The source material were in the links I posted ...
Anyways, if you are interested, you can start of with these:
“The form ADONI (‘my lord’), a royal title (I Sam. 29:8 ), is to be carefully distinguished from the divine title ADONAI (‘my Lord’) used of Yahweh.”
“ADONAI — the special plural form [the divine title] distinguishes it from adonai [with short vowel] = my lords”
(International Standard Bible Encyclopedia, “Lord,” p. 157).
“Lord in the OT is used to translate ADONAI when applied to the Divine Being. The [Hebrew] word…has a suffix [with special pointing] presumably for the sake of distinction…between divine and human appellative”
(Hastings Dictionary of the Bible, “Lord,” Vol. 3, p. 137).
“Hebrew Adonai exclusively denotes the God of Israel. It is attested about 450 times in the OT…Adoni [is] addressed to human beings (Gen. 44:7, Num. 32:25, II Kings 2:19 [etc.]). We have to assume that the word adonai received its special form to distinguish it from the secular use of adon [i.e., adoni]. The reason why [God is addressed] as adonai, [with long vowel] instead of the normal adon, adoni or adonai [with short vowel] may have been to distinguish Yahweh from other gods and from human lords”
(Dictionary of Deities and Demons in the Bible, p. 531).
"Adonai and Adoni are variations of pointing to distinguish divine reference from human"
(Hebrew and English Lexicon of the Old Testament, Brown, Driver, Briggs, under adon)
“The form ‘to my lord,’ l’adoni, is never used in the OT as a divine reference…the generally accepted fact that the masoretic pointing distinguishes divine references (adonai) from human references (adoni)”
(Wigram, The Englishman’s Hebrew and Chaldee Concordance of the OT, p. 22)
(Herbert Bateman, “Psalm 110:1 and the NT,” Bibliothecra Sacra, Oct.-Dec., 1992, p. 438).
For an analysis of the occurrences of adoni, see Herbert Bateman’s “Psalm 110:1 and the New Testament”, Bibliotheca Sacra 149, (1992) pages 438-453.
The author, a Trinitarian, argues that the Psalm cannot apply primarily to Jesus because adoni describes a human Messiah! Bateman’s Trinitarianism causes him to dismiss the obvious direct Messianic reference of this Psalm.
Aineo, GODSPEED with your research!
Adieu