Dedicated solvents for Headspace GC

Transcription

1 Dedicated solvents for Headspace GC Dr. Frank Michel sigma-aldrich.com sigma-aldrich.com/analytical

2 Headspace GC - Basics Analysis of headspace above an (aqueous) sample: Gas and vapors are analyzed Injection of a gas mixture Low influence by the sample preparation Use of Headspace vials Equilibrium of volatile analytes between headspace and sample depends on: Indentity and concentration of analytes Matrix (sample modifications) Time Temperature 2

3 Headspace GC - Injection techniques Gastight syringe Electropneumatic dosing system Multiple Headspace Injection (MHI) or Multiple Headspace Extraction (MHE) Dynamic headspace analysis => Purge & Trap 3

4 Headspace GC - Application examples Alcohol in blood Residual solvents in pharmaceutical drugs Phenols in sewage sludge BTEX (Benzene-Toluene-Ethylbenzene-Xylene) in soil Flavor and natural compound analysis Monomers and solvents in polymers Indoor air monitoring (carpet, furniture) Forensic analysis 4

5 Solvents and Additives in Headspace GC Increasing the sensitivity Dissolution of the sample Improved heat transfer Low volatility Examples Organic solvents with high boiling points for polar analytes Salts for non-polar analytes in aqueous samples, adjustment of ph value (if appropriate) 5

6 GC-Headspace Solvents Comparison GC conditions (Ph. Eur System A): Column: SPB-624, 30mx0.32mmx1.8µm Temp.: 40 C (20 min.) 10 C /min. to 240 C 240 C (20 min) Carrier gas: Helium, 35 cm/s Inj./Det.: 140 C/250 C (FID) Headspace Chromatograms of DMSO (different grades): GC-HS Grade (black) normal grade (red) 6

7 GC-Headspace Solvents Comparison Headspace Parameters Oven: 100 C Sample loop: 110 C Transfer Line: 150 C GC Conditions: Column: SPB-624, 30 x 0.32 x1.8µm Temp.: 40 C (4 min.) 8 C /min. to 60 C 5 C /min. to 85 C (2 min.), 30 C /min. to 220 C (2 ) Carrier gas: Helium, 1.5 ml/min. const. fl. Inj./Det.: 225 C/270 C (FID) Headspace Chromatograms of DMAC: GC-HS Grade HPLC grade Sample of residual solvents 7

8 Ionic Liquids as Headspace Solvents Low volatility Very good dissolving properties High stability E. Hollender, E. W. Hammersley, Chromatography Today (2011) Vol. 4, Iss. 3 8

9 GC-Headspace Solvents Highly pure solvents, especially tested for headspace application Ensure high sensitivity Long life time packaged under inert gas Specifications according to USP, Ph.Eur. and ICH Guidelines Microfiltration (0.2 µm) 9

10 GC-Headspace Solvents Overview Name Purity Bp. ( C) Mp. ( C) Vapor press. (mm Hg) Pack. Prod.- Nr. Dimethylsulfoxide (DMSO) 99.9% (20 C) 1 L N,N-Dimethylformamide (DMF) 99.9% (20 C) 1 L N,N-Dimethylacetamide (DMAC) 99.9% (25 C) 1 L ,3-Dimethyl-2-imidazolidinone (DMI) 99.5% (83 C) 1 L Methyl-2-pyrrolidinone (NMP) 99.9% (20 C) 1 L Cyclohexanone 99.9% (20 C) 1 L Water L Further information please find at: sigmaaldrich.com/gc-hs 10

11 New Certified Reference Materials for Gas Chromatography Frank Michel sigma-aldrich.com/analytical

12 Use of Certified Reference Materials (CRMs) Quality Assurance Ensuring Accuracy of the Mean and Precision Ensuring an Analytical Method provides correct Results Traceability of results to acknowledged standards Calibration Validation of Analytical Methods Interlaboratory Trials ISO accredited labs have to use CRMs on regular base 12

13 Definition Certified Reference Material Reference material, accompanied by a certificate, one or more of whose property values are certified, by a procedure which establishes its traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty to a stated level of confidence. VIM:1995, ISO guide 30/31 13

14 National Metrological Institutes (NMIs) Providing acknowledged standards Examples for NMIs are: USA: National Institute of Standards and Technology (NIST) Germany: Federal Institute for Materials Research and Testing (BAM) 14

15 Traceability ISO Section 5.6: Measurement traceability Reference standards and reference materials Definition: property of a value to be related by an unbroken chain of comparison measurements to a reasonable normative. (VIM 6:10 ref: BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML, International Vocabulary of Basic and Metrological Terms in Metrology; 2nd edition, ISO Geneve, 1993) The uncertainty of a result has got to contain all uncertainties of all comparison measurements and the uncertainty of the reference. The length of this traceability chain is not limited, but: the uncertainty is increasing! X % Cu ±Y % X 3 % Cu ±Y 3 % X 2 % Cu ±Y 2 % 15

