QUALITY ASSURANCE SUMMARY FOR 

MONTANA TEST OF CES’s CEM

1.0. INTRODUCTION

Cooper Environmental Service’s (CES) X-ray-based Continuous Emissions 

Monitor (XCEM) extracted an isokinetic sample from the test duct through a oneinch diameter nozzle. This stack gas sample was slowed in a downward-flow 

stilling chamber where a second isokinetic sample was drawn through a test filter 

tape that trapped both particulate and ionic vapor-phase elements. The entire 

sample extraction system was heated to about 350°F. The sample analyzed by the 

X-ray fluorescence analysis part of the XCEM consisted of a spot with a diameter 

of about 0.25 inch, which was positioned near the center of the X-ray excitation 

beam.

There are two parameters (elemental mass and volume) that go into the 

calculation of stack gas concentrations, but there are four categories for potential 

errors in this measurement: sample extraction efficiency, filter sampling 

efficiency, elemental mass determination, and measurement of stack gas volume 

sampled.

Sample Extraction. The sample extraction system was designed to minimize 

loss of particulate due to impaction and settling. The use of a one-inch diameter 

nozzle made the extraction system relatively insensitive to flow variations. The 

stilling chamber was three inches in diameter and three feet long. The stilling 

chamber meets the eight diameter rule and previous tests of a similar stilling 

chamber has shown that the particle concentration at the test sample extraction 

point is uniform to within ±3%. Although there is bound to be some loss of 

particles and gaseous species to the walls of any extractive CEM, these losses can 

be minimized and the results adjusted for these small losses. In this particular 

test, the particulate losses prior to filter sampling appear to be less than about 

10%. This estimate is based on the following reasons:

 Only about 10% of the Method 29 metals were deposited in the much 

smaller Method 29 nozzle and transport tubing.

 The average reported lead and chromium concentrations are 8% and 11%, 

respectively, less than the Method 29 concentrations. The arsenic, 

cadmium, chromium and lead concentrations after adjusting for calibration 

errors are only a couple of percent lower than the corresponding Method 

29 results. Assuming similar particle size distributions for the other 

elements, it is unlikely that particle loss in the XCEM extraction 

component is a significant source of error.

 The potential loss of gaseous species is expected to be low because the 

addition of chlorine gas resulted in the increase in only lead, and then only 
about one microgram. If other potential vapor phase species had been lost 

to the walls, the high temperatures and chlorine gas is expected to indicate 

this as it did with the small amount of lead.

Filter Sampling Efficiency. The filter sampling efficiency has been determined 

in the laboratory to be on the order of 98% for particulate and ionic vapor phase 

elements. Elemental vapors such as mercury have trapping efficiencies of less 

than 1%. The original test plan called for the addition of chlorine gas to convert 

the elemental mercury to mercuric chloride, which would then be trapped by the 

filter. Because of system problems, chlorine gas was used only for a few samples. 

Thus, the XCEM low reported mercury results are expected to be due to the 

presence of elemental mercury and its poor sampling efficiency. The Method 29 

results suggest that the other metals were dominated by particulate species. Thus, 

the sampling efficiency is not expected to have contributed to differences in the 

XCEM and Method 29 results.

Elemental-Mass Determination. The elemental mass in the filter deposit was 

determined using an energy-dispersive X-ray fluorescence analyzer. This method 

is a particularly powerful tool for this application because the analysis is nondestructive and its results are potentially National Institute of Standards and 

Testing (NIST) traceable. In addition, the spectral results for each analysis are 

recorded, all of the elements are determined simultaneously, the elemental 

sensitivities are a smoothly varying function of atomic number, and the elemental 

analyzer is extremely stable, typically requiring recalibration only about once or 

twice a year. In this particular evaluation, the instrument was calibrated prior to 

the field tests, but the calibration could not be validated before the tests because 

of limited time. However, post calibration tests were conducted and indicated less 

than a 3% change in the calibration. Additional post calibration tests did indicate 

a bias in the XCEM calibration factors, which can explain most of the difference 

in the reported XCEM and Method 29 concentrations for arsenic, cadmium, 

chromium and lead concentrations. If the independent laboratory based XCEM 

calibrations factors are used, arsenic, cadmium, chromium and lead would all 

meet the EPA relative accuracy criteria of 20%. These adjustments are discussed 

in Section 4.0.

