Report No. 799 Waters Proficiency Testing Round 150...

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- Total

PTA wishes to gratefully acknowledge the technical assistance provided for this program by Ms R Ryan, Global Proficiency go to Global Proficiency Ltd (New Zealand) and Global Proficiency Pty Ltd (Australia) for the supply and distribution of the samples.

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Waters Proficiency Testing

Total


PO Box 7507 SILVERWATER NSW 2128,

Report No.


Total Recoverable Oil and Grease


© Copyright Proficiency Testing Australia,


Report No.


Round

ecoverable Oil and Grease

January 2013

Acknowledgments




Report No.


Round 150


January 2013

Acknowledgments

PTA wishes to gratefully acknowledge the technical assistance provided for this program by Ms R Ryan, Global Proficiency Ltdgo to Global Proficiency Ltd (New Zealand) and Global Proficiency Pty Ltd (Australia) for the supply and distribution of the samples.



Report No. 799


150


January 2013

Acknowledgments

PTA wishes to gratefully acknowledge the technical assistance provided for this Ltd (New Zealand

go to Global Proficiency Ltd (New Zealand) and Global Proficiency Pty Ltd (Australia) for the supply and distribution of the samples.



799



PTA wishes to gratefully acknowledge the technical assistance provided for this New Zealand). Also our thanks

go to Global Proficiency Ltd (New Zealand) and Global Proficiency Pty Ltd

© Copyright Proficiency Testing Australia, 2013

PO Box 7507 SILVERWATER NSW 2128, Australia



PTA wishes to gratefully acknowledge the technical assistance provided for this . Also our thanks


2013

Australia

ecoverable Oil and Grease -

PTA wishes to gratefully acknowledge the technical assistance provided for this . Also our thanks


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CONTENTS

1. Foreword ............................................................................................................................ 1

2. Program Features and Design ........................................................................................... 1

3. Statistical Format ............................................................................................................... 2

4. PTA and Technical Advisor’s Comments .......................................................................... 4

5. Outlier Results ................................................................................................................. 10

6. References ...................................................................................................................... 10

APPENDIX A – Results and Data Analysis

Total Recoverable Oil and Grease Sample PTA 1 ................................................................ A1


APPENDIX B – Sample Homogeneity and Stability

Homogeneity and Stability Testing ........................................................................................ B1

APPENDIX C – Documentation

Instructions to Participants ................................................................................................... C1

Method Codes ....................................................................................................................... C3

Results Sheet ........................................................................................................................ C4

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1. Foreword

This report summarises the results of a proficiency testing program on the determination of total recoverable oil and grease in waters. This is round 150 in a planned series of programs involving the analysis of chemical and physical parameters of waters. The exercise was conducted in November 2012 by Proficiency Testing Australia (PTA). The main aim of the program was to assess laboratories’ abilities to competently perform the prescribed analyses. The Program Coordinator was Ms D Mihaila and the Technical Advisor was Ms R Ryan from Global Proficiency Ltd, New Zealand. This report was authorised by Mrs F Watton, PTA Quality – Business Development Manager.

2. Program Features and Design 2.1 Each laboratory was randomly allocated a unique code number for the program to

ensure confidentiality of results. Reference to each laboratory in this report is by code number only. Please note that a number of laboratories reported more than one set of results and, therefore, their code numbers (with letter) could appear several times in the same data set.

2.2 Laboratories were provided with the "Instructions to Participants" and "Results Sheet"

(see Appendix C). Laboratories were requested to perform the tests according to their routine methods.

2.3 Participants were provided with two glass vials (labelled PTA 1 and PTA 2) containing

solutions of total recoverable oil and grease. 2.4 A total of 56 laboratories received samples, comprising:

- 39 Australian participants; and

- 17 overseas participants, including:

- Brunei Darussalam (1), Indonesia (2), Malaysia (6), New Zealand (2), Papua New Guinea (3), Singapore (1), Thailand (1), Vietnam (1).

