NIOSH Manual of Analytical Methods (NMAM), Fifth Edition

NIOSH Manual of Analytical Methods (NMAM) 5th Edition 

BACKUP DATA REPORT 

NIOSH Method No. 7306

Title: Elements by Cellulosic Internal Capsule

Analyte: 33 elements

Author/developer: Kevin Ashley, Ronnee N. Andrews, and H. 

Amy Feng

Date: 9/10/2015

 

Disclaimer: Mention of any company or product does not constitute endorsement by the National 

Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. In addition, 

citations to websites external to NIOSH do not constitute NIOSH endorsement of the sponsoring 

organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of 

these websites. All web addresses referenced in this document were accessible as of the publication 

date. 
1 

Elements by cellulosic internal capsule samplers and ICP-AES: 

Backup data report for NIOSH method 7306

Summary

Performance evaluation materials for the interlaboratory study (ILS) consisted of cellulose acetate 

capsules attached to mixed-cellulose ester (MCE) filters (37 mm, 0.8 μm pore size). Batches of 

capsules were dosed with 33 elements from standard aqueous solutions. Triplicates of spiked 

capsules at three different loadings, plus blank media, were conveyed to each volunteer laboratory; 

loading levels were unknown to the participants. The laboratories were asked to prepare the samples 

by acid dissolution and to analyze aliquots of extracted samples by ICP-AES in accordance with 

applicable NIOSH 7300-series methods [1-4]. Participants were asked to report their results in units of 

μg of each target element per sample. For the majority of the elements investigated, interlaboratory 

precision and recovery estimates from the participating laboratories amply demonstrated the utility of 

the cellulosic internal capsules for the measurement of sampled trace elements.

Introduction

Airborne particles that are collected using closed-face filter cassettes (CFCs), which are used widely to 

sample workplace aerosols, can deposit in places other than on the filter, notably on the inside walls of 

the cassette [5]. If only the filter is then analyzed, these particulate wall deposits will not be included in 

the ensuing elemental analysis, potentially leading to underestimation of exposure [6]. An effective

technique for ensuring that internal non-filter deposits are included in the analysis is to collect airborne 

particles within an acid-soluble internal capsule which, following sampling, can be dissolved along with 

the filter for subsequent elemental analysis [7]. The schematic of the CFC with an internal capsule is 

illustrated in Figure 1. In this project, an interlaboratory study (ILS) was carried out to evaluate the use 

of cellulosic CFC internal capsules for their suitability in the determination of trace elements in airborne 

samples from workplaces. 
2 

Figure 1. Schematic of closed-face filter cassette (CFC) aerosol sample collection using an 

internal capsule (Used with permission of Zefon International, Inc. [8])

The overall goal of this effort was to evaluate and validate a method that accounts for all aerosol 

particles entering the inlet of the CFC sampler, thereby including material that would not otherwise be 

measured by filter-only analysis procedures. A principal aim of this work was to carry out an 

interlaboratory study (ILS) to evaluate the analytical suitability of cellulosic internal capsules for their 

use with traditional plastic air sampling cassettes. The ILS entailed fortifying the filter of the internal 

capsule with various loadings of metals and metalloids of interest and sending them to volunteer 

laboratories for analysis. The inserts were subjected to acid dissolution and analyzed by the 

participating laboratories for their elemental content by inductively coupled plasma – atomic emission 

spectrometry (ICP-AES). The procedure described is meant to replace the practice of filter-based

sample collection and subsequent filter-only analysis using CFCs. 

Experimental

The performance evaluation materials used in this ILS consisted of Solu-SertTM cellulosic acid-soluble 

capsules, which were obtained from Zefon International (Ocala, FL). The Solu-SertTM capsules were 

spiked with 33 elements of interest by High-Purity Standards (Charleston, SC), in order to prepare 

certified reference materials (CRMs) having desired loading levels of the metals and metalloids of 

concern in occupational exposure assessment (Table 1). The values listed in Table 1 include the 

impurity in the filter. Certificates of analysis for the CRMs, provided by the vendor, provided certified 

reference values for each element at each loading level. The target loading levels of the 33 elements 

within the Solu-SertTM capsules (Table 1) were chosen based upon reasonable assumptions of what a 

variety of laboratories could confidently measure. Spiking of Solu-SertTM capsules was carried out 

using standard solutions (containing the elements of interest) traceable to national standards, i.e., 

National Institute for Standards and Technology (NIST). 
3 

Table 1: Elements and nominal spiking levels (in μg) on internal capsule (Solu-SertTM) 

The Solu-SertTM CRMs were conveyed to volunteer laboratories, which were requested to carry out 

sample dissolution and ICP-AES analysis in accordance with NIOSH methods (7300 methods series). 

Triplicates of Solu-SertTM samples spiked at each loading level, plus media blanks (also in triplicate), 

were conveyed to each participant. Loading levels were unknown to the participants. Sampling chainof-custody procedures were followed throughout the ILS, in accordance with ASTM D4840 [9]. 

Element (Symbol) Level 1 (Low level) Level 2 (Medium level) Level 3 (High level)

Silver (Ag) 5.0 ± 0.1 10.1 ± 0.2 20.1 ± 0.4

Aluminum (Al) 10.6 ± 0.2 30.9 ± 0.6 60.8 ± 1.2

Arsenic (As) 5.0 ± 0.1 20.2 ± 0.4 40.1 ± 0.8

Barium (Ba) 2.21 ± 0.04 7.3 ± 0.1 15.2 ± 0.3

Beryllium (Be) 2.01 ± 0.02 7.0 ± 0.1 14.9 ± 0.1

Calcium (Ca) 114 ± 2 165 ± 3 215 ± 4

Cadmium (Cd) 2.01 ± 0.02 7.0 ± 0.1 14.9 ± 0.1

Cobalt (Co) 2.01 ± 0.02 7.0 ± 0.1 14.9 ± 0.1

Chromium (Cr) 2.91 ± 0.04 7.9 ± 0.2 15.8 ± 0.3

Copper (Cu) 3.16 ± 0.06 15.1 ± 0.3 29.9 ± 0.6

Iron (Fe) 21.3 ± 0.4 41.0 ± 0.8 80.5 ± 1.6

Indium (In) 5.04 ± 0.05 14.9 ± 0.1 39.7 ± 0.4

Potassium (K) 10.6 ± 0.2 15.7 ± 0.3 20.7 ± 0.4

Lanthanum (La) 3.01 ± 0.03 10.1 ± 0.1 20.1 ± 0.2

Lithium (Li) 2.01 ± 0.02 7.0 ± 0.1 14.9 ± 0.1

Magnesium (Mg) 12.7 ± 0.1 27.9 ± 0.3 103 ± 1

Manganese (Mn) 2.01 ± 0.02 7.0 ± 0.1 14.9 ± 0.1

Molybdenum (Mo) 2.01 ± 0.02 7.1 ± 0.1 15.0 ± 0.2

Nickel (Ni) 2.01 ± 0.02 7.0 ± 0.1 14.9 ± 0.1

Phosphorus (P) 10.1 ± 0.2 24.9 ± 0.5 99 ± 2

Lead (Pb) 10.0 ± 0.2 25.2 ± 0.5 100 ± 2

Antimony (Sb) 5.0 ± 0.1 25.1 ± 0.5 40.2 ± 0.8

Selenium (Se) 3.0 ± 0.2 15.1 ± 0.3 30.1 ± 1.5

Tin (Sn) 2.01 ± 0.04 7.0 ± 0.1 14.9 ± 0.3

Strontium (Sr) 2.01 ± 0.02 7.1 ± 0.1 15.0 ± 0.2

Tellurium (Te) 3.0 ± 0.1 12.6 ± 0.3 20.1 ± 0.4

Titanium (Ti) 2.01 ± 0.04 7.0 ± 0.1 14.9 ± 0.3

Thallium (Tl) 3.0 ± 0.1 10.1 ± 0.2 20.1 ± 0.4

Vanadium (V) 3.02 ± 0.06 7.0 ± 0.1 14.9 ± 0.3

Tungsten (W) 10.1 ± 0.2 25.1 ± 0.5 40.2 ± 0.8

Yttrium (Y) 2.01 ± 0.04 7.1 ± 0.1 15.0 ± 0.3

Zinc (Zn) 5.2 ± 0.1 25.1 ± 0.5 59.7 ± 1.2

Zirconium (Zr) 2.01 ± 0.04 7.0 ± 0.1 14.9 ± 0.3
4 

Laboratories that participated in the ILS and reported analytical results included: CDC/NIOSH, 

Cincinnati, OH; Occupational Safety and Health Administration (OSHA) Salt Lake Technical Center, 

Sandy, UT; Bureau Veritas North America (BVNA), Novi, MI; ALS Laboratories, Salt Lake City, UT; 

Institut National de Recherche et de Sécurité (INRS), Vandoeuvre-lès-Nancy, France; Forensic 

Analytical Services, Hayward, CA; BWXT Y-12 National Security Organization, Oak Ridge, TN; and the 

Wisconsin Occupational Health Laboratory (WOHL), Madison, WI. The sample preparation methods 

used by the participating laboratories are summarized in Table 2. For data presentation, laboratories 

are identified by code to maintain confidentiality.

