PLACING OF 'USED'

Before a noun

When 'used' is placed before a noun as an adjective, it generally means 'second-hand' (used by someone else).

e.g. This garage sells used cars.

"Good quality used toys are also very welcome." (Article in The Bolton News)

After a noun

e.g. All chemicals used were of analytical grade.

The above sentence is found in many scientific papers. It means that all the chemicals that were used in a particular experiment or series of experiments were of analytical grade. In this context, 'used' should always be placed after the noun.

All used chemicals were of analytical grade.

Placing 'used' before the noun implies that the chemicals are 'second-hand'. Although this grammatically incorrect phrase has crept into some published papers, 98% of papers containing this phrase (according to Google Scholar) place 'used' after the noun.