Of these 56 laboratories, 8 were unable to submit results by the due date. 2.5 Results (as reported by participants) with corresponding summary statistics (i.e.

number of results, median, uncertainty of the median, normalised interquartile range, robust coefficient of variation, minimum, maximum and range) are presented in Appendix A (for each sample and for each of the analyses performed).

2.6 A robust statistical approach, using z-scores, was utilised to assess laboratories’

testing performance (see Section 3). Robust z-score and z-score charts relevant to each test are presented in Appendix A.

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The document entitled Guide to Proficiency Testing Australia, 2012 (reference [1]) defines the statistical terms and details the statistical procedures referred to in this report.

2.7 A tabulated listing of laboratories (by code number) identified as having outlier results

can be found on page 10. 2.8 Prior to sample distribution, a number of randomly selected samples were analysed

for homogeneity. Based on the results of this testing (see Appendix B) it was considered that the samples utilised for this program were homogenous. As such, any results later identified as outliers could not be attributed to any notable sample variability.

3. Statistical Format

For each test, where appropriate, the following information is given:

- a table of results and calculated z-scores;

- a list of summary statistics; and

- ordered z-score charts.

3.1 Outlier Results and Z-scores In order to assess laboratories’ testing performance, a robust statistical approach,

using z-scores, was utilised. Z-scores give a measure of how far a result is from the consensus value (i.e. the median), and give a "score" to each result relative to the other results in the group.

A z-score close to zero indicates that the result agrees well with those from other

laboratories, whereas, a z-score with an absolute value greater than or equal to 3.0 is considered to be an outlier and is marked by the symbol “§”.

Each determination was examined for outliers with all methods pooled. The table on

page 10 summarises the outlier results detected. 3.2 Results Tables and Summary Statistics Each of these tables contains the results returned by each laboratory, including the

code number for the method used, and the robust z-score calculated for each result. Results have been entered exactly as reported by participants. That is, laboratories

which did not report results to the precision (i.e. number of significant figures) requested on the Results Sheet have not been rounded to the requested precision before being included in the statistical analysis.

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A list of summary statistics appears at the bottom of each of the tables of results and consists of:

- the number of results for that test/sample (No. of Results);

- the median of these results, i.e. the middle value (Median);

- the uncertainty of the median;

- the normalised interquartile range of the results (Normalised IQR);

- the robust coefficient of variation, expressed as a percentage (Robust CV) - i.e. 100 x Normalised IQR / Median;

- the minimum and maximum laboratory results; and

- the range (Maximum - Minimum).

The median is a measure of the centre of the data. The normalised IQR is a measure of the spread of the results. It is calculated by multiplying the interquartile range (IQR) by a correction factor which converts the IQR to an estimate of the standard deviation. The IQR is the difference between the upper and lower quartiles (i.e. the values above and below which a quarter of the results lie, respectively). For normally distributed data, the uncertainty of the median is approximated by:

n

normIQR×2

π

Please see reference [1] for further details on these robust summary statistics.

3.3 Ordered Z-Score Charts On these charts each laboratory's robust z-score is shown, in order of magnitude, and

is marked with its code number. From these charts, each laboratory can readily compare its performance relative to the other laboratories.

These charts contain solid lines at +3.0 and -3.0, so that outliers are clearly

identifiable as those laboratories whose "bar" extends beyond these "cut-off" lines. The y-axis of these charts has been limited, so very large z-scores appear to extend beyond the chart boundary.

4

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4. PTA and Technical Advisor’s Comments 4.1. Metrological Traceability and Measurement Uncertainty of Assigned Values Consensus values (median) derived from participants’ results are used in this program. These values are not metrologically traceable to an external reference.

Sample preparation was undertaken according to Global Proficiency Ltd’s Standard Operating Procedures to ensure samples were fit-for-purpose, homogenous and stable. Weight checks were undertaken on all samples to ensure that the variability on doping concentrations for all samples was less than 2.0%.

Sample PTA 1 was prepared from high purity mineral oil which has a low viscosity in distilled water. Sample PTA 2 was prepared from a mixture of sunflower oil and anhydrous milk fat in distilled water. Samples were prepared as concentrates (~30 mL) equivalent to 1 litre of wastewater, packaged in Teflon capped glass vials and preserved with acid to pH 2.

