Tinosorb M and Tinosorb S Testing: How Our Validated HPLC Method Supports SPF Product Development

1-Minute Summary

Tinosorb S, also known as bemotrizinol, received FDA approval for use in U.S. sunscreens on June 9, 2026.
Tinosorb M, also known as bisoctrizole, is widely used internationally but is not approved as a U.S. OTC sunscreen active ingredient.
Certified Laboratories developed a dual-analyte HPLC method for Tinosorb M and Tinosorb S to support SPF product development, quality control, and stability programs.
The method validation evaluated specificity, system suitability, linearity, sensitivity, accuracy, precision, robustness, and solution stability.
The validation results support a fit-for-purpose method for manufacturers working with advanced UV filter technologies.

Why Tinosorb Testing Matters for SPF Product Development

After decades of inactivity, SPF product development is finally changing in the U.S.

Bemotrizinol, also known as Tinosorb S or PARSOL Shield, is an advanced organic UV filter used internationally in sunscreen formulations. On June 9, 2026, FDA approved its use in U.S. sunscreen products, the first change to sunscreen options in 20 years.

Bisoctrizole, also known as Tinosorb M, is another next-generation UV filter used globally. It is a hybrid particulate filter that absorbs, reflects, and scatters UV radiation. Unlike bemotrizinol, it is not currently approved as an OTC sunscreen active ingredient in the U.S., but it’s still important for brands that sell in jurisdictions where it is permitted for use.

All of this is to say that there is a need for analytical chemistry methods to measure these two compounds during formulation screening, raw material evaluation, finished product testing, and OTC/cosmetic stability programs.

Certified Laboratories has developed and validated such a method that is intended for cosmetic and OTC matrices. Let’s dive into the science behind our method.

Why SPF Products are Difficult Analytical Matrices

First, the chemical complexity of SPF products makes sunscreen testing especially difficult.

A finished SPF product may contain…

Oils
Emulsifiers
Waxes
Polymers
Preservatives
Fragrances
Film formers
Pigments
Mineral UV filters
Multiple organic UV filters

These ingredients can create background signals, affect extraction, or interfere with chromatographic separation.

From an analytical chemistry perspective, the central question is whether the method can measure the correct compound accurately in a real product matrix.

A validated, fit-for-purpose method should answer several questions:

Is the analyte peak free from interference?
Is the response linear across the intended working range?
Does the method recover the analyte accurately from the sample matrix?
Can different analysts reproduce the result?
Does the method remain reliable when normal method variables shift slightly?

Certified Laboratories validated its Tinosorb testing method to address these questions.

Our Approach: A Validated HPLC Method for Two UV Filters

Certified Laboratories developed a dual-analyte HPLC method for Tinosorb M and Tinosorb S. The method is designed to quantify both analytes in a single analytical run, supporting efficient Tinosorb testing for SPF product development and quality programs.

7-minute run time
Dual-analyte capability
Alignment with ICH Q2(R2) expectations

Let’s look at the method’s specificity, system suitability, linearity, accuracy, precision, robustness, and solution stability.

Specificity: Can the Method Measure the Right Compound?

Specificity is one of the most important characteristics for sunscreen testing.

A sunscreen matrix can contain many ingredients that absorb in similar regions or behave similarly during chromatographic analysis. If the method cannot distinguish the analyte from nearby interferences, the result may be biased.

Certified Laboratories evaluated blanks, standards, placebo preparations, and samples. The validation showed no interference at the relevant retention windows for Tinosorb M or Tinosorb S, and retention time reproducibility met the predefined acceptance criterion.

For manufacturers, this supports confidence that the reported value represents the target compound, not an excipient, fragrance component, preservative, or another UV filter.

Overlay of Blank (Blue), 48 ppm Standard (Pink), Placebo (Garnet), and Sample (Black) for Tinosorb

Overlay chromatograms showing specificity for Tinosorb M and Tinosorb S in SPF product matrices.

Linearity: Does Response Track with Concentration?

Linearity shows whether detector response is proportional to analyte concentration across the method’s working range.

Certified Laboratories evaluated each analyte using a five-point calibration curve. Both Tinosorb M and Tinosorb S met the predefined linearity criterion, with coefficients of determination exceeding the acceptance threshold.

This matters during product development because manufacturers may test multiple prototype concentrations, formulation adjustments, and stability time points. A validated linear range gives technical teams confidence that changes in concentration are reflected accurately in the analytical result.