Table 2. Sample preparation methods used by laboratories participating in internal capsule 

(Solu-SertTM) interlaboratory study

Laboratory No. Sample dissolution procedure __________

1 hot block extraction; HNO3, 90-95 oC (NIOSH 7303)

2a1 hot plate digestion; HNO3/HClO4, 120-130 oC (NIOSH 7300)

2b1 microwave digestion; HNO3, 150 oC (NIOSH 7302)

3 hot block extraction; HNO3/HCl, 95 oC (NIOSH 7303)

4 microwave digestion; HNO3/H2O2, 210 oC (modified NIOSH 7302)

5 hot block extraction; HNO3, 95 oC (NIOSH 7303)

6 hot block extraction; HNO3/HCl, 95 oC (NIOSH 7303)

7 hot block extraction; HNO3/HCl, 95 oC (NIOSH 7303)

8 hot plate digestion; HNO3/H2SO4/H2O2, 120-130 oC (modified NIOSH 7300) 

1This lab used two different procedures (i.e., hot plate and microwave digestion treatment) and it was treated as a separate 

laboratory for the data analysis.

After sample dissolution by means of hot plate, hot block or microwave treatment in acid solutions, 

each laboratory analyzed sample extracts for multielement analysis by ICP-AES. Five participating

laboratories used hot block extraction, two used hot plate digestion, and two used microwave digestion

(Table 2). One of the above laboratories used two different procedures, where hot plate or microwave 

digestion was used on separate sets of Solu-SertTM CRMs. For the purposes of the ILS, results from 

these two different sample dissolution procedures from the same laboratory were treated as being from 

separate laboratories. The participating laboratories were requested to report their results in units of 

micrograms per sample of each element analyzed.
5 

Results

Reported results from the participating laboratories are presented in Table 3a for media blanks and in 

Tables 3b-d for three different Solu-SertTM CRM elemental loadings, Levels 1 (low), 2 (medium) and 3

(high). The results presented are as reported and no rounding of the values was done. Not all 

laboratories reported results for all elements. Some laboratories reported results above the estimated 

method detection limit (MDL), while others only reported results above their reporting limit (RL). 

Laboratory-reported results that were below the MDL or RL are indicated by a (<) sign in table entries, 

with the MDL or RL value listed in each instance. The MDL or RL values were determined using the 

laboratory’s usual procedure. 
6 

Table 3a. Internal capsule (Solu-SertTM) interlaboratory study - Elemental determination by ICP-AES: Media blank results 

Element

Lab 1 (μg/sample)

(RL)

Lab 2a (μg/sample)

(MDL)

Lab 2b (μg/sample)

(MDL)

Lab 3 (μg/sample)

(MDL)

Lab 43 (μg/sample)

(MDL)

Ag <0.250 <0.250 <0.250 <0.017 <0.017 <0.017 0.102 0.056 0.022 <0.03 <0.03 <0.03 <4.2 <4.2

Al <5.00 <5.00 <5.00 2 <1. <1. 1.7 1.2 1.1 <2 <2 <2 0.78 0.387

As <2.50 <2.50 <2.50 0.14 0.12 <0.098 0.885 0.852 0.610 <2 <2 <2 <0.83 <0.83

Ba <0.250 <0.250 <0.250 0.218 0.203 0.235 0.345 0.220 0.230 <0.6 <0.6 <0.6 0.205 0.332

Be <0.0130 <0.0130 <0.0130 <0.0040 <0.0040 <0.0040 <0.0090 <0.0090 <0.0090 0.016 <0.001 <0.001 <0.0053 <0.0053

Ca <15.0 <15.0 <15.0 16.5 13.8 15.7 17.3 14.9 14.3 <3 <3 <3 11.10 12.1

Cd <0.0750 <0.0750 <0.0750 <0.22 <0.22 <0.22 0.0364 0.0263 0.013 <0.03 <0.03 <0.03 <0.022 <0.022

Co <0.0750 <0.0750 <0.0750 <0.0099 <0.0099 <0.0099 0.0541 0.0351 0.013 <0.03 <0.03 <0.03 <0.049 <0.049

Cr <1.30 <1.30 <1.30 0.288 0.269 0.398 0.421 0.387 0.792 <0.4 <0.4 <0.4 1.01 0.82

Cu <0.500 <0.500 <0.500 0.19 0.15 0.353 0.12 0.16 0.084 <0.8 <0.8 <0.8 <0.046 <0.038

Fe <5.00 <5.00 <5.00 1 1.2 1.3 2.38 1.55 3.20 1.1 1.9 1.2 1.91 1.04

In NA2 NA NA <0.11 <0.11 <0.11 1.01 0.699 0.31 <0.3 <0.3 <0.3 <0.17 <0.17

K <13.0 <13.0 <13.0 2 2 1 1.29 1.00 0.823 <6 <6 <6 <0.15 <0.15

La NA NA NA <0.047 <0.047 <0.047 0.298 0.194 0.107 <0.02 <0.02 <0.02 <0.017 <0.014

Li <0.500 <0.500 <0.500 <0.019 <0.019 <0.019 0.013 0.0073 <0.0062 <0.02 <0.02 <0.02 <0.0050 <0.0068

Mg <1.40 <1.40 <1.40 2.65 2.21 2.55 3.86 3.17 2.88 <1 <1 <1 2.42 2.60

Mn <0.130 <0.130 <0.130 <0.012 <0.012 <0.012 <0.020 <0.020 <0.020 0.024 0.062 <0.02 <0.031 <0.026

Mo <0.380 <0.380 <0.380 <0.012 0.014 <0.012 0.0861 0.0769 0.0432 <0.1 <0.1 <0.1 <0.12 <0.12

Ni <0.130 <0.130 <0.130 0.0375 0.022 0.0457 0.194 0.154 0.0867 <0.1 0.1 <0.1 <0.30 <0.26

P <5.00 <5.00 <5.00 0.67 0.73 <0.62 2.20 2.12 1.67 <2 <2 <2 <0.49 <0.49

Pb <1.30 <1.30 <1.30 <0.40 <0.40 <0.40 0.495 0.393 0.243 <1 <1 <1 0.085 <0.082

Sb <1.50 <1.50 <1.50 <0.7 <0.7 <0.7 0.750 0.588 0.346 <1 <1 <1 <0.41 <0.41

Se <2.50 <2.50 <2.50 0.064 <0.055 <0.055 1.27 1.15 0.744 <5 <5 <5 <0.51 <0.84

Sn <2.50 <2.50 <2.50 <0.2 <0.2 <0.2 0.457 0.462 0.321 <0.4 <0.4 <0.4 <0.14 <0.14

Sr <0.380 <0.380 <0.380 0.0456 0.0385 0.0427 0.0599 0.0496 0.0453 0.010 <0.009 <0.009 0.0389 0.0427

Te <1.30 <1.30 <1.30 <0.09 0.1 <0.09 0.942 0.774 0.376 <0.6 <0.6 <0.6 <0.42 <0.44

Ti <0.0750 <0.0750 <0.0750 0.033 0.031 0.033 0.116 0.0982 0.0766 0.024 <0.02 <0.02 0.1039 0.0830

Tl <1.30 <1.30 <1.30 <0.025 <0.025 <0.025 0.496 0.426 0.282 <1 1.1 <1 NA NA

V <0.230 <0.230 <0.230 <0.011 <0.011 <0.011 0.0644 0.0454 0.019 <0.02 <0.02 <0.02 <0.025 <0.025

W <1.30 <1.30 <1.30 <0.43 <0.43 <0.43 0.175 0.260 0.055 <0.1 <0.1 <0.1 <0.30 <0.30

Y <0.0750 <0.0750 <0.0750 <0.0083 <0.0083 <0.0083 0.0319 0.014 <0.0049 0.018 <0.005 <0.005 <0.0053 <0.0053

Zn <0.500 <0.500 <0.500 <0.74 <0.74 <0.74 0.485 0.1 0.2 <0.1 0.84 0.53 <0.089 <0.089