Solutions were stable and homogeneous, and medians obtained from this proficiency round were in good agreement with the expected levels (dope Concentration), as shown in Table 1.

As the assigned value for this program is the median of the results submitted by the participants, the uncertainty of the median has been calculated and is presented in Table 1.

Analyte Sample Dope

Concentration (mg/L)

Median (mg/L)

Uncertainty of the median

(mg/L)


PTA 1 21.7 +/- 0.2 20.80 0.64

PTA 2 92.6 +/- 0.3 85.10 2.18

Table 1. Comparison of manufacturing concentrations (Dope) and proficiency medians. The values of the calculated uncertainty of the median are also presented. Overall, the performance of participants in this round was good, with robust CVs of less than 20%, consistent with the results of the last two rounds. The median concentrations indicated that on average 95% of total recoverable oil and grease was recovered for sample PTA 1 and 92% for sample PTA 2.

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4.2. Analysis of Round 150 Results The following table compares the Total Recoverable Oil and Grease medians and robust CVs from this round to those obtained in previous PTA rounds.

Round Sample Median (mg/L) Robust CV (%) No. of Res ults

This study PTA 1 20.80 17.1 48

PTA 2 85.10 14.1 48

Report 735 PTA 1 40.75 17.2 53

PTA 2 52.70 12.9 51

Report 678 PTA 1 21.20 32.2 58

PTA 2 24.70 15.9 58

Table 2. Comparison of current round variability and proficiency medians of Total Recoverable Oil and Grease testing with the results of the previous two rounds. Bias / Accuracy

Total Recoverable Oil and Grease testing was successfully carried out, with satisfactory results (|z-score| ≤ 2.0) ranging between 13.7 – 27.9 mg/L for sample PTA 1 and 61.0 – 109.2 mg/L for sample PTA 2.

Out of 48 participants, two questionable results (2.0 < |z-score| < 3.0) were obtained for sample PTA 1 (laboratories 306 and 651) and three questionable results were obtained for sample PTA 2 (laboratories 150, 188 and 403).

Six outlier results (|z-score| ≥ 3.0) were obtained for sample PTA 1 requiring follow-up action by laboratories 159, 188, 255, 335, 596 and 608. Four of the outlying results are approximately twice the doped concentration and could be due to calculation errors. The remaining two outlying results are lower than the doped concentration. They are most likely due to analyte loss during sample extraction.

Two outlier results were obtained for sample PTA 2, requiring follow-up action by laboratories 159 and 596. These two outliers are lower than the doped concentration and are also most likely due to analyte loss during sample extraction.

The Total Recoverable Oil and Grease dataset formed a normal distribution with no significant bias attributable to any one method (Figures 1 and 2). The main method used in this round was APHA 5520B - Liquid-Liquid, Partition-Gravimetric method, which was used by almost half of the participants, followed by the APHA 5520D - Soxhlet extraction method, which was used by approximately 20% of participants.

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Figure 1. Spread of results for Total Recoverable Oil and Grease proficiency testing of Sample PTA 1, with a median of 20.80 mg/L.

Figure 2. Spread of results for Total Recoverable Oil and Grease proficiency testing of Sample PTA 2, with a median of 85.10 mg/L.

0

2

4

6

8

10

12

14

16

18

20

22

0 5 10 15 20 25 30 35 40 45 50 55 60 65

Fre

quen

cy

Results (mg/L)

Total Recoverable Oil and Grease - Sample PTA 1

APHA Part 5520B

APHA Part 5520C

APHA Part 5520D

ASTM D 7066-04

US EPA 1664A

Modified US EPA1664A method

Other

0

2

4

6

8

10

12

14

16

18

20

0 15 30 45 60 75 90 105 120 135 150 165 180 195

Fre

quen

cy

Results (mg/L)

Total Recoverable Oil and Grease - Sample PTA 2

APHA Part 5520B

APHA Part 5520C

APHA Part 5520D

ASTM D 7066-04

US EPA 1664A


Other

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Measurement Uncertainty (MU)

The results submitted for Total Recoverable Oil and Greaseparticipants4 belowthe expected uncertainty for these samples based on the reproducibility

Out of 48 participantsaccurately reflect the difference between the median and the participantsproficiency sample.

