Test #2 – Quantitative Analysis – Flashcards
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| significant figures and addition and subtraction |
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| round according to the number with the most uncertainty, that is, the answer is limited by the least certain number |
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| significant figures and multiplication and division |
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| the answer is limited to the number of digits contained in the number with the fewest significant figures |
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| significant figures and logarithms and antilogarithms |
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| the number of digits in the mantissa of (log x) is the number of significant figures in x. |
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| characteristic |
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| the part of a logarithm to the left of the decimal point |
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| mantissa |
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| the part of a logarithm to the right of the decimal point |
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| significant figures in graphs |
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| depends on the purpose of the graph. if to display qualitative behavior of data, then sig figs are irrelevant. if to display precise values, then several sig figs |
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| systematic error determinate error |
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| occurs in the same direction each time (high or low), often resulting from poor technique |
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| how to detect systematic error |
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| analyze samples of known composition, 'blank' samples containing none of the sought analyte; use different analytical methods to measure same quantity; Round Robin experiment |
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| Round Robin experiment |
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| assign different people/labs to analyze identical samples |
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| random error indeterminate error |
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| measurement has an equal probability of being high or low; obeys laws of statistics |
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| accuracy |
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| agreement of a particular value with the "true" value. |
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| precision |
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| degree of agreement among several elements of the same quantity |
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| absolute uncertainty |
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| expression of the margin of uncertainty associated with a measurement |
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| relative uncertainty |
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| compares the size of the absolute uncertainty with the size of its associated measurement |
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| percent relative uncertainty |
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| 100 * relative uncertainty |
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| propagation of uncertainty from random error addition and subtraction |
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| if A=B+-C+-D Ua=(Ub^2+Uc^2+Ud^2)^1/2 abs uncertainty used |
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| propagation of uncertainty from random error multiplication and division |
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| A=B*/C*/D %RUa=[(%RUb)^2+(%RUc)^2+(%RUd)^2]^1/2 percent relative uncertainty used |
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| propagation of uncertainty mixed operations |
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| same manner as the calculations are performed |
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| real rule of significant figures |
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| THe first uncertain figure is the last significant figure |
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| propagation of uncertainty exponents |
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| %RUy=a(%RUx) |
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| propagation of uncertainty logarithms |
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| Uy=(1/ln10)*RUx |
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| propagation of uncertainty natural log |
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| Uy=RUx |
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| propagation of uncertainty power of 10 |
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| RUy=(ln10)Ux |
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| propagation of uncertainty base e |
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| RUy=Ux |
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| uncertainty in molecular masses |
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| Use rule for addition and subtraction, then multiply by n moles per identical atom |
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| Gaussian distribution |
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| Theoretical bell-shaped distribution of measurements when all error is random. The center of the curve is the mean, and the width is characterized by the standard deviation. |
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| mean |
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average
[image] |
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| standard deviation |
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measure of how closely the data are clustered to the mean.
[image] |
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| degrees of freedom |
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| the number of independent measurements |
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| variance |
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| standard deviation squared |
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| relative standard deviation |
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| 100 * std. dev./ mean |
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| significant figures in mean and standard deviation |
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| where uncertainty begins according to std. dev., that's where significant figures are. |
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| formula for Gaussian curve |
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| [image] |
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| Z |
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| [image] |
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| confidence interval |
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| [image] |
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| Student's t |
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| statistical tool used to express confidence intervals and to compare results from different experiments. |
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| Student's t test |
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| used to compare one set of data with another to decide whether or not they are "the same" |
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| null hypothesis |
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| the two sets of data are the same |
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| alternate hypothesis |
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| the two sets of data are different |
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| when to use Student's t test |
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| comparing a measured result with a known value, replicate measurements, individual differences |
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| t calc equation known value |
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| [image] |
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| t calc equation replicate measurements if std. devs. equal |
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| [image] |
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| s pooled replicate measurements |
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| [image] |
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| t calc equation replicate measurements if std. devs. inequal |
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| [image] |
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| F test |
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| compares standard deviations |
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| F calc |
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| [image] |
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| Grubbs test |
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| determines whether one measurement can be thrown away -- whether it is an outlier or not |
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| G calc |
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| [image] |
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| Real rule for bad data |
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| Dropped sample? Pretty obvious Be hesitant if not certain Grubbs test is not very reliable |
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| Calibration curve |
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a graph showing the value of some property versus concentration of analyte. When the same property of an unknown is measured, its concentration can be determined from the graph.
