Analytical Strategy: HS 2014 Rafael Hodel, Stefanie Jucker. Quality Control: Quantitative Nuclear Magnetic Resonance

Transcription

1 Analytical Strategy: HS 2014 Rafael Hodel, Stefanie Jucker Quality Control: Quantitative Nuclear Magnetic Resonance

2 Quality Control (QC) - Why? 1) Purchasing raw materials and educts Did we get what we paid for? Is it pure or contaminated? if raw material contains high amount of heavy metals, it is likely that the final product will have a too high amount too. For good products we need good educts 2) In-Process Control Again: only good intermediates lead to good products it s cheaper to dismiss a intermediate than a final product determine mistakes in process design and correct them in each step

3 Quality Control (QC) - Why? 3) QC of final product Guarantee quality of produced products sell only good product of high quality to establish a good reputation guarantee safety for customers is delivered product the right one? (labelling error) proof for responsible procedure (good documentation needed)

4 Quality Control (QC) - Why? 4) Stability Tests How long is product stable? how long can we sell it? how long is it safe to use it? (loss of efficiency or decomposition products?) Can we sell it in other regions? different temperature and humidity might have drastic influence on stability determine required packing conditionsdocumentation needed)

5 Methods for QC in Industry 1) GLP/GMP compliant work to guarantee that results are valid (validation of methods and devices) 2) Methods must be relatively simple: high throughput in short time routine analysis 3) Reproduceable results 4) Not too expensive

6 Methods for QC in Industry Wet Chemistry: Titrimetry, ID-Tests, turbidity, ph, Photometry: UV, IR, AAS, ICP MS: Quadrupole, MALDI, Chromatography: TLC, GC, HPLC, qnmr

7 Chromatography Principle of Separation - separation of analyte compounds due to different dwelling time in the stationary phase of the single compounds - mobile phase acts as transport media - equilibrium distribution of analyte compounds between mobile and stationary phase - different compounds show different equilibrium distribution (variing adsorption behaviour to stationary phase due to differences in polarity)

8 Chromatography - Detection Depending on the chosen analytic system and the nature of he sample, we can choose between many ways of detection: DC GC HPLC Day light FID Oxidizes carbon in sample (high sensitivity) UV/VIS conjugated double bonds, aromatic systems UV WLD Universal (low sensitivity) Fluorescence rigid aromatic systems and fluorescent molecules Treatment Ex.: Ninhydrine to detect amines or amino acids Electron Capture (ECD) Halogenes Refractometric (RI) sugar Molecules Electro analytic Electro active substances

9 Quantification with GC and HPLC Area-%: Mainly for solvents like heptane - fast and easy but of limited use External Standard: If certified standard is available and the expected concentration is known. To guarantee the stability of the analysis, standard solution should be measured at the beginning, at the end and for long sample series also after every few injected samples. - accurate but many standard measurements needed

10 Quantification with GC and HPLC Internal Standard In every sample a standard similar to the probe is added. The area of each sample is then compared with its internal standard. Thereby the standard undergoes the same treatment as the sample and we can reduce systematic errors. On the other side it s possible that the same concentration of sample and standard lead to different intensities due different chemical structure.

11 Performance Problems Fronting Tailing Peak overlap Reasons for abnormal peak behaviour Non optimal eluent, overloading of column, wrong ph, instrumental problems

12 Chromatography: Pro and Cons + versatile (many different compounds can be analyzed and the methods can be optimized) + rel. cheap (compared to NMR) + sensitive - different substances lead to different signal intensities - compounds might get stuck in stationary phase - false results because resolution might not be high enough (overlap) - versatile (analytes need the right column and mobile phase )

13 Quantitative NMR

14 qnmr - principle Using NMR to determine the concentration of one or more species in solution Area under peak directly proportional to concentration Quantification by absolute integral or with internal standard

15 Quantification Absolute Integral Needs a standard reference with well known concentration to determine the NMR response factor per nuclide under the given experimental conditions. With this conversion factor one can later calculate the concentration in the samples. Internal Standard A standard of known concentration and foreign to the analyte compounds is added to each sample (no overlapping peaks). The integral of the sample is then compared to the integral of the standard.

16 Requirements for......the sample completely soluble in deuterated solvent has NMR active nucleus signals must be separated

17 Requirements for......the Internal Standard same as requirements as for the sample is stable & does not react with the sample or the solvent different chemical shifts than the probe limited number of signals No residual water proton exchange with water leads to line broadening to reduce weighing errors, the Standard should not be hygroscopic or volatile preferably not causing any kind of health issues

18 Pro qnmr Primary method: signal intensity does not depend on structure but directly on the number of protons Different peaks for quantification within one measurement we got multiple peaks (from different protons on the molecule) which we can integrate and compare to the standard Non-destructive No similar Standard needed robust

19 Contra qnmr Expensive devices and maintenance Quantification only possible for non overlapping peaks from NMR active material

20 Comparison of Chromatography and qnmr Chromatography qnmr + flexible + cheap + sensitive + primary method + no need for similar standard + non-destructive + use of different protons for quantification in one material - signal intensity depends on compound - destructive - optimisation of mobile and stationary phase - expensive - needs protons with non overlapping signals

21 Certified Reference Material - CRM Definition: Reference material characterized by a metrologically valid procedure accompanied by a certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability (ISO Guide 34:2009(E)) Metrological traceability: a measurement result that can be traced back to either SI unit, defined scale or mass fraction Also need to comply with ISO/IEC General requirements for the competence of testing and calibration laboratories and ISO Guide 35 - Reference materials -- General and statistical principles for certification

22 CRM example of certificate

23 Certification Process for qnmr

24 Schematic for qnmr Purity Determination reference qnmr measurand solvation Weighing such that equal NMR signal intensities result Both substances need to be soluble in same deuterated solvent

25 Measurement Uncertainty Definition: Non-negative parameter characterizing the dispersion of the quantity values being attributed to a measurand based on the information used (ISO Guide 34:2009(E)) For example: standard deviation

26 Major Measurement Uncertainties for qnmr Typical contributions to relative uncertainties: Weighing (reference, analyte): < 0.02 % Molecular mass (reference, analyte): < 0.01 % Purity of reference: < 0.1 % Signal integration: < 0.1% Schoenberger (2012) Anal Bioanal Chem, 403:

27 Major Measurement Uncertainties for qnmr Weighing (reference, analyte) accurate balance anti static measures Signal integration signal/noise ratio integration region

28 Conclusion Chromatography cheap, but standard and analyte need to be the same qnmr more expensive, but does not need same standard as analyte Purity determinations expected to show different results Magnetic field determines accuracy for NMR Length of column determines accuracy for chromatography Peak overlap

29 Thank you