oSIST prEN 17992:2023
(Main)Food authenticity - Determination of the sum of 16-O-methylcafestol, 16-O-Methylkahweol and their derivatives in roasted coffee by ¹H-qNMR
Food authenticity - Determination of the sum of 16-O-methylcafestol, 16-O-Methylkahweol and their derivatives in roasted coffee by ¹H-qNMR
This document specifies a method for the determination of soluble 16-O-Methylcafestol and 16-O-Methyl kahweol content (the sum of free forms and derivatives, e.g. fatty acid esters, henceforth abbreviated as 16-OMD = "diterpenes") in roasted coffee (beans or ground), using quantitative proton nuclear magnetic resonance spectroscopy (1H-qNMR).
If complying with the experimental parameters described below, this test procedure has been proven for the following concentration range:
16-OMD: 20 mg/kg to 2 000 mg/kg.
The concentration range can be expanded by suitable changes of the experimental parameters, e.g. a different weighed portion of ground coffee or the accumulation of more NMR-transients.
Lebensmittelauthentizität - Bestimmung des Gehalts von 16-O-Methylcafestol, 16-O-Methylkahweol und deren Derivaten als Summenparameter in Röstkaffee mittels ¹H-qNMR
Dieses Dokument legt ein Verfahren zur Bestimmung des Gehalts an löslichem 16-O-Methylcafestol und 16 O-Methylkahweol (Summe der freien Formen und Derivate, z. B. Fettsäureester, im Folgenden abgekürzt als 16-OMD = "Diterpene") in geröstetem Kaffee (Bohnen oder gemahlen) mittels quantitativer Protonen-nuklearmagnetischer Resonanzspektroskopie (1H-qNMR) fest.
Bei Einhaltung der nachstehend beschriebenen Versuchsparameter hat sich dieses Prüfverfahren für den folgenden Konzentrationsbereich bewährt:
16-OMD: 20 mg/kg bis 2 000 mg/kg.
Der Konzentrationsbereich kann durch geeignete Änderungen der Versuchsparameter erweitert werden, z. B. durch eine andere Einwaage des gemahlenen Kaffees oder die Akkumulation von mehr NMR-Transienten.
Authenticité alimentaire du café - Détermination de la teneur en 16-O-méthylcafestol - Méthode par NMR
No Scope Available
Pristnost živil - Določanje vsote 16-O-metilkafestola, 16-O-metilkaveola in njunih derivatov v praženi kavi z metodo ¹H-qNMR
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
oSIST prEN 17992:2023
01-september-2023
Pristnost živil - Določanje vsote 16-O-metilkafestola, 16-O-metilkaveola in njunih
derivatov v praženi kavi z metodo ¹H-qNMR
Food authenticity - Determination of the sum of 16-O-methylcafestol, 16-O-
Methylkahweol and their derivatives in roasted coffee by ¹H-qNMR
Lebensmittelauthentizität - Bestimmung des Gehalts von 16-O-Methylcafestol, 16-O-
Methylkahweol und deren Derivaten als Summenparameter in Röstkaffee mittels ¹H-
qNMR
Authenticité alimentaire du café - Détermination de la teneur en 16-O-méthylcafestol -
Méthode par NMR
Ta slovenski standard je istoveten z: prEN 17992
ICS:
67.140.20 Kava in kavni nadomestki Coffee and coffee substitutes
oSIST prEN 17992:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 17992:2023
DRAFT
EUROPEAN STANDARD
prEN 17992
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2023
ICS 67.140
English Version
Food authenticity - Determination of the sum of 16-O-
Methylcafestol, 16-O-Methylkahweol and their
1
derivatives in roasted coffee by H-qNM
Authenticité alimentaire du café - Détermination de la Lebensmittelauthentizität - Bestimmung des Gehalts
teneur en 16-O-méthylcafestol - Méthode par NMR von 16-O-Methylcafestol, 16-O-Methylkahweol und
deren Derivaten als Summenparameter in Röstkaffee
1
mittels H-qNMR
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 460.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 17992:2023 E
worldwide for CEN national Members.