Zr <0.500 <0.500 <0.500 <0.072 <0.072 <0.072 0.0656 0.0477 0.029 0.053 <0.02 <0.02 0.018 0.023

Note: RL=Reporting Limit; MDL=Method Detection Limit 2

NA: Not applicable; not reported by the laboratory 3

one sample lost; not reported by the laboratory
7 

Table 3a con’t. Internal capsule (Solu-SertTM) interlaboratory study - Elemental determination by ICP-AES: Media blank results

Element Lab 5 (μg/sample)

(RL)

Lab 6 (μg/sample)

(RL)

Lab 7 (μg/sample)

(RL)

Lab 8 (μg/sample)

(RL)

Ag <0.15 <0.15 <0.15 < 0.5 < 0.5 < 0.5 < 0.3 < 0.3 < 0.3 NA2 NA NA

Al <10 <10 <10 < 5 < 5 < 5 NA NA NA NA NA NA

As <0.75 <0.75 <0.75 < 5 < 5 < 5 < 0.6 < 0.6 < 0.6 NA NA NA

Ba 0.38 0.2 0.2 0.225 0.159 0.169 < 0.5 < 0.5 < 0.5 NA NA NA

Be <0.013 <0.013 <0.013 < 0.012 < 0.012 < 0.012 < 0.08 < 0.08 < 0.08 <0.1 <0.1 <0.1

Ca 29 <20 <20 15.3 15.3 14.5 17 18 26 NA NA NA

Cd <0.25 <0.25 <0.25 < 0.25 < 0.25 <0.25 < 0.6 < 0.6 < 0.6 <0.5 <0.5 <0.5

Co <0.25 <0.25 <0.25 < 0.5 < 0.5 < 0.5 < 0.3 < 0.3 < 0.3 <2.5 <2.5 <2.5

Cr <4 <4 <4 < 0.5 < 0.5 0.505 < 0.9 < 0.9 < 0.9 <10 <10 <10

Cu <1.5 <1.5 <1.5 < 0.5 < 0.5 < 0.5 < 0.5 < 0.5 < 0.5 <2.5 <2.5 <2.5

Fe <5 <5 <5 1.37 < 1.2 < 1.2 < 20 < 20 < 20 <25 <25 <25

In NA NA NA NA NA NA < 0.6 < 0.6 < 0.6 NA NA NA

K <7.5 <7.5 <7.5 < 50 < 50 < 50 NA NA NA NA NA NA

La NA NA NA NA NA NA NA NA NA NA NA NA

Li <0.5 <0.5 <0.5 < 0.25 < 0.25 < 0.25 NA NA NA NA NA NA

Mg 5.1 <5 <5 < 5 < 5 < 5 NA NA NA NA NA NA

Mn <0.25 <0.25 <0.25 < 0.12 < 0.12 < 0.12 < 0.8 < 0.8 < 0.8 <2.5 <2.5 <2.5

Mo <0.5 <0.5 <0.5 < 0.5 < 0.5 < 0.5 < 2 < 2 < 2 <25 <25 <25

Ni <1 <1 <1 < 1.2 < 1.2 < 1.2 < 0.3 < 0.3 < 0.3 <25 <25 <25

P NA NA NA < 12 < 12 < 12 NA NA NA NA NA NA

Pb <1.8 <1.8 <1.8 < 2.5 < 2.5 < 2.5 < 0.8 < 0.8 < 0.8 <5 <5 <5

Sb <1.5 <1.5 <1.5 < 5 < 5 < 5 < 0.5 < 0.5 < 0.5 <25 <25 <25

Se <1.3 <1.3 <1.3 < 5 < 5 < 5 < 0.9 < 0.9 < 0.9 NA NA NA

Sn <5 <5 <5 NA NA NA < 30 < 30 < 30 NA NA NA

Sr <0.15 <0.15 <0.15 < 0.12 < 0.12 < 0.12 NA NA NA NA NA NA

Te NA NA NA NA NA NA NA NA NA NA NA NA

Ti <0.5 <0.5 <0.5 < 1.2 < 1.2 < 1.2 NA NA NA NA NA NA

Tl <2.5 <2.5 <2.5 < 5 < 5 < 5 < 3 < 3 < 3 NA NA NA

V <0.25 <0.25 <0.25 < 0.5 < 0.5 < 0.5 < 0.5 < 0.5 < 0.5 <1.5 <1.5 <1.5

W NA NA NA NA NA NA NA NA NA NA NA NA

Y NA NA NA NA NA NA NA NA NA NA NA NA

Zn <1.8 <1.8 <1.8 < 1.2 < 1.2 < 1.2 < 0.8 < 0.8 < 0.8 <25 <25 <25

Zr NA NA NA < 5 < 5 < 5 NA NA NA NA NA NA

Note: RL=Reporting Limit; MDL=Method Detection Limit 2

NA: Not applicable; not reported by the laboratory 
8 

Table 3b. Internal capsule (Solu-SertTM) interlaboratory study - Elemental determination by ICP-AES: Level 1 (Low loading) results

Element Lab 1

(μg/sample)

Lab 2a 

(μg/sample)

Lab 2b 

(μg/sample)

Lab 3

(μg/sample)

Lab 4 

(μg/sample)

Lab 5

(μg/sample)

Lab 6 

(μg/sample)

Lab 7

(μg/sample)

Lab 8 

(μg/sample)

Ag 5 5.07 4.67 4.46 4.34 4.62 4.82 4.82 4.75 6.5 2.9 6.9 <4.2 <4.2 <4.2 4.9 4.9 5 3.15 3.07 2.81 5.1 5.1 5 NA2 NA NA

Al 10.4 10.5 8.97 11 10 11 11.3 11.0 11.0 9.8 8.9 9.3 9.33 9.35 9.59 10 10 11 10.2 10.4 10.7 NA NA NA NA NA NA

As 4.59 5.21 4.59 4.72 4.47 4.82 5.62 5.63 5.66 4.5 5.3 4.8 4.42 4.68 4.60 5.4 5 5.1 < 5 < 5 < 5 5 5.2 5.1 NA NA NA

Ba 2.07 2.1 1.92 2.12 2.09 2.13 2.17 2.17 2.12 1.8 1.8 1.8 2.41 2.38 2.43 2.4 2.2 2.3 2.14 2.17 2.12 2.2 2.2 2.2 NA NA NA

Be 2.06 2.08 1.79 1.94 1.88 1.99 2.15 2.14 2.14 2.0 2.0 2.1 2.14 2.17 2.21 2.1 2 2.1 1.93 1.91 1.88 2 2 2 1.99 1.98 2.00

Ca 101 102 93.7 109 107 112 116 115 114 73 73 73 111.8 110.8 111.4 140 120 120 110 110 108 130 130 130 NA NA NA

Cd 2.07 2.07 1.8 1.86 1.80 1.96 2.09 2.09 2.05 2.0 2.0 2.0 2.02 2.03 2.06 2.2 2 2.1 2.06 2.02 2.01 2.1 2.1 2.1 2.09 2.07 2.10

Co 2.09 2.12 1.84 1.83 1.79 1.89 2.17 2.18 2.16 2.0 2.0 2.0 2.07 2.05 2.09 2.4 2.3 2.3 2.06 1.99 2.02 2.2 2.2 2.2 2.08 2.03 2.08

Cr 2.21 2.19 1.95 2.27 2.17 2.24 2.58 2.86 3.28 1.8 1.5 1.5 2.45 2.40 2.51 <4 <4 <4 2.41 2.48 2.38 2.8 2.5 2.3 2.40 2.45 2.40

Cu 3.29 3.28 2.82 3.10 5.53 3.61 3.29 3.41 3.21 3.0 2.9 2.9 3.02 3.03 3.15 3.2 3.1 3.2 3.17 3.11 3.11 3.2 3.2 3.1 3.38 3.32 3.50

Fe 22.2 21.8 18.7 21.2 20.0 21.3 22.9 25.7 23.3 21 21 22 21.8 23.2 21.9 46 23 24 21.1 21 20.6 20 20 20 23.85 25.35 24.55

