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What you must know about blank experiments! Are blank experiments always ignored? I did it, but I don’t know why? Today, we will thoroughly explain the underlying logic behind blank experiments and their practical applications, along with the 5 key scenarios in which blanks must be used – essential reading for those who conduct experiments! 🔍 What is a blank experiment? ✅ Official definition: An experiment in which a pure solvent/blank sample is used in place of the actual sample, with participation in all pre-treatment and measurement steps throughout the process. ✅ Simple understanding: It involves \"checking\" the testing process to identify background interference values. ⚠️ Note: A blank experiment does not mean no sample is used! It is necessary to participate in all steps such as digestion/extraction/color development throughout the process. 📌 The 3 key functions of a blank experiment: 1️⃣ Eliminating background interference ✔ Identifying sources: · Insufficient reagent purity (e.g., heavy metals in acids) · Contamination of instruments (e.g., ions released from glassware) · Environmental contamination (e.g., air dust) ✔ Calculation formula: True signal = Sample signal – Blank signal 2️⃣ Assessing the reliability of the method ✔ Acceptance criteria: · Blank value ≤ 1/3 of the method’s detection limit · Variability among blank samples ≤ 20% ✔ Handling abnormalities: · High blank value → Use higher-purity reagents · Large fluctuations in blank values → Check for environmental contamination 3️⃣ Monitoring experimental contamination ✔ Early warning function: · Sudden increase in blank value → Indicates recent contamination · Continuous abnormal blank values → Indicates system contamination ✔ Tracing the cause: · Identify the source of contamination through blank experiments. ⚡ 5 situations where blank experiments are necessary: 1️⃣ Trace analysis ✔ Analyzed substances: · Heavy metals (Pb, Cd, Hg) · Organic pollutants (PAHs, PCBs) ✔ Reason: Background interference may be greater than the sample signal. 2️⃣ High-precision quantification ✔ Analyzed substances: · Determination of drug concentrations · Calibration of reference materials ✔ Reason: It is necessary to account for systematic errors introduced by reagents/instruments. 3️⃣ Development of new methods ✔ Key stages: · During method validation · Inter-laboratory comparisons ✔ Reason: To assess the background level of the method. 4️⃣ Analysis of environmental samples ✔ Analyzed substances: · Water quality testing (surface water, wastewater) · Air particles ✔ Reason: Large fluctuations in environmental backgrounds. 5️⃣ Re-testing of disputed samples ✔ Application scenarios: · Verifying results that exceed limits · Samples used in legal proceedings ✔ Reason: To ensure the validity of the data. 🧪 Guidelines for selecting the type of blank experiment Blank type Application scenario Analyzed content Reagent blank Routine testing Reagent purity Instrument blank Trace analysis Instrument contamination Full-process blank Disputed samples Full-process contamination Field blank Environmental monitoring During sampling process contamination ⚠️ 5 common mistakes in conducting blank experiments ❌ Using tap water as a blank (pure water should be used) ❌ Testing the blank before the sample (it should be tested interspersed with the samples) ❌ Ignoring the blank value (reporting data without deducting the blank value) ❌ Not including the blank value in preprocessing (losing the purpose of deduction) ❌ Using expired reagents as a blank (they are already contaminated). 💡 Practical tips for conducting blank experiments ✔ Number of blanks: At least 2 parallel blanks per batch. ✔ Placement: Place them at the beginning, middle, and end of the sample sequence. ✔ Result evaluation: If the blank value exceeds 1/3 of the detection limit, retest. ✔ Recording requirements: The blank value must be included in calculations and recorded. Blank experiments are like the “conscience” of data—doing them isn’t necessarily great, but not doing them can be dangerous! Share this guide to make laboratory data more reliable~ Feel free to ask any questions in the comments section👇