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Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Reagents . 8
5 Apparatus . 9
6 Measurement and test methods . 10
6.1 General. 10
6.2 Sampling . 11
6.3 Sample preparation . 11
6.4 NMR experiments . 12
6.5 Calibration and evaluation . 14
6.6 Determination of the PULCON factor . 15
6.7 Calculation of the analyte mass concentrations in coffee . 16
6.8 List of analytes and relevant parameters . 17
7 Accuracy . 17
7.1 Ring test / Interlaboratory comparison test . 17
7.2 Repeatability . 17
7.3 Reproducibility . 17
7.4 Limit of quantification (LOQ) . 18
8 Test report . 18
Annex A (informative) Summary of the statistical evaluation of the method validation study
“16-OMC in coffee” . 19
Annex B (informative) Common collaborative study of the NMR and HPLC methods (prEN
XXXX and prEN YYYY) . 22
B.1 Background of the collaborative study . 22
B.2 Explanation of systematic differences between the results of the NMR and HPLC
methods (prEN XXXX and prEN YYYY) . 22
Bibliography . 23
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European foreword
This document (prEN 17992:2023) has been prepared by Technical Committee CEN/TC 460 “Food
authenticity”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
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Introduction
This document was developed in response to demand for an efficient and reliable test method allowing
the confirmation of coffee authenticity both for commercial quality control and for official food control.
The coffee species with the greatest commercial importance are Coffea Arabica and Coffea canephora var.
robusta, commonly known as “arabica” and “robusta”. Within these species, Arabica coffees have a
significantly higher market value than robusta coffees. In unblended coffee the botanical origin of coffee
can be determined unambiguously by analysing the concentration of 16-O-methylcafestol and 16-O-
Methylkahweol and their derivatives (e.g. fatty acid esters) because these marker substances are present
in arabica coffee at very low concentrations (typically < 20 mg/kg). In robusta coffees the concentration
1
levels are significantly higher in the approximate range of 800 to 2 500 mg/kg. [1 – 5]
1
These published values are quoted as an orientation only and not intended as strict threshold recommendations.
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1 Scope
This document specifies a method for the determination of soluble 16-O-Methylcafestol and 16-O-Methyl
kahweol content (the sum of free forms and derivatives, e.g. fatty acid esters, henceforth abbreviated as
16-OMD = “diterpenes”) in roasted coffee (beans or ground), using quantitative proton nuclear magnetic
1
resonance spectroscopy ( H-qNMR).
If complying with the experimental parameters described below, this test procedure has been proven for
the following concentration range:
16-OMD: 20 mg/kg to 2 000 mg/kg.
The concentration range can be expanded by suitable changes of the experimental parameters, e.g. a
different weighed portion of ground coffee or the accumulation of more NMR-transients.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN ISO 1042, Laboratory glassware - One-mark volumetric flasks (ISO 1042)
ISO 3310-1, Test sieves — Technical requirements and testing — Part 1: Test sieves of metal wire cloth
ISO 3509, Coffee and coffee products — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3509 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp/
— IEC Electropedia: available at https://www.electropedia.org/
3.1
16-OMC and 16-OMK (= 16-O-Methyl Diterpene (“16-OMD”) derivatives content extractable with
chloroform
content in coffee, determined according to this test procedure and quoted as a mass fraction w in mg per
kg coffee, calculated as free 16-OMC
Note 1 to entry: An additional fraction of the total 16-OMD content (ca. 25 %) can only be extracted by vigorous
chemical processing.
Note 2 to entry: Approximately a mass fraction of 90 % of the 16-OMD is represented by 16-O-methylcafestol, and
16-O-methylkahweol represent the remaining mass fraction of 10 % of the mixture.
Note 3 to entry: The relative error due to differences in molar weight is 0,6 %.
[SOURCE: [1]]
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3.2
16-OMC
16-O-Methylcafestol
2
(CAS RN® : 108214-28-4), M = 330,5 g/mol
Note 1 to entry: The substance appears in its free form or esterified, see Figure 1.
3.3
16-OMK
16-O-Methylkahweol
(CAS RN®: not yet available), M = 328,5 g/mol
Note 1 to entry: The substance appears in its free form or esterified, see Figure 1.
a) 16-OMC b) 16-OMK
c) kahweol d) dehydrokahweol
Key
R residue (H or fatty acid)
NOTE The atom numbering is the same for the shown substances.
