Talk:Atmospheric-pressure chemical ionization

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CHEM 4558 Peer Review

It looks like the "Instrument structure" section could use some more links to corresponding Wikipedia pages, like corona discharge (I went ahead and added the link; article should be skimmed over for appropriate addition of Wikilinks). Also, the whole article could use some simplification of language - less jargon - so that the article is accessible to someone at a high school level. Remember, not everyone is a chemist! Samlhotard (talk) 16:22, 30 March 2017 (UTC)[reply]

diagram in Instrument Structure; mixed mode interfaces

(1) Is it just me, or is that diagram fundamentally unhelpful? In a typical APCI source, at least of the ones I've seen, the nebuliser gas goes through a narrow tube concentric to the liquid sample, and ending long before the heater. It has to, otherwise it can't nebulise. This makes a spray of droplets that enters the heater region, which heats the droplets and evaporates them, before the corona discharge region where the vapour gets ionised and the chemistry can start. I'll forgive the inline plan, but if anyone's redrawing the diagram, every APCI source I've ever used has been at an angle to the inlet to the mass spec, not pointing straight at the first skimmer. (2) Does anyone feel up to writing anything about mixed mode interfaces, which seem to be increasing in popularity? Agilent of course make one, which does APCI properly, Shimadzu make one that gives an APCI effect in a largely ESI design, and Waters do a corona discharge needle in at least some of their ESI spray chambers to create a similar mixed-mode effect. There's definitely room for addition here. Elemimele (talk) 11:53, 10 April 2022 (UTC)[reply]

Good call about the diagram. The nebuliser gas does enter concentrically in a narrow tube around the liquid tube, with the exits approximately co-planer. That, as you say, provided the nebulisation. The gas flow shown in the drawing is actually a second flow of auxiliary gas that carries the vapour into the ionisation region. The nebuliser tip extends into the heated zone so that droplets impinge on the heated walls.

You are correct that the probes are not aimed at the inlet to the mass spectrometer anymore, but they were in the original design (ca 1980s), and in the photograph in the article, which is the view looking into the source from the skimmer/orifice. I'm sure the figure could be updated to show an angled or perpendicular probe but the details would vary with manufacturer. My objection is still that this is a drawing of an APCI source with an LC-MS probe or inlet, not an APCI source alone. But as long as that is made clear it is fine I guess. Virtually all commercial APCI sources are used for LC-MS, I would guess (sorry, no citation for that).

As to your second point, I agree that mixed mode sources are in use, but I don't know how common they are, nor how to address the different ways they are operated.

I will have another (gentler) go at editing this article to try to add a bit to the history and clarify the definition of APCI source vs APCI source with LC-MS inlet. With citations. Brucet8585 (talk) 23:44, 10 April 2022 (UTC)[reply]

Yup, you're probably right about the prevalence of APCI sources. I'm biased towards LC-MS, so I don't know enough about non-LC APCI to comment. I could certainly take a photo of a modern APCI LC-MS ion source if it would help, though I'm not the greatest photographer, and ion sources are really hard to photograph clearly (the existing photo has the advantage of being photographically clear and of good quality). I could try to make a new diagram but it might not be brilliant. I'm looking forward to your bit on history etc.; I find the history of mass spec fascinating, and a story worth telling, a story about which I should know more, so I shall read with interest! Elemimele (talk) 18:55, 11 April 2022 (UTC)[reply]

Thanks for your response and encouragement. 76.70.92.184 (talk) 16:20, 13 April 2022 (UTC)[reply]

New Diagram for Instrument Section

@Elemimele: I notice that you have replaced the original diagram with a new one, which shows the LC interface in an orthogonal configuration and corrects the problem with the original drawing. This orthogonal representation is certainly consistent with most, or maybe all, of the modern commercial LC interfaces for APCI. But it is inconsistent with the photograph in the article. I don't have anything to replace the photograph with that of a more up-to-date source in the orthogonal configuration. I also prepared a new diagram that is a little more accurate in its representation, but does show the probe in the in-line configuration, as the original version was configured, and as the photograph shows. Here is the drawing I prepared. Do you think it is an improvement or do you prefer the orthogonal version that you produced?

I am also working on text improvements to the article to add to the history and clarify some of the description and will proceed with these.--Brucet8585 (talk) 15:09, 19 April 2022 (UTC)[reply]

@Brucet8585: I have no particular feelings either way about the schematic diagrams. The main thing was to get rid of the problem of the nebulizer gas being wrongly drawn in the previous version, and both mine and your new version do that; if you feel that your version fits the text (particularly after you've updated it) better than mine, then please go ahead and change. So far as the photographs are concerned, if you're planning to add more on the history of APCI, then the ideal would be to retain the current photo but add one of a modern, orthogonal source for comparison. I'm a pretty rubbish photographer; I did try, but my first efforts were not great. You've probably noticed that MS sources tend not to be easy to photograph; too close, it's hard to get everything in focus at once; too far, it's hard to get the resolution to see the details; and they tend to be made of materials that are hard to photograph, either mirror-finish metal parts, or absolute matt black bits. Since I've got access to a few sources from various manufacturers, maybe my best contribution would be to have another go at photographing them! Elemimele (talk) 16:48, 19 April 2022 (UTC)[reply]