Volume Sampled. The volume of stack gas sampled was determined by

subtracting the dilution gas volume from the total sample volume determined by a 

NIST-traceable mass flow meter. In the early part of the tests, the dilution 

volume was estimated with a rotameter, which was subsequently calibrated 

against the mass flow meter. In the latter portion of the tests, a second mass flow 

meter was used to determine the dilution gas used. 

In general, uncertainties in the stack gas volume sampled are not expected to have 

contributed significantly to any of the differences in the Method 29 and XCEM 

results. This is based on the fact that the same volume is used in the calculations 

for each of the elements. Since the chromium and lead were very close to the 
Method 29 results, the volume used in the calculations for all the elements could 

not be significantly in error with either of the two methods.

2.0. PRE-TEST LABORATORY DETERMINATIONS

2.1. Energy calibration

The X-ray fluorescence analyzer component of the XCEM is periodically

calibrated for energy. During this evaluation, the instrument was calibrated for 

energy prior to calibrations, and the online field tests.

2.2. Determination of elemental line interferences

Elements expected to be present in the test stack gas were determined from filter 

samples collected at the test facility. The analyzer was calibrated for these 

elements and potential spectral interferences determined. The elements present in 

the stack gas during the tests were as determined from the pre-test samples.

2.2. Blank interference and variability determinations

Blank filter tape elemental concentrations were determined prior to the tests and 

during the online field tests. In no case, was there a measurable amount of the 

reported elements present in the blank tape, nor was there a significant amount of 

a potentially interfering element. The only major elements present were sulfur 

and chlorine. The only measurable trace element impurities were a few 

nanograms per cm2 of iron, zinc and bromine. 

2.3. Elemental sensitivity determination

The analyzer elemental sensitivities or calibration factors were determined using 

thin-film standards (Micromatter), which are NIST traceable through gravimetric 

standards. These standards were internally evaluated by plotting elemental 

sensitivities versus atomic number. Because the electron binding energies and

probabilities for creating electron vacancies is a smoothly vary function of atomic 

number, any elemental sensitivity falling off a best-fit smoothly varying curve 

was considered suspect and evaluated. The calibration factors used to calculate 

the originally reported results were based on these thin film standards. These 

factors were subsequently adjusted based on post analysis of XCEM spots by an 

independent analytical laboratory as discussed in Section 4.0.

Mercury was an exception to this procedure. Thin film mercury standards are not 

available. For these tests, a secondary mercury sample was used for spectral 

response calibration and a theoretical instrument ratio to lead was used to 

calculate a mercury intensity calibration factor. The instruments manufacturers 

theoretical ratio of 0.85 was used. This ratio has not yet been validated, and may

be a source of some of the differences in the XCEM-reported results.

3.0. PRE-TEST ONLINE QUALITY ASSURANCE TESTS

3.1 Energy calibration
The XCEM was energy calibrated prior to the tests after it had been installed in 

the test facility. This energy calibration was checked periodically during the test 

period.

3.2 Elemental sensitivity check

The elemental sensitivity or calibration factors were checked at the site after 

system installation and just prior to the test runs by analyzing the thin film 

calibration standards as unknowns. The resulting XCEM results are compared to 

post-tests XCEM results in the following section. This comparison shows that 

instrument calibration drift was less than 3% between the online field application 

and post-test laboratory measurements over a month after the field tests.

4.0. POST TEST LABORATORY QUALITY ASSURANCE TESTS

The XCEM was disassembled after the online field tests and reassembled at 

CES’s laboratory several weeks later. Several post-test quality assurance checks 

were conducted at this time. The results of these post quality assurance tests are 

discussed in the following subsections.

4.1. Energy calibration check

The system was calibrated for energy prior to instrument use to assure proper 

peak shape and location in the recorded X-ray spectra.

4.2. XCEM analysis of thin film standards as unknown

Thin film standards were used to calibrate the XCEM prior to online analysis. 

These same thin film standards were run again as unknowns prior to the online 

tests assuming a sample volume of 0.01 m3. After the XCEM was returned to the 

laboratory, these thin film standards were again analyzed as unknowns as a post 

calibration check. The pre-test and post-test equivalent stack gas concentrations 

reported by the XCEM are compared below.

In-field In-lab

Pre-test results Post-test results Difference

Element μg/m3 μg/m3 μg/m3 Percent

Sb 2541 2515 26 1.0

Pb 3108 3056 52 1.7

As 2044 2003 41 2.0

Cd 1510 1550 -40 -2.6

Clearly, there had not been a significant change in the XCEM calibration since the 

system was in use at the Montana tests and reassembled at CES’s laboratory. 