Figure 1 — Four diterpenes present in coffee
3.4
FID
free induction decay
time-domain NMR signal that results from the precession of the nuclear magnetization vector inside the
probe coil after application of an excitation RF pulse to a sample in a static magnetic field
[SOURCE: ISO 24583:2022, 3.6]
2
CAS Registry Number® is the trademark of a product supplied by CAS. This information is given for the
convenience of users of this document and does not constitute an endorsement by CEN of the product named.
Equivalent products may be used if they can be shown to lead to the same results.
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3.5
FWHM
full width at half maximum
width of a line shape at half the maximum signal intensity
Note 1 to entry: It is expressed in Hz.
[SOURCE: ISO 24583:2022, 3.9 – modified: Note 2 to entry deleted]
3.6
kahweol
1,2-Dehydrocafestol (CAS RN®: 6894-43-5)
Note 1 to entry: The substance appears in its free form or esterified, see Figure 1.
3.7
dehydrokahweol
1,2,15,16-bis-dehydrocafestol (CAS RN®: not yet available)
Note 1 to entry: It is a roasting product from kahweol.
Note 2 to entry: The substance appears in its free form or esterified, see Figure 1.
3.8
NMR
nuclear magnetic resonance spectroscopy
method based on the selective absorption of high frequency radio waves by atomic nuclei subjected to a
stationary magnetic field
Note 1 to entry: NMR provides chemical and structural properties of molecules.
[SOURCE: ISO 23118:2021, 3.10]
3.9
ppm
part per million
unit for the chemical shift (δ) of a resonance signal
Note 1 to entry: Dividing a signal’s real resonance frequency fres (in Hz, cycles per second) by the frequency rating
6
of the NMR spectrometer fspect and multiplying with 10 , a normalized shift measure is obtained that is independent
of the spectrometer’s field strength. See the following formula for explanation:
f
res
δ × 1 000 000
res
f
spect
3.10
PULCON
PUlse-Length-based CONcentration determination
quantitative NMR method with external standard factoring in the duration of the 90° excitation pulse into
the calculation of concentrations
7
=
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3.11
QuantRef
Quantification Reference
external standard to determine the spectrometer’s response (signal integral per amount of NMR-active,
measured nuclei)
Note 1 to entry: The QuantRef shall be a stable solution of one or more certified reference substances showing at
least one intensive and baseline-separated resonance in the NMR-spectrum. Preferably substances with short T
1
transversal relaxation value should be used, thus enabling the use of shorter recycle delays between FIDs. The
concentration(s) should be high enough to yield an SNR > 150 (reducing the uncertainty due to noise under 1 %)
under applied NMR acquisition parameters (typical concentrations should be between 10 to 50 mmol/L). Reference
substances intended for use in a QuantRef shall have a proven long-lasting stability in this mixture (ambient light,
normal room temperature) Signals of the reference substances should not be close to the residual non-deuterated
solvent signal or a trace water signal. Care shall be taken to ensure signals are separated by a clear, flat baseline
13
without signal overlap, e.g. from C satellites.
3.12
sample temperature
calibrated temperature of the sample during the NMR experiment(s)
3.13
SNR
signal to noise ratio
4 Reagents
4.1 General requirements
Only certified and traceable substances of highest purity shall be used as reference substances. These
reference substances shall be stored separately from the samples.
4.2 Deuterated Chloroform (CDCl ), minimum degree of deuteration 99,8 % (at.), CAS RN® 865-49-6
3
Deuterated solvent for the extraction and the NMR measurement of lipophilic substances in coffee.
4.3 Tetramethylsilane (TMS), CAS RN®: 75-76-3
Internal standard used for the calibration of the ppm-scale δ(TMS) = 0,00 ppm (def). May be omitted if
the solvent’s residual non-deuterated signal is used for calibration of the chemical shift scale
4.4 Deuterated Chloroform with TMS
TMS is added to CDCl to achieve a TMS content between 0,03 % and 0,1 %. The solution shall be stored
3
in the dark, preferably in a brown glass bottle. Some centimetres of silver tape should be added to hinder
the formation of aggressive compounds (phosgene, hydrogen chloride) that could later deteriorate the
3
samples. The possible addition of molecular sieves (3 Å or 4 Å) helps to absorb any residual water.
