Determination of the optimal injection parameters for the SPME Arrow analysis of VOCs

The injection step in SPME Arrow-GC-MS analysis is critical for sensitivity, repeatability, and peak shape, but is often less systematically optimized than extraction. In this study, the injection efficiency of SPME Arrow fibers was investigated using 1-methylnaphthalene as a model volatile organic compound. Real-time desorption-and-transfer profiles were recorded to evaluate the effects of liner geometry, carrier-gas flow rate, and column insertion depth for two coatings, PDMS/CWR and PDMS/DVB. Here, desorption denotes analyte release from the coating, while transfer denotes the subsequent transport of the released analyte through the injector and into the column or detector connection. Total peak area was used as a measure of transferred analyte amount, while the half-mass point described transfer kinetics. The results show that SPME Arrow injection is governed by a combined desorption-and-transfer process rather than by thermal desorption alone. For PDMS/CWR, a narrow 1.2 mm i.d. liner markedly improved injection efficiency compared with a conventional 2.0 mm i.d. liner, providing relative desorption-and-transfer response close to 100% over a broad range of carrier-gas flow rates. The narrow liner also reduced half-mass points, indicating faster transfer. For PDMS/DVB, however, the highest total peak areas were obtained with the wider liner at elevated carrier-gas flow rates, although the narrow liner produced faster transfer. These results demonstrate that optimal injection conditions are strongly coating-dependent and cannot be predicted solely from liner diameter or carrier-gas velocity. The study highlights the need to optimize SPME Arrow injection parameters separately for each coating and analytical objective. Both total transferred amount and transfer kinetics should be considered, since the fastest transfer condition does not necessarily provide the highest analyte recovery.