This is a very nice article demonstrating an elegant method to determine multiple kinetic and spin dynamical parameters on complexes involved in SABRE-style PHIP experiments, using clever combinations of signals from pulse sequences that are identical except for changes to the phase. The results are of very high quality attesting to the control and reproducibility of the experimental technique. I think this is a valuable contribution to the difficult task of disentangling the multiple chemical and spin dynamical processes contributing to the magnitude of PHIP-enhanced signals. My sole criticisms concern the figures which I do not think are very good. For example in Figure 1 the labels have a ludicrously large size with respect to the important content, some of which so crowded and small that it cannot be read. Obscuring some of the details by the jagged "hyperpolarization" stars does not help - surely a better visual device can be found. The figure should also give the structure of the mtz ligand. Figure 2 is better but again the choice of fonts and font sizes is a little eccentric. These are minor distractions from this report of a fine piece of work.

This manuscript is a great contribution from the team of the leader in the field of NMR hyperpolarization, Prof. Tessari. They have pioneered the use of SABRE technique for enhancing NMR signals for the purpose of analytical quantification of dilute compounds (e.g., metabolites). This manuscript serves really several purposes. For one, it validates why their approach works. Second, it provides a convenient approach to measure the hydrogen exchange and relaxation parameters in SABRE-related complexes. This information is of great importance in the context of technique optimization either to achieve the best spectral resolution or to boost signal enhancements of SABRE-hyperpolarized resonances. As noted by the other referee, the manuscript is well written. I completely agree. Moreover, the manuscript is certainly a great fit for the special issue. I am sure the rapidly growing community of parahydrogen NMR researchers will greatly enjoy reading this research contribution. However, some of these researchers definitely would like to establish this sequence on their NMR spectrometers. To facilitate better sharing of the best laboratory practices, I would suggest to make the sequence readily available to the reader – perhaps through Mendeley or other options. This way, the sequence could be readily implemented by others. This is obviously a very minor suggestion, which I leave completely to the choice of the co-authors. My second suggestion is related to the experimental setup they have employed. It would be great to have a schematic (e.g., Scheme 1) providing the details of their experimental setup, and which lines of the NMR spectrometer, they have employed to actuate the valves. Details of the experimental setup would greatly help to disseminate their clever approach to the hands of other researchers. Additional review of this manuscript is not required.

This paper describes an original and interesting approach for obtaining important kinetic (as well as relaxation) parameters of the reversible H₂ exchange between an asymmetric Ir complex and parahydrogen at micromolar concentration range. These parameters can be widely used for optimizing SABRE experiments and achieving the highest possible level of reliability and sensitivity in parahydrogen-based hyperpolarization applications related but not limited to dilute biofluids and natural extracts. The approach is based on acquiring data by a repetitive and controlled bubbling of parahydrogen followed by pulse sequences of two types with selective excitations/refocusing of hydride resonances and H₂ resonance. The results are very well presented in the paper, and the next review round is not needed.

In addition to the suggestions of the other reviewers, the following really minor improvements could be considered: (1) In several places, a previously reported 1000-fold magnetization enhancement is mentioned. Of course, the authors are aware that signal enhancements are field dependent, so when quoting the enhancement, maybe it is good to specify the field strength used in that publications. (2) I couldn’t find any information about positions of H_A and H_X hydrides for the studied isoquinoline complex. This is probably the first publication with Ir-mtz and isoquinoline. Among other matters, adding ppm values for H_A and H_X is quite important for understanding why the bandwidths of 500 Hz and 2000 Hz were chosen, especially, in the case of the open and filled reburp pulses. (3) In addition, authors may think to mention that Eqns. 1 and 2 can be coupled by the presence of cross-correlated relaxation terms. This will lead to a more complicated form of solutions in Eqns. 3-9. At the same time, for the studied asymmetric complex this effect most likely is weak and can be neglected. (4) The last two pulses in the sequence Fig.2b are sort of special because they represent combined selective excitation/refocusing of both H₂ and the high-field hydride resonances. These pulses could be marked somehow in the figure to show this difference.