4.5 1,2,4,5-Tetrachloro-3-nitrobenzene (TCNB), CAS RN®: 117-18-0, M = 260,89 g/mol
Exemplary reference substance for the QuantRef solution, δ (in CDCl ) = 7,74 ppm, s, 1 H; very stable in
3
CDCl , but long T transversal relaxation value.
3 1
4.6 Ethylbenzene, CAS RN®: 100-41-4, M = 106,17 g/mol
3
1 Å = 10⁻¹⁰ m, molecular sieves of different pore sizes are generally offered in Ångström units.
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Exemplary reference substance for the QuantRef solution, δ (in CDCl ) = 7,30 ppm to 7,26 ppm, m, 2 H;
3
7,23 ppm to 7,15 ppm, m, 2 H; 7,23 ppm to 7,15 ppm, m, 1 H; 2,65 ppm, q (7,6 Hz), 2 H and 1,24 ppm, t
(7,6 Hz), 3 H.
4.7 1,3,5-Trimethoxybenzene, CAS RN®: 621-23-8, M = 168,19 g/mol
Exemplary reference substance for the QuantRef solution, δ (in CDCl ) = 6,1 ppm, s, 3 H and 3,8 ppm, s,
3
9 H.
4.8 p-Xylene, CAS RN®: 106-42-3, M = 106,2 g/mol
Exemplary reference substance for the QuantRef solution, δ (in CDCl ) = 7,06 ppm, s, 4 H and 2,31 ppm,
3
s, 6 H.
4.9 Dimethylsulfon, CAS RN®: 67-71-0, M = 94,13 g/mol
Exemplary reference substance for the QuantRef solution, δ (in CDCl ) = 2,31 ppm, s, 6 H.
3
4
4.10 Cyclohexane, CAS RN®: 110-82-7, M = 84,16 g/mol
Exemplary reference substance for the QuantRef solution, δ (in CDCl ) = 1,43 ppm, s, 12 H. Caution:
3
resonance close to water signal in CDCl .
3
4.11 QuantRef solution
In a 5 mL volumetric flask at least one of the reference substances (4.5 to 4.10) is/ are dissolved in CDCl
3
to achieve concentrations between 5 to 10 mg/mL. The exact weighed portions shall be documented
(6.3.1). After thorough mixing, fill 0,6 mL of this QuantRef solution into an NMR tube that subsequently
is fused shut. By repeated weighing the tube shall be checked against leakage, the proven tube shall be
labelled with a distinct ID and the date of preparation.
In general, other reference substances and concentrations may be used for the QuantRef solution as long
as the conditions stated in 3.9 are fulfilled. By using more than one substance, a higher reliability of the
QR solution can be reached.
4.12 Quality control sample for monitoring repeatability and reproducibility
To supervise the whole process regularly, an appropriately sized sample of real coffee with a substancial
16-OMD content shall be stored in a tightly closed vessel in the dark. From this quality control sample
one aliquot shall be prepared and measured with each new sample series, the results shall be documented
in a control chart. The mean (expected value) and the upper/ lower thresholds shall be based on an
appropriate number of replicates (prior period). Warning thresholds of ± 2 σ and action thresholds
of ± 3 σ are recommended. The current result should stay within warning thresholds and shall stay within
action thresholds else the measurement batch should be repeated.
5 Apparatus
5.1 General
4
Chloroform can slowly deteriorate the coffee extract and is a hazardous solvent. Cyclohexane has been proven
(elsewhere) to extract the 16-OMD as well as chloroform, thus it can be used as a substitute: Prepare a 95/5 mixture
of non-deuterated/deuterated cyclohexane, use this in the extraction step, then centrifuge the suspension
(centrifugation works well with cyclohexane, but not with chloroform). From the clear supernatant take a filtered
600 µL aliquot for NMR measurement. Adapt the NMR experiment to suppress the cyclohexane resonance
(1,41 ppm, s), then proceed as usual. Cyclohexane’s extraction capacity for other substances (HMF, furfuryl alcohol)
can be unsatisfying. This modification would need individual validation.
