Table 2.
General comparison of each portable device, MobE, MobH, and MobT, to the reference (Stationary) in terms of mass spectral reproducibility (% RSD of the relative abundance in replicate analysis per selective ion), mass spectral similarity (% absolute error: absolute value of the “normalized ratio” minus one and expressed in percentage), and signal-to-noise ratio (S/N per selective ion by RMS). A series of non-parametric Mann–Whitney U tests reported significant differences between each portable device (mean ± standard error (SE)) and the reference system (mean ± SE), labelled in bold. Significance was defined as p value < 0.05
| Analytical parameter | Unit of measure | Parameter | Stationary | MobE | MobH | MobT |
|---|---|---|---|---|---|---|
| Mass spectral reproducibility | % RSD (observed relative abundance in replicate measurements) | Mean ± SE | 3.5 ± 0.4 | 10.9 ± 1.5 | 5.3 ± 0.9 | 12.6 ± 1.3 |
| p value | – | < 0.001 | 0.07 | < 0.001 | ||
| (nanalyte, nion, nsample) | (17, 50, 7) | (13, 36, 3) | (15, 41, 9) | (6, 18, 17)b, (9, 27, 2)c | ||
| Mass spectral similarity | % absolute error | Mean ± SE | 21.6 ± 4.3 | 23.5 ± 3.3 | 37.6 ± 6.9 | 38.2 ± 4.5 |
| p value | – | 0.053 | < 0.01 | < 0.001 | ||
| (nanalyte, nion, nsample) | (17, 49, 7) | (13, 33, 3) | (15, 37, 9) | (6, 18, 17)b, (9, 27, 2)c | ||
| Sensitivity | (Signal/noise by RMS method) | Mean ± SE | 6340 ± 2320 | 119 ± 26 | n.a.a | 556 ± 135b |
| p value | – | < 0.001 | < 0.001 | |||
| (nanalyte, nion, nsample) | (11, 44, 7) | (11, 36, 3) | (5, 20, 17)c, (7, 28, 2)d |
For further details related to c and d, refer to “Experimental design and instrumental parameters of analysis on mobile TD/GC–MS instruments” and Supp. S.1
nanalyte number of identified analytes, nion number of selective ions from all identified analytes, nsample number of replicates, n.a. values not available
aS/N could not be estimated by using GC–MS solution software as for the other instruments
bS/N values for MobT cannot be compared because a different injection system and sorbent material were used
cDetected compounds using HS-SPME with a PDMS-DVB fiber, MobT HS
dDetected compounds using DI-SPME with a PDMS-DVB fiber, MobT DI