A New Breakthrough in Total Phosphorus Monitoring of Surface Water: A Practical Guide to On-site Pre-treatment Using a Portable Centrifuge

I. Pre-Centrifugation Processing: The “Gatekeeper” of Accurate Total Phosphorus Detection
Pain points of the national standard method:
《Water Quality—Determination of Total Phosphorus—Ammonium Molybdate Spectrophotometric Method》 (HJ 670-2013) requires:
“When the water sample contains suspended solids, it should be centrifuged to separate the supernatant, which then is used for measurement.”
Scientific basis:
Turbidity-causing substances lead to falsely high absorbance readings, with errors as high as 30%.
Traditional settling and sedimentation takes more than 4 hours and cannot completely separate colloidal particles.
Revolutionary value of on-site pre-processing:

II. Portable Centrifuge: A “Mobile Laboratory” Designed for Field Monitoring

Core Competency Matrix:

Parameter adaptation for total phosphorus detection:
Precise control of centrifugal force: 3,000–5,000 g (effectively precipitates colloids and fine particles)
Rotational speed response time: Reaches maximum speed within 30 seconds (reducing single-sample processing time to 3 minutes).
Environmental adaptability: Stable operation from -10℃ to 50℃ (to cope with temperature fluctuations in outdoor environments)
III. Real-World Scenarios: Three Essential Solutions for Water Quality Monitoring
1. Tracking Sudden Waterway Pollution Events
Scene characteristics: time-sensitive, geographically dispersed.
Device Selection: Pocket-sized Centrifuge (≤1 kg, USB charging supported)
Operation Plan:
① Centrifuge immediately after sampling (4000 rpm/2 min)
② Add ascorbic acid preservative to the supernatant.
③ On-site readings with a portable spectrophotometer
2. Comprehensive Survey of Lake Eutrophication
Scene characteristics: Large sample size, requiring multi-point comparison.
Equipment Selection: Vehicle-mounted centrifuge (with 12V power supply, capable of processing 24 tubes per run)
Efficiency Improvement:
Complete the pre-processing of 60 samples at 10 sampling points in a single day.
Avoid the redissolution of sample deposits in traditional methods.
3. Wastewater Treatment Plant Discharge Monitoring
Scene characteristics: High turbidity, compliance verification required.
Technical highlights:
The turbidity of the supernatant after centrifugation must be ≤5 NTU (as required by the national standard).
Extend the centrifugation time to 5 minutes (for high-concentration suspensions).
IV. Operational Guidelines: The Five-Step Method for Field Centrifugation
Sample preprocessing:
Allow the sampling bottle to stand for 2 minutes to allow large particles to settle.
Use a pipette to draw the middle-layer liquid into a centrifuge tube (avoiding the sediment at the bottom).
Balancing operation:
Place the centrifuge tubes symmetrically (error ≤ 0.1 g).
If the sample size is insufficient, replenish the weight with distilled water.
Parameter Settings:
Standard water quality: 4000 rpm (approximately 3500 g) / 3 min
High-turbidity water: 5000 rpm (approximately 4500 g) / 5 min
Supernatant Treatment:
Transfer the supernatant within 10 minutes after centrifugation is complete.
Use a blunt-ended pipette to prevent disturbing the sediment layer.
Equipment Maintenance:
Rinse the rotor chamber with clean water after each use.
Lubricate the spindle monthly to prevent salt corrosion (critical for offshore monitoring).
As the portable centrifuge hums to life on the riverbank, it’s more than just a piece of equipment—
For the monitor: It’s a technical shield against “false positive” errors.
For ecosystems: it’s a true window into the dynamics of phosphorus pollution.
Historical data: the cornerstone for building a long-term, comparable database.