INTER-LABORATORY COMPARISON OF SELENIUM IN MINE DRAINAGE

Louis McDonald1, Donglin (Lynn) Huang1 ,

Ben Faulkner2, Ron Lilly3, and Jason Unrine4

1West Virginia University, Division of Plant & Soil Science, Morgantown, WV 2Bratton Farm, Princeton, WV, 3Mallard Environmental Services, Shady Sp. WV 4University of

Kentucky, Department of Plant and Soil Sciences, Lexington, KY

Collection Procedure• Don powder free nitrile gloves at each sample location. • Label each tube with sample ID and indicate lab destination. • Reglove.• Uncap 5 borosilicate tubes and place caps on clean (dedicated

plastic wrap).• Immerse all 5 bottles into standing pool or in flowing stream and

fill completely.• Cap with no head space. • Place tube in 100 ml zip lock bag and prepare for shipment.

Bubble wrap and ship in iced durable cooler overnight or 2 day express or hand deliver. COC sticker on container.

• Tubes contain no preservative, sample is not filtered.• 250 ml certified, unpreserved and finally, pre-acidified poly

sample bottles will then be filled and transported (also without filtering). *

• Duplicate – one blind duplicate per location designated X-001• Blind Field Blank (DI water supplied by ) - accomplished at

exact field location at time of sample collection. Designated “B”• Certified Reference Material also submitted as blind sample –

designated by “J”

Certified Reference Material ($352/250 ml = $5,330/gallon)

Samples

Eight (8) Total Five (5) field samples One (1) field blank One (1) certified reference One (1) duplicate field sample

Split five (5) ways for five (5) labs All labs determined total Se Se speciation at two (2) labs

Se determined three (3) times on three (3) different days

Samples – expected results

01 Pond (5-10 µg/L) 02 Pond (0-10 µg/L) 05 Pond (0-10 µg/L) 14 Sediment Channel inlet (5-10 µg/L) X5 Blind DUPLICATE of 05 Pond B Blind BLANK (DI Water) (nd) J Standard Reference Material (11.97

µg/L)

Instrumentation

1. Graphite Furnace - Atomic Absorption

(GF-AA)

2. Atomic Absorption Zeeman-Corrected

(AAZ)3. Hydride Generation –Atomic Fluorescence

(HG-AF)4. Hydride-Generation – Inductively Coupled Plasma

(HG-ICP)5. Ion Chromatography-ICP-Dynamic Reaction Cell-

Mass Spectroscopy

(IC-ICP-DRC-MS)

Sample Handling

Certified borosilicate glass bottles, 40 mL, unpreserved

Polyethylene plastic bottles, 250 mL Preserved (2 mL HNO3) or Unpreserved Filtered or unfiltered

Interpreting Results

Repeatability – If you send the same sample twice, do you get the same result for both?

Precision – If the same sample is run several times, how close are they to each other?

Accuracy – How close is the result to the ‘true’ value?

Image Credit: R. Allen Chem222. UVa

AccurateNot Precise

Not AccuratePrecise

AccuratePrecise

Total Se - Repeatability

One duplicate sample (05) - Are they different?

NO No significant differences in duplicate

sample for any lab. Conclusion

Same sample submitted twice, you’ll get the same result.

Total Se – Precision

CV (%)L 4.4A 6.7R 10S 9.3W 13*

CV = coefficient of variation = 100*standard deviation/meanTable 1. CV for

CRM

* = only two reps

Total Se - Precision

Table 2. Mean and range CV for other samples

Lab mean min maxL 3.2 0.9 4.7A 3.4 1.6 6.7R 4.2 1.3 10S 9.3 4.6 16W 10 1.0 21

Conclusion – reasonably good precision for all labs.

Total Se - Accuracy

Figure 1. Accuracy in determination of Certified Reference Standard.

Total Se - Accuracy

Assume IC-ICP-DRC-MS method = true

Lab

Sample L R S W

----------------------- % ----------------------------

01 50 6 65 -13

02 1 2 0 -20

05 -1 4 -1 -3

21 14 7 15 -2

Table 3. Percent error in determinations of field samples.

Results - Speciation

IC – ICP – DRC – MS

-1000

1000

3000

5000

7000

9000

11000

0 50 100 150 200 250 300 350 400 450

80Se

(cps

)

retention time (s)

selenomethionine

selenomethionineselenomethionine

selenocystine

Selenite

selenate

Results - Speciation

• HG - ICP

Fully Reduced toSe (IV)

Aliquot 2Se (IV) + Se(IV)

Aliquot 1 Se (IV)

Selenium Sample

Se (IV) acidified with HCl

Aliquot 3Se (0) +Se (IV) +Se (VI)

Se fully oxidized Reduced to Se (IV)

Results - Speciation

Organic Se (selenocyanate, methylseleninic acid IC-ICP-DRC-MS = not detected HG-ICP = not measured

Selenite IC-ICP-DRC-MS = not detected HG-ICP = not detected

Results - Speciation

Selenate

Sample IC-ICP-DRC-MS

HG-ICP

--------------- μg L-1 ---------------

01 8.4 10.1

02 7.0 9.0

05 6.3 7.4

21 8.2 9.2

Table 4. Selenate concentrations in four samples by two instrumental methods

Summary – Total Se

That most labs accurately determined the Certified Standard is promising

Summary – Total Se

That most labs accurately determined the Certified Standard is promising.

That most CVs were small is encouraging Little variation for different days

Summary – Total Se

The variability in some labs indicates the need for Certified Standard(s) for mine

drainages

Summary – Total Se

The variability in some labs indicates the need for Certified Standard(s) for mine drainages Broader use of standard addition

method to account for matrix effects.

Summary – Total Se

The variability in some labs indicates the need for Certified Standard(s) for mine drainages Broader use of standard addition method to

account for matrix effects Further research into the causes of

variability

Summary – Total Se

The variability in some labs indicates the need for Certified Standard(s) for mine drainages Broader use of standard addition method to

account for matrix effects Further research into the causes of variability Continued program of Inter-laboratory

Proficiency Testing High CVs in our results Replaced parts, now getting significantly

better data

Summary – Total Se

The variability in some labs indicates the need for Certified Standard(s) for mine drainages Broader use of standard addition method to

account for matrix effects Further research into the causes of variability Continued program of Inter-laboratory

Proficiency Testing The high CVs in our results Replaced parts, now getting significantly better

results Work toward developing a SOP for sample

handling

Summary – Se Speciation

Selenium speciation is difficult, expensive

Some techniques are limited in their ability

But – speciation defines toxicity and treatment

Recommendations for Users

Insist on a QA/QC plan that convinces you of data quality

Consider spiking samples with and checking recovery in-house

Move toward speciation to guide treatment decisions