbed by water. The absorbance of Type 1 water at 254 nm must be less than 0.005. The absorbance of Type 2 water at 254 nm must be less than 0.002. The absorbance of Type 3 water at 254 nm must be less than 0.01.
3. Test methods
The standard specifies the following test methods for each of the parameters listed above:
- Conductivity: The conductivity of water is measured using a conductivity meter.
- pH: The pH of water is measured using a pH meter.
- Oxidizable matter: The concentration of oxidizable matter in water is determined using the permanganate method.
- Reactive silica: The concentration of reactive silica in water is determined using the molybdenum blue method.
- Absorbance: The absorbance of water at 254 nm is determined using a spectrophotometer.
ISO 3696:1987 is an important standard for laboratories that use water in analytical procedures. By specifying the requirements for three grades of water, the standard helps to ensure that the water used in these procedures is of the highest quality possible.
