Common Contributors to Measurement Uncertainty Chemical
Analyses(representative list - may not be all inclusive for all
types of analyses) (QC sample types in this list are typical of
those utilized in AIHA-LAP, LLC laboratories) additional tabbed
sheets for examplesRepresentative and Applicable QC Data
S
Contributors to Uncertainty Transportation/Storage/Handling:
shipping time, container and temperature
NA / (FS)
lab storage time, conditions and temperature
NA / (LCS, FS)
contamination in lab storage areas
NA / LCS, FB
Laboratory Subsampling sample nonhomogeneity blending techniques
sample size Sample Preparation: volumetric glassware dispensing
device balance temperature sample extraction extractant background
Lab Environmental Conditions: temperature variance humidity
variance Analysts: different analysts analyst training level and
experience data interpretation by analyst Measuring Instruments:
instrument stability carry over effects
DUP DUP DUP LCS, DUP LCS, DUP LCS, DUP LCS, DUP LCS, DUP LCS,
DUP, MB LCS, DUP LCS, DUP LCS, DUP LCS, DUP LCS, DUP LCS, DUP LCS,
DUP
day to day calibration differences interferences Calibration
Standards/Reference Materials: preparation variances calibration
stock material uncertainty
LCS LCS
LCS CERTIFICATE
LCS reference material uncertainty Test Procedure Variations:
variation within and between reagent lots extraction or digestion
times, temperatures, and conditions sample dependent modifications
desorption efficiencies within and between lots for sorbents Data
Manipulation: sampling media/blank correction instrument blank
correction accuracy of calculations
CERTIFICATE
LCS LCS LCS LCS LCS, MB LCS LCS NA
area or air volume sampled
Where: DUP = Duplicate, resulting from sub-sampling of a bulk
(NOTE: NOT LCS/LCSD duplicate spiked sampling media) FB = Field
Blank FS = Field Spike - Not typically conducted unless part of
sampling method validation. Should be considered only when laborato
is responsible for field sampling. LCS = Laboratory Control
Standard, matrix matched and typically taken through the entire
analytical process with each sample batch MB = Method or Matrix
Blank NA = Not Applicable
utors to Measurement Uncertainty Chemical AnalysesSee
ive list - may not be all inclusive for all types of analyses)
al of those utilized in AIHA-LAP, LLC laboratories) additional
tabbed sheets for examples
Comments to Clarify Contributor Effects
NOTE: This is not part of analytical uncertainty, but must be
considered by labs providing sampling and when providing guidance
regarding sample packaging and shipping. Usually no impact if
recommended shipping conditions and holding times in referenced
methods are maintained. Improper packing materials, bulks shipped
w/samples, etc. may adversely affect data. Field blanks, field
spiked samples or duplicate field samples shipped with samples or
included in method validation studies may reflect these
contributors. Field variability (FS/DUP) is only considered when
lab is responsible for sampling. Usually no impact if recommended
storage conditions and holding times in reference methods are
maintained. Impact is monitored per sample batch only if LCS
samples are prepared on receipt and stored with field samples.
Field spiked samples or stability study samples included in some
method validation studies may also reflect these contributors.
Field variability (FS/DUP) is only considered when lab is
responsible for sampling. Usually no impact if recommended storage
conditions and holding times in reference methods are maintained.
Improper storage such as sorbent tubes stored with bulk solvent
samples or near solvent sources may adversely affect data. Impact
is monitored only if LCS is prepared on receipt & stored with
field samples. Field blank can be used to assess contamination from
collection, transport, and storage. NOTE: This primarily applies to
bulk/solid samples which requires use of laboratory duplicate
sample data to determine impact on uncertainty. It is not
applicable for LCS/LCSD media spike duplicates. Sample composition,
etc. Stirring, sieving, grinding, etc. Large enough to allow
adequate subsampling. NA for Class A; applies for graduated tubes
or cylinders, etc. Pipettes, and other types of dispensers that are
not Class A. Balance error is often insignificant compared to other
MU sources. Hot plate or ashing temperatures. Applies to LCS or DUP
if it goes throughthe entire sample preparation process. Analyte or
interferant is present in acids, solvents, etc. Room temp during
bulk asbestos, gravimetry, etc. processes. Gravimetry involving
hydroscopic media, etc. Must use inter-analyst instead of
intra-analyst repeat data, where applicable. Must use inter-analyst
instead of intra-analyst repeat data, where applicable.
