Practical guide for selection of 1 H qNMR acquisition and processing parameters confirmed by automated spectra evaluation

Metabolite quantification: A fluorescence-based method for urine sample normalization prior to 1H-NMR analysis

INTRODUCTION

Metabolomics is a multi-discipline approach to systems biology that provides a snapshot of the metabolic status of a cell, tissue, or organism. Metabolomics uses mass spectroscopy (MS) and nuclear magnetic resonance (NMR) to analyze biological samples for low molecular weight metabolites.

OBJECTIVE

Normalize urine sample pre-acquisition to perform a targeted quantitative analysis of selected metabolites in rat urine.

METHODS

Urine samples were provided from rats on a control diet (n = 10) and moderate sucrose diet (n = 8) collected in a metabolic cage during an eight hour fast. Urine from each sample was prepared by two different methods. One sample was a non-normalized sample of 1200 µL and the second sample was a variable volume-normalized to the concentration of urobilin in a standard sample of urine. The urobilin concentration in all samples was determined by fluorescence. Ten metabolites for each non-normalized and normalized urine sample were quantified by integration to an internal standard of DSS.

RESULTS

Both groups showed an improvement in pH range going from non-normalized to normalized samples. In the group on the control diet, eight metabolites had significant improvement in range, while the remaining two metabolites had insignificant improvement in range comparing the non-normalized sample to the normalized sample. In the group on the moderate sucrose diet all ten metabolites showed significant improvement in range going from non-normalized to normalized samples.

CONCLUSIONS

These findings describe a pre-acquisition method of urine normalization to adjust for differences in hydration state of each organism. This results in a narrower concentration range in a targeted analysis.

Two Ways to Achieve the Same Goal-Two Validated Quantitative NMR Strategies for a Low-Abundance Natural Product in Standardized Extracts: The Case of Hepatodamianol in Turnera diffusa

The quantification of low-abundance secondary metabolites in plant extracts is an analytical problem that can be addressed by different analytical platforms, the most common being those based on chromatographic methods coupled to a high-sensitivity detection system. However, in recent years nuclear magnetic resonance (NMR) has become an analytical tool of primary choice for this type of problem because of its reliability, inherent simplicity in sample preparation, reduced analysis time, and low solvent consumption. The versatility of strategies based on quantitative NMR (qNMR), such as internal and external standards and electronic references, among others, and the need to develop validated analytical methods make it essential to compare procedures that must rigorously satisfy the analytical well-established acceptance criteria for method validation. In this work, two qNMR methods were developed for the quantification of hepatodamianol, a bioactive component of T. diffusa. The first method was based on a conventional external standard calibration, and the second one was based on the pulse length-based concentration determination (PULCON) method using the ERETIC2 module as a quantitation tool available in TopSpin software. The results show that both procedures allow the content of the analyte of interest in a complex matrix to be determined in a satisfactory way, under strict analytical criteria. In addition, ERETIC2 offers additional advantages such as a reduction in experimental time, reagent consumption, and waste generated.

Quantitative NMR as a Versatile Tool for the Reference Material Preparation

The assessment of primary calibrator purity is critical for establishing traceability to the International System of Units (SI). Recently, quantitative nuclear magnetic resonance (qNMR) has been used as a purity determination method for reference material development, and many related measurement techniques have been designed to acquire accurate and reliable results. This review introduces the recent advances in these techniques (including multidimensional methods), focusing on the application of qNMR to reference material preparation.

Collaborative Study to Validate Purity Determination by 1H Quantitative NMR Spectroscopy by Using Internal Calibration Methodology

NMR spectroscopy has recently been utilized to determine the absolute amounts of organic molecules with metrological traceability since signal intensity is directly proportional to the number of each nucleus in a molecule. The NMR methodology that uses hydrogen nucleus (¹H) to quantify chemicals is called quantitative ¹H-NMR (¹H qNMR). The quantitative method using ¹H qNMR for determining the purity or content of chemicals has been adopted into some compendial guidelines and official standards. However, there are still few reports in the literature regarding validation of ¹H qNMR methodology. Here, we coordinated an international collaborative study to validate a ¹H qNMR based on the use of an internal calibration methodology. Thirteen laboratories participated in this study, and the purities of three samples were individually measured using ¹H qNMR method. The three samples were all certified via conventional primary methods of measurement, such as butyl p-hydroxybenzoate Japanese Pharmacopeia (JP) reference standard certified by mass balance; benzoic acid certified reference material (CRM) certified by coulometric titration; fludioxonil CRM certified by a combination of freezing point depression method and ¹H qNMR. For each sample, ¹H qNMR experiments were optimized before quantitative analysis. The results showed that the measured values of each sample were equivalent to the corresponding reference labeled value. Furthermore, assessment of these ¹H qNMR data using the normalized error, E_n-value, concluded that statistically ¹H qNMR has the competence to obtain the same quantification performance and accuracy as the conventional primary methods of measurement.

