Ch 5 Calibration

Question 1

when to use each, and which have single vs multiple point

1. external standard
2. internal standard
3. standard addition

Answer 1

1. external: without sample
   single point: analyze at 1 conc in 1 sol’n
   multiple point: analyze at several conc in several sol’ns
2. internal: with sample; spike directly in sol’n
3. standard addition: with sample
   single point: analyze at 1 conc. in 1 sol’n
   multiple point: analyze at several conc. in several sol’ns

Question 2

external standard calibration use

Answer 2

measure response of instrument to analyte

Question 3

external standard calibration multiple point formulas

Answer 3

y = mxc + b

use LINEST to solve for xc

sc (formula sheet)

CL = tdf * sc

Question 4

vertical deviation (residual)

Answer 4

residual = yi - (b + mxi)

Question 5

overall error in a line of best fit

Answer 5

SS resid = ∑i=1 to N [yi - (b+mxi)^2]e

Question 6

least squares analysis assumption

Answer 6

• errors in y values are normally distributed
• size of random error same for all data

Question 7

read excel linest function

Answer 7

[m] [b]
[sm] [sb]
[R^2] [sr]
[df]

Question 8

when to use LINEST

Answer 8

multiple point (external standard, standard addition)

Question 9

standard error of estimate formula (sr)

Answer 9

deviation from regression line
sr = √ [(SSresid) / (N-2)]

Question 10

should you average repeated measurements of calibration y values before linear regression

Answer 10

no

Question 11

CL for multiple point calibration formula

Answer 11

CL = t df * sc

Question 12

coefficient of determination (R^2) meaning

Answer 12

measures fraction of variation in y explained by linear relationship
how straight is the line that the points make
close to 1 = better

Question 13

coefficient of determination formula

Answer 13

R^2 = 1 - SSresid/SStot = SSr/SStot

SStot = √ [SSresid / (N-2)]

Question 14

reagent blank

Answer 14

• Solution containing all the reagents and solvents used
  in the analysis but no deliberately added analyte
• intercept is a response of this

Question 15

detection limit

Answer 15

Smallest concentration (x) that can be reported
with a certain level of confidence

Question 16

detection limit formula

Answer 16

DL = 3*s blank /m

Question 17

single point calibration formulas

Answer 17

single standard (s) run: ys = mxs

unknown (u) run: yu = mxu

must run blank

Question 18

matrix effect

Answer 18

• change in analytical signal caused by a component in sample other than analyte
• leads to systematic error

Question 19

how to fix matrix effect

Answer 19

1. duplicate sample matrix in standard if possible
2. add masking agent
3. use standard addition calibration

Question 20

standard addition calibration multiple point formulas

Answer 20

Cu = b/m = -x0

LINEST to solve for cu

sxo (formula sheet)

CL = pdf * sxo

Question 21

internal standard calibration use

Answer 21

difficult to reproduce the same conditions between individual standards/sample

Question 22

internal standard calibration formulas

Answer 22

y(analyte) / y(is) = mxa + b

Question 23

internal standard calibration response factor formula

Answer 23

A(analyte signal) / A(standard signal) = F ( [analyte] / [standard] )

A: area
F: response factor