Laboratories452, 472, 512, 523, 568,calculations, as To keep it in perspective, confidence in the medians is 20.8and 85.1

Figure 3. compared to median

Figure 4.compared to median

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surement Uncertainty (MU)

results submitted for Total Recoverable Oil and Greaseparticipants compared to the median 4 below. In figures 5 and 6, the expected uncertainty for these samples based on the reproducibility (95 %CI).

ut of 48 participantsurately reflect the difference between the median and the participants

proficiency sample.

Laboratories 112, 142, 150, 159, 237, 241, 250, 255, 285, 306, 335, 368, 372, 403, 409, 436, 452, 472, 512, 523, 568,calculations, as at least To keep it in perspective, confidence in the medians is 20.8and 85.10 ± 2.18 mg/L for sample

Figure 3. Total Recoverable Oil and Greasecompared to median

Figure 4. Total Recoverable Oil and Greasecompared to median


results submitted for Total Recoverable Oil and Greasecompared to the median

In figures 5 and 6, the the expected uncertainty for these samples based on the

(95 %CI).

ut of 48 participants, 34 (71%) submitted MU informatiourately reflect the difference between the median and the participants

proficiency sample.

112, 142, 150, 159, 237, 241, 250, 255, 285, 306, 335, 368, 372, 403, 409, 436, 452, 472, 512, 523, 568, 569, 596, 608, 634, 651 and

at least one of their resultsTo keep it in perspective, confidence in the medians is 20.8

mg/L for sample

Total Recoverable Oil and Greasecompared to median and doped

Total Recoverable Oil and Greasecompared to median and doped


results submitted for Total Recoverable Oil and Greasecompared to the median and doped

the MU is displayed by tthe expected uncertainty for these samples based on the

(71%) submitted MU informatiourately reflect the difference between the median and the participants

112, 142, 150, 159, 237, 241, 250, 255, 285, 306, 335, 368, 372, 403, 409, 436, 569, 596, 608, 634, 651 and

of their resultsTo keep it in perspective, confidence in the medians is 20.8

mg/L for sample PTA 2.

Total Recoverable Oil and Greaseand doped concentration

Total Recoverable Oil and Greaseand doped concentrat

7

results submitted for Total Recoverable Oil and Greaseand doped concentration s displayed by t

the expected uncertainty for these samples based on the

(71%) submitted MU informatiourately reflect the difference between the median and the participants

112, 142, 150, 159, 237, 241, 250, 255, 285, 306, 335, 368, 372, 403, 409, 436, 569, 596, 608, 634, 651 and

of their results was further from the median than their To keep it in perspective, confidence in the medians is 20.8

PTA 2.

Total Recoverable Oil and Grease results concentrations.

Total Recoverable Oil and Grease results for sample PTA 2 including concentrations.

results submitted for Total Recoverable Oil and Greaseconcentration

s displayed by the methods used,the expected uncertainty for these samples based on the 95% confidence interval for overall

(71%) submitted MU information. Severalurately reflect the difference between the median and the participants

112, 142, 150, 159, 237, 241, 250, 255, 285, 306, 335, 368, 372, 403, 409, 436, 569, 596, 608, 634, 651 and 656 may wish to re

further from the median than their To keep it in perspective, confidence in the medians is 20.80 ± 0.6

results for sample

results for sample PTA 2 including

results submitted for Total Recoverable Oil and Grease including the are displayed

he methods used, giving an indication of 95% confidence interval for overall

everal of the stated urately reflect the difference between the median and the participants

112, 142, 150, 159, 237, 241, 250, 255, 285, 306, 335, 368, 372, 403, 409, 436, may wish to re

further from the median than their ± 0.64 mg/L for sample PTA 1

for sample PTA 1 including


including the MU stated by displayed in Figures

giving an indication of 95% confidence interval for overall

of the stated MUsurately reflect the difference between the median and the participants’ results for each

