A closely followed exchange traded fund following the Nasdaq-100 turned positive for the session in afternoon dealings Monday as top holding Apple (NasdaqGS: AAPL) saw its shares touch $400 for the first time.

PowerShares QQQ (NasdaqGM: QQQ) was fractionally higher at last check while the Dow and S&P 500 were in negative territory.

Apple shares have surged more than 20% over the past month after breaking out of their 2011 trading range. The stock now represents 13.6% of the Nasdaq ETF.

The stock has rallied in the wake of strong quarterly results driven by better-than-expected sales of iPhones and iPads. [Tech ETFs Look for Boost from Apple’s Blowout Quarter]

“Expectations for Apple’s third-quarter results were high, and the company handily crushed them,” investment researcher Morningstar said in a note.

“Apple is an exceptional company with a clear and convincing investment case and high return potential,” added analysts at Indigo Equity Research. “High sales growth and increasing margins have led to a remarkable explosion of earnings growth since 2003. This has been from a few products in high growth segments (iPods, iPhones & iPads), as well as laptops.”