Summary
Headspace solid-phase microextraction (SPME) was used to trap and concentrate trace volatiles from two polymer samples for analysis by combined gas chromatography/mass spectrometry (GC-MS) using the HTA 2800T combination autosampler and the JEOL UltraQuad™ SQ-Zeta single quadrupole GC-MS system.
Introduction
Two polymer samples from canine training aid delivery materials were submitted for analysis by headspace GC-MS. One sample (blue polymer) contained an unknown compound that was causing a strong reaction from the dogs. The other sample (black polymer) was believed to be free of any significant odor and was proposed as a substitute for the troublesome material.
Because regular headspace GC-MS did not detect a significant difference between the samples, the autosampler was reconfigured to operate in headspace SPME mode. The combination of headspace SPME and the excellent trace sensitivity of the UltraQuad™ SQ-Zeta single quadrupole GC-MS system successfully detected low levels of a pungent odor compound that was unique to the blue polymer.
Experimental
Hardware
Sample analysis was carried out using a JEOL JMS-Q1600 UltraQuad™ SQ-Zeta single quadrupole mass spectrometer equipped with an Agilent 8890 gas chromatograph and an HTA 2800T All-in-one combination liquid, headspace, and SPME GC autosampler. The autosampler was configured to operate in headspace SPME mode with a Supelco 50/30mm DVB/Carboxen/PDMS Stableflex SPME fiber assembly.
Sampling
Approximately 1 cm segments of each polymer were placed in 20 mL headspace vials and volatiles were collected on the SPME fiber for 10 minutes at room temperature and again at 50°C. Three replicate measurements were made for each of the two samples.
Following the analysis, one microliter of an alkane retention index standard was injected at a split ratio of 20:1 and otherwise measured under the same conditions.
GC Conditions
| Column |
ZB5-MSplus |
| Length |
30m |
| Film |
0.25 m |
| Diameter |
250 m |
| Inlet |
250° C |
| Injector |
Splitless |
| Flow |
1.2 mL/min (constant flow) |
| Oven |
Rate (°C /min) |
Temp.(°C) |
Hold (min) |
| Initial |
|
50 |
3 |
| Step 1 |
20 |
320 |
2 |
Mass spectrometer
| Solvent delay |
4 min. |
| Start m/z |
35 |
| End m/z |
400 |
| Cycle time |
300 ms |
| Step size |
1 |
| End time |
18.5 min |
Data analysis
- Software: JEOL msFineAnalysis iQ
- Database search: NIST mainlib, replib, Wiley main, and Wiley flavors and fragrances databases
- Variance analysis (3 replicates each sample) with alkane retention index standard
Results
The msFineAnalysis iQ software carried out chromatographic deconvolution and alignment and peak detection for all replicates. Database search results were integrated with elemental composition determinations for all peaks and filtered by retention index. Statistical analysis (Figure 1) revealed the number of components that are common between samples and that differ between Sample A (black polymer) and Sample B (blue polymer).
| Total |
A only |
A > B |
A = B |
B > A |
B only |
Others |
| 2,360 |
45 |
12 |
99 |
22 |
72 |
2,110 |
Figure 1. Variance analysis showing differences between the two polymer samples.
The tabular results provide an overview of the chemical differences. Compounds that are more abundant in Sample A are highlighted in blue, and those that are more abundant in Sample B are highlighted in red.
An early-eluting peak that was only present in Sample B was identified (Figures 2 and 3) as Pivalic Acid (2,2-dimethyl propanoic acid), a compound with a pungent, unpleasant odor. This is believed to be the major compound responsible for the trace odor in the blue polymer.
Figure 2. Tabular results with the entry for pivalic acid highlighted.
Figure 3. Differences displayed by class showing the pivalic acid in Sample B.
Pivalic acid
Two other peaks were only detected in Sample B at retention times 10.12 minutes and 10.92 minutes with relative abundances greater than 5%. These were identified as 2,4,4-Trimethyl-3-(3-methylbutyl)-Cyclohex-2-enone (Figure 4) and 2,6-di-tert-butyl-p-benzoquinone respectively. The latter compound is an UV stabilizer and antioxidant.
Figure 4. Identification of the peak eluting at 10.12 minutes in Sample B
Conclusions
Headspace SPME sample introduction and GC-MS sample analysis using the JEOL JMS-Q1600GC UltraQuad™ SQ-Zeta detected traces of a pungent odor compound at trace levels in one of two polymer samples. msFineAnalysis iQ software revealed differences in the volatile compounds released by both polymers.