112, 142, 150, 159, 237, 241, 250, 255, 285, 306, 335, 368, 372, 403, 409, 436, may wish to re-examine their MU

further from the median than their stated mg/L for sample PTA 1

PTA 1 including


stated by in Figures 3 and

giving an indication of 95% confidence interval for overall

MUs did not for each

112, 142, 150, 159, 237, 241, 250, 255, 285, 306, 335, 368, 372, 403, 409, 436, examine their MU

stated MU. mg/L for sample PTA 1

PTA 1 including MU

results for sample PTA 2 including MU

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Figure 5. MU for Total Recoverable Oil and Grease proficiency testing of Sample PTA 1, as reported by participants, compared with 95% confidence interval for overall reproducibility (----) (± 6.9 mg/L) in this round.

Figure 6. MU for Total Recoverable Oil and Grease proficiency testing of Sample PTA 2, as reported by participants, compared with 95% confidence interval for overall reproducibility (----) (± 23.6 mg/L) in this round.

0

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Fre

quen

cy

Measurement Uncertainty (mg/L)

Total Recoverable Oil and Grease ± MU - Sample PTA 1

APHA Part 5520B

APHA Part 5520C

APHA Part 5520D

ASTM D 7066-04

US EPA 1664A


0

1

2

3

4

5

6

7

0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5

Fre

quen

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Measurement Uncertainty (mg/L)

Total Recoverable Oil and Grease ± MU - Sample PTA 2

APHA Part 5520B

APHA Part 5520C

APHA Part 5520D

ASTM D 7066-04

US EPA 1664A


Other

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Using the t-value (outliers removed, 95% confidence interval), overall results indicated that the estimate of reproducibility (~2SD) for Total Recoverable Oil and Grease analysis was 20.8 ± 6.9 mg/L for sample PTA 1 and 85.1 ± 23.6 mg/L for sample PTA 2.

Using the t-value, results submitted by laboratories using method APHA 5520B (n=24) indicated a method reproducibility of ± 5.5 mg/L for sample PTA 1 and of ± 23.6 mg/L for sample PTA 2.

4.3. Analysis of Results by Method Groups Further analysis of results by method groups is undertaken to provide specific information on individual method performance. The APHA Liquid-Liquid, Partition-Gravimetric method (APHA Part 5520B - method code 1) was most frequently employed for Total Recoverable Oil and Grease analysis in this round. Out of 48 participants, 22 laboratories indicated the use of this method for analysis of sample PTA 1 and 24 laboratories for sample PTA 2. Table 3 below presents the median, uncertainty of the median and robust CV for Total Recoverable Oil and Grease results obtained by method 1.

Sample Method code Participants

Median ± Uncertainty of the Median

(mg/L)

Robust CV (%)

PTA 1 1 22 19.95 ± 0.79 14.8

PTA 2 1 24 82.70 ± 2.92 13.8

Table 3. Variability and proficiency median of Total Recoverable Oil and Grease results obtained by method 1. The median concentrations determined for results submitted using method APHA 5520B indicated that on average 92% of total recoverable oil and grease was recovered for sample PTA 1 and 89% for sample PTA 2. These results compare well with the average recovery published for method APHA 5520B (Standard Methods 22nd edition) of 93%. In order for methods to be grouped for analysis, PTA requires more than ten sets of results from the same method group. For methods other than those presented above, there were less than ten results submitted, therefore reliable conclusions cannot be drawn from analysing them separately and these results have not been analysed by grouped methods.

10

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5. Outlier Results

Laboratories reporting outlier results are listed in the following table:

Lab Code


PTA 1 PTA 2

159 § §

188 §

255 §

335 §

596 § §

608 §

1 A “§” indicates the occurrence of a z-score outlier result (i.e. those results for which

|z-score|≥3.0). 6. References

[1] Guide to Proficiency Testing Australia, 2012 (This document can be found on the PTA website, www.pta.asn.au).

[2] APHA “Standard Methods for the Examination of Water and Wastewater” 22nd Edition.