This is important because the subsequent laboratory tests and potential 

adjustments of the field data rely on this determination that there has been no 

change in the elemental calibration factors since the online field tests.
4.3. XCEM reanalysis of selected XCEM field test samples

Seven XCEM deposit spots from the online field tests were reanalyzed in CES’s 

laboratory. This was done to validate the online field test results and to assure the 

deposits had not lost a significant amount of mass when they came in contact with 

tape on the spool. The results of the laboratory analyses are compared with the 

online field test results in Table 1. The average difference between the laboratory

and field measurements was 1.9%, with the laboratory results generally less than 

the field test results. This confirms the field measurements to an uncertainty of 

about 6% and suggests that possible loss of deposit mass was reasonably small. 

Four of these spots were submitted to Chester LabNet for GFAA (graphite 

furnace atomic absorption) analysis of arsenic, lead and cadmium (There was 

insufficient sample to analyze for antimony and chromium.), and two additional 

deposit spots were analyzed by CVAA (cold vapor atomic absorption) for 

mercury. The results from these analyses are discussed in the following 

subsection. 

4.4. AAGF/CVAA analysis of selected XCEM field test samples

The seven selected deposit spots analyzed above were submitted to an 

independent laboratory (Chester LabNet) for wet-chemical analysis. Because of 

the small deposit mass, all of the reported elements could not be analyzed in each 

of the spots as noted above. 

The results of post-test wet chemical analyses of the selected deposit spots from 

the field tests are summarized in Table 2. This table shows that there is no 

significant difference in the lead concentrations measured by the independent 

laboratory and measured at CES’s laboratory. There was, however, significant 

differences in the two laboratory results for Hg, As, and Cd. The average 

difference for two mercury spots was 28%. This suggests that the mercury

reported by the XCEM was low by, on average, 28%. This is not necessarily

surprising since a theoretical sensitivity factor was used because of the absence of 

available mercury standards. The mercury results, however, would still be low 

relative to Method 29 results even with a 28% adjustment because of the low filter 

trapping efficiency for elemental mercury.

In the case of cadmium, the average difference in the laboratory XCEM results 

and the independent laboratory reported cadmium results is 17%. If the 

independent laboratory results were assumed to be the best representation of the 

true cadmium mass, the online XCEM calibration factor and field results would 

need to be increased by 17 %. With this adjustment, the average XCEM field test 

cadmium results would be in good agreement with the Method 29 cadmium 

results; that is, 98 μg/m3versus 100 μg/m3.

The independent laboratory arsenic results also suggest an average XCEM 

calibration bias of 24%. Again, if the independent laboratory results assumed to 

be the best representation of the arsenic mass in the XCEM spot, the XCEM 
arsenic calibration factor and field results would need to be increased by 24%. 

Again, with this adjustment, the average XCEM arsenic results are in good 

agreement with the method 29 results, 25 μg/m3for Method 29 versus 21 μg/m3 

for the XCEM.

The good agreement for the independent laboratory and XCEM laboratory lead 

results is strongly supportive of the online field XCEM results. The XCEM 

results would be a couple of percent closer in agreement with the Method 29 

results if the independent laboratory lead results were used to adjust the XCEM 

calibration factor for lead. With this adjustment, the average XCEM lead is 67 

μg/m3compared to 70 μg/m3for Method 29.

The antimony results, however, differ by more than five fold. There was 

insufficient sample available for the determination of chromium and antimony on 

the spots submitted for independent analysis. However, it is clear at this time that 

the reported Method 29 antimony results are grossly in error and probably due to 

poor recovery of antimony in the analytical laboratory. This conclusion is based 

on the generally good agreement between the two methods (after adjusting 

calibration factors) for arsenic, cadmium, chromium and lead, the higher XCEM 

results, and the XCEM measured antimony to cadmium ratio. The good 

agreement for these four elements strongly validates the volumes used in both 

methods. Thus, the antimony difference cannot be explained by a difference in the 

volumes used to calculate the antimony concentration. 

The fact that the XCEM results are about six-fold greater than the Method 29 

results implies that the difference is not due to loss of antimony in the XCEM. 

However, there is a well-established potential for loss of antimony in some EPA 

filter digestion procedures such as EPA Method 3050, SW 846. 