Chromatographic peak ID, interference corrections, etc. Must use
inter-analyst instead of intra-analyst repeat data, where
applicable. Baseline drift, repeatability of averaged readings, lab
environmental stability, etc. Impact of high samples on following
sample readings; can be monitored by proper use of CCBs.
Variation in instrument response and calibration process Due to
matrix, inter-element effects, co-eluting GC peaks, etc.
Due to analysts, balances, dispensing devices used, etc Obtain
from certificate or estimate, can be ignored if less than 1/3 of
the largest contributor. Only has impact when LCS data are used to
correct customer sample results. Obtain from certificate or
estimate. Can be ignored if less than 1/3 of the largest
contributor. Note that use of an LCS with a large uncertainty can
result in over estimation of overall analytical uncertainty.
Similar to extractant background effects under Sample
Preparation above. May affect complete dissolution of analyte or
loss of material in some cases. Changes in conditions due to sample
size, customer requests, etc. May vary by lot or manufacturer; also
applies to diffusion rates for passive monitors. When significant
and when data are blank corrected. When allowed. Manual,
spreadsheet, LIMS, etc. Typically provided by the customer. This is
not part of analytical uncertainty, but must be considered by labs
providing sampling and providing combined sampling and analytical
uncertainty.
pling of a bulk (NOTE: NOT LCS/LCSD duplicate spiked sampling
media)
d unless part of sampling method validation. Should be
considered only when laboratory
ix matched and typically taken through the entire analytical
process with each sample
Example of Contributors to Measurement Uncertainty Chemical
Analyses of Sorbent Tubes using Chromatography See Example
Calculations (to the right of the table)Representative and
Applicable QC Data
Contributors to Uncertainty Transportation/Storage/Handling
shipping time, container & temperature
Comments to Clarify Contributor Effects
NA
Limited impact on most sorbent tubes Usually no impact if
recommended storage conditions and hold times are maintained. LCS
samples are representative if prepared on receipt & stored with
field samples - usually no impact if recommended storage conditions
and holding times are maintained. Field spiked samples or stability
study samples included in some method validation studies may also
reflect these contributors. Usually no impact if appropriate
storage conditions are maintained. Field blank can be used to
assess contamination from collection, transport, and storage
lab storage time, conditions & temperature
NA NA
contamination in lab storage areas Laboratory Subsampling sample
nonhomogeneity blending techniques sample size Sample Preparation:
volumetric glassware dispensing device balance temperature sample
extraction extractant background Lab Environmental Conditions:
temperature variance humidity variance Analysts: different analysts
analyst training level & experience data interpretation by
analyst Measuring Instruments: instrument stability carry over
effects day to day calibration differences interferences
NA NA NA LCS LCS NA NA LCS LCS, MB LCS NA
Not applicable to sorbent tube analysis Not applicable to
sorbent tube analysis Not applicable to sorbent tube analysis Same
type of glassware used for samples and LCS Same type of dispensing
device Not applicable to sorbent tube analysis Not applicable to
sorbent tube analysis Applies to LCS if goes through sample
preparation Analyte or interferant in solvents or other prep
reagents used, etc. LCS results reflect any temperature effects on
chromatography instrument Not applicable to sorbent tube
analysis
LCS LCS LCS
LCS results reflect variability due to different analysts, as
applicable, on different days LCS results reflect variability due
