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ABI Prism® 7900HT Sequence Detection System ... - OpenWetWare

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Low Precision or Irreproducibility<br />

Improper Threshold<br />

Setting<br />

8-4 Troubleshooting<br />

Overview There are many reasons why an assay run with the <strong>ABI</strong> PRISM <strong>7900HT</strong> <strong>Sequence</strong><br />

<strong>Detection</strong> <strong>System</strong> can have less than optimal precision. Factors that can affect<br />

precision are described in detail below.<br />

Factor See Page<br />

Improper Threshold Setting 8-4<br />

Imprecise Pipetting 8-5<br />

Non-Optimized Chemistry 8-5<br />

Incomplete Mixing 8-5<br />

Air Bubbles 8-5<br />

Splashing PCR Reagents 8-5<br />

Drops 8-6<br />

Writing on the Reaction Plates 8-6<br />

Fluorescent Contamination on the Plates 8-6<br />

Errors 8-6<br />

Contaminated Sample Block 8-7<br />

Improper or Damaged Plastics 8-7<br />

Low Copy Templates 8-7<br />

Use of Non-Applied Biosystems PCR Reagents 8-7<br />

The key to high-precision quantitative PCR is accurate detection of the geometric<br />

phase. The <strong>ABI</strong> PRISM <strong>7900HT</strong> <strong>Sequence</strong> <strong>Detection</strong> <strong>System</strong> typically delivers<br />

sufficient sensitivity so that at least 3 cycles of the geometric phase are visible,<br />

assuming reasonably optimized PCR conditions. The SDS software calculates a fixed<br />

signal intensity, called a threshold, which each signal generated from PCR<br />

amplification must reach before it is recognized as actual amplification. The calculated<br />

threshold is an approximation, and should be examined and modified as needed.<br />

Modifying the Threshold<br />

In a real-time document of the SDS software, the threshold can be modified via the<br />

Amplification Plot view following analysis of the run data. See “Setting the Baseline<br />

and Threshold Values for the Run” on page 6-10 for more information.

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