2 H SOLCOR: A novel tool for reducing volume variation as a source of error in external standard quantitative NMR

Tube to tube volume difference presents a challenge in obtaining correct external standard quantitative NMR (esqNMR) results. Deuterium (² H) NMR is easily observable, intrinsically quantitative, present in all samples, free of interfering signals, and insensitive to probe tune/match and sample saltiness. These properties make ² H peak integral an ideal parameter in esqNMR for correcting volume differences between the reference standard and analyte. We demonstrate a novel and practical technique abbreviated as "² H SOLCOR" (² H SOLvent CORrected), where the ² H peak integral from the solvent is used as a universal internal standard to correct volume variations in NMR tubes, thereby improving accuracy and precision of esqNMR method. Herein, this simple yet effective technique is described, and practical considerations for successful implementation are presented. ² H SOLCOR can be applied anywhere esqNMR is used, including where precious samples need to be accurately quantified for qualification as an authentic analytical standard.

Quantitative 1H-NMR spectroscopy as an efficient method for identification and quantification of PVC, ABS and PA microparticles

This work presents a new, size-independent, fast, mass based MP-analysis of PVC, ABS and PA 6.6 using quantitative ¹H-NMR spectroscopy.

NMR spectroscopy in drug discovery and development: Evaluation of physico-chemical properties

Determination of physico-chemical properties of compounds is one of the corner-stones in selection of hit molecules for further progression into lead development in the modern drug discovery process. The speed of traditional analyses and limited quantities of hit molecules are obstacles for efficient acquisition of experimental data. Herein, the range of applications of quantitative nuclear magnetic resonance (NMR) spectroscopy as a fast technique used to evaluate solubility, log P and pKa are discussed.

Quantitative analysis of PET microplastics in environmental model samples using quantitative 1H-NMR spectroscopy: validation of an optimized and consistent sample clean-up method

Identification and quantification of microplastics (MP) in environmental samples is crucial for understanding the risk and distribution of MP in the environment. Currently, quantification of MP particles in environmental samples and the comparability of different matrices is a major research topic. Research also focusses on sample preparation, since environmental samples must be free of inorganic and organic matrix components for the MP analysis. Therefore, we would like to propose a new method that allows the comparison of the results of MP analysis from different environmental matrices and gives a MP concentration in mass of MP particles per gram of environmental sample. This is possible by developing and validating an optimized and consistent sample preparation scheme for quantitative analysis of MP particles in environmental model samples in conjunction with quantitative ¹H-NMR spectroscopy (qNMR). We evaluated for the first time the effects of different environmental matrices on identification and quantification of polyethylene terephthalate (PET) fibers using the qNMR method. Furthermore, high recovery rates were obtained from spiked environmental model samples (without matrix ~ 90%, sediment ~ 97%, freshwater ~ 94%, aquatic biofilm ~ 95%, and invertebrate matrix ~ 72%), demonstrating the high analytical potential of the method. Graphical abstract.

Quo Vadis qNMR?

The quantification of a drug, its impurities, and e.g. components of a mixture has become routine in NMR laboratories and many applications have been described in the literature. However, besides simply using 1D ¹H or ¹³C NMR, a number of more advanced methods has been developed and used in the past. Here, we want to describe the applicability of nuclei beyond the classical ones ¹H and ¹³C. Mixtures can be characterized much better by applying various chemometric methods and separating the signals of mixture components can be achieved by DOSY experiments. All these methods contribute to the platform of qNMR methods and extend the possibilities of NMR for quantification and quality evaluation of drugs, excipients, polymers, and plant extracts. However, for quantification purposes, validation is always an issue and it is necessary to think about taking NMR related measures which might be different from the ones considered for chromatographic methods.

