China’s Ministry of Ecology and Environment issued two environmental protection standards: Ambient air — Determination of benzo[a]pyrene — High performance liquid chromatography (HJ 956-2018) and Ambient air — Determination of fluoride — Filter sampling / fluoride ion-selective electrode method (HJ 955-2018). The head of the Ministry’s Environmental Monitoring Department answered questions about the standards.
Why were these standards revised?
HJ 956-2018 revises GB/T 15439-1995, the benzo[a]pyrene analytical method supporting the Ambient Air Quality Standards (GB 3095-2012). Advances in monitoring exposed limitations in sample collection, extraction and detection. The previous method required high-volume sampling of inhalable particulate matter, restricted extraction to ultrasonic extraction with acetonitrile, and used ultraviolet detection instead of the more sensitive and selective fluorescence method. Some performance indicators also did not meet the requirements of HJ 168-2010, the technical guideline for developing and revising environmental monitoring analytical-method standards.
HJ 955-2018 revises HJ 480-2009, the filter-sampling / fluoride ion-selective electrode method supporting GB 3095-2012. The earlier method had shortcomings in sampling, preparation and quality control. Medium-volume sampling was used for both hourly and daily averages, with excessive flow rates. It did not adequately specify the sampling-head design, flow stability or pump vacuum capability needed for effective double-filter sampling. Quality assurance and quality control provisions were also insufficient to support the fluoride-monitoring requirements of GB 3095-2012.
What changed?
HJ 956-2018 extends the method from benzo[a]pyrene in PM10 to benzo[a]pyrene in all particulate matter. It allows low-, medium- and high-volume sampling, and adds conventional Soxhlet extraction, automated Soxhlet extraction, pressurised-fluid extraction and ultrasonic extraction. It adds extraction solvents and sample-cleanup methods, adopts fluorescence detection for greater sensitivity and selectivity, revises gradient-elution conditions and quantification methods, and adds quality assurance and quality control requirements.
HJ 955-2018 changes sampling flow rates, expands sampling-head and sampler-performance requirements, simplifies calibration-curve preparation, and adds provisions for reporting results, quality assurance and quality control, waste disposal and informative appendices.
To align with the amendment to GB 3095-2012 announced in Ministry notice No. 29 of 2018, neither standard converts analytical results to concentrations at standard conditions.
What improvements do the revised methods offer?
HJ 956-2018 offers more sampling and extraction options consistent with established sampling practice. More advanced extraction, cleanup and detection techniques improve resistance to interference, accuracy and precision. Detection limits, precision and accuracy meet the relevant requirements, and the revised technical approach aligns with related international standard methods.
HJ 955-2018 accounts for both gaseous and particulate fluoride through double-filter collection, so the result reflects total fluoride in ambient air. It specifies sampling-head design, flow stability and pump vacuum capability to standardise sampling. The widely used ion-selective electrode method offers high sensitivity, low detection limits and straightforward operation. Explicit quality assurance and quality control requirements support reliable and accurate monitoring data.