儀器分析英文課件Chapter1-Introduction.pptVIP

INSTRUMENTAL ANALYSIS,Chapter 1. Introduction,Analytical Chemistry: determining the chemical composition of samples of matter. Qualitative analysis: identify of functional groups, or atomic, molecular structure of analyte ( what?) Quantitative analysis: amount of analyte ( how much?),1.1 Classical methods (Chemical analysis),Qualitative analysis: Analytes,Products,recognized,yield,treated with reagents,Colors Boiling (melting) points Solubilities Odors Optical activities Refractive indexes,Quantitative analysis: gravimetric; titrimetric,1. Classification of analytical methods,1.2 Instrumental methods (Instrumental analysis),Early in 20th century,Measurements of physical (chemical) properties of analytes: -conductivity; electrode potential; light absorption (emission); mass-to-charge ratio; fluorescence,Highly efficient chromatographic and electrophoretic techniques,replaced,Distillation, extraction, precipitation,a. Development of instruments and computer,b. Development of separation methods,c. classification of instrumental analysis,Optical Analysis (spectrometry); Electrochemical Analysis; Chromatography,2 types of instrumental methods,Chemical (physical) characteristics Emission of radiation Absorption of radiation Scattering of radiation Diffraction of radiation Rotation of radiation Electrical potential Electrical charge Electrical current Electrical resistance Mass Mass-to-charge ratio Rate of reaction Thermal characteristics Radioactivity,Instrumental methods Emission spectroscopy, fluorescence, phosphorescence, luminescence Absorption spectroscopy Raman spectroscopy X-Ray diffraction Circular dichroism Potentiometry, chronopotentiometry Coulometry Amperometry, polarography Conductometry Quartz crystal microbalance Mass spectrometry Kinetic methods Thermal gravimetry and titrimetry Activation and isotope dilution methods,3 Instruments for analysis,manipulated and interpreted by human,Overall process of instrumental measurement,Data domain: way of encoding analytical response in electrical or nonelectrical signals (namely electrical domains and nonelectrical domains ),Detector (general): device that indicates change in environment Transducer (specific): device that converts non-electrical to electrical data Sensor (specific): device that converts chemical to electrical data,Analog domains,Time domains,Digital domains,Analog - continuously variable magnitude (current, voltage, charge) Time - vary with time (frequency, phase, pulse width) Digital - discrete values (count, serial, parallel, number*),Table 1-2Examples of instrument components (p.4),4 Selecting an analytical method,What accuracy is required?-Accuracy/Bias How much sample is available?-sensitivity What is the concentration range of the analyte?-Dynamic range What components of the ample will cause interference?-Selectivity What are the physical and chemical properties of the sample matrix? -analytical methods How many samples are to be analyzed?-economic standpoint,Defining the problem:,Performance characteristics of instruments (Figures of merit),Precision: the degree of mutual agreement among data that have been obtained in the same way.,Three types of such errors: Instrumental: something wrong with the instrument (batteries low, temperature effects the circuitry, calibration errors, etc.) Personal: judgment errors, reading the meter from the wrong angle, lack of careful technique. Method: often a result of non-ideal chemical behaviour; slow reactions, contaminants, instability of reagents, loss of analyte by adsorption. Must use guaranteed standards.,Precision and accuracy,Sensitivity: a measure of the ability of an instrument (method) to discriminate between two small differences in analyte concentration,Calibration sensitivity: the slope of the calibration curve at the concentration of interest,Calibration curve,Signal (s) s0,S=mC +Sbl,concentration,Analytical sensitivity: include precision in a meanongful mathematical statement of sensitivity,=m/ss,Calibration sensitivity,Standard deviation of measurement,Detection limit (檢出限): the minimum concentration (mass) of analyte that can be detected at a known confidence level.,Sm = Sbl + k s,Minimum distinguishable analytical signal,Mean blank signal,Standard deviation on blank signal,Usually taken to be 3, Depends upon signal/noise ratio. Analysis signal must be larger than blank signal. How much larger?,(at 95% confidence level),Cm = (Sm - Sbl )/m,S=mC +Sbl,Example 1：,Concentration Signal NET Signal 0 ppm (blank) 0.136 0.000 10. ppm 0.721 0.585 1.0 ppm 0.195 0.059 0.10 ppm 0.142 0.006 0.010 ppm 0.137 0.001 S = 3 blank= 3 (0.002) = 0.006 Sm = Sblank+S=0.136+0.006= 0.142 (0.10 ppm Pb),Suppose that: blank = 0.002,Example 2： A fluorescence method was applied to determine component A in the solution. The results are shown in the table.,Suppose that the SD of blank is 0.352. An unknown sample give results of 525,536 and 529. Please calculate: 1.The sensitivity and the detection limit of the method. 2.The concentration of A in the sample, standard deviation and relative standard deviation of the detection.,Let us make the working curve (Ic) first,I=0.834+109c Relative coefficient: r=0.99998,Sensitivity: 109 ml /g Detection limit: CDL= (IDL I0)/m=30.352/（109 ml /g） =0.00969g/ml,I0=0.834 IDL=I0+3SD=0.834+109cDL,I=(526+536+529)/3=530 Concentration of A in the sample: c=(530-0.834)/109=4.85g/ml standard deviation s=5.57 relative standard deviation: RSD=5.57/530100%=1.05%,Limit of Quantitation （LOQ 檢測限）,Sq = S0 + 10 s,The detection limit answers the question “Is this analyte present or not?” However, to actually answer the question “How much of the analyte is present?” requires a still larger signal. The widely accepted level at which the analyte can be quantified is TEN times the standard deviation. (Detection is THREE times.),Signal Relationships,Measured Signal Level,0,Mean Background Signal Level,Distribution of blank measurements,Detection Limit,3 sbl,Quantitation Limit,10 sbl,Dynamic range: concentration range between LOQ and LOL,Selectivity: the degree that the method is “free” from reference by other species contained in the sample matrix.,No analytical method is completely free from interference by concomitants. Best method is more sensitive to analyte than interfering species (interferent).,Example 3 (p.15): The selectivity coefficient for an ion-selective electrode (ISE) for K+ with respect to Na+ is reported to be 0.052. Calculate the relative error in the determination of K+ in a solution that has a K+ concentration of 3.0010-2 M if the Na+ concentration is (a) 2.0010-2 M; (b) 2.0010-3 M; (c) 2.0010-4 M. Assume that Sbl for a series of blank was approximately zero.,Solution: (a) Since kNa+, K+=0.052, Sbl=0, cK+ = 3.0010-2 M, cNa+ = 3.0010-2 M then S=mK+(cK+ + kNa+, K+cNa+) + 0= 4.0410-3 mK+ If Na+ were not present, then S0=mK+(cK+ + kNa+, K+cNa+) + 0= 3.0010-3 mK+ Erel=(S-S0)/S0 =35%; Similarly, we get (b) Erel=(S-S0)/S0 =3.5% (c) Erel=(S-S0)/S0 =0.35%,5 Calibration of instrumental methods,5.1 calibration curves (working curves; analytical curves; standard curves),Our familiar method Unfortunately, matching the matrix of complex samples is often difficult or impossible. Two methods to minimize the matrix effects: Separating the analyte from interference prior to measurements; Employing standard additional methods,5.2 standard addition methods,Adding (spiking) one or more increments of a standard solution to sample aliquots of the sa