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APPENDIX A

Results and Data Analysis Total Recoverable Oil and Grease Sample PTA 1 ................................................................ A1


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Total Recoverable Oil and Grease Results

Sample PTA 1

A1

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Results by Laboratory Code

Sample PTA 1

Lab Code

Result ± MU1 (mg/L)

Robust z-score2

Method Code3

112 15 ± 4 -1.63 9 118 21.9 ± 5.2 0.31 1 136 20.1 ± 5.3 -0.20 1 142 26.6 ± 2.7 1.63 4 150 20 ± 10 -0.22 5 159 43.9 ± 1.8 6.49 § 10 181 19.8 ± 4.75 -0.28 1 188 47.0 # 7.36 § 3 224 21.0 # 0.06 1 237 23.4 ± 2.5 0.73 1 241 19.6 ± 2.0 -0.34 1 242 17.3 # -0.98 1 250 25.7 ± 0.4 1.38 3 255 41.4 ± 8.3 5.79 § 1 273 20.5 ± 6.0 -0.08 1 278 22.8 ± 6.0 0.56 1 285 19.0 ± 3.0 -0.51 9 286 23.7 ± 5.9 0.82 1 306 28.0 ± 4.8 2.02 3 330 20.6 # -0.06 9 335 46.2 ± 6.4 7.14 § 9 368 19.2 ± 3 -0.45 1 372 22.1 ± 1.1 0.37 1 390a 21.5 # 0.20 11 390b 22.1 # 0.37 11 403 19 ± 1 -0.51 1 405 15.0 # -1.63 1 409 26.7 ± 2.0 1.66 11 422 20.0 # -0.22 9 436 20.7 ± 1.6 -0.03 9

1 Where reported, results are shown with their corresponding

measurement uncertainty (MU). 2 "§"s denote outliers (i.e. those results for which |z-score| ≥ 3.0). Robust

z-scores are calculated as: z = (A - median) ÷ normalised IQR, where A is the participant laboratory's result.

3 Please refer to Appendix C (page C3) for method code descriptions.

A2

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Total Recoverable Oil and Grease - cont.


Sample PTA 1

Lab Code


Robust z-score2

Method Code3

438 21.4 ± 4.3 0.17 9 452 25.5 ± 0.4 1.32 11 472 24.4 ± 3 1.01 9 507 21.4 # 0.17 1 512 20.8 ± 0.7 0.00 3 523 16 ± 1.4 -1.35 1 548a 16.5 # -1.21 1 548b 17.5 # -0.93 1 568 20.3 ± 1.8 -0.14 1 569 23.8 ± 4.8 0.84 3 596 6.4 ± 3.2 -4.05 § 11 608 3.8 ± 0.8 -4.78 § 5 621 20.8 # 0.00 9 626 18.7 # -0.59 1 634 25.0 ± 2 1.18 5 639 14.6 # -1.74 1 651 28.8 ± 1.7 2.25 5 656 20.8 ± 0.8 0.00 4

No of Results: 48

Median: 20.80

Uncertainty of the Median:

0.64

Normalised IQR:

3.56

Robust CV: 17.1%

Minimum: 3.8

Maximum: 47.0

Range: 43.2


measurement uncertainty (MU). 2 "§"s denote outliers (i.e. those results for which |z-score| ≥ 3.0).

Robust z-scores are calculated as: z = (A - median) ÷ normalised IQR, where A is the participant laboratory's result.


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Total Recoverable Oil and Grease - PTA 1 - Robust Z -Scores

Robust Z-Scores

Ordered R

obust Z-S

core Charts

A3

Total R

ecoverable Oil and G

rease - PT

A 1

608 59

6

639

112

405 523

548a 24

2

548b 62

6

285

403

368

241

181

150

422

136

568

273

330

436

512

621

-5

-4

-3

-2

-1

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3

4

5

z-sc

ore

lab code

-5

-4

-3

-2

-1

0

1

2

3

4

5

z-sc

ore

lab code

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Total Recoverable Oil and Grease Results

