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Method development in quantitative NMR towards metrologically traceable organic certified reference materials used as (31)P qNMR standards.

Weber M, Hellriegel C, Rueck A, Wuethrich J, Jenks P, Obkircher M - Anal Bioanal Chem (2014)

Bottom Line: These substances contain both nuclei, (1)H and (31)P, and the concept is to show that it is possible to indirectly quantify a potential phosphorus standard via its protons using (1)H qNMR.The same standard with its assigned purity can then be used for the quantification of an analyte via its phosphorus using (31)P qNMR.For the validation of the concept, triphenyl phosphate and phosphonoacetic acid have been used as (31)P qNMR standards to determine the purity of the analyte tris(2-chloroethyl) phosphate, and the resulting purity values perfectly overlap within their expanded measurement uncertainties.

View Article: PubMed Central - PubMed

Affiliation: Sigma-Aldrich Switzerland, Industriestrasse 25, 9471, Buchs, Switzerland.

ABSTRACT
Quantitative nuclear magnetic resonance (qNMR) spectroscopy is employed by an increasing number of analytical and industrial laboratories for the assignment of content and quantitative determination of impurities. Within the last few years, it was demonstrated that (1)H qNMR can be performed with high accuracy leading to measurement uncertainties below 1 % relative. It was even demonstrated that the combination of (1)H qNMR with metrological weighing can lead to measurement uncertainties below 0.1 % when highly pure substances are used. Although qNMR reference standards are already available as certified reference materials (CRM) providing traceability on the basis of (1)H qNMR experiments, there is an increasing demand for purity assays on phosphorylated organic compounds and metabolites requiring CRM for quantification by (31)P qNMR. Unfortunately, the number of available primary phosphorus standards is limited to a few inorganic CRM which only can be used for the analysis of water-soluble analytes but fail when organic solvents must be employed. This paper presents the concept of value assignment by (31)P qNMR measurements for the development of CRM and describes different approaches to establish traceability to primary Standard Reference Material from the National Institute of Standards and Technology (NIST SRM). Phosphonoacetic acid is analyzed as a water-soluble CRM candidate, whereas triphenyl phosphate is a good candidate for the use as qNMR reference material in organic solvents. These substances contain both nuclei, (1)H and (31)P, and the concept is to show that it is possible to indirectly quantify a potential phosphorus standard via its protons using (1)H qNMR. The same standard with its assigned purity can then be used for the quantification of an analyte via its phosphorus using (31)P qNMR. For the validation of the concept, triphenyl phosphate and phosphonoacetic acid have been used as (31)P qNMR standards to determine the purity of the analyte tris(2-chloroethyl) phosphate, and the resulting purity values perfectly overlap within their expanded measurement uncertainties.

No MeSH data available.


Table of deuterated solvents in which the 31P CRM candidates triphenyl phosphate, phosphonoacetic acid, and the analyte tris(2-chloroethyl) phosphate are soluble and corresponding relaxation times (T1) for both nuclei, 1H and 31P. In the boxes which do not display time specifications, the substance was not sufficiently soluble. *Due to overlaps with the CDCl3 signals, the solvent CD2Cl2 was used as a substitute
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Fig4: Table of deuterated solvents in which the 31P CRM candidates triphenyl phosphate, phosphonoacetic acid, and the analyte tris(2-chloroethyl) phosphate are soluble and corresponding relaxation times (T1) for both nuclei, 1H and 31P. In the boxes which do not display time specifications, the substance was not sufficiently soluble. *Due to overlaps with the CDCl3 signals, the solvent CD2Cl2 was used as a substitute

Mentions: Based on various parameters, including solubility, structure, chemical shifts, stability, homogeneity, and purity, two different organic compounds have been selected as candidates for their use as 31P qNMR references, triphenyl phosphate and phosphonoacetic acid. As a prerequisite to the concept of certification, they carry both types of nuclei, 1H and 31P. Triphenyl phosphate was chosen as a standard that can be applied for measurements in organic solvents, whereas phosphonoacetic acid can be used in aqueous solutions. Tris(2-chloroethyl) phosphate was selected as phosphorus-containing analyte in order to show the proof of concept in a 31P qNMR application. In order to overcome restrictions in solubility, the molecules have further been tested for solubility in other solvents that are typically used in NMR experiments (see Fig. 4). For their subsequent use in qNMR analyses, one of the major requirements is that the signals of the internal reference standard and the analyte do not overlap within the mixture. This applies for those 1H signals and the 31P signals respectively used for quantification. For visualization of the respective peak positions, the corresponding 1H and 31P NMR spectra of the two candidates and the analyte have been measured separately (Figs. 1 and 2).Fig. 1


Method development in quantitative NMR towards metrologically traceable organic certified reference materials used as (31)P qNMR standards.