In NA NA NA 4.78 4.66 4.94 6.40 6.35 6.22 5.2 5.0 5.1 4.47 4.40 4.98 NA NA NA NA NA NA 2.2 2.2 2.2 NA NA NA

K <13.0 <13.0 <13.0 13 12 12 11.8 11.9 11.6 11 6.9 10 4.66 3.44 3.29 9 11 10 < 50 < 50 < 50 NA NA NA NA NA NA

La NA NA NA 2.80 2.73 2.90 3.40 3.39 3.30 2.9 2.9 2.9 3.07 3.12 3.17 NA NA NA NA NA NA NA NA NA NA NA NA

Li 2.09 2.06 1.88 1.84 1.66 1.71 1.64 1.64 1.62 1.8 1.8 1.8 1.87 1.85 1.82 2 2.1 2.1 2.02 1.97 1.99 NA NA NA NA NA NA

Mg 9.66 9.63 8.91 11.3 11.1 11.7 13.3 13.1 12.9 10 10 9.9 12.78 12.85 13.33 17 13 14 12.1 12.1 11.8 NA NA NA NA NA NA

Mn 2.1 2.09 1.82 1.92 1.89 1.99 1.67 1.68 1.62 2.1 2.1 2.1 2.16 2.17 2.21 2.2 2 2.1 2 1.97 1.95 2 2.1 2 2.09 2.05 2.08

Mo 2.13 2.12 1.94 1.80 1.80 1.95 2.28 2.29 2.24 1.9 2.0 1.9 1.99 2.01 2.02 2.2 2.1 2.1 2.01 1.89 1.85 2 2 2 2.05 2.00 2.05

Ni 2.22 2.21 1.94 1.89 1.84 1.95 2.35 2.83 2.33 2.0 2.0 2.1 2.20 2.13 2.26 2.1 2.1 2 2.04 1.98 2 2.5 2.5 2.4 2.30 2.30 2.25

P 10.6 10.5 9.08 9.91 9.37 10.1 12.0 12.1 12.2 11 11 9.8 9.9 10.0 9.9 NA NA NA < 12 < 12 < 12 NA NA NA NA NA NA

Pb 10.4 10.3 9.82 9.11 8.87 9.51 11.1 11.2 11.0 10 10 10 9.55 9.45 9.74 10 9.8 9.9 9.77 9.7 9.51 11 11 11 10.26 10.02 10.42

Sb 4.7 4.94 4.86 4.5 4.3 4.7 5.56 5.65 5.56 5.2 4.8 4.7 5.15 5.19 5.17 5 4.8 4.8 < 5 < 5 < 5 5.1 5.1 5 4.70 4.70 4.75

Se 3.18 2.83 <2.50 2.70 2.50 2.77 4.03 4.12 4.11 <5 <5 <5 3.03 3.32 3.51 3.9 3.5 3.5 < 5 < 5 < 5 3.5 3.6 3.5 NA NA NA

Sn <2.50 <2.50 <2.50 2.0 2.0 2.1 2.56 2.60 2.58 2.1 2.0 2.0 1.26 1.26 1.39 <5 <5 <5 NA NA NA < 

30

< 

30

< 

30 NA NA NA

Sr 2.04 2.04 1.91 1.99 1.96 2.02 2.10 2.09 2.08 2.0 2.0 2.0 2.25 2.29 2.34 2 2 2 2.03 2.01 1.99 NA NA NA NA NA NA

Te 2.97 3.01 2.68 2.8 2.6 2.9 4.04 4.04 3.98 4.0 2.9 3.0 2.65 2.66 2.72 NA NA NA NA NA NA NA NA NA NA NA NA

Ti 2.08 2.11 1.8 1.97 1.97 2.00 2.29 2.28 2.28 2.0 2.0 2.1 2.19 2.15 2.20 2.2 2.2 2.3 2.08 2.06 2.04 NA NA NA NA NA NA

Tl 3.09 2.77 3.12 2.79 2.68 2.85 3.44 3.42 3.35 3.2 2.8 3.7 NA NA NA 3.1 2.9 3.1 < 5 < 5 < 5 3 3 3 NA NA NA

V 3.15 3.17 2.74 3.04 3.01 3.10 3.34 3.34 3.28 3.0 3.0 3.0 3.03 3.04 3.11 3.2 3.2 3.3 2.99 2.95 2.91 2.7 2.7 2.7 3.07 3.01 3.07

W 7.47 8.41 7.68 6.12 6.73 8.09 9.36 9.64 9.69 9.2 8.4 8.5 8.51 8.66 9.32 NA NA NA NA NA NA NA NA NA NA NA NA

Y 2.09 2.11 1.94 1.92 1.88 1.95 2.14 2.13 2.09 2.0 2.0 2.0 2.03 2.04 2.09 NA NA NA NA NA NA NA NA NA NA NA NA

Zn 5.33 5.35 4.71 4.96 5.10 5.65 5.68 5.65 5.65 5.1 5.1 5.1 4.78 4.65 4.76 5.9 5.2 5.4 5.17 4.98 4.89 5.1 5.1 5 5.60 5.60 5.75

Zr 2.02 2.07 1.75 1.99 1.97 2.03 2.20 2.20 2.17 1.9 1.9 1.9 2.13 2.12 2.17 NA NA NA < 5 < 5 < 5 NA NA NA NA NA NA

2

NA: not applicable; not reported by the laboratory
9 

Table 3c. Internal capsule (Solu-SertTM) interlaboratory study - Elemental determination by ICP-AES: Level 2 (Medium loading) 

results

 

Element Lab 1

(μg/sample)

Lab 2a 

(μg/sample)

Lab 2b 

(μg/sample)

Lab 3 

(μg/sample)

Lab 4

(μg/sample)

Lab 5 

(μg/sample)

Lab 6

(μg/sample)

Lab 7 

(μg/sample)

Lab 8

(μg/sample)

Ag 10 10.2 9.96 9.01 9.10 9.25 9.67 9.93 9.95 13 2.6 1.5 <4.2 <4.2 <4.2 9.6 9.7 8.9 2.54 9.67 2.58 10 9.9 10 NA2 NA NA

Al 30.2 30.3 29.8 29 29 30 28.8 29.7 29.7 28 28 28 29.2 29.5 29.5 31 31 31 29.6 29.8 29.6 NA NA NA NA NA NA

As 20 20.7 20 18.5 19.2 19.0 22.2 23.0 22.7 21 20 21 20.9 21.8 21.9 21 22 21 19.9 20.6 20.1 21 21 21 NA NA NA

Ba 7.06 7.32 7.13 6.67 6.79 6.84 7.02 7.17 7.15 6.9 6.9 6.9 8.18 8.37 8.37 7.3 7.3 7.2 7.12 7.17 7.16 7.2 7.1 7.2 NA NA NA

Be 6.97 7.07 6.98 6.25 6.46 6.51 7.43 7.61 7.62 6.9 7.1 7.0 7.83 8.01 8.10 6.9 7.1 7.1 6.54 6.6 6.58 7.1 7.1 7.2 6.86 6.70 6.75

Ca 150 154 151 157 161 159 167 174 172 110 110 110 168 170 169 180 180 180 158 158 158 190 180 190 NA NA NA

Cd 6.91 7.12 7.01 6.32 6.80 6.53 7.10 7.36 7.34 7.1 7.1 7.1 7.45 7.59 7.73 6.9 6.9 6.9 6.85 6.92 6.92 7 7.1 7.1 7.14 7.03 7.04

Co 6.96 7.21 7.13 6.45 6.59 6.62 6.86 7.06 7.04 7.0 7.0 7.0 7.52 7.64 7.81 7.7 7.8 7.8 6.81 6.85 6.84 7.3 7.4 7.4 6.87 6.77 6.77

Cr 7.17 7.38 7.29 7.18 7.43 7.40 8.00 7.97 8.29 6.8 7.0 6.9 8.89 8.65 8.81 7.3 7.6 7.9 7.49 7.62 7.81 7.1 7.7 7.3 7.50 7.30 7.55

Cu 15.6 15.9 15.6 14.6 14.7 14.6 15.6 16.0 15.9 15 15 15 15.7 16.0 16.3 15 15 15 14.7 14.8 14.8 14 14 15 15.83 15.57 15.75

Fe 41.5 42.4 42.3 39.1 39.5 41.2 42.0 42.4 42.7 42 41 42 44.8 45.4 48.3 45 46 46 40.3 41 40.5 40 40 40 44.65 43.10 44.45

