HPLC Method for Analysis of Diethyl p-Toluene Sulfonyloxy Methyl Phosphonate (DESMP) in Spent Salt

Introduction

The source of Diethyl p-Toluene Sulfonyloxy Methyl Phosphonate (DESMP) in spent salt is the parent industrial process in which DESMP is either a product, intermediate, impurity or reaction residual and where inorganic salts are generated during neutralization, quenching or work-up steps. When acids or bases are added to terminate reactions or adjust pH, large quantities of salts are formed and DESMP present in the process stream partitions into or becomes physically entrapped within the salt matrix. Additionally, during solvent extraction and drying operations, traces of DESMP dissolved in the organic phase can be transferred to the salt and remain after solvent removal. Thus, spent salt acts as a secondary carrier of DESMP originating directly from the upstream chemical manufacturing or processing operation.

Principle of the Method

DESMP absorbs in the UV region and shows adequate sensitivity at 260 nm. The compound is separated using a reverse-phase C18 column with an acidified water–acetonitrile mobile phase and quantified using external standard calibration.

Chromatographic Conditions
Parameter	Condition
Detector	UV
Wavelength	260 nm
Column	ZORBAX C18
Mobile Phase	Water : Acetonitrile (70:30 v/v) with 0.2 mL phosphoric acid
Flow Rate	1.5 mL/min
Injection Volume	20 µL
Column Oven Temperature	40 °C
Run Time	35 minutes
Mode	Isocratic

Preparation of Mobile Phase

Prepare the mobile phase by mixing water and acetonitrile in the ratio of 70:30 (v/v). Add 0.2 mL of phosphoric acid to the mixture, volume made up to 1000mL, mix thoroughly, sonicate to degas, and filter through a suitable membrane filter before use.

Standard Preparation

Accurately weigh 10 mg of DESMP reference standard and transfer it into a 10 mL volumetric flask. Dissolve the standard in acetonitrile and make up to volume with the same solvent. Mix well to obtain a standard stock solution of 1 mg/mL.

Sample Preparation (Spent Salt)

Accurately weigh 1.0 g of spent salt sample and transfer it into a 10 mL volumetric flask. Add acetonitrile, dissolve completely, and make up to volume. Mix thoroughly to ensure efficient extraction of DESMP. Filter the solution through a 0.2 µm membrane filter before HPLC injection.

Analysis and Quantification

Inject 20 µL of the standard and sample solutions into the HPLC system. Quantification is performed using the external standard method by comparing the peak area of DESMP in the sample with that of the standard.

Conclusion

The described HPLC-UV method is simple, reliable, and suitable for routine determination of DESMP in spent salt matrices. The method provides good reproducibility and selectivity and can be adopted for quality control, process monitoring and research applications.

In simple terms, DESMP is found in spent salt because it gets carried along during the normal processing steps used in industry, such as neutralization, washing, and solvent removal. When salts are formed or separated, small amounts of DESMP can become trapped or stick to the salt and are not removed completely. Since DESMP does not easily break down or evaporate, it remains in the spent salt. Therefore, analyzing DESMP in spent salt is important to understand product loss, ensure proper waste handling, and improve overall process efficiency.

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