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With the widespread application of high-sensitivity analytical instruments such as high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (LC-MS), and inductively coupled plasma mass spectrometry (ICP-MS) in pharmaceutical, food, and environmental fields, the purity of laboratory water has become a key factor affecting the accuracy of analytical results.
Many laboratories have used bottled drinking water as analytical water for instruments. This type of water is not a chemical reagent, lacks reliability and traceability, and poses significant experimental risks. The introduction of GB/T 33087-2016 aims to fill this gap and provide a reliable standard for water quality in rapidly developing instrumental analysis technologies.
Prior to this standard, GB/T 6682—2008, "Specifications and Test Methods for Water Used in Analytical Laboratories," was the most widely used standard in China. This standard revised and adopted relevant requirements from ISO 3696—1995, "Specifications and Test Methods for Water Used in Analytical Laboratories." Currently, GB/T 6682—2008 Specifications and Test Methods for Water Used in Analytical Laboratories and GB/T 33087—2016 Specifications and Test Methods for High-Purity Water Used in Instrumental Analysis together constitute a more comprehensive standard system for laboratory water.
GB/T 33087-2016 specifies the following six core indicators for high-purity water used in instrumental analysis:
GB/T 33087-2016 specifies six core indicators for high-purity water used in instrumental analysis
Project | Specifications | Scientific significance |
Resistivity (25℃) | ≥ 18MΩ·cm | The total content of ionic impurities in water is the most direct indicator of water purity. |
Total organic carbon (TOC) | ≤ 50μg/L | Control organic contamination and avoid chromatographic baseline drift and mass spectrometry background interference. |
Sodium ions (Na⁺) | ≤ 1μg/L | Common cationic contaminants have a significant impact on mass spectrometry and spectral analysis. |
Chloride ions (Cl⁻) | ≤ 1 μg/L | Common anionic contaminants easily form adduct ions, interfering with mass spectrometry detection. |
Silicon (Si) | ≤ 10 μg/L | Trace amounts of silicon can deposit in chromatographic columns and mass spectrometry ion sources, causing irreversible contamination. |
Total number of bacteria | Pass (testing required) | Microbial metabolites can introduce organic matter and ion pollution. |
The Scientific Logic Behind the Indicators
1. Resistivity ≥ 18 MΩ·cm: This is the "threshold value" for ultrapure water. The theoretical resistivity of pure water is approximately 18.2 MΩ·cm (25℃), and any ionic impurities will lower this value. This indicator is monitored online to ensure that water quality meets the standard in real time.
2. TOC ≤ 50 μg/L: Organic matter is one of the most troublesome interference sources in liquid chromatography and mass spectrometry analysis. High TOC not only leads to increased baseline noise but may also form background ions in the ion source, masking the target analyte signal.
3. Na⁺, Cl⁻ ≤ 1 μg/L: These two ions are the most common pollutants in the environment. In ICP-MS analysis, high background of Na⁺ and Cl⁻ can severely interfere with the determination of isotopes; in mass spectrometry, Cl⁻ also easily forms [M+Cl]⁻ adduct ions with the target analyte, leading to false positives.
4. Si ≤ 10 μg/L: Silicon is one of the more difficult impurities to remove in ultrapure water systems. Trace amounts of silicon are irreversibly adsorbed in the chromatographic column, leading to a decrease in column efficiency. In ICP-MS, the interference of polyatomic ions of Si (such as the interference of ²⁸Si¹⁶O⁺ on ⁴⁴Ca⁺) should not be ignored.
How to choose the applicable standard?
1. If the standard explicitly requires the reference of GB/T 6682-2008 (such as some GB 23200 series food safety standards), then acceptance must be carried out according to this standard.
2. If using high-sensitivity instruments such as HPLC, LC-MS, ICP-MS, and ICP-OES, it is recommended to prioritize GB/T 33087-2016, as it provides more precise control over ions and organic matter.
3. For general chemical titration and routine spectroscopic analysis, Grade I or Grade II water in GB/T 6682-2008 is sufficient.
The evolution of my country's laboratory water standards system, from GB/T 6682-2008 to GB/T 33087-2016, reflects the development trajectory of analytical science and technology from simply usable water to precise water. For every laboratory worker, understanding the scientific logic behind the standards, choosing the appropriate water grade for their own experimental needs, and strictly adhering to sampling and quality control specifications are the first line of defense in ensuring the reliability of analytical data. After all, in the world of trace analysis, the purity of water determines whether the signal you see is real or an illusion.