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Normal laboratory equipment is needed, furthermore the instruments stated in 5.2to 5.12.
Volumetric equipment shall comply to class A according to EN ISO 1042.
Any vessel or tool coming into direct contact with the sample or the solutions shall be reliably clean to
prevent contamination and to minimize the blank values.
5.2 High-field NMR spectrometer, Typically, a 400 MHz FT-NMR with a 5 mm proton probe adapted
for the analysis of solutions and temperature stabilization of ± 0,2 K, or an instrument with at least
equivalent performance, is used.
5.3 NMR tubes, 5 mm outer diameter, suitable for high-field NMR measurements, less than ± 1 %
variation of the inner diameter to ensure a low variance of stimulated volume from sample to sample and
with tight-fitting cap plug suitable for CDCl (e.g. PTFE). The same type of tubes shall be used for the
3
QuantRef and all samples.
5.4 Spinner for 5-mm-NMR-tubes
5.5 Gauge for the correct depth-adjustment of the NMR tube in the probe
5.6 Analytical balance, suitable for weighing with a precision of at least ± 0,000 1 g.
5.7 Coffee- or laboratory mill, suitable for the milling of roasted coffee beans. The mill shall be
calibrated to deliver a homogenous particle size, as used for the preparation of filtered coffee. At least
2/3 of the ground coffee particles shall be finer than 0,63 mm. The mill should have a minimal dead
volume and be easy to clean.
5.8 Laboratory sieves, Wire sieves with 0,63 mm mesh and 0,25 mm mesh fulfilling the requirements
according to ISO 3310-1.
5.9 Disposable syringes 1 mL or 2 mL, preferably non-siliconised and with Luer lock.
5.10 Syringe filter, with chloroform-resistant membrane (e.g. PTFE), porosity (Por.) of 0,45 µm, a
combination filter (glass fibre + PTFE) can ease the filtration.
5.11 Centrifuge filters (optional), with chloroform-resistant membrane (e.g. PTFE), Por. ≤ 0,45 µm,
capacity ≥ 800 mL.
5.12 Positive displacement pipette, adjustable up to 1 000 µL or 2 000 µL.
To minimize the volume error of the added Chloroform-d, preferably a positive displacement pipette
should be used, alternatively the sample could be weighed after addition of the CDCl to be aware of the
3
true amount added.
5.13 cyclic shaker (vortexer), capable of > 500 r/min.
6 Measurement and test methods
6.1 General
WARNING — The use of this document can involve hazardous materials, operations and equipment. It
does not purport to address all of the safety or environmental problems associated with its use.
A well homogenized sample of ground coffee is weighed and mixed with a defined amount of deuterated
chloroform. After thorough extraction the suspension is separated, filtered and filled into an NMR tube
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for measurement. The analytes are quantified by integration of specific resonances using the PULCON
qNMR method. Alternatively, an internal standard could be added to the coffee extract for quantification.
The ground coffee sample should be analysed in duplicate, if the difference between results is larger than
5 %, the analysis shall be repeated from the sieved mid-fraction (0,63 mm > x > 0,25 mm particle size) of
the coffee powder.
6.2 Sampling
The sampling method is not regulated by this document. Sampling should be done as agreed on by the
stakeholders. Care shall be taken to ensure that samples are not damaged or adulterated during transport
or interim storage.
6.3 Sample preparation
6.3.1 General
All numerical values used to calculate the result(s), e.g. weighed portions or liquid volumes, shall be
measured and documented with at least three, better four significant numbers.
The roasted coffee beans (or ground coffee) shall be homogenized thoroughly to ensure the sub-sample
is representative. The sub-sample should weigh at least 200 g (approx. 1 000 beans). If beans are to be
analysed, they shall be ground to a powder of a homogenous fineness as typical for the preparation of
filtered coffee using a mill as described in 5.7.