to different analysts, as applicable, on different days LCS results
reflect variability due to different analysts, as applicable, on
different days
LCS LCS LCS LCS
LCS results reflect instrument variability on different days LCS
results reflect instrument variability on different days LCS
results reflect instrument variability on different days LCS
results reflect instrument variability on different days
Calibration Standards/Reference Materials: preparation variances
calibration stock material uncertainty LCS reference material
uncertainty Test Procedure Variations variation within and between
reagent lots extraction or digestion times and temps sample
dependent modifications desorption efficiencies within and between
lots for sorbent tubes Data Manipulation: sampling media blank
correction instrument blank correction Accuracy of calculations Due
to analysts, dispensing devices used, etc LCS CERTIFICATE Obtain
from certificate or estimate Use if customer sample data corrected
for desorption efficiency. Obtain from certificate or
CERTIFICATE estimate. LCS LCS LCS LCS LCS LCS LCSLCS subjected
to same treatment as customer samples LCS subjected to same
treatment as customer samples LCS subjected to same treatment as
customer samples LCS subjected to same treatment as customer
samples LCS subjected to same treatment as customer samples LCS
subjected to same treatment as customer samples LCS subjected to
same treatment as customer samples
LCS = Laboratory Control Standard, typically taken through the
entire analytical process with each sample batch MB = Method or
matrix blank NA = Not Applicable
Examples of Analytical Measurement Uncertainty for Analysis of
Organic Solvents on Charcoal Tubes mg Toluene on Charcoal Tube
using CS2 Desorption per NIOSH 1501 LCS/LCSD = 0.0867 mg toluene
spike/tube LCSD %Rec 102.0 mg n-Butanol on Charcoal Tube using CS2
Desorption per NIOSH 1401Mod LCS/LCSD = 0.0810 mg n-butanol spike
/tube (includes correction for DE = 0.80) LCS mg 0.0862 LCS %Rec
106.4 LCSD mg 0.0832 LCSD %Rec 96.0
LCS mg 0.0876
LCS %Rec LCSD mg 101.0 0.0884
0.0824 0.0867 0.0832 0.0789 0.0798 0.0850 0.0824 0.0858 0.0850
0.0876 0.0832 0.0884 0.0867 0.0902 0.0850 0.0876 0.0834 0.0819
0.0797
95.0 100.0 96.0 91.0 92.0 98.0 95.0 99.0 98.0 101.0 96.0 102.0
100.0 104.0 98.0 101.0 96.2 94.5 91.9
0.0850 0.0858 0.0841 0.0789 0.0806 0.0850 0.0867 0.0867 0.0850
0.0858 0.0884 0.0919 0.0893 0.0884 0.0876 0.0902 0.0892 0.0812
0.0784 98.2 4.0 4.05%
98.0 99.0 97.0 91.0 93.0 98.0 100.0 100.0 98.0 99.0 102.0 106.0
103.0 102.0 101.0 104.0 102.9 93.7 90.4
0.0799 0.0839 0.0923 0.0847 0.0702 0.0632 0.0933 0.1005 0.0987
0.0826 0.0913 0.0770 0.0910 0.0832 0.0984 0.0872 0.0809 0.0926
0.0979
98.6 103.6 114.0 104.6 86.7 78.0 115.2 124.1 121.9 102.0 112.7
95.1 112.3 102.7 121.5 107.7 99.9 114.3 120.9
0.0812 0.0825 0.0874 0.0819 0.0907 0.0676 0.0870 0.0924 0.0933
0.0919 0.0756 0.0920 0.0960 0.0928 0.0884 0.0861 0.0655 0.0956
0.0889 103.1 11.5 11.2%
93.7 95.2 100.8 94.5 104.6 78.0 100.3 106.6 107.6 106.0 87.2
106.1 110.7 107.0 102.0 99.3 75.5 110.3 102.5
40 point Mean % Rec 40 point Std Dev RSD
40 point Mean % Rec 40 point Std Dev RSD
Reference material used for calibration indicates assay of
99.5%. Expanded uncertainty of reference material estimated at 0.5%
(95%) Divide by 2 to yield 0.25 % Rel. SD. Insignificant compared
to 4.0% can be eliminated from calculation Expanded MU @ 95% Conf
k=2 8.1% % Bias @ 98.2% Rec = -1.8% Example of reporting for 0.085
mg toluene: 0.085 mg toluene with an analytical uncertainty of
+/0.007 mg at the 95% confidence level with probable bias of -0.002
mg No significant background in method blank.
Reference materials used for calibration and LCS preparation
indicate assay of 99.5%. Expanded uncertainty of reference
materials estimated at 0.5% (95%). Divide by 2 to yield 0.25 % Rel.