In addition, the XCEM results show that the antimony stack gas concentration is 

clearly almost two times greater than the cadmium concentration, not almost six 

times less than the cadmium concentration as suggested by the Method 29 results. 

Since the cadmium results are in good agreement, the difference in the elemental 

ratio must be associated with the antimony. Because the XCEM measures the 

antimony and cadmium simultaneously, its measure of the ratio is highly reliable 

and expected to have an uncertainty of no more than about 10%. In addition, 

since the spectra for each sample spot was saved, they were reviewed and the 

analyte line intensities and reported relative concentrations were confirmed. 

Additional spots have been submitted to an independent laboratory for antimony

and cadmium determinations. These results will contribute significantly to our 

understanding of the differences in reported antimony results
Thus, for the above stated reasons, it is highly likely that the Method 29 results 

are in error due to loss of antimony, most likely through either volatilization or in 

the filtered precipitate prior to instrumental analysis.

It is also important to note that this type of post-independent laboratory analysis 

is possible because of the nondestructive nature of the XCEM analysis and the 

above-demonstrated minimal loss of deposit to other portions of the tape on the 

spool. The comparison of results is essentially equivalent to a pre-analysis spike 

recovery test. The primary limitation of this type of post-test analysis recovery

evaluation is the analytical sensitivity and accuracy of the method used by the 

independent laboratory.

4.5. XCEM analysis of spikes

In addition to the above quality assurance steps, a post-test analysis of spiked 

filter samples was conducted. The resulting calibration factors using spikes for 

arsenic, cadmium, lead and antimony are generally supportive of the above 

conclusions.

Table 1. Comparison of Online Field Test Results with Post-Test Lab Results

CES 

Lab Field % Diff CES Lab Field % Diff CES Lab Field % Diff

CR CR CR HG HG HG AS AS AS

64 39 34.0 34.4 -0.9 19.4 21.3 -9.4 22.3 15.4 36.3

65 40 32.7 37.7 -14.2 20.6 20.8 -0.9 23.5 25.7 -8.8

66 41 36.4 31.6 14.2 19.7 20.5 -3.9 22.2 19.8 11.5

67 42 36.5 36.7 -0.5 19.9 23.2 -15.1 22.4 18.5 18.9

68 43 30.4 31.2 -2.5 18.9 18.7 1.4 18.7 20.4 -8.6

69 44 31.9 28.7 10.6 15.7 20.8 -28.3 21.9 18.6 16.1

33.7 33.4 1.1 19.0 20.9 -9.4 21.8 19.8 10.9

CES 

Lab Field % Diff CES Lab Field % Diff CES Lab Field % Diff

PB PB PB CD CD CD SB SB SB

64 39 98.1 95.2 3.0 109 118 -8.0 197 211 -6.9

65 40 98.0 108.2 -9.9 110 118 -7.5 208 211 -1.2

66 41 96.1 101.4 -5.4 106 105 0.5 193 188 2.9

67 42 97.9 114.1 -15.3 111 111 -0.2 211 196 7.3

68 43 87.2 97.6 -11.2 97 104 -7.3 188 205 -8.4

69 44 86.0 92.5 -7.3 94 95 -0.5 169 185 -9.3

Average 93.9 101.5 -7.7 104.4 108.6 -3.9 194.3 199.2 -2.6

Overall 

XRF Run

12/9/99 

Run No.

Overall 

XRF Run

12/9/99 

Run No.

Average
Table 2. Comparison of XCEM Results (In CES lab) With Independent Lab Results

XCEMaAAb % Diff. XCEMaAAb % Diff. XCEMaAAb % Diff. XCEMaAAb % Diff.

63 24 35 33

64 15 23 32 118 143 18 95 100 4

65 26 30 16 118 140 16 108 108 0

66 20 25 20 105 129 18 101 103 2

67 19 21 12 111 130 14 114 111 -3

68 20 35 41 104 125 17 97 105 7

69 24 31 23

Mean 20 27 24 111 133 17 103 106 2 24 33 28

SD 4 6 12 7 8 2 8 4 4 0 3 7

Range 15-26 23-35 104-118 125-143 95-108 100-111 24 31-35

a) Reported final corrected concentrations

b) Concentrations based on elemental mass determination by GFAA for As, Cd and Pb, and CVAA for Hg

Hg

Run

As Cd Pb