Mishnah Berurah — משנה ברורה

A blessing of thanks - And it is not a blessing that is connected to another (ie. it is not connected to the previous blessing), therefore one is permitted to recite [the blessings] in the morning upon waking up (ie. Al Netilat Yadayim and Asher Yatzar) until אלקי נשמה, and then in shul he starts with אלקי נשמה [Tur]. Nevertheless, one should do it the ideal way, [which is] to connect Elokai to Asher Yatzar. See Biur HaGra in siman 46, where his opinion is also that אלקי נשמה should be connected to Asher Yatzar. Therefore, one should be careful with this from the outset. If one did not recite אלקי נשמה until [he realized] after praying Shemona Esrei, he should not recite it at any point after that, since he already said מחיה המתים, it's similar to [אלקי נשמה which speaks about] restoring souls [Pri Chadash]. Shaarei Teshuva questions this very much and concludes that nevertheless, if at the time that one recited מחיה מתים he had in mind to recite אלקי נשמה after Shemona Esrei, he is permitted to recite it afterwards - see there further for his reason. So too is it implied in Pri Megadim siman 52. And see what's written there in Biur Halacha. [Regarding] the wording of the blessing, one should not say אתה יצרת בי, rather אתה יצרת אתה נפחת בי.