Poole on 1 Chronicles 1:32, 33: The Sons of Keturah
[circa 1853] Verse 32: Now (Gen. 25:1, 2) the sons of Keturah, Abraham’s concubine: she bare Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah. And the sons of Jokshan; Sheba, and Dedan.
[Of Keturah, Abraham’s concubine] She was not a mistress (Lapide), but a secondary wife (Lapide, Menochius, Tirinus). In Genesis 25:1, she is called a wife. Concerning a concubine, see Genesis 35:22 (Vatablus).
Verse 33: And the sons of Midian; Ephah, and Epher, and Henoch, and Abida, and Eldaah. All these are the sons of Keturah.
[The sons of Midian; Ephah] From whom was that city Midian, and Ephah near to it; concerning which see Isaiah 60:6 (Bochart’s A Sacred Catalogue of Animals 1:2:3:81).
 Hebrew: וּבְנֵ֙י קְטוּרָ֜ה פִּילֶ֣גֶשׁ אַבְרָהָ֗ם יָלְדָ֞ה אֶת־זִמְרָ֧ן וְיָקְשָׁ֛ן וּמְדָ֥ן וּמִדְיָ֖ן וְיִשְׁבָּ֣ק וְשׁ֑וּחַ וּבְנֵ֥י יָקְשָׁ֖ן שְׁבָ֥א וּדְדָֽן׃  Hebrew: וּבְנֵ֣י מִדְיָ֗ן עֵיפָ֤ה וָעֵ֙פֶר֙ וַחֲנ֔וֹךְ וַאֲבִידָ֖ע וְאֶלְדָּעָ֑ה כָּל־אֵ֖לֶּה בְּנֵ֥י קְטוּרָֽה׃