Trinitarians generally interpret this verse to refer to Yahweh the Father sending Yahweh the Son.
Examination of the Claim
1. Who is who?
Although they have no evidence for their interpretation, Trinitarians somehow think it is okay to imagine that Jesus is speaking here as Yahweh the Son and he is saying that Yahweh the Father sent him and His Spirit.
2. Preying Upon Ignorance
Trinitarians make this claim supposing that nobody will be able to provide them with a response. So they disingenuously suppose this gives them a right to make up whatever they like for the sake of their doctrine. They don't have any evidence for their claim. They are just trying to get people to believe that they get to interpret this verse however they like if you don't provide them with a response. Essentially, they are behaving like the wolves Jesus taught us about - preying upon people who are not aware of all the facts. The laughable part here is that these particular Trinitarians don't know what this verse is about either. They somehow just get it in their own heads that they get to make up an interpretation that suits their Trinitarian traditions.
3. Eisgetical Interpretation.
It is typical for Trinitarians to resort to the disingenuous practice of eisegesis and read their doctrine into the text wherever they think possible. This is just one more example of total disregard for the contextual facts.
Analysis of the Evidence
The solution to this question is really quite easy.
Listen to Me, O Jacob, even Israel whom I called;
I am He, I am the first, I am also the last.
“Surely My hand founded the earth,
And My right hand spread out the heavens;
When I call to them, they stand together.
Assemble, all of you, and listen!
Who among them has declared these things?
Yahweh loves him; he will carry out his good pleasure on Babylon,
And His arm will be against the Chaldeans.
I, even I, have spoken; indeed I have called him,
I have brought him, and he will prosper in his way.
Come near to Me, listen to this:
From the first I have not spoken in secret,
From the time it took place, I was there.
And now MY Lord Yahweh has sent ME, and His Spirit."
I have called HIM.... my Lord Yahweh has sent ME...
Secondly, if we just read the context, it becomes completely clear how we should identify "ME" in the expression, "Yahweh has sent ME. Please remember that chapter and verse divisions did not exist in the original writings of the Bible. All we need to do is read carefully and observe how "ME" is often speaking in this context:
Come near to Me, listen to this: from the first I have not spoken in secret, from the time it took place, I was there.
And now MY Lord Yahweh has sent ME and His Spirit."
Thus says Yahweh, YOUR Redeemer, the Holy One of Israel, "I am Yahweh YOUR God, who teaches YOU to profit, who leads you in the way you should go. If only you had paid attention to My commandments! Then your peace would have been like a river, and your righteousness like the waves of the sea. Your seed would have been like the sand, and your offspring like its grains; Their name would never be cut off or destroyed from My presence. Go forth from Babylon! Flee from the Chaldeans! Declare with the sound of joyful shouting, proclaim this, Send it out to the end of the earth; Say, "Yahweh has redeemed His servant Jacob." They did not thirst when He led them through the deserts. He made the water flow out of the rock for them;
He split the rock and the water gushed forth. There is no peace for the wicked,” says Yahweh.
Listen to me, O islands,
And pay attention, you peoples from afar.
Yahweh called ME from the womb;
From the body of MY mother He named ME.
He has made MY mouth like a sharp sword,
In the shadow of His hand He has concealed ME;
And He has also made ME a select arrow,
He has hidden ME in His quiver.
He said to ME, “You are my servant, Israel,
in whom I will show My glory.”
But I said, “I have toiled in vain,
I have spent MY strength for nothing and vanity;
Yet surely the justice due to ME is with Yahweh,
And my reward with MY God.”
In Isaiah, Israel, or "Jacob," is Yahweh's servant and routinely depicted as a single man. It is quite clear that "ME" at Isaiah 48:16 is Yahweh's servant Israel.