Evaluating Turbidity Standards: The Technical and Operational Advantages of Styrene-DivinylBenzene (SDVB)

Accurate turbidity measurement relies on calibration against traceable reference standards, most commonly Formazin or Styrene-divinylbenzene (SDVB). While applications may vary between Formazin and SDVB, HORIBA’s TB220 Portable Turbidity Meter utilizes SDVB standards, providing a stable and reliable calibration solution tailored for high-precision applications.

Some differences between Formazin and SDVB are summarized in Table 1 below.

Table 1. Differences between Formazin and SDVB

	Formazin1	SDVB
Composition	Insoluble polymer formed by reacting hydrazine sulfate and hexamethylene-tetramine (HMTA).	Suspension of styrene-divinylbenzene  polymer microspheres.
Appearance	Dense, opaque white suspension at high concentrations. Yellowish-white appearance at lower concentrations.	Milky-white, stable suspension.
Type of Standard	Primary turbidity reference standard2.	Secondary standard – traceable to Formazin primary standard2.
Stability and Shelf Life	Highly sensitive to temperature2. High tendency to settle and form floc2. Only stable at high concentrations2  > 400 NTU >1 year 20-400 NTU 1 month 2-20 NTU 12-24 hours <2 NTU <1 hour	1 year. Does not settle, uniform particle size4.
Safety and Handling	Toxic precursor chemicals (hydrazine sulfate and hexamethylenetetramine are poisonous and carcinogenic2), requires careful preparation. Proper disposal according to chemical waste rules and regulations.	Non-hazardous/non-toxic4. Ready-to-use3.
Optical properties	Made up of polymer chains of varying lengths, which fold in random configurations.  Wide array of particle shapes and sizes, ranging from <0.1µm to >10µm. Reproducible light scattering pattern2.	Inert, spherical polymer microbeads. Narrow bead size range, from 0.06µm to 0.2µm. Ideal for characterizing light scatter at 90° 4. Minimal variation across different lots3.
Applications	Primary turbidity calibration, used by many standards5 (US EPA 180.1, ISO 7027, APHA Method 21306).	Used for routine checks of calibration stability, without the need for preparing fresh formazin dilutions2.  Suitable for field use where dilution using pure, turbidity-free water and necessary volumetric glassware under controlled conditions is not feasible4.  Under ISO 7027-1 and US EPA 180.1, acceptable alternative to be used as a calibration standard8,9.

In summary, SDVB standards are advantageous because:

• It has better stability (1 year) compared to formazin (hours to months, depending on the concentration), therefore minimizing the need for constant preparation of fresh standard. Diluted formazin standards (2-20 NTU) often require fresh preparation every 24 hours. For turbidity standards lesser than 2 NTU, it is extremely challenging to accurately prepare as the necessary dilution ratio is so high that even a small variation in the volumes measured can lead to a high level of uncertainty².
• It is safe, commercially available, and comes in ready-to-use bottles³. The preparation of formazin involves the usage of toxic chemicals like hydrazine sulfate, which is a known carcinogen², and requires strict personal protective equipment (PPE) during preparation and appropriate waste disposal protocols in place. 
• It is ideal for use in the field, where dilution of formazin using pure water and volumetric glassware is not practical⁴.
• It is recognized for use under ISO 7027-1 and US EPA 180.1 as a primary turbidity calibration standard, requiring no preparation or dilution prior to use⁷.
• Note: AMCO turbidity standards are one version of SDVB standards that is recognized by the US EPA for the calibration of turbidity meters and is approved for use in EPA Method 180.1. It was developed by an American Company, Advanced Polymer Systems, in 1982^4,7.

While formazin remains as the accepted traceable primary standard used to define the turbidity scale², its instability, toxicity, and difficulty in handling makes it challenging for routine use. As such, SDVB standards are safer, more stable and easier to handle compared to formazin, while maintaining traceability², for accurate turbidity calibrations. This ensures that measurements obtained using SDVB remain consistent, while improving operational efficiency. It is also more practical for routine usage in the field, while ensuring rigorous accuracy of the instrument, without the human errors associated with manual formazin preparation. In modern turbidity measurement workflows, SDVB standards provide a practical balance between traceability and operational efficiency, making it the preferred choice for routine applications. 

HORIBA’s TB220 Turbidity Meter is designed, programmed, and calibrated to work with HORIBA’s SDVB turbidity standards, and performance is not guaranteed if turbidity standards from other manufacturers are used with the TB220. 

References and Suggested Readings

Revision 0, 9 June 2026