{{reply to| Elemimele}} I have no access to sources to photograph, so if you want to replace the photo with a more modern orthogonal version, then I could modify my drawing to an orthogonal configuration.Brucet8585 (talk) 17:41, 19 April 2022 (UTC)[reply]

Oh, I'm happy to keep the original photo, which is relevant and of good quality, and I have nothing against your diagram, which is very clear and of good quality too. By all means use it. Mine was more of a stop-gap than the definitive work! If I can take some photos of more modern sources, I'll do so, but not necessarily to replace the original. It would be nicer to have an additional photo so our readers have a broader picture of the variety and evolution of APCI sources. Elemimele (talk) 17:44, 19 April 2022 (UTC)[reply]

I decided to revise my figure and show an angled probe which is I think more realistic. I also replaced the paragraph in this Instrument Configuration section to generalize the description of the source, indicating that the LC inlet is one example of a sample inlet, and hopefully improve the flow of the paragraph. Brucet8585 (talk) 03:46, 20 April 2022 (UTC)[reply]

Sorry, I meant I replaced the paragraph in the Instrument structure section.Brucet8585 (talk) 03:49, 20 April 2022 (UTC)[reply]

Possible images for use in the article

Brucet8585 I'm not sticking these straight into the article as I'd value your opinion, and anyone else's, on which (if any) are useful. But here are a few. The first two are a modern APCI source (from Agilent). This design fits on the front of the mass spec, with the inlet of the mass spec on the side from which the photo is taken; the corona discharge needle points nearly towards the entrance into the mass spec (which is a metal spray-shield surrounding a long thin capillary acting as interface between atmospheric pressure in the spray chamber, and a vacuum in the mass spec)

In these, the nebulizer cannot be seen because it's fitted into the top of the spray chamber. I took a picture with the nebulizer removed and held just above where it fits in; these are the second two.

I also took two photos of a mixed-mode source that offers APCI and electrospray in parallel. These sources are of increasing importance, particularly in biological research, drug-discovery etc., where it may not be obvious to the researcher which method of ionisation is most appropriate for the sample and analyte - and in some cases, some analytes need ESI, while others need APCI:

These were hard to photograph because the ion source is a mirror finish, and most of the relevant bits are hidden by casework etc. Finally, I also took some pictures of Shimadzu's dual ion source, which isn't a "proper" APCI (no heater!) but offers APCI-style ionisation and electrospray together, as a multi-mode approach

Elemimele (talk) 10:37, 21 April 2022 (UTC)[reply]

Elemimele Interesting.You've put a lot of work into getting these. I think the most useful would be the annotated view of the Agilent APCI source - the second photo. The mixed mode sources are difficult to understand, and would require significant explanation, I think, with a schematic drawing. It is at least the subject for another section if not another article. With regard to the Shimadzu dual ion source, APCI doesn't require heat, per se, unless it is used with an LC interface (which it obviously is in this case). But I fail to see how the APCI component operates effectively without heat to vaporize the analyte, which has to be vaporized in order to be ionized by chemical ionization. This is one of the difficulties with properly explaining the dual mode or mixed mode sources - understanding and explaining how the two modes operate either together (giving mixed spectra) or in rapid sequence? I suspect every manufacturer's mixed-mode source, and the way they are operated may be different. But I think it is quite reasonable to point out in this article that there are mixed-mode sources, with perhaps a general description of what that provides. Perhaps you can do that with the Agilent source since you know the analytical aspect of its use

By the way, I am preparing some changes to expand the History section of this article.Brucet8585 (talk) 14:36, 21 April 2022 (UTC)[reply]

There has to be some heat for evaporating solvent in electrospray too, so Shimadzu's system has heated gas entering the spray chamber around the heat block, which is the metal lump around the actual inlet to the mass spec. When using it in dual mode, they just crank up the temperature as far as possible to improve evaporation before the vapour hits the end of the corona discharge needle, which is the extra bit that you fit to do dual mode compared to ESI. It doesn't attempt to keep the two processes separate, but works on the philosophy that the user just wants ions, and doesn't really care how they happened.

The Agilent system is a bit more complicated, having a single nebulizer at the top, spraying at a vertical partition running down the middle of the spray chamber. There are heaters on both sides; one side has electrodes to encourage electrospray, the other side has a corona discharge needle, so the ESI and APCI happen in different places. But the two streams meet at the bottom, where the partition wall stops, so again the MS draws its ions from a mixed pool created by both mechanisms.

I agree that mixed mode sources would need a separate section, and if I can find some referencing, I might add one. I don't think mixed mode is interesting enough to merit its own article, or sufficiently separate from ESI or APCI. I would be inclined to make it a section here, as it's basically what you want to do if you feel you'd like to have APCI while retaining ESI.

I agree the second picture is probably the most useful.

Elemimele (talk) 14:46, 21 April 2022 (UTC)[reply]

Elemimele Thanks for the information, and nice addition to this section.Brucet8585 (talk) 18:15, 21 April 2022 (UTC)[reply]

Expanded History Section

I added new material to the History section to indicate that APCI sources preceded the Horning group, and to reference the Sciex APCI air monitoring systems of the 1980s. Most people today seem to think that an APCI source is only for LC/MS, but the LC interface is only one possibility for a sample inlet to an APCI source. — Preceding unsigned comment added by Brucet8585 (talk • contribs) 23:29, 21 April 2022 (UTC)[reply]