In NA NA NA 14.1 14.3 14.2 16.6 17.2 17.1 15 15 15 14.0 14.4 14.4 NA NA NA NA NA NA 7.2 7.1 7.3 NA NA NA

K 14.9 15.8 15.5 20 18 21 17.3 18.1 17.8 13 15 15 9.6 8.9 8.8 16 17 15 < 50 < 50 < 50 NA NA NA NA NA NA

La NA NA NA 9.40 9.57 9.62 10.6 10.8 10.8 9.9 10 9.9 10.99 11.23 11.29 NA NA NA NA NA NA NA NA NA NA NA NA

Li 6.95 7.21 7.1 6.39 6.33 6.84 5.64 5.76 5.78 6.5 6.5 6.5 6.76 6.85 6.93 7 7.1 7 6.81 6.8 6.77 NA NA NA NA NA NA

Mg 23.5 24.4 23.8 26.0 26.1 26.4 28.2 29.5 29.1 26 26 26 30.5 31.1 31.3 30 30 30 26.7 26.8 26.9 NA NA NA NA NA NA

Mn 7.01 7.13 7.04 6.35 6.47 6.42 7.07 7.21 7.20 7.0 7.1 7.1 7.86 7.95 8.22 7 7 6.9 6.71 6.75 6.76 6.9 6.9 7 6.99 6.85 6.85

Mo 7.46 7.75 7.55 6.69 6.71 6.77 7.63 7.85 7.77 7.3 7.1 7.2 7.48 7.75 7.75 7.3 7.4 7.4 6.86 7.01 6.98 7 7 7 7.25 7.10 7.15

Ni <3.80 <3.80 <3.80 6.36 6.51 6.56 7.35 7.33 7.37 7.2 7.2 7.1 7.98 8.19 8.47 6.9 7 7 6.73 6.81 6.84 7.8 7.9 7.9 7.10 6.90 7.05

P 7.35 7.59 7.46 21.6 22.1 20.9 27.5 28.6 28.3 27 26 26 26.3 27.2 28.0 NA NA NA 25.5 25.2 25.2 NA NA NA NA NA NA

Pb 25.1 25.9 25.7 22.8 23.8 23.3 26.0 26.9 26.5 26 26 26 26.5 27.2 27.7 25 25 25 24.2 24.2 24.4 26 26 26 23.92 23.21 23.33

Sb 24.8 24.8 24.9 22 22 24 25.6 26.7 26.5 26 25 26 27.0 27.4 27.6 24 25 24 23.8 24.1 24.3 24 25 25 24.40 23.95 23.80

Se 14.8 15.3 14.7 13.5 14.7 14.5 18.1 19.0 18.6 17 15 15 17.1 17.7 18.2 17 17 17 16.5 16.3 16.4 17 17 17 NA NA NA

Sn 6.75 6.98 6.93 6.2 5.0 2.6 8.08 8.35 8.24 6.9 6.5 6.9 7.10 7.01 7.19 7.1 7.1 7.1 NA NA NA < 30 < 30 < 30 NA NA NA

Sr 7.02 7.25 7.1 6.53 6.61 6.62 7.24 7.44 7.45 7.2 7.1 7.1 8.22 8.36 8.40 7 7.1 7.1 6.94 6.95 6.94 NA NA NA NA NA NA

Te 12.5 12.9 12.5 11 12 12 13.7 14.4 14.3 14 13 14 12.2 12.7 13.4 NA NA NA NA NA NA NA NA NA NA NA NA

Ti 7.08 7.18 7.09 6.29 5.72 4.67 7.46 7.63 7.60 6.9 7.0 7.1 7.65 7.74 7.83 7.6 7.6 7.5 6.91 6.96 6.93 NA NA NA NA NA NA

Tl 9.49 10 9.8 9.24 9.44 9.43 10.9 11.2 11.1 9.4 10 10 NA NA NA 9.8 10 9.7 10.7 10.6 10.5 10 10 10 NA NA NA

V 7.15 7.28 7.18 6.91 6.95 7.00 7.72 7.89 7.89 7.1 7.0 7.1 7.46 7.58 7.75 7.4 7.4 7.3 6.72 6.74 6.76 6.4 6.4 6.4 6.98 6.84 6.84

W 24.1 24.3 24.4 21.9 20.3 18.9 24.8 25.6 25.7 24 25 24 27.2 28.1 29.2 NA NA NA NA NA NA NA NA NA NA NA NA

Y 7.3 7.41 7.25 6.44 6.57 6.60 7.22 7.40 7.38 7.1 7.2 7.1 7.57 7.74 7.78 NA NA NA NA NA NA NA NA NA NA NA NA

Zn 25.5 26.2 25.9 23.0 24.1 24.3 25.9 25.9 25.9 25 25 25 26.9 27.6 28.3 25 26 25 24 24.2 24.2 24 24 25 26.90 26.50 26.65

Zr 6.95 7.02 6.95 6.34 6.20 5.88 7.51 7.65 7.64 6.5 6.7 6.7 7.72 7.82 7.93 NA NA NA 6.6 6.63 6.66 NA NA NA NA NA NA

2

NA: not applicable; not reported by the laboratory
10

Table 3d. Internal capsule (Solu-SertTM) interlaboratory study - Elemental determination by ICP-AES: Level 3 (High loading) 

results; as reported 

Element Lab 1

(μg/sample)

Lab 2a

(μg/sample) Lab 2b (μg/sample) Lab 3(μg/sample)

Lab 4

(μg/sample) Lab 5 (μg/sample) Lab 6 (μg/sample)

Lab 7 

(μg/sample)

Lab 8 

(μg/sample)

Ag 20.2 19.6 19.9 18.0 17.0 16.1 19.1 19.2 19.7 9.5 7.6 6.0 <4.2 <4.2 <4.2 6.9 11 11 2.63 2.63 2.08 20 20 20 NA2 NA NA

Al 60.1 57.8 60.5 60 56 55 57.2 56.4 58.2 56 55 68 56.1 56.6 57.7 60 60 60 60.1 59.3 58.6 NA NA NA NA NA NA

As 41 39.4 41.7 38.4 35.1 33.3 42.7 42.4 44.6 40 41 43 40.9 40.3 42.2 43 43 43 39.8 40.6 40.2 40 42 42 NA NA NA

Ba 15.5 15 15.3 14.9 14.1 13.7 14.5 14.6 15.0 15 15 15 16.7 16.7 17.1 16 15 15 15.3 15 15 15 15 15 NA NA NA

Be 15.1 15 15.2 14.4 13.8 13.1 15.1 14.8 15.7 15 15 15 16.2 16.4 16.8 15 15 15 14.2 14.2 14.1 15 15 15 14.49 14.60 14.64

Ca 201 196 200 203 197 189 216 216 226 15 15 16 210 211 212 230 230 230 209 205 205 230 240 240 NA NA NA

Cd 15.1 14.9 15.1 13.9 13.3 12.4 15.1 15.0 15.6 150 150 150 15.4 15.7 16.2 15 15 15 14.8 14.9 14.8 15 16 15 15.23 15.35 15.23

Co 15.4 15.2 15.5 13.9 13.4 12.9 15.0 14.9 15.6 15 15 16 15.5 15.7 16.2 17 16 16 14.7 14.7 14.7 16 16 16 14.62 14.74 14.68

Cr 15.4 15.4 15.1 15.1 14.3 14.1 16.2 15.6 16.3 15 15 16 16.1 16.2 16.8 16 15 15 15.3 14.9 15.3 15 15 15 15.30 14.82 15.35

Cu 31.7 31.9 31 29.3 28.1 27.4 30.6 30.1 31.6 30 30 30 29.7 30.1 30.6 30 30 30 30 29.2 29.2 29 29 29 30.19 30.57 30.41

Fe 83.6 82.9 83.6 75.7 73.8 72.0 83.7 82.7 87.7 85 84 84 85.2 85.8 87.6 89 88 88 80.4 79.9 79.8 80 80 80 86.25 87.05 87.80

In NA NA NA 36.3 35.5 34.0 41.6 41.3 43.0 41 41 42 36.7 37.6 38.2 NA NA NA NA NA NA 15 15 15 NA NA NA

K 22.1 20.7 21.4 30 27 29 23.6 24.0 24.3 17 23 22 16.3 14.5 15.2 21 22 21 < 50 < 50 < 50 NA NA NA NA NA NA

La NA NA NA 18.7 17.8 17.2 20.8 20.8 21.6 20 20 20 21.2 21.1 21.8 NA NA NA NA NA NA NA NA NA NA NA NA

Li 15.5 15.3 15.3 15.2 14.3 14.6 13.0 12.9 13.3 15 15 16 14.5 14.9 15.1 15 15 15 14.8 14.4 14.4 NA NA NA NA NA NA

Mg 96.4 94.2 95.6 97.1 93.5 87.2 107 108 112 110 110 110 107.7 107.4 110.7 110 110 110 101 101 101 NA NA NA NA NA NA

Mn 15.2 15.3 14.9 13.7 13.4 12.6 15.4 15.3 15.9 15 15 15 16.2 16.3 16.7 15 15 15 14.5 14.5 14.4 15 15 15 14.62 14.72 14.58

