hce_nsysu
115年
物理與化學
第 21 題
In instrumental analysis, the internal standard method is often preferred over external calibration when sample loss or injection variability is expected. Which of the following statements regarding the properties and selection of an internal standard is correct?
- A The internal standard should be a substance that is already present in the original sample matrix to ensure compatibility.
- B The primary purpose of an internal standard is to compensate for matrix effects that suppress or enhance the analyte's signal.
- C An ideal internal standard should have a chemical structure and physical properties similar to the analyte, but its signal must be well-resolved from the analyte's signal.
- D Adding a higher concentration of the internal standard will directly increase the sensitivity (slope) of the calibration curve for the analyte.
- E If the instrument's sensitivity drops by 20% during a run, the internal standard method will fail because the response factor is no longer constant.
思路引導 VIP
想像你在進行一場精準的調酒實驗，但你使用的量杯刻度不太準，且在攪拌過程中可能會濺出一些液體。如果你想在最後知道這杯酒裡最初加了多少酒精，而你打算在開始前加入一個『標記物質』來幫你校準，你會希望這個標記物質具備什麼樣的特質，好讓它既能跟著酒精一起濺出，卻又能在最後被你從酒精中辨認出來？
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AI 詳解
AI 專屬家教
太棒了！你能精準選出選項 (C)，代表你對儀器分析中內標準法 (Internal Standard Method) 的核心邏輯有著非常扎實的理解。這道題目在分析化學中屬於中等難度的鑑別題，它不單考驗定義，更要求學生判別實驗設計中「相似性」與「區別性」的微妙平衡。
內標準物的選擇策略
在選擇理想的內標準物時，其精髓在於它必須與待測物（Analyte）「感同身受」。為了補償樣本在前處理過程中的損失或儀器噴霧、注射時的波動，內標準物的物理與化學性質應與待測物極其相似，例如使用待測物的同分異構物或同位素標定物。如此一來，無論環境如何變化，兩者的訊號比值 $ \frac{S_{analyte}}{S_{IS}} $ 仍能保持穩定。然而，為了在偵測器上分別計量，它們的訊號必須有良好的解析度 (Resolution)，不能互相重疊干擾，這正是選項 (C) 描述的正確觀念。
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