## 4 Applications of \({}^{31}\)P qNMR for Phosphorus-Containing Compounds
### In the Field of Food  
\({}^{31}\)P qNMR is widely used to analyze diverse matrices, including complex natural products, dietary supplements, fungicides, and traditional medicines. [PERSON] et al. [44] developed a rapid and reliable quantitative method for hydroxyethyl diphosphate acid during vegetable washing using \({}^{31}\)P NMR, which has been successfully applied to determine hydroxyethyl diphosphonic acid in 10 agricultural food processing industrial water samples used for fruit and vegetable washing. Moreover, [PERSON] et al. [45] demonstrated the successful application of \({}^{31}\)P NMR for the quantitative analysis of phospholipid-rich and moderately phospholipid-rich samples, such as soybeans, egg yolks, and dietary supplements. When compared to the two-dimensional thin-layer chromatography method, the total phospholipid contents of polar lipids determined by \({}^{31}\)P NMR aligned closely with those obtained via molybdenum blue colorimetry. However, the quantitative values for specific phospholipid classes varied depending on their content, especially when exceeding or falling below 10%. Furthermore, [PERSON] et al. [47] established a \({}^{31}\)P qNMR method for the simultaneous quantification of the active forms of vitamins B\({}_{1}\), B\({}_{2}\), and B\({}_{6}\). The \({}^{31}\)P NMR signals corresponding to the analytes and the internal standard were clearly resolved and distinctly identifiable. EDTA and pH optimization (to 8.0) were utilized to enhance  
Figure 5: The \({}^{31}\)P NMR spectra include ammonium dihydrogen phosphate in D\({}_{2}\)O (brown), triphenyl phosphate in CDCl\({}_{3}\) (blue), phosphoonoacetic acid in D\({}_{2}\)O (red), and tris(2-chloroethyl) phosphate in CDCl\({}_{3}\) (black). Copyright (2015) Springer.  
signal resolution and eliminate interference from metal ions in complex matrices. The proposed method uses phosphorus-31 NMR to target the phosphate group present in the active forms of vitamins. The advantages include simultaneous analysis of multiple active vitamins, which reduces complexity and sample preparation time compared to conventional methods like HPLC or LC-MS. Additionally, the high sensitivity and reproducibility make it suitable for routine quality control in the food and supplement industry, ensuring the accurate quantification of active vitamin content in complex multivitamin formulations. [PERSON] et al. [47] report the use of quantitative \({}^{31}\)P NMR spectroscopy to measure the phosphorus content in a cola beverage sample. The single \({}^{31}\)P resonance, referred to as the \"phosphate peak,\" is the concentration-weighted average signal of the phosphate species (PO\({}_{4}\)\({}^{3-}\), HPO\({}_{4}\)\({}^{2-}\), H\({}_{2}\)PO\({}_{4}\)\({}^{-}\), H\({}_{3}\)PO\({}_{4}\)). Since the 0 ppm reference is the 85% H\({}_{3}\)PO\({}_{4}\) solution, the lower the pH, the smaller the chemical shift of the phosphate peak becomes. External calibration involves creating a dilution series of sodium phosphate solutions to establish a calibration curve. The experiment compares the results of external calibration and standard addition methods using peak height and integral values.