Mo 16.1 15.5 16.3 14.2 13.5 13.7 16.0 16.0 16.8 15 16 16 15.5 15.3 16.0 16 16 16 14.9 14.9 14.9 14 15 15 14.70 15.00 14.95

Ni 16 15.8 16.1 13.9 13.4 12.7 15.5 15.2 16.1 15 15 16 16.5 16.6 17.2 15 15 15 14.5 14.5 14.6 16 17 17 14.90 15.10 14.90

P 99.5 99.8 102 81.8 73.9 75.4 99.7 98.4 104 100 100 110 100.9 102.7 104.2 NA NA NA 99.4 99 98.6 NA NA NA NA NA NA

Pb 104 100 105 91.7 88.3 84.0 101 101 106 110 110 110 102.1 102.0 105.0 100 98 98 98.3 99.2 98.5 100 110 110 86.59 90.49 91.96

Sb 39.9 39.8 40.2 33 25 29 40.7 40.4 41.7 41 42 43 41.3 42.2 44.0 39 39 39 39.2 38.8 38.2 39 40 40 39.48 37.74 39.46

Se 29.7 29.3 30.6 27.6 24.9 23.2 35.0 35.0 36.9 28 30 30 32.2 31.7 33.2 33 33 33 31.6 32.2 32.1 32 34 34 NA NA NA

Sn 15.1 14.8 15 1.6 1.1 1.6 16.5 16.3 17.1 15 15 16 14.3 14.6 15.1 15 15 15 15 14.7 14.7 < 30 < 30 < 30 NA NA NA

Sr 15.2 14.9 15.2 14.4 13.8 13.5 14.6 14.6 15.2 15 15 16 16.8 16.8 17.3 15 15 15 NA NA NA NA NA NA NA NA NA

Te 19.8 19.8 20 18 17 15 21.8 21.4 22.5 23 22 24 19.3 19.7 20.4 NA NA NA NA NA NA NA NA NA NA NA NA

Ti 15.2 15.2 14.9 4.26 4.83 10.5 15.5 15.2 16.0 15 15 15 15.7 15.8 16.2 16 16 16 14.8 14.7 14.6 NA NA NA NA NA NA

Tl 19.8 19 19.9 17.7 17.0 16.4 21.2 21.2 22.0 20 21 22 NA NA NA 19 19 19 20.3 20.8 20.8 19 20 20 NA NA NA

V 15.6 15.6 15.3 14.5 14.1 13.6 16.5 16.3 17.0 15 16 15 15.4 15.7 16.1 16 16 16 14.6 14.4 14.4 14 14 14 14.89 15.00 14.95

W 38.3 38.3 39.8 23.9 31.2 28.7 43.1 42.6 44.6 41 40 40 42.4 42.8 44.4 NA NA NA NA NA NA NA NA NA NA NA NA

Y 15.6 15.2 15.9 14.6 13.8 13.4 15.0 15.0 15.7 15 15 15 15.6 15.6 16.1 NA NA NA NA NA NA NA NA NA NA NA NA

Zn 61.9 61.2 62.1 58.6 55.1 51.0 59.6 58.9 62.3 60 61 60 62.4 62.9 65.3 61 60 60 58.2 57.7 57.4 58 59 58 64.30 64.45 64.30

Zr 15 15 14.7 8.15 6.08 11.6 15.4 15.2 15.9 14 14 14 15.8 15.9 16.4 NA NA NA 14.3 14.1 14 NA NA NA NA NA NA

2

NA: not applicable; not reported by the laboratory
11

Mean overall laboratory-reported results and standard deviations are shown in Table 4a for media 

blanks and in Tables 4b-d for the three different Solu-SertTM CRM elemental loadings, i.e., Levels 1

(low loading), 2 (medium loading) and 3 (high loading). For elements with 1 or 2 results reported <MDL 

or <RL, half of the MDL or RL was used to calculate the mean blank results. If all results reported were 

<MDL or <RL, the average MDL or RL was reported as a less than value. Also for each loading level, 

relative standard deviations and recoveries, the latter computed with respect to CRM reference values, 

are presented in Tables 4b-d. Calculations were performed before the results were rounded to 3 

significant figures. For a few of the data sets in Tables 4b-d, outliers (identified by means of Grubbs’ 

test) were removed prior to carrying out subsequent statistical computations.
12

Table 4a. Blank Internal capsule (Solu-SertTM) media – Mean laboratory results & certified 

reference values

Element

No. 

Labs4 Mean5 (μg) Std. Dev.6 (μg)

Reference value 

(μg)7 

Ag 1 0.060 - <0.01

Al 3 1.1 0.49 0.6

As 2 0.44 0.48 <0.01

Ba 5 0.24 0.037 0.2

Be 1 0.0085 - <0.01

Ca 6 17 4.6 14

Cd 1 0.025 - <0.01

Co 1 0.034 - <0.01

Cr 4 0.57 0.25 0.9

Cu 2 0.18 0.077 0.14

Fe 5 1.5 0.48 1.2

In 1 0.67 - <0.01

K 2 1.4 0.44 0.6

La 1 0.20 - <0.01

Li 1 0.0078 - <0.01

Mg 4 3.3 1.2 2.7

Mn 1 0.032 - <0.01

Mo 2 0.041 0.039 <0.01

Ni 3 0.093 0.055 <0.01

P 2 1.3 1.0 <0.01

Pb 2 0.22 0.22 <0.01

Sb 1 0.56 - <0.01

Se 2 0.56 0.70 <0.01

Sn 1 0.41 - <0.01

Sr 4 0.036 0.018 <0.01

Te 2 0.40 0.43 <0.01

Ti 4 0.061 0.039 <0.01

Tl 2 0.73 0.46 <0.01

V 1 0.043 - <0.01

W 1 0.16 - <0.01

Y 2 0.014 0.0033 <0.01

Zn 2 0.37 0.15 0.2

Zr 3 0.035 0.014 <0.01

4Number of laboratories reporting at least one result >MDL (or RL)

5values based only on reported results above MDL (or RL); 

6standard deviation (if p>1); 7as reported by the CRM provider 
13

Table 4b. Internal capsule (Solu-SertTM) interlaboratory study laboratory means vs. certified 

reference values – Level 1 (Low Loading)

Element No. 

Labs4

Mean(μg) Std. Dev. 

(μg)6 

RSD8 Reference 

value (μg)7

Uncertainty in ref. 

value (μg)7 

Recovery (%)

Ag 7 4.66 0.78 0.17 5.0 0.1 93.2

Al 7 10.1 0.62 0.061 10.6 0.2 95.7

As 7 4.97 0.36 0.073 5.0 0.1 99.4

Ba 8 2.14 0.18 0.084 2.21 0.04 97.0

Be 9 2.03 0.090 0.044 2.01 0.02 100.8

Ca 8 109. 18 0.16 114 2 95.8

Cd 9 2.03 0.070 0.036 2.01 0.02 101.1

Co 9 2.08 0.14 0.068 2.01 0.02 103.4

Cr 8 2.33 0.38 0.16 2.91 0.06 80.2

Cu 8# 3.16 0.14 0.045 3.16 0.06 100.1

Fe 9 22.9 3.4 0.15 21.3 0.4 107.4

In 5 4.61 1.5 0.33 5.0 0.1 92.1

K 5 9.44 3.4 0.36 10.6 0.2 89.0

La 4 3.05 0.25 0.081 3.01 0.03 101.3

Li 7 1.87 0.16 0.085 2.01 0.02 93.0

Mg 7 11.9 1.9 0.16 12.7 0.1 93.9

Mn 9 2.01 0.15 0.076 2.01 0.02 99.8

Mo 9 2.02 0.13 0.062 2.01 0.02 100.7

Ni 9 2.18 0.21 0.096 2.01 0.02 108.2

P 5 10.5 0.94 0.090 10.1 0.2 103.9

Pb 9 10.1 0.63 0.062 10.0 0.2 100.9

Sb 8 4.95 0.33 0.067 5.0 0.1 99.1

Se 6 3.37 0.50 0.15 3.0 0.2 112.2

Sn 4 1.98 0.52 0.26 2.01 0.04 98.7

Sr 6# 2.01 0.040 0.019 2.01 0.02 100.2

Te 5 3.13 0.55 0.18 3.0 0.1 104.3

Ti 7 2.11 0.12 0.057 2.01 0.04 104.9

Tl 6 3.07 0.22 0.071 3.0 0.1 102.4

V 9 3.04 0.17 0.057 3.02 0.06 100.7

W 5 8.39 0.99 0.12 10.1 0.2 83.0

Y 5 2.03 0.080 0.038 2.01 0.04 100.8

Zn 9 5.23 0.31 0.060 5.2 0.1 100.6

Zr 5 2.03 0.13 0.062 2.01 0.04 101.2

4

Number of laboratories reporting at least one result >MDL (or RL)

6

standard deviation (if p>1); 7

as reported by the CRM provider

8

RSD: relative standard deviation

#

excludes outlier (Grubbs’ test)
14

Table 4c. Internal capsule (Solu-SertTM) interlaboratory study laboratory means vs. certified 

reference values – Level 2 (Medium Loading)

Element No. 