Linearity Curves for Tinosorb M and Tinosorb S Analytical Method Validation

Linearity
r² ≥ 0.995	Tinosorb M: 1.000 Tinosorb S: 1.000
Recovery for check standard +/- 3%	Tinosorb M: 100.27% Tinosorb S: 100.07%
Overall Results: PASS

LOD and LOQ: How Low Can the Method Reliably Measure?

Our validation calculated limits of detection and quantitation using the calibration slope and standard deviation of response.

The validated method established low ppm-level sensitivity for both compounds:

Tinosorb M: LOD approximately 0.32 ppm; LOQ approximately 0.98 ppm.
Tinosorb S: LOD approximately 0.73 ppm; LOQ approximately 2.21 ppm.

Accuracy: Can the Method Recover the Analyte from the Product Matrix?

Accuracy is where method validation becomes especially practical.

As mentioned, SPF products can challenge extraction and quantitation because the analyte may interact with oils, waxes, emulsifiers, or other formulation components.

Certified Laboratories evaluated accuracy using spiked samples at three concentrations prepared and analyzed in triplicate. The method met predefined recovery criteria for both Tinosorb M and Tinosorb S.

Accuracy
% recovery for each injection shall be 95.0 – 105.0%	Tinosorb M level 1: 100.78%; level 2: 100.50%; level 3: 100.51% Tinosorb S level 1: 100.00%; level 2: 99.67%; level 3: 99.76%
% RSD for three injections per level shall be < 3.0%	Tinosorb M level 1: 0.04%; level 2: 0.25%; level 3: 0.09% Tinosorb S level 1: 0.05%; level 2: 0.06%; level 3: 0.09%
Overall Results: PASS

Recovery data are one of the best indicators that a method is fit-for-purpose. They show whether the sample preparation and analytical procedure can measure the analyte accurately in the presence of the product matrix.

Precision: Can the Method Be Reproduced?

Precision evaluates whether the method gives consistent results across replicate preparations and analysts.

Certified Laboratories tested precision using replicate sample preparations prepared by two operators. The method met predefined criteria for recovery, analyst percent RSD, and operator-to-operator agreement.

Precision
% recovery for each concentration shall be 90 – 110%	Tinosorb M: 101.69% Tinosorb S: 101.16%
% RSD of Operator A shall be < 2.0%	Tinosorb M: 0.34% Tinosorb S: 0.29%
% RSD of Operator B shall be < 2.0%	Tinosorb M: 0.57% Tinosorb S: 0.95%
% difference between Operators A and B shall be combined < 3.0%	Tinosorb M: 1.67% Tinosorb S: 0.67%
Overall Results: PASS

This is important because Tinosorb testing is not performed once, by one person, under ideal conditions. A method used for development, release testing, or stability support needs to be reproducible across trained analysts and normal laboratory workflows.

Robustness and Solution Stability: Can the Method Handle Normal Variation?

Robustness evaluates whether small, deliberate changes affect method performance.

Certified Laboratories challenged the method by evaluating controlled changes to organic content and column temperature and comparing results to the original control conditions. The validation report concluded that the method met predefined robustness criteria for both analytes.

The report also evaluated refrigerated standard solution stability. Working standards met acceptance criteria through 14 days.

This data show that the method does not depend on a narrow set of perfect conditions. It remains reliable when normal, controlled variation occurs.

Robustness – Solution Stability
Aged stock standard concentrations shall differ by no more than 3.0% from original assay value
Day 7	Tinosorb M: 0.61% Tinosorb S: 0.44%
Day 14	Tinosorb M: 1.13% Tinosorb S: 0.14%
Each analysis variation should yield NMT 3.0% concentration difference from control conditions
Increased organic composition	Tinosorb M: 0.04% Tinosorb S: 0.16%
Decreased organic composition	Tinosorb M: 0.07% Tinosorb S: 0.21%
Increased column temperature	Tinosorb M: 0.15% Tinosorb S: 0.03%
Decreased column temperature	Tinosorb M: 0.07% Tinosorb S: 0.04%
Overall Results: PASS

A Fit-for-Purpose Tinosorb Testing Method for SPF Product Development

Certified Laboratories’ method for Tinosorb M and Tinosorb S was built and validated for the needs of SPF product manufacturers.

The validated method supports:
Dual-analyte testing for Tinosorb M and Tinosorb S.
Efficient 7-minute analysis.
Specificity in complex product matrices.
Linear response across the validated range.
Low ppm-level sensitivity.
Demonstrated accuracy and precision.
Robustness under controlled method variation.
Standard stability for routine laboratory workflows.

As our validation data show, Certified Laboratories provides validated analytical testing for SPF product manufacturers working with advanced UV filter technologies.