Sample PTA 2

A4

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Sample PTA 2

Lab Code


Robust z-score2

Method Code3

112 89 ± 18 0.32 9 118 92.6 ± 17.9 0.62 1 136 84.2 ± 4.0 -0.07 1 142 82.0 ± 8.2 -0.26 4 150 56 ± 15 -2.42 5 159 48.9 ± 1.8 -3.01 § 10 181 81.2 ± 19.49 -0.32 1 188 52 # -2.75 3 224 84.6 # -0.04 1 237 91.2 ± 9.2 0.51 1 240 64.4 # -1.72 1 241 76.6 ± 7.0 -0.71 1 242 73.9 # -0.93 1 250 93.1 ± 0.4 0.67 3 255 106.8 ± 21.4 1.80 1 273 90.2 ± 26.4 0.42 1 278 86.0 ± 22.4 0.07 1 285 85.0 ± 13.6 -0.01 9 286 89.3 ± 22.3 0.35 1 306 95.4 ± 16.2 0.86 3 330 92.1 # 0.58 9 335 96.2 ± 13.3 0.92 9 368 89.0 ± 15 0.32 1 372 86.8 ± 4.3 0.14 1 390a 91.0 # 0.49 11 390b 90.0 # 0.41 11 403 60 ± 1 -2.09 1 405 61.7 # -1.95 1 409 74.4 ± 2.0 -0.89 11 422 89.0 # 0.32 9


measurement uncertainty (MU). 2 "§"s denote outliers (i.e. those results for which |z-score| ≥ 3.0). Robust

z-scores are calculated as: z = (A - median) ÷ normalised IQR, where A is the participant laboratory's result.


A5

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Total Recoverable Oil and Grease - cont.


Sample PTA 2

Lab Code


Robust z-score2

Method Code3

436 74.0 ± 5.9 -0.92 9 438 90.2 ± 18.0 0.42 9 452 74.4 ± 1.1 -0.89 11 472 93.0 ± 9 0.66 9 507 80.1 # -0.42 1 512 88.7 ± 2.8 0.30 3 523 66 ± 2.8 -1.59 1 548a 69.8 # -1.27 1 548b 73.0 # -1.01 1 568 92.2 ± 8.5 0.59 1 569 85.2 ± 17 0.01 3 578 85.8 ± 7.8 0.06 1 596 34.3 ± 3.2 -4.22 § 11 621 95.7 # 0.88 9 626 74.5 # -0.88 1 639 75.0 # -0.84 1 651 87.0 ± 5.0 0.16 5 656 73.0 ± 0.8 -1.01 4

No of Results: 48

Median: 85.10

Uncertainty of the Median:

2.18

Normalised IQR:

12.03

Robust CV: 14.1%

Minimum: 34.3

Maximum: 106.8

Range: 72.5


measurement uncertainty (MU). 2 "§"s denote outliers (i.e. those results for which |z-score| ≥ 3.0).

Robust z-scores are calculated as: z = (A - median) ÷ normalised IQR, where A is the participant laboratory's result.


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Total Recoverable Oil and Grease - PTA 2 - Robust Z -Scores

Robust Z-Scores

A6

Total R

ecoverable Oil and G

rease - PT

A 2

Ordered R

obust Z-S

core Charts

596

159

188 15

0 403

405

240

523

548a

548b 656

242

436

409

452

626

639

241 507

181

142

136

224

285

-5

-4

-3

-2

-1

0

1

2

3

4

5

z-sc

ore

lab code

-5

-4

-3

-2

-1

0

1

2

3

4

5

z-sc

ore

lab code

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APPENDIX B

Sample Homogeneity and Stability

B1

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Homogeneity and Stability Testing

Samples for this program were obtained from Global Proficiency Ltd, New Zealand. All samples underwent quality control weight checks to ensure a consistent mass of oil and grease was delivered to each vial. Sample PTA 1 contained 21.7 ± 0.2 mg/L (3x Standard deviations = 99% CI) of mineral oil, and sample PTA 2 contained 92.6 ± 0.3 mg/L (99% CI) of a mixture of vegetable oil and anhydrous milk fat. Random selections of ten samples were chosen from sample PTA 1. Seven were stored chilled and three were subjected to 35ºC for 3 days for an accelerated ageing stability trial. Samples were then analysed by Hill Laboratories for Oil and Grease, using method APHA 5520D 21st ed. 2005. All stability samples showed no increased variability when compared to chilled samples. Based on the assumption that the rate of ageing doubles with every 7ºC elevated temperature, these samples were assumed stable for more than 96 days (3days*2(35/7)) from the date of manufacture (1 November 2012).