Labs4

Mean 

(μg)

Std. Dev. 

(μg)6 RSD8 Reference value (μg)7

Uncertainty in ref. 

value (μg)7 Recovery (%)

Ag 7 8.43 2.2 0.26 10.1 0.2 83.5

Al 7 29.6 0.91 0.031 30.9 0.6 95.7

As 8 20.8 1.1 0.053 20.2 0.4 103.0

Ba 7# 7.08 0.18 0.025 7.3 0.1 96.9

Be 9 7.05 0.48 0.068 7.0 0.1 100.7

Ca 8 161 24 0.15 165 3 97.4

Cd 9 7.05 0.28 0.040 7.0 0.1 100.7

Co 9 7.12 0.40 0.057 7.0 0.1 101.7

Cr 9 7.60 0.55 0.072 7.9 0.2 96.3

Cu 9 15.2 0.61 0.040 15.1 0.3 100.8

Fe 9 42.5 2.3 0.055 41.0 0.8 103.7

In 5 13.5 3.7 0.27 14.9 0.1 90.8

K 6 15.4 3.6 0.24 15.7 0.3 98.0

La 4 10.4 0.75 0.072 10.1 0.1 102.4

Li 7 6.64 0.46 0.070 7.0 0.1 94.9

Mg 7 27.5 2.5 0.091 27.9 0.3 98.7

Mn 9 7.03 0.43 0.061 7.0 0.1 100.4

Mo 9 7.27 0.35 0.048 7.1 0.1 102.4

Ni 9 7.26 0.54 0.074 7.0 0.1 103.7

P 6 25.7 2.3 0.089 24.9 0.5 103.1

Pb 9 25.3 1.4 0.053 25.2 0.5 100.4

Sb 9 24.9 1.4 0.057 25.1 0.5 99.0

Se 8 16.4 1.4 0.087 15.1 0.3 108.8

Sn 6 6.78 1.2 0.18 7.0 0.1 96.9

Sr 7 7.22 0.54 0.075 7.1 0.1 101.7

Te 5 13.0 1.0 0.077 12.6 0.3 102.8

Ti 7 7.07 0.73 0.10 7.0 0.1 101.0

Tl 7 10.1 0.58 0.058 10.1 0.2 99.6

V 9 7.12 0.44 0.062 7.0 0.1 101.7

W 5 24.5 2.8 0.12 25.1 0.5 97.6

Y 5 7.20 0.43 0.059 7.1 0.1 101.5

Zn 9 25.4 1.3 0.049 25.1 0.5 101.2

Zr 6 6.97 0.64 0.092 7.0 0.1 99.5

4

Number of laboratories reporting at least one result >MDL (or RL)

6

standard deviation (if p>1); 7

as reported by the CRM provider

8

RSD: relative standard deviation

#

excludes outlier (Grubbs’ test)
15

Table 4d. Internal capsule (Solu-SertTM) interlaboratory study laboratory means vs. certified 

reference values – Level 3 (High Loading)

Element No. 

Labs4

Mean 

(μg)

Std. Dev. 

(μg)6 

RSD8 Reference 

value (μg)7

Uncertainty in ref. 

value (μg)7

Recovery (%)

Ag 7 13.7 7.1 0.52 20.1 0.4 68.2

Al 7 58.5 1.4 0.024 60.8 1.2 96.2

As 8 40.8 2.4 0.058 40.1 0.8 101.8

Ba 8 15.2 0.75 0.050 15.2 0.3 99.9

Be 9 14.9 0.76 0.051 14.9 0.1 100.1

Ca 8 206 27 0.13 215 4 95.8

Cd 8# 15.2 0.28 0.019 14.9 0.1 102.2

Co 9 15.2 0.87 0.058 14.9 0.1 102.0

Cr 9 15.4 0.55 0.035 15.8 0.3 97.2

Cu 9 30.0 0.96 0.032 29.9 0.6 100.2

Fe 9 83.1 4.5 0.054 80.5 1.6 103.2

In 5 34.2 11 0.32 39.7 0.4 86.2

K 6 21.9 4.4 0.20 20.7 0.4 105.8

La 4 20.1 1.6 0.079 20.1 0.2 99.9

Li 7 14.7 0.77 0.052 14.9 0.1 98.6

Mg 7 104 7.4 0.072 103 1 100.8

Mn 9 14.9 0.85 0.057 14.9 0.1 100.2

Mo 9 15.3 0.80 0.052 15.0 0.1 102.1

Ni 9 15.4 1.1 0.070 14.9 0.1 103.0

P 5# 101 1.8 0.017 99 2 102.2

Pb 9 100. 7.3 0.073 100 2 100.0

Sb 8J 40.2 1.5 0.036 40.2 0.8 100.0

Se 8 31.3 3.2 0.10 30.1 1.5 104.1

Sn 5# 15.3 0.76 0.050 14.9 0.3 102.8

Sr 7 15.1 0.92 0.061 15.0 0.2 100.9

Te 5 20.2 2.5 0.12 20.1 0.4 100.5

Ti 6# 15.4 0.52 0.034 14.9 0.3 103.2

Tl 7 19.8 1.5 0.075 20.1 0.4 98.3

V 9 15.2 0.89 0.058 14.9 0.3 101.9

W 5 38.7 6.4 0.16 40.2 0.8 96.4

Y 5 15.1 0.72 0.048 15.0 0.3 100.6

Zn 9 60.2 2.9 0.048 59.7 1.2 100.8

Zr 6 13.9 2.7 0.19 14.9 0.3 93.1

4

Number of laboratories reporting at least one result >MDL (or RL)

6

standard deviation (if p>1); 7

as reported by the CRM provider

8

RSD: relative standard deviation

#

excludes outlier (Grubbs’ test)
16

Estimates of bias, precision and accuracy, computed statistically in accordance with established NIOSH 

guidelines [10,11], are presented in Table 5. For each data subset, Grubbs’ test at 1% confidence level 

was used to identify outliers which, if identified, were removed prior to further statistical calculations. 

Bias, precision and accuracy estimates were computed based on results from all three Solu-SertTM 

loading levels. All calculations were based on the original data and not the mean laboratory results 

presented in Tables 4b-d. Analysis of Variance procedure was used to test for homogeneity of bias; 

Bartlett’s test was used for testing homogeneity of RSD (precision) on the data sets for each element. 

Where results were homogeneous across spiking levels, pooled estimates of bias and precision were 

used to compute method accuracy for each element. If homogeneity tests failed to pass, the most 

conservative, i.e. largest, estimates of precision and bias were used to estimate accuracy for each 

element. It must be pointed out that the accuracy estimates presented in Table 5 also include a 

conservative imprecision component of ±5% sampling pump error, in accordance with recommended 

guidelines [10].

Discussion 

The laboratory-reported data from the ILS shown in Tables 3a-d demonstrated no statistically 

significant differences due to sample preparation procedure regardless of loading level. Using SAS 

Mixed model procedure, statistical tests of data subsets for heating method (hot plate, hot block or 

microwave) and acid mixture sample treatment yielded no statistically significant differences in the 

reported multielement analysis results at 5% significance level (p=0.23 for heating method, p=0.73 for 

acid mixure). The test factors included heating method, acid mixture, level and element as the fixed 

factor and lab and sample nested with lab and level as the random factors. The interactions of heating 

method with element and acid mixture with element were also included. Thus the implication is that, for 

the Solu-SertTM samples evaluated, the various sample preparation procedures performed equivalently. 

These results are consistent with previous reports entailing elemental analysis of soluble capsules for 

use as cassette inserts [7,12].