16 Traceability ISO Section 5.6: Measurement traceability Reference standards and reference materials Definition: property of a value to be related by an unbroken chain of comparison measurements to a reasonable normative. (VIM 6:10 ref: BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, OIML, International Vocabulary of Basic and Metrological Terms in Metrology; 2nd edition, ISO Geneve, 1993) Y 3 > Y 2 > Y The uncertainty of a result has got to contain all uncertainties of all comparison measurements and the uncertainty of the reference. The length of this traceability chain is not limited, but: the uncertainty is increasing! X % Cu ±Y % X 3 % Cu ±Y 3 % X 2 % Cu ±Y 2 % 16

17 Uncertainty Definition: part of the measurement/result, describes the variation of the values -1s 68.3 % + 1s Mistake and Uncertainty are not the same! - 2s 95.5 % + 2s Mistake = can not be determined - 3s + 3s (dictionary: mistake, oversight, accidental slip,...) 99.7 % Typical uncertainties in chemical analysis: Simple sample, metrological level: % Simple sample (no Matrix), normaler level % Analysis in Matrix 2-50% Problem: Users prefer low uncertainties... Consequence is: many CRM manufacturers calculate (or estimate) the uncertainty too optimistic (ignoring relevant shares). 17

18 ISO ISO Guide 34 Accreditation ISO 17025: General Requirements for the Competence of Calibration and Testing Laboratories Many labs do have Accreditation Important: Tracebility, uncertainty, education, infrastructure Accreditation is bound to a lab and scope ISO Guide 34: General Requirements for the Competence of Reference Material Producers Only few labs do have ISO Guide 34 Accreditation Important: Tracebility, uncertainty, homogenity, stability, shelf life Accreditation is bound to a lab and scope Produced in double accredited laboratory fulfilling and ISO/IEC and ISO Guide 34 ISO : Gold Standard Accreditation for Reference Material manufacturers ISO/IEC Only very few labs do have both Acknowledgement of competence and reliability STS 490 ISO Guide 34 und ISO/IEC SRMS

19 Organic CRMs: Challenges Numberless organic compounds Only few international standards available Traceability? 19

20 Alternative approach: qnmr Quantitative NMR (qnmr) is a Relative Primary Method NMR spectrum of an equimolar mixture of CH 3 Cl and CH 3 Br Signal intensity is: proportional to the number of protons independent of chemical structure (chemical shift is impacted) 20

21 Advantages of Quantitative NMR Traceability independent of chemical identity Low Uncertainties Expanded uncertainties between 0.1% and 0.5% Non-destructive Structural information on target compound Information on impurities Jancke H. NMR als primäre Methode. Nachrichten aus Chemie, Technik und Laboratorium, 1998, 46, 722 Jancke, H. NMR Spectroscopy as a Primary Analytical Method, Document 98/02 to the 4 th Session of the CCQM, Sèvres

22 Quantitative NMR (qnmr): Procedure Internal Standard Highprecision weighing Sample Solvent 1 H-NMR measurements Data processing 22

23 Content Assignment by qnmr Internal Standard Content known NIST traceable Analyte Acenaphthene 4 protons Dimethylsulfone 6 protons ppm

24 Content Assignment by qnmr Internal standard and the reference standard are weighed together into one NMR tube (with solvent) Intensities of appropriate signals of the reference standard (I x ) and the internal standard (I Std ) are used for calculation Content P x can be calculated by the following equation: Number of nuclei contributing to the resonance (N x, N Std ) Molar masses (M x, M Std ) Initial weight (m x, m Std ) and purity of internal standard (P Std ) 24

25 Tracebility to NIST Standard Reference Materials Benzoic acid NIST SRM Dimethylsulfone (IS) Fluka Acenaphthene Fluka

26 Signal allocation and purity: 2D-NMR: H-H COSY enhancement 1000x ppm HO O NO 2 mono Nitrobenzoic acid ppm 2D-COSY of 3,5-dinitrobenzoic acid. Signals of impurity 3-nitrobenzoic acid detectable. Easy detection at concentration below 0,1% 26

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28 Organic TraceCERT: CRMs for Gas Chromatography Polyaromatic Hydrocarbons (PAHs) Fatty Acid Methyl Esters (FAMEs) Hydrocarbons Semi-volatile hydrocarbons (SVHC) 28

29 Summary New Method for Content Assignment of Organic Compounds by qnmr Traceability independent of chemical identity Low Uncertainties Non-destructive Structural information and information on impurities Generation of new CRMs for Chromatography Quality Assurance Ensuring Accuracy of the Mean and Precision Ensuring an Analytical Method provides correct Results 29

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