Dear Chas:

Abraham's Bosom (Hebrews, Sheol; Greek, Hadesi) is a term used by St. Luke (Luke 16:22) to describe the "blissful abode of the righteous souls after death", where the Old Testament saints waited for the coming of the Messiah to release them into the beatific vision. The term "Paradise" (cf. Luke 23:43) also refers to this place. This is where Jesus went between his death and Resurrection, to "set the captives free". Abraham's bosom was a place of bliss not purgation.

Purgatory (Latin, "purgare", to make clean, to purify), on the other hand, is a "place or condition of temporal punishment for those who, departing this life in God's grace, are, not entirely free from venial faults, or have not fully paid the satisfaction due to their transgressions" (Catholic Encyclopedia).

Thus, while both states, Abraham's Bosom of the Old Testament, and that of Purgatory, have in common the deprivation of the beatific vision, they are not the same -- one was a blissful state waiting in anticipation for the coming Messiah, and the other is a state of suffering to cleanse one from all venial sins, attachments, and necessary satisfactions before entering the beatific vision that awaits those who believe in the Messiah, the Son of God, already come and will come again.

As for the Old Testament saints undergoing a purgation, as the Catholic Encyclopedia explains concerning this:

The tradition of the Jews is put forth with precision and clearness in 2 Maccabees. Judas, the commander of the forces of Israel,

    making a gathering . . . sent twelve thousand drachmas of silver to Jerusalem for sacrifice to be offered for the sins of the dead, thinking well and religiously concerning the resurrection (For if he had not hoped that they that were slain should rise again, it would have seemed superfluous and vain to pray for the dead). And because he considered that they who had fallen asleep with godliness, had great grace laid up for them. It is therefore a holy and wholesome thought to pray for the dead, that they may be loosed from sins. (2 Maccabees 12:43-46)

At the time of the Maccabees the leaders of the people of God had no hesitation in asserting the efficacy of prayers offered for the dead, in order that those who had departed this life might find pardon for their sins and the hope of eternal resurrection.

This passage refers specifically that the dead "might find pardon for their sins and the hope of eternal resurrection." The Navarre Bible Commentary, one of the best Catholic commentaries in publication, states concerning this passage in Maccabees:

As the sacred writer [of Maccabees] sees it, the offering of ... prayer[s] for those who died, mean[t] not only the hope in the resurrection, but a conviction that it is possible for a person to be cleansed of sin after death, and the prayers and offerings for the dead can help bring that purification about.

After Jesus "set the captives free" that were in Abraham's Bosom, in times past unofficially called, "Limbo", that place came to an end as there was no need for a "place to await the Messiah".

Today the the places to which we go after death are purgatory (if needed) and Heaven if we die in God's grace and friendship, or to the place of torments usually spoken of as Gehenna (cf. Matthew 5:29, 30; 18:9; Mark 9:42 sqq. in the Latin Vulgate), or commonly called, "Hell", for those who reject God's grace and friendship.

In the writings of the patristic fathers we will see the term Abraham's Bosom, but referring to Heaven. As the Catholic Encyclopedia remarks, "Since the coming of Our Lord, "the Bosom of Abraham" gradually ceased to designate a place of imperfect happiness, and it has become synonymous with Heaven itself". 

God Bless,
Bro. Ignatius Mary