It is important to note that lab-to-lab differences were taken into account in the above statistical 

calculations. Some differences in the sample preparation methods may have been found had such 

variations not had to be considered. The presence and identity of the outliers may prove valuable in 

that regard. Of particular importance are the less than quantitative recoveries for Sb, Sn, and Ti using 

the hot plate method of Lab 2a. This sample preparation method may not be amenable to the analysis 

of Sb, Sn and Ti.
17

It can be seen from the reference values listed in Table 4a that appreciable media background levels 

were found for several elements, notably Al, Ca, Cr, Fe, K, and Mg. Trace media background levels of 

a few other elements, i.e., Ba, Cu and Zn, were also obtained. Additionally, appreciable (>0.5 μg) 

media background levels of In, P, Sb, Se, and Tl were reported by the participating laboratories. 

However, it is noted that only a few laboratories had MDLs or RLs low enough to report measurable 

elemental analysis results for media blanks (Table 4a). For Levels 1, 2 and 3, the reported results for 

laboratory means compared to certified values yielded quantitative recoveries (i.e., within 100% ± 10% 

of the reference value) for the vast majority of elements and spike levels (Tables 4b-d). Mean overall 

recoveries below 90% were found only for Cr, K, and W at low loadings and for Ag at medium and high 

spike levels and for In at the high spike level. The significant media background levels reported for 

certain elements did not negatively affect recoveries. Most values for precision (expressed as RSD) 

were <0.20 (Tables 4b-d), which compare favorably with the variability typically observed in 

interlaboratory multielement analysis of air filter samples by atomic spectrometric methods [13].

While there was measurable background for certain elements (mentioned above; see Table 4a), this 

background was effectively corrected for, as evidenced by the quantitative recoveries obtained for the 

vast majority of elements and loading levels (Tables 4b-d). Where the background levels may pose a 

greater influence is in the calculation of the method LOD. In Table 6 method LODs are calculated using 

the responses of 7 respective sample types: reagent blank solutions, MCE filters and Solu-sertsTM 

taken through the sample preparation steps of NIOSH 7302 (microwave digestion). The standard 

deviation of the results is multiplied by 3.143 to give the method LOD. For many elements, the method 

LOD is greater when using the internal capsule. Care should be taken in choosing the appropriate 

media in concert with the expected sample concentrations. Please note: the MCE filter calculations did 

not include a wipe or rinse of the sampling cassette as is currently recommended [5]. This may 

increase the method LOD using MCE filters and lessen the difference between the method LODs of 

MCE filters and Solu-SertTM samplers. 
18

Table 5. Internal capsule (Solu-SertTM) interlaboratory study – Estimates of bias, precision and 

accuracy

Element Bias n9 Š10 ŜrT11 Accuracy AU9512

Ag -0.184 21 0.041 0.065 0.290 0.314

Al -0.0414 21 0.006 0.050 0.124 0.143

As 0.0141 23 0.016 0.052 0.107 0.124

Ba -0.0206 23 0.036 0.062 0.128 0.149

Be 0.00536 27 0.025 0.056 0.110 0.127

Ca -0.0367 24 0.001 0.050 0.119 0.136

Cd 0.0133 26 0.022 0.055 0.111 0.127

Co 0.0238 27 0.036 0.062 0.129 0.149

Cr -0.0281 26 0.046 0.068 0.144 0.166

Cu 0.00347 26 0.017 0.053 0.104 0.119

Fe 0.0476 27 0.011 0.051 0.132 0.148

In -0.103 15 0.056 0.075 0.226 0.260

K -0.0239 17 0.029 0.058 0.123 0.147

La 0.0119 12 0.025 0.056 0.112 0.140

Li -0.0447 21 0.039 0.064 0.149 0.173

Mg -0.0219 21 0.012 0.051 0.109 0.128

Mn 0.00127 27 0.039 0.063 0.124 0.143

Mo 0.0169 27 0.032 0.060 0.121 0.140

Ni 0.0498 27 0.055 0.074 0.172 0.196

P 0.0310 16 0.010 0.051 0.115 0.137

Pb 0.00439 27 0.006 0.050 0.099 0.114

Sb -0.00631 25 0.013 0.052 0.102 0.118

Se 0.0864 22 0.055 0.075 0.209 0.236

Sn -0.00541 15 0.117 0.128 0.250 0.304

Sr 0.00930 20 0.011 0.051 0.102 0.120

Te 0.0256 15 0.063 0.081 0.166 0.201

Ti 0.0305 20 0.032 0.059 0.131 0.154

Tl 0.00128 20 0.030 0.058 0.114 0.135

V 0.0143 27 0.020 0.054 0.109 0.126

W -0.0240 15 0.010 0.051 0.110 0.134

Y 0.00971 15 0.020 0.054 0.107 0.130

Zn 0.00873 27 0.013 0.052 0.103 0.118

Zr -0.0206 17 0.033 0.060 0.124 0.149

9

Number of reported results minus outliers (Grubbs’ test, 1% confidence level)

10precision, S



= (true) relative standard deviation (TRSD) 

11overall precision precision = ( )2 2 S + 0.05 

12upper 95% confidence limit of accuracy estimate
19

Table 6. Method limits of detection (LOD) calculated using different media

Sample Reagent Blanks 

(μg/sample)

MCE Filters 

(μg/sample)

Solu-SertsTM 

(μg/sample)

Solu-SertTM / MCE Filter

Ag 0.022 0.017 0.020 1

Al 0.72 0.12 0.38 3

As 0.069 0.099 0.099 1

Ba 0.0052 0.010 0.55 56

Be 0.0094 0.0036 0.0064 2

Ca 0.35 0.59 3.9 7

Cd 0.0073 0.0061 0.0052 1

Co 0.011 0.0078 0.0090 1

Cr 0.012 0.042 0.28 7

Cu 0.058 0.0087 0.15 17

Fe 0.30 1.0 5.3 5

In 0.15 0.15 0.26 2

K 0.25 0.34 0.70 2

La 0.023 0.026 0.026 1

Li 0.0065 0.0016 0.010 6

Mg 0.12 0.11 1.1 10

Mn 0.022 0.047 0.031 1

Mo 0.0093 0.011 0.021 2

Ni 0.020 0.057 0.56 10

P 0.16 0.12 0.27 2

Pb 0.063 0.056 0.062 1

Sb 0.10 0.085 0.11 1

Se 0.16 0.13 0.14 1

Sn 0.017 0.21 0.065 0

Sr 0.0012 0.0027 0.014 5

Te 0.11 0.087 0.22 3

Ti 0.0055 0.0045 0.042 9

Tl 0.042 0.049 0.046 1

V 0.013 0.010 0.0091 1

W 0.020 0.041 0.055 1

Y 0.0052 0.0066 0.0039 1

Zn 0.076 0.27 0.69 3

Zr 0.0093 0.0051 0.0099 2

 

The results for accuracy summarized in Table 5 demonstrate the suitability of Solu-SertTM samplers for 

multielement analysis by acid dissolution and ICP-AES. For a method to be deemed unbiased and 

accurate with 95% probability of results ±25% of the actual concentration, the accuracy estimates 
20

should be ≤0.25 and the bias should be ≤0.10 [10]. The mean accuracy estimate is ≥0.25 for only two 

elements: Ag and In. The upper 95% confidence limit for the accuracy estimate exceeds ±0.25 for only 

three elements: Ag, In and Sn. Bias estimates beyond ±0.10 are obtained only for two elements: Ag 

and In. Estimates of precision and overall precision are >0.10 for only one element: Sn. For 30 of the 

33 elements evaluated, accuracy estimates of 0.25 or better demonstrate that the method is valid for 

quantitative multielement analytical determination.

Difficulties with atomic spectrometric interlaboratory analysis of Ag have been observed previously [13]. 

Since Ag+ ions are light-sensitive and subject to photoreduction, it is recommended to carry out sample 

preparation in light-protected vessels if this element is to be analyzed [14]. ILS results reported here for 

In (Table 5) are limited, unfortunately, since many participants did not report results for this element. It 

is anticipated that better estimates for tighter precision and lesser bias would be obtained with a larger 

number of participating laboratories. The somewhat higher estimates for ILS variability and accuracy 

for Sn (Table 5) may be improved with data from additional laboratory participants [15], especially for 

low-level samples. 

Disclaimer: Mention of any company or product does not constitute endorsement by the National 

Institute for Occupational Safety and Health. 

References

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[www.cdc.gov/niosh/nmam/].

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21

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22

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