Quality Control of Therapeutic Peptides by 1H NMR HiFSA Sequencing

Ensuring identity, purity, and reproducibility are equally essential during synthetic chemistry, drug discovery, and for pharmaceutical product safety. Many peptidic APIs are large molecules that require considerable effort for integrity assurance. This study builds on quantum mechanical ¹H iterative Full Spin Analysis (HiFSA) to establish NMR peptide sequencing methodology that overcomes the intrinsic limitations of principal compendial methods in identifying small structural changes or minor impurities that affect effectiveness and safety. HiFSA sequencing yields definitive identity and purity information concurrently, allowing for API quality assurance and control (QA/QC). Achieving full peptide analysis via NMR building blocks, the process lends itself to both research and commercial applications as 1D ¹H NMR (HNMR) is the most sensitive and basic NMR experiment. The generated HiFSA profiles are independent of instrument or software tools and work at any magnetic field strength. Pairing with absolute or 100% qHNMR enables quantification of mixtures and/or determination of peptide conformer populations. Demonstration of the methodology uses single amino acids (AAs) and peptides of increasing size, including the octapeptide, angiotensin II, and the nonapeptide, oxytocin. The feasibility of HiFSA coupled with automated NMR and qHNMR for use in QC/QA efforts is established through case-based examples and recommended procedures.

Automated multicomponent phospholipid analysis using 31P NMR spectroscopy: example of vegetable lecithin and krill oil

Nuclear magnetic resonance (NMR) spectroscopy is widely applied in the field of metabolomics due to its quantitative nature and the reproducibility of data generated. However, one of the main challenges in routine NMR analysis is to obtain valuable information from large datasets of raw data in a high-throughput, automatic, and reproducible manner. In this study, a method to automatically annotate and quantify 12 phospholipids (PLs) in vegetable lecithin (soy, sunflower, rape) and krill oil is introduced. Automated routines were written in MATLAB environment for quantification of phosphatidylcholine (PC), phosphatidylinositol (PI), lyso-phosphatidylcholine (LPC), phosphatidylserine (PS), phosphatidylethanolamine (PE), diphosphatidylglycerol or cardiolipin (DPG), phosphatidylglycerol (PG), and lyso-phosphatidylethanolamine (LPE) in lecithin and of PC, PC-ether, LPC, PE, N-acyl phosphatidylethanolamine (APE), and LPE in krill oil matrix. The routine includes NMR spectra import, extraction of data points, peaking of local minima and local maxima in the data, integration, quantitation against internal standard, reporting of results as Word file, and their importing in our internal database. Our extensive studies on a representative set of more than 1000 lecithin (soy, rape, sunflower) and krill samples showed that the routine can automatically and accurately calculate the concentrations of all PLs. No systematic or proportional differences between automated and manual evaluation were detected. The developed automated program produces accurate results and requires less than 5 s for each analysis. This tool is already used in high-throughput PL analysis of krill and lecithin and will be adjusted to other matrices (egg, milk, chocolate, etc.) as well.

Monitoring daily routine performance in quantitative NMR (qNMR) spectroscopy: Is the system suitability test necessary?

Nuclear magnetic resonance spectrometry (NMR) finds numerous applications in pharmacy, cosmetic, and food control as well as in developing tools for "big data" analysis. However, there remains a need for automated tools to assess instrument system suitability in real time for each particular routine sample. An automated procedure has been introduced to monitor a number of characteristics (resolution, symmetry, and half width) in real time after the measurement of two samples distributed by the vendor (0.3% CHCl3 in acetone-d6 with tetramethylsilane and 2 mM sucrose in H2 O-D2 O). The results over 11 months were discussed in terms of average values, standard deviations, and spectrometer variability. Moreover, multivariate statistical procedure was implemented to evaluate metrics generated from three NMR spectrometers. Performance of three NMR spectrometers (500 MHz with BBO Prodigy Cryoprobe, 500 MHz with BBFOPLUS SmartProbe, and 600 MHz with BBO Cryoprobe) differed significantly. The developed routine was also applied to calculate the performance characteristics during routine quantitative NMR experiments. The procedure was evaluated for NMR spectra of 659 active pharmaceutical ingredients dissolved in CDCl3 , DMSO, and CH3 OD. This test is more preferable than the routine procedure using standard solutions because the performance is estimated separately for each matrix at the specific time point of measurements. Our automated routine is the ideal tool for any NMR laboratory. In full automation, the NMR data are validated directly for each sample, making unnecessary daily measurements of standard solutions and manual evaluation to their NMR spectra.