Weber M, Hellriegel C, Rueck A, Wuethrich J, Jenks P, Obkircher M - Anal Bioanal Chem (2014)

Table of deuterated solvents in which the 31P CRM candidates triphenyl phosphate, phosphonoacetic acid, and the analyte tris(2-chloroethyl) phosphate are soluble and corresponding relaxation times (T1) for both nuclei, 1H and 31P. In the boxes which do not display time specifications, the substance was not sufficiently soluble. *Due to overlaps with the CDCl3 signals, the solvent CD2Cl2 was used as a substitute
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4383826&req=5

Fig4: Table of deuterated solvents in which the 31P CRM candidates triphenyl phosphate, phosphonoacetic acid, and the analyte tris(2-chloroethyl) phosphate are soluble and corresponding relaxation times (T1) for both nuclei, 1H and 31P. In the boxes which do not display time specifications, the substance was not sufficiently soluble. *Due to overlaps with the CDCl3 signals, the solvent CD2Cl2 was used as a substitute
Mentions: Based on various parameters, including solubility, structure, chemical shifts, stability, homogeneity, and purity, two different organic compounds have been selected as candidates for their use as 31P qNMR references, triphenyl phosphate and phosphonoacetic acid. As a prerequisite to the concept of certification, they carry both types of nuclei, 1H and 31P. Triphenyl phosphate was chosen as a standard that can be applied for measurements in organic solvents, whereas phosphonoacetic acid can be used in aqueous solutions. Tris(2-chloroethyl) phosphate was selected as phosphorus-containing analyte in order to show the proof of concept in a 31P qNMR application. In order to overcome restrictions in solubility, the molecules have further been tested for solubility in other solvents that are typically used in NMR experiments (see Fig. 4). For their subsequent use in qNMR analyses, one of the major requirements is that the signals of the internal reference standard and the analyte do not overlap within the mixture. This applies for those 1H signals and the 31P signals respectively used for quantification. For visualization of the respective peak positions, the corresponding 1H and 31P NMR spectra of the two candidates and the analyte have been measured separately (Figs. 1 and 2).Fig. 1

Bottom Line: These substances contain both nuclei, (1)H and (31)P, and the concept is to show that it is possible to indirectly quantify a potential phosphorus standard via its protons using (1)H qNMR.The same standard with its assigned purity can then be used for the quantification of an analyte via its phosphorus using (31)P qNMR.For the validation of the concept, triphenyl phosphate and phosphonoacetic acid have been used as (31)P qNMR standards to determine the purity of the analyte tris(2-chloroethyl) phosphate, and the resulting purity values perfectly overlap within their expanded measurement uncertainties.

View Article: PubMed Central - PubMed

Affiliation: Sigma-Aldrich Switzerland, Industriestrasse 25, 9471, Buchs, Switzerland.

ABSTRACT
Quantitative nuclear magnetic resonance (qNMR) spectroscopy is employed by an increasing number of analytical and industrial laboratories for the assignment of content and quantitative determination of impurities. Within the last few years, it was demonstrated that (1)H qNMR can be performed with high accuracy leading to measurement uncertainties below 1 % relative. It was even demonstrated that the combination of (1)H qNMR with metrological weighing can lead to measurement uncertainties below 0.1 % when highly pure substances are used. Although qNMR reference standards are already available as certified reference materials (CRM) providing traceability on the basis of (1)H qNMR experiments, there is an increasing demand for purity assays on phosphorylated organic compounds and metabolites requiring CRM for quantification by (31)P qNMR. Unfortunately, the number of available primary phosphorus standards is limited to a few inorganic CRM which only can be used for the analysis of water-soluble analytes but fail when organic solvents must be employed. This paper presents the concept of value assignment by (31)P qNMR measurements for the development of CRM and describes different approaches to establish traceability to primary Standard Reference Material from the National Institute of Standards and Technology (NIST SRM). Phosphonoacetic acid is analyzed as a water-soluble CRM candidate, whereas triphenyl phosphate is a good candidate for the use as qNMR reference material in organic solvents. These substances contain both nuclei, (1)H and (31)P, and the concept is to show that it is possible to indirectly quantify a potential phosphorus standard via its protons using (1)H qNMR. The same standard with its assigned purity can then be used for the quantification of an analyte via its phosphorus using (31)P qNMR. For the validation of the concept, triphenyl phosphate and phosphonoacetic acid have been used as (31)P qNMR standards to determine the purity of the analyte tris(2-chloroethyl) phosphate, and the resulting purity values perfectly overlap within their expanded measurement uncertainties.

No MeSH data available.