6.3.2 Sample preparation for roasted coffee
Roasted coffee beans shall be ground in a mill (5.7). The milling grade shall be adjusted to yield between
30 % and 50 % of the ground coffee as the mid fraction (between 0,25 mm and 0,63 mm particle size) At
least 2/3 of the ground coffee particles shall be finer than 0,63 mm.
Commercially available ground roasted coffee shall be milled again if it does not comply with the ground
particle size requirements stated above.
6.3.3 Extraction and preparation of the measuring solution
The ground coffee shall be thoroughly homogenized again, afterwards 200 mg are given into a vial with
a tight closure. The exact weighed portion shall be documented. 1,50 mL (= 2,25 g) deuterated chloroform
+ TMS are added into the vial, then the closed vial should be mechanically shaken vigorously (>500 r/min,
e.g. by vortexer or cyclic shaker) for 20 min.
To remove solid particles, the extract should be strained through a syringe filter:
Pull out the plunger from the syringe, firmly attach the syringe filter (the Luer lock prevents the popping
off of the filter due to pressure). Pour the coffee-chloroform-sludge into the syringe, then reattach the
plunger. Hold the filter system over a receiving vial and press down the plunger with controlled strength.
WARNING — Overpressure could pop off the filter (esp. if used without Luer lock) or even burst the
filter’s seams.
Finally, 600 µL of the finished measuring solution are given into an NMR tube which is then capped tightly
shut. The fill level in the NMR tube depends on the coil height and needs to be adjusted according to the
used spectrometer.
With the aid of a depth gauge the tube is then set correctly into an NMR spinner and put into the NMR
spectrometer.
Due to the chloroform’s tendency to photochemically decompose to phosgene and hydrogen chloride, the
extract and the measuring sample shall be protected from light and the measurement shall be finished
within 48 h after preparation.
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6.4 NMR experiments
6.4.1 General
The samples are measured in accordance with the NMR spectrometer’s operating manual. The QuantRef
solution and the repeatability monitoring sample or the control sample should be measured on each
workday. The current result of the control sample (4.12) should stay within warning thresholds and shall
stay within action thresholds else the measurement batch should be repeated.
6.4.2 Fundamental criteria for the NMR Spectrum
The spectrometer shall be tested and calibrated regularly with appropriate reference samples (e.g. CHCl
3
line shape test for shim and FWHM quality, test for SNR, FWHM and resolution) to ensure the values
proven at installation (the spectrometer’s figures of merit) are still attained.
Prior to acquiring the spectrum, the sample in the spectrometer shall have reached thermal equilibrium
at the desired measurement temperature. The spectrometer shall be locked to the sample’s correct
solvent signal, the probe shall be tuned and matched using an appropriate routine, the magnet shall be
shimmed to achieve optimal field homogeneity and the 90° pulse shall be calibrated to yield optimal
excitation. A constant excitation pulse should be used for all samples and for the QuantRef, else the ratio
between QR pulse and sample pulse(s) shall be factored in with the PULCON Formula (2). Without
factoring in the ratio pulse lengths, the quantification will suffer from a slightly bigger error. Usually with
samples in organic solvents a constant excitation pulse for all samples gives good reproducible results.
Spectral width: Broad enough to show ca. 20 % of undisturbed baseline on both sides of the
region where signals are expected (−1 ppm to 13 ppm). This ensures that the
algorithms for phasing and baseline correction can work properly.
FID resolution: min. 0,25 Hz
Receiver gain: Set identical for all samples and the QuantRef.
RG is generally set to maximize the signal to noise ratio. Attention should be paid
that the RG used does not convey any receiver saturation.
SNR: Better than 10 (equivalent to 10 % relative error) for the signal of 16-OMD near
its LOQ
Sample Set identical for all samples and the QuantRef (±0,2 K).
temperature:
Pulse calibration: Each sample and the QuantRef shall be locked, tuned and matched. The excitation
pulse shall be optimized e.g. with the spectrometer's automatic algorithm.
Sample spinning: none
6.4.3 Valid exemplary measuring conditions/ parameters for the 1D experiment
1
Pulse programme: Standard H experiment with 90° excitation pulse
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Key
1
H to indicate the proton (frequency) channel of the spectrometer is u
...
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