Vocabulary of analytical chemistry

Lecture Vocabulary of analytical chemistry Contents  Measurements, analysis, determination  levels of methodology  Criteria to select an analytical method  Develop a procedure Measurements, determinations and analysis Analyse (Phân tích) Determine (Xác định) Measure (Đo) Analyse drinking water in Hanoi: Determine identities, properties, concentrations of toxic chemicals such as As Measure absorbance of AsH3 by HVG-AAS technique levels of analytical methodology  Technique (kĩ thuật) : any chemical or physical principle to study an analyte Exp: AAS; F-AAS; ICP-MS techniques  Method (phương pháp): application of a technique for a specific analyte in a specific matrix Exp: F-AAS method to determine Pb in drinking water; F-AAS method to determine Pb in ores  Procedure (qui trình): a set of written directions telling us how to apply a method to a particular sample, including information on obtaining samples, handling interferents, and validating results A method may have several procedures  Protocol (thủ tục) : a set of stringent guidelines specifying a procedure that must be followed if an agency is to accept the results APHA: American Public Health Association ASTM: American Society for Testing Materials EPA: Environmental Protection Agency Criteria to select an analytical method  Accuracy (độ chính xác) : agreement between experimental data and the “true” or expected result Absolute error: E = xi - xt (where xt = true or accepted value) x −x Relative error: t × 100% E = i r x t  Precision (độ chụm): the agreement between replicate experimental analyses d i = xi − x individual value Mean value Or standard deviation (Sd)= Σd2/n *Độ chính xác(accuracy) = độ đúng (trueness) + độ chụm (precission) Example 1:  Glucose concentration in blood: mg/L  You determine concentration: mg/L  What’s the error =?  Example 2:  You measure times: 5.0; 5.2; 4.7; 5.1; 4.9 (mg/L)  Your colleague measures times: 4.0; 6.7; 6.8; 6.3; 5.4 (mg/L) Who’s precision better? Who’s accuracy better?  Illustrating the difference between “accuracy” and “precision” Low accuracy, low precision Low accuracy, high precision High accuracy, low precision High accuracy, high precision  Sensitivity (độ nhạy): Ability to detect the change of signal when there is a change in the amount of analyte (equivalent to ka in S a = kana or Sa = kaCa) Sensitive to change in temperature, hot or cold, skin, hair, thermometer, skin: 0.1°, thermometer: 0.1° – 0.001°)  Detection limit (gioi han phat hien): smallest amount of analyte that can be determined with confidence  Titration: LOD: 10-4M  ICP-MS: LOD: 10-9M Criteria to select an analytical method  Specificity (độ đặc thù): if the signal depends only on the analyte  Selectivity (độ chọn lọc): a measure of a method’s freedom from interferences  Selectivity coefficient: ka,I= kI/ka - K can be positive (interferent increases signal), negative (interferent decreases signal), magnitude can be > or < 1; the smaller K, the more selectivity the method Criteria to select a method  Robustness (tính ổn định): ability to use an analytical method on many analytes in a wide variety of sample matrices  Ruggedness (tính không ổn định): in contrast with robustness, ability to provide accurate results despite variations in executing a method (variation in pH, T, …)  Scale of operation: the amount of sample available for the analysis, the expected concentration of analyte in the samples, and the minimum amount of analyte that produces a measurable signal Develop a procedure  Method blank (thí nghiệm trắng): compensate for interferences, measure the signal of solution that does not contain the sample  Calibration curve (đường chuẩn): determine ka using one or more standards Develop a procedure  Sampling (lấy mẫu) : collecting and preparing samples (more in Chapter 7)  Validation (xác nhận giá trị sử dụng của phương pháp): uses a standard sample, whose composition closely matches the samples that will be analyzed or compared, with a method with known accuracy (more in Chapter 14) ... Hanoi: Determine identities, properties, concentrations of toxic chemicals such as As Measure absorbance of AsH3 by HVG-AAS technique levels of analytical methodology  Technique (kĩ thuật) : any... (variation in pH, T, …)  Scale of operation: the amount of sample available for the analysis, the expected concentration of analyte in the samples, and the minimum amount of analyte that produces a... application of a technique for a specific analyte in a specific matrix Exp: F-AAS method to determine Pb in drinking water; F-AAS method to determine Pb in ores  Procedure (qui trình): a set of written