16 August / September 2019 References


1. L. Akbal, G. Hopfgartner, J Chromatogr A. 2017 Sep 29; 1517:176-184.


DOI: 10.1016/j.chroma.2017.08.044. Epub 2017 Aug 19


2. V. Desfontaine, F. Capetti, R. Nicoli, T. Kuuranne, J. L. Veuthey, D. Guillarme, Journal of Chromatography B 1079 February 2018. DOI: 10.1016/j.jchromb.2018.01.037


Table 1: Comparison of % RSD for retention and peak area of Reserpine using split and no-split design inter- face for SFC-MS hyphenation.


area in the given example, values were found to be significantly lower in the no-split approach (Table 1).


Sensitivities


Observing that in SFC mostly gaseous CO2 and varying portions of organic modifier


are introduced into the ESI source, higher ionisation efficiency and therefore higher sensitivity can be expected due to highly efficient evaporation compared to LC with a high water content in the mobile phase. Another advantage of SFC is the possibility of using a make-up solvent to increase ionisation efficiency and possibly also spray stability, if not enough solvent is introduced with the mobile phase flow. It was found that 0.1 - 0.2 mL/min of total flow introduced into the MS was suitable for obtaining a stable spray with good sensitivity and repeatability [7].


Optimisation


With the make-up flow being introduced behind the column, it can be used to optimise ionisation efficiency without affecting chromatography. Also, pH stability of the column doesn’t have to be considered in the choice of the optimum make-up solvent [1]. In a careful evaluation of MS interface parameters, it was found that unlike LC-MS where low capillary voltage gave higher peak intensity, high capillary voltage was preferable in SFC-MS. This was attributed to the high water content in LC, which is not present in SFC mobile phases [7]. It showed that MS parameters also need to be carefully optimised in order to get the most out of the technique.


After optimisation, 395 out of 442 pesticides showed better sensitivity in SFC-MS compared to LC-MS [7], which agrees with other published data [8, 11]. Matrix effects were also investigated, and in the matrices


studied (food samples) signal suppression due to co-elution of interfering matrix components was reduced significantly compared to results obtained by LC- MS, most likely due to the differences in retention. In a more in-depth study, Desfontaine et al. reported the advantage of SFC-MS over LC-MS with regards to matrix interference for the analysis of basic compounds in biological matrices. They also attributed the reduced occurrence of matrix effects in SFC-MS to an advantage in the alternate elution profile, therefore depending on the choice of separation column. In addition, it was suggested that differences in the properties of the mobile phase could lead to differences in ionisation efficiency and matrix effects [2].


Conclusion


In recent studies, SFC-MS could be established as a reliable, robust and beneficial alternative to routine LC-MS methodology, and new generation SFC-MS instrumentation prove to be very similar to LC-MS systems with regard to ease-of-use and application development.


However, retention mechanisms are not as well defined in SFC-MS as they are in LC-MS, making the method development process more empirical. Method development can still be performed quickly and efficiently using the method scouting approach. After proper optimisation, SFC-MS can offer considerable advantages in terms of separation selectivity and MS sensitivity.


SFC-MS and LC-MS should be considered as complementary techniques due to the differences in separation patterns as well as detection sensitivity, since not all compounds show higher signals when analysed by SFC.


3. L. T. Taylor, Anal. Chem. 82 (12) 4925–4935 (2010)] DOI: 10.1021/ac101194x


4. N. Gibitz Eisath, S. Sturm, H. Stuppner, Planta Med 2018; 84(06/07): 361-371


DOI: 10.1055/s-0037-1599461


5. A. Dispas, R. Marini, V. Desfontaine, J. L. Veuthey, D. Kotoni, L. G. Losacco, A. Clarke, C. Muscat Galea, D. Mangelings, B. M. Jocher, E. L. Regalado, K. Plachká, L. Nováková, B. Wuyts, I. François, M. Gray, A. J. Aubin, A. Tarafder, M. Cazes, C. Desvignes, L. Villemet, M. Sarrut, A. Raimbault, E. Lemasson, E. Lesellier, C. West, T. Leek, M. Wong, L. Dai, K. Zhang, A. Grand-Guillaume Perrenoud, C. Brunelli, P. Hennig, S. Bertin, F. Mauge, N. Da Costa, W. Farrell, M. Hill, N. Desphande, M. Grangrade, S. Sadaphule, R. Yadav, S. Rane, S. Shringare, M. Iguiniz, S. Heinisch, J. Lefevre, E. Corbel, N. Roques, Y. V. Heyden, D. Guillarme, P. Hubert, J Pharm Biomed Anal. 2018 Nov 30;161:414-424 DOI: 10.1016/j. jpba.2018.08.042. Epub 2018 Aug 23.


6. I. Brondz, A. Brondz, International Journal of Analytical Mass Spectrometry and Chromatography, 2014, 2, 15-24 DOI: 10.4236/ijamsc.20


14.21002


7. Y. Fujito, Y. Hayakawa, Y. Izumi, T. Bamba, J. Chromatogr. A 1508 (2017) 138–147 DOI: 10.1016/j.chroma.2017.05.071. Epub 2017 Jun 2


8. V. Cutillas, M. M. Galera, L. Rajski, A. R. Fernández-Alba, J Chromatogr. A. 2018 Apr 13;1545:67-74 DOI: 10.1016/j. chroma.2018.02.048. Epub 2018 Feb 23


9. E. Lesellier, C. West, J Chromatogr. A. 2015 Feb 20;1382:2-46.


DOI: 10.1016/j.chroma.2014.12.083. Epub 2015 Jan 10


10. D. Guillarme, V. Desfontaine, S. Heinisch, J. L. Veuthey, J. Chromatogr. B, 1083, (2018) 160-170 DOI: 10.1016/j.jchromb.2018.03.010


11. V. Cutillas, M. Murcia-Morales, M. M. Gómez-Ramos, S. M. Taha and A. R. Fernández-Alba, Analytica Chimica Acta, Volume 1059, 20 June 2019, Pages 124-135 DOI: 10.1016/j.aca.2019.01.010


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