49 Table 1. Example NO+ Furaneol
Flavour compound Reaction(s) of NO+ C6 O3 + NO+
H8
[95%] H8
C6 O3 + NO+ + N2
[5%]
Methyl cinnamate C10H10O2 + NO+ [100%]
Methyl hexanoate C7H14O2 + NO+ [70%]
C7H14O2 + NO+ 160) + N2
4-Decanolide [30%]
C10H18O2 + NO+ NO + N2
→ C10H18O2 .NO+ [100%]
* Mass-to-charge ratio of the product ion is shown in parenthesis; the percentage of product formed in a given reaction path is shown in square brackets.
** Nitrogen (or helium) carrier gas mediates formation of this product. The ‘third body’ carries some excess kinetic energy away enabling binding of C6
H8
without pre-concentration, and results compare well with gas chromatography mass spectrometry (GC-MS) [6].
Rapid switching between reagent ions provides high selectivity, because the multiple reaction mechanisms can provide additional independent measurements of each analyte. The multiple reagent ions also help to remove uncertainty from isobaric overlaps in mixtures containing multiple analytes.
In this study, full mass scan analyses (SCAN) were carried out using a Voice200ultra SIFT-MS instrument (Syft Technologies, Christchurch, New Zealand). Only the NO+ reagent ion was utilised due to this ion being the least affected by the relatively high ethanol residues in the flavour mixes due to the slower reaction rate coefficient of NO+
with ethanol. The NO+
has two other significant benefits for flavour analysis:
O3.NO+. • NO+ reacts via multiple reaction
mechanisms (association, hydride abstraction, electron transfer (ET) and dissociative ET), the relevance of which depends on the molecule’s ionisation energy and chemical functionality. This maximises selectivity both for conventional targeted analysis and for the fingerprinting approach applied here.
• NO+ is highly immune to moisture variations. reagent ion also
Since the flavour mixes analysed in this study are proprietory formulations, identities of specific components in the spectra was not provided. However, Latrasse [7] indicates the types of compounds that are likely to be present, which include alcohols, aldehydes, esters, furanone derivatives. Table 1 provides some examples of the reaction chemistry for several compounds identified in the
Table 2. Strawberry flavour mix samples supplied for analysis, identification codes and abbreviations used in this article.
Sample type/name Batch
Flavour standard 1 (‘S1’)
Flavour standard 2 (‘S2’)
Unknown 1 (‘U1’) Unknown 2 (‘U2’)
Unknown 3 (‘U3’)
Batch A Batch B Batch C
Batch A Batch B Batch C
Abbreviation for figures Labelling of replicates (5) in class projection plots
S1a S1b S1c
S2a S2b S2c
U1 U2
U3
S1a-1 to S1a-5 S1b-1 to S1b-5 S1c-1 to S1c-5
S2a-1 to S2a-5 S2b-1 to S2b-5 S2c-1 to S2c-5
U1-1 to U1-5 U2-1 to U2-5
U3-1 to U3-5 (m/z 200) + Association** → C10 H10 O2 → C6H11O+ + N2 → C7 + (m/z 162) + NO (m/z 99) + NO H14 O2 .NO+ (m/z Electron transfer
Hydride abstrac- tion
Association**
reaction chemistry for several potential components of the flavour mixes [7]. with the compound*
→ C6 H8 O3 + (m/z 128) + NO + N2 → C6
O3.NO+ H8 (m/z 158) flavour mixes.
Mechanism name Electron transfer
Association** 2. Automated SIFT-MS analysis
In SIFT-MS, direct sample analysis facilitates high-throughput headspace analysis, because the rate-limiting chromatographic analysis is eliminated. In contrast to automated chromatographic techniques, which require rapid injection to achieve good peak shapes and temporal separation, SIFT-MS requires steady sample injection for the duration of the analysis. In SIFT- MS, sample injection and analysis occur simultaneously.
Automated headspace analysis was carried out using a SIFT-MS instrument coupled with a Gerstel multi-purpose sampler (MPS; Gerstel, Mülheim an der Ruhr, Germany). Samples were first incubated in a Gerstel agitator prior to sampling of the headspace and subsequent injection into the SIFT-MS instrument through a Gerstel septumless sampling head. A make-up gas flow (high- purity H2
) was also introduced through the
sampling head, maintaining the standard sample gas flow (nominally 25 cm3 the SIFT-MS instrument.
min-1 ) into
The Gerstel MPS2 autosampler was controlled using Gerstel’s Maestro software. In addition to controlling the injection into the SIFT-MS instrument, the Maestro software’s PrepAhead function allows for optimal scheduling of pre-injection preparation steps, such as syringe flush or incubation. This ensures that the highest sample throughput is achieved – a feature that is more important for SIFT-MS than for chromatographic methods.
3. Samples and analysis conditions
Table 2 summarises the powdered strawberry flavour samples supplied for analysis. For each flavour mix, five replicate samples (10 ± 1 mg) were weighed into 20 mL headspace vials and incubated at 50°C for 15 minutes. The headspace was sampled with a 2.5 mL headspace syringe and injected at a flow-rate of 10 µL s-1
into
the SIFT-MS instrument’s inlet together with the make-up gas, giving a total flow rate of ca. 420 µL s-1
. A blank was analysed between
each set of replicates and subsequently subtracted from the following group. Flavour mixes and blanks were analysed in less than one minute per sample.
4. Multivariate statistical analysis The SIFT-MS SCAN data (NO+
reagent ion
only) were post-processed using multivariate statistical analysis to determine the ability of SIFT-MS to discriminate between the flavour mixes.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