SD. Insignificant compared to 11.2% can be eliminated from
calculation Expanded MU @ 95% Conf k=2 22.3% % Bias @ 103.1% Rec =
3.1% Example of reporting for 0.085 mg n=butanol: 0.085 mg nbutanol
with an analytical uncertainty of +/- 0.019 mg at the 95%
confidence level with probable bias of 0.003 mg
No significant background in method blank.
ration and LCS %. Expanded uncertainty 0.5% (95%). Divide by 2
nt compared to 11.2%
n=butanol: 0.085 mg nnty of +/- 0.019 mg at the e bias of 0.003
mg
Example of Contributors to Measurement Uncertainty Chemical
Analyses of Lead (Pb) in Paint using ICP-AES See Example
Calculations (to the right of the table)Representative and
Applicable QC Data
Contributors to Uncertainty Transportation/Storage/Handling
shipping time, container & temperature lab storage time,
conditions & temperature contamination in lab storage areas
Laboratory Subsampling sample nonhomogeneity blending techniques
sample size Sample Preparation: volumetric glassware dispensing
device balance temperature sample extraction extractant background
Lab Environmental Conditions: temperature variance humidity
variance Analysts: different analysts analyst training level &
experience data interpretation by analyst Measuring Instruments:
instrument stability carry over effects day to day calibration
differences interferences Calibration Standards/Reference
Materials: calibration stock material uncertainty Test Procedure
Variations variation within and between reagent lots extraction or
digestion times and temps sample dependent modifications
NA NA NA DUP DUP DUP LCS, DUP LCS, DUP LCS, DUP LCS, DUP LCS,
DUP LCS, DUP, MB NA NA
LCS, DUP LCS, DUP LCS, DUP LCS LCS, DUP LCS DUP, MS
LCS, DUP CERTIFICATE LCS reference material uncertainty NA LCS
LCS LCS
preparation variances
desorption efficiencies within and between lots for sorbent
tubes Data Manipulation:
NA
sampling media blank correction instrument blank correction
Accuracy of calculations
NA LCS LCS
DUP = Duplicate, resulting from sub-sampling of a bulk (NOTE:
NOT LCS/LCSD duplicate spiked sampling media) FB = Field Blank FS =
Field Spike LCS = Laboratory Control Standard, matrix matched and
typically taken through the entire analytical process, with each
sample batch MB = Method or matrix blank NA = Not Applicable
ontributors to Measurement Uncertainty yses of Lead (Pb) in
Paint using ICP-AES e Calculations (to the right of the table)
Examples of Analytic
Comments to Clarify Contributor Effects
Pb in Paint using hotblock acid digestion and Analysis in
accordance with EPA SW846 305 (Mod) LCS Recovery of Paint SRM 2582
at 208.8 +/or SRM 2581 at 4490 +/- 110 mg/Kg P True value mg/Kg
208.8 208.8 4490 4490 208.8 208.8 4490 4490 208.8 208.8 4490 4490
208.8 208.8 4490 4490 208.8 208.8 4490 4490 208.8 208.8 4490 4490
208.8
No impact on bulk paint samples from transportation, storage or
normal handling
Sample composition, etc. Stirring, sieving, grinding, etc Large
enough to allow adequate subsampling NA for Class A; applies for
graduated tubes or cylinders, etc. pipettes, and other types of
dispensers not Class A balance error is often insignificant
compared to other MU sources Hot plate or ashing temperatures
Applies to LCS or DUP if goes through sample preparation Analyte or
interferant in acids, or other reagents No impact on bulk paint
samples No impact on bulk paint samples Analyst contributors affect
all aspects of analysis from subsampling through data
manipulation
LCS mg/Kg 195.4 189.6 4157 4186 184 184 4641 4831 179 177 4539
4858 198 207 4458 4514 184 187 4551 4580 179 186 4245 4302 188
Baseline drift, repeatability of averaged readings, etc Impact
of high samples on following sample readings; can be monitored by
proper use of CCBs Due to matrix, inter-element effects, etc.
