I made a beracha before toveling several utensils, primarily glass, which I started with. Then I noticed that one of the utensils was metal. Since toveling metal is a Torah obligation and for glass it is Rabbinic, could the beracha on the glass utensil count for metal? Should I have made another beracha on the metal utensil? Answer:
Tevilat keilim for the six metals mentioned in the Torah (Bamidbar 31:22) is, according to many, from the Torah (see Beit Yosef, Yoreh Deah 120). For glass, it is indeed Rabbinic (Avoda Zara 75b). Let us work with your assumptions.
369 - Fulfilling Kiddush from One Who Did Not Eat
370 - Toveling which Utensil First
371 - Accidentally Staying on the Bus Longer than Envisioned
There are several halachic discussions about using Rabbinic fulfillments for Torah-level obligations, and we will mention a couple: making Kiddush when it is only Shabbat on a Rabbinic level; a bar mitzva boy doing sefirat haomer for adults when he became bar mitzva in the middle of the omer (see Mikraei Kodesh (Frank) Sukkot II, 13).
However, the issue does not apply here for two reasons. Tevilat Keilim ((Cohen) 9:(22)) points out that even when tevila is on a Torah level, the beracha is only a Rabbinic obligation. Therefore, he argues, the beracha of one doing tevila on glass can be used for one toveling metal. In truth, though, even regarding Birkat Hamazon, one who ate only enough for a Rabbinic obligation can be motzi (when there is a need) one who ate enough for a Torah-level Birkat Hamazon (Shulchan Aruch, Orach Chayim 197:4). Furthermore, in your case, the beracha applies to all of the utensils that were slated for you to tovel, not just the first one (see parallel application of this concept in Shulchan Aruch, YD 19:7). We even find that one can make a beracha directly before something that may not be a mitzva, and it can go on that which follows. An example is that while we do not know which set of tekiot are the correct one, we make the beracha before the first set and it works even if the second or third set is correct.
We can still ask whether there is at least a preference, had you thought of the issue, to have immersed the metal first, right after the beracha. We do find in regard to berachot before food that the gemara (Berachot 41a) brings rules of kedimut (precedence) – which berachot are made first, and which food should be eaten first after a given beracha. Even if one does not follow the proper order, the beracha takes effect (Magen Avraham 211:11), but we do like to do things correctly. Here, though, it is a different type of beracha – not a birkat hanehenin (on benefit, primarily food), but a beracha on a mitzva. So really the question is whether one mitzva has precedence over another.
The gemara (Zevachim 90b) does address order in mitzvot. Tadir (a more common mitzva) has priority over a less common one. Also, mekudash (a more holy mitzva) has precedence over others. What about a mitzva from the Torah over a Rabbinic one? Beit Shamai and Beit Hillel (Berachot 51b) disagree whether the beracha on wine comes before or after the beracha of Kiddush. The Sha’agat Aryeh (22) claims that the fact that pieces of logic including tadir are raised and the matter that Kiddush is essentially a mitzva from the Torah whereas the beracha over wine is not is not raised, shows that that Torah/Rabbinic obligation must not cause kedimut. On the other hand, R. Akiva Eiger (to Orach Chayim 7:1) assumes that being from the Torah is like being mekudash. The P’nei Yeshoshua (Berachot ibid.) also assumes that being from the Torah gives mitzva precedence, and explains that Kiddush over wine is usually only Rabbinic. Yabia Omer (IX, OC 100) bring several others who concur. However, I have not succeeded to find, in our context of tevillat keilim, that the utensil one puts in the mikveh first should be one that is obligated by Torah law.
In summary, it might be preferable to tovel the metal utensil first, but this is not clear in the sources, and it certainly does not make a difference after the fact.