[image] |
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| method of least squares |
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| process of fitting a mathematical function to a set of measured points by minimizing the sum of the squares of the distances from the points to the curve. |
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| standard solutions |
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| a solution whose composition is known by virtue of the way it was made from a reagent of known purity or by virtue of its reaction with a known quantity of standard reagent |
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| blank solution |
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| a solution that does not contain analyte; used to correct for interferences |
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| linear range |
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| the analyte concentration range over which response is proportional to concentration |
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| dynamic range |
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| the analyte concentration range over which there is a measurable response to analyte. |
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| quality assurance |
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| Quantitative indications that indicate whether data requirements have been met. Also refers to the broader process that includes quality control, quality assessment, and documentation of procedures and results designed to ensure adequate data quality. |
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| Use objective |
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| states the purpose for which results will be used |
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| specifications |
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| describes how good analytical results need to be and what precautions are required in an analytical method. |
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| false positive |
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| a conclusion that the concentration of analyte exceeds a certain limit when, in fact, the concentration is below the limit |
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| false negative |
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| a conclusion that the concentration of analyte is below a certain limit when, in fact, the concentration is above the liimit. |
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| selectivity |
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| being able to distinguish analyte from other species in the the sample |
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| sensitivity |
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| the capability of responding reliably and measurably to changes in analyte concentration. Slope of the calibration curve |
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| method blank |
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| a sample containing all components except analyte and is taken through all steps of the analytical process. Response is subtracted from sample's response. |
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| reagent blank |
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| a solution prepared from all of the reagents, but no analyte; for measuring response of analytical method to impurities in reagents and other effects caused by anything but the analyte |
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| field blank |
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| a blank sample exposed to the environment at the sample collection site and transported in the same manner as other samples between the lab and the field. |
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| matrix |
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| everything in the sample other than analyte Also, the virtual reality which the machines have set us in while they harvest our bodies for energy. Ignore that it would be incredibly inefficient. |
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| spike |
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| addition of a known compound (with known concentration) to an unknown |
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| spike recovery |
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| [image] |
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| calibration check |
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| the analysis of a solution formulated by the analyst to contain a known concentration of analyte Ensures that procedures and instruments are functioning correctly. |
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| performance test samples |
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| inserted in a series of measurements to see if a procedures gives correct results when the analyst does not know the right answer |
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| standard operating procedures |
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| a written procedure that must be rigorously follow to ensure the quality of a chemical analysis |
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| control chart |
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| a visual representation of a confidence interval for a Gaussian distribution |
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| assessment |
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| the process of collecting data to show that analytical procedures operating within specified limits and verifying that final results meet use objectives |
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| method validation |
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| the process of proving that an analytical process is acceptable for its intended purpose |
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| specificity |
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| the ability of an analytical method to distinguish the analyte from everything else that might be in the sample |
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| linearity |
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| measures how well a calibration curve follows a straight line |
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| square of the correlation coefficient |
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| measure of goodness of fit of data points to a straight line. Closer to 1 = better |
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| how to demonstrate accuracy |
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| Analyze a standard reference material compare results of different methods spike a blank sample with analyte standard additions |
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| reproducibility of results |
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| precision (alternate definition) |
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| range |
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| concentration interval over which linearity, accuracy, and precision are all acceptable |
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| detection limit |
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| the smallest quantity of analyte that is "significantly different" from the blank. * * |
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| procedure for detection limit determination |
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| [image] |
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| quantitation limit |
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| [image] |
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| reporting limit |
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| the concentration below which regulatory rules say that a given analyte is reported as "not detected" |
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| robustness |
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| the ability of an analytical method to be unaffected by small, deliberate changes in operating parameters |
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| standard addition |
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| known quantities of analyte are added to the unknown and the responses are recorded. This keeps any matrix effect constant. |
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| matrix effect |
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| a change in the analytical signal caused by anything in the sample other than the analyte |
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| standard addition equations |
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| [image] |
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| standard addition with constant total volume |
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| [image] |
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| standard addition with varying total volume |
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| [image] |
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| internal standard |
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| a known amount of a compound, different from analyte, that is added to the unknown. Signal from the analyte is compared with signal from the internal standard to find out how much analyte is present. |
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| response factor, F |
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| [image] |
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