Cannot be routinely determined for typical industrial hygiene
sampling media
Due to analysts, balances, dispensing devices used, etc Obtain
from certificate or estimate Sample results not corrected for LCS
recovery
Similar to extractant background effects under Sample
Preparation above May affect complete dissolution of analyte or
loss of material in some cases Changes in conditions due to sample
size, customer requests, etc
202 208.8 4217 4490 4300 4490 203 208.8 190 208.8 30 point Mean
% Rec. 30 point Std Dev RSD
No sampling media with bulk samples when allowed Manual,
spreadsheet, LIMS, etc
g of a bulk (NOTE: NOT LCS/LCSD duplicate spiked sampling
media)
matched and typically taken through the entire analytical
process, with each
Example analytical unc Expanded analytical un
Bias = 4400 mg/kg X -0.
Example of reporting fo 4400 mg/Kg Pb in paint confidence level
and a
Examples of Analytical Measurement Uncertainty for Lead in Paint
Sample duplicata data in mg/Kg for Pb in Paint using hotblock acid
digestion and ICP-AES in accordance with EPA SW-846 3050 & 6010
(Mod)
otblock acid digestion and ICP-AES ance with EPA SW846 3050
& 6010 (Mod) aint SRM 2582 at 208.8 +/- 4.9 mg/Kg 81 at 4490
+/- 110 mg/Kg Pb
LCS % Rec 93.6 90.8 92.6 93.2 88.1 88.1 103.4 107.6 85.7 84.8
101.1 108.2 94.8 99.1 99.3 100.5 88.1 89.6 101.4 102.0 85.7 89.1
94.5 95.8 90.0 96.7 93.9 95.8 97.2 91.0 94.7 6.3 6.7%
mg/Kg Sample 1604 511 9470 161 1683 956 23470 625 723 23000
14190 10350 5702 109 7079 196 14510 15710 1187 9265 4240 1979 2357
2254 53160 24810 22860 1133 151 7774
mg/Kg Sple Dup 1502 602 8794 93 1411 830 26570 730 472 22000
13900 9142 5854 122 6427 186 14300 17150 1192 9246 3918 1574 3068
3062 44300 23000 22930 1125 96 4366
Std Dev (S) 72.12 64.35 478.00 48.08 192.33 89.10 5.66 74.25
177.48 38.89 205.06 854.18 107.48 9.19 461.03 7.07 148.49 1018.23
3.54 13.44 227.69 286.38 502.75 571.34 6264.97 1279.86 49.50 5.66
38.89 2409.82
CV 0.0464 0.1156 0.0523 0.3786 0.1243 0.0998 0.0002 0.1096
0.2970 0.0017 0.0146 0.0876 0.0186 0.0796 0.0683 0.0370 0.0103
0.0620 0.0030 0.0015 0.0558 0.1612 0.1853 0.2150 0.1286 0.0535
0.0022 0.0050 0.3149 0.3970 CV2
CV2 0.0022 0.0134 0.0027 0.1433 0.0155 0.0100 0.0000 0.0120
0.0882 0.0000 0.0002 0.0077 0.0003 0.0063 0.0047 0.0014 0.0001
0.0038 0.0000 0.0000 0.0031 0.0260 0.0344 0.0462 0.0165 0.0029
0.0000 0.0000 0.0992 0.1576 0.6977 0.1525 15.2%
CV pooled = (CV2/30) =
Reference material used for calibration indicates concentration
and expanded uncertainty of 1001 +/- 5 ug/mL at 95% confidence
level. Expanded uncertainty divided by 2 to yield 0.25 % Rel. SD.
Insignificant compared to 15.2% and can be eliminated from
calculation. No significant background in method blank. Combined
Rel. Std Dev (SDc) = [ SD12 + SD22] SDc = [(6.7)2 + (15.2)2] =
16.6% Expanded MU @ 95% Conf (k=2) = Bias @ 94.7% Rec of LCS =
-5.3% 33.2%
Example analytical uncertainty for 4400 mg/Kg Pb in paint
sample: Expanded analytical uncertainty of 4400 mg/Kg Pb in paint =
4400 X 0.332 = 1460 mg/kg Bias = 4400 mg/kg X -0.053 = 233.2
mg/kg
Example of reporting for 4400 mg/Kg Pb in paint: 4400 mg/Kg Pb
in paint with an analytical uncertainty of +/- 1500 mg/Kg at the
95% confidence level and a probable bias of -230 mg/Kg
RSD
