Pretty cool offering! I do have some questions since i also have an orbitrap, as well as other MS instruments, in my lab. (By the way, I perform pharmaceutical analysis and thus nothing to do with testing seawater)
Hi,
great to see someone from the field and very pinpointed questions here! I guess youre running a bunch of QQQs alongside the HR instrument? Are you in impurity testing/profiling of pharmaceuticals? Would be great to hear more about your field of application of MS.
The MS response factors of these compounds vary considerably and may not be linear over such a large range. Do you have individual standards for each of these components at different levels?
We have two sections in the report. The
"targeted section" includes compounds for which we have standards and perform calibration. In this section, we report concentration levels in ppb.
The second section is
"non-targeted", which lists unexpected compounds identified based on MS2 database matches. For these, we report only signal counts (or area) and not concentration levels, due to the unknown ionization efficiency. However, we still provide the counts to allow for relative comparisons between different samples or time points.
Are you doing this by MS/MS? Is this LC-MS or direct inject? Also do you need to do any solid phase or liquid extraction? I’d imagine the matrix effects could be pretty significant.
We perform LC-MS analysis, with each sample injected four times using different chromatographic conditions and scan parameters. As you know, not all compounds respond well under a single set of conditions. We haven’t attempted direct injection with seawater, due to its matrix - this would just be asking for trouble.
We are running full scans along with data-dependent MS2 (dd-MS2) for both confirmation and unknown compound screening.
You mentioned glycine, which I think would actually be rather difficult since its mass is low and may have a lot of interference. What kind of sensitivity are you seeing for that analyte?
Amino acids are generally challenging to analyze—many exhibit poor ionization, even those that retain on the column for a reasonable duration. To address this, we developed an in-house protocol specifically for amino acids in seawater. It involves pre-column chemical modification to enhance both retention and, significantly, ionization efficiency. Please understand i cannot disclose further details here.
Have you demonstrated the accuracy and precision of the method for each of the analytes?
We verify our methods using system suitability tests (SSTs) and closely monitor blanks and linearity, which provides strong assurance of method performance. Additionally, applying narrow mass accuracy windows, retention time tolerances, and MS2 confirmation further increases confidence in our results. However, we do not perform full-scale method validation as required under GMP or pharmaceutical standards.
Finally, any plans to publish your method?
We don’t currently plan to publish the methodology, as it doesn’t seem particularly meaningful on its own. However, we expect that over time, the accumulated data will lead to publishable insights. For example, mass spectrometric analysis of palytoxin is a particularly intriguing area, along with several other marine toxins. There’s still a great deal to explore and learn in this field.
All the best from Austria,
Christoph