Table H-1. Extraction (Test) and QC Weight Check Results of Oil and Grease Samples.

Round PTA 150

PTA 1 PTA 2

Sample ID

QC weight

check mg

Tested result mg/L Sample ID

QC weight

check mg

Tested result mg/L

Homogeneity PTA 1 (h1) 21.7 16 PTA 2 (a) 92.4 88 PTA 1 (h2) 21.7 16 PTA 2 (b) 92.4 87 PTA 1 (h3) 21.6 13 PTA 1 (h4) 21.6 13 PTA 1 (h5) 21.6 16 PTA 1 (h6) 21.6 17 PTA 1 (h7) 21.6 16

Stability PTA 1 (s1) 21.7 26 PTA 1 (s2) 21.6 20 PTA 1 (s3) 21.7 18 RSD 0.24% 22%

From statistical analyses based on the results of this testing and rigorous quality control, it was considered that all samples were sufficiently homogenous and stable, so that any results later identified as outliers should not be attributed to any notable sample variability.

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APPENDIX C

Documentation Instructions to Participants ................................................................................................... C1

Method Codes ....................................................................................................................... C3

Results Sheet ........................................................................................................................ C4

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C1

C2

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4. Safety i) Samples are for laboratory use only. ii) Participants should have sufficient experience and training to take the necessary

precautions when handling the samples and reagent chemicals and during disposal.

iii) Use of safety glasses, gloves, and fume hoods, where appropriate during the

determinations, is recommended. 5. Reporting

i) Report results using one decimal place, e.g 10.1 mg/L.

ii) Report results in milligrams/litre (mg/L) - i.e., the total mg extracted/sample treated as 1L for reporting.

iii) Do not correct results for recovery.

iv) In addition to reporting the results, record the method of analysis using the

attached codes.

v) Laboratories are also requested to calculate and report an estimate of measurement uncertainty (MU) for each reported measurement result. All estimates of MU must be given as a 95% confidence interval (coverage factor k ≈ 2) and reported in mg/L.

6. Testing should commence as soon as possible after receiving the samples and results

reported NO LATER THAN 14 DECEMBER 2012 to:

Delfina Mihaila Proficiency Testing Australia PO Box 7507 SILVERWATER NSW 2128 AUSTRALIA Phone: +612 9736 8397 Fax: +612 9743 6664 Email: [email protected]

7. For this program your laboratory has been allocated the code number shown on the

attached Results Sheet. All reference to your laboratory in reports associated with the program will be through this code number, thus ensuring the confidentiality of your results.

8. As a guide, ranges for the samples can be expected to be (in mg/L):

Analyte Range

Total Recoverable Oil and Grease 10-100

C3

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Method Codes to be used for the Results Sheet

ANALYSIS METHOD DESCRIPTION

METHOD REFERENCE CODE


Partition-Gravimetric APHA 5520B (Liquid-Liquid) 1

APHA 5520G (Solid Phase) 2

Hexane Extraction & Gravimetry

US EPA 1664A 3

Infrared APHA 5520C 4

ASTM D 7066-04 5

ASTM D 3921-96 6

US EPA 413.2 7

US EPA 418.1 8

Soxhlet Extraction APHA 5520D 9

Modified Method Please also specify original method 10

Other or In-house Please specify 11

Method Reference Key i) APHA SM APHA “Standard Methods for the Examination of Water and Wastewater” (18, 19,

20, 21 and 22 Edition).

ii) US EPA U.S Environmental Protection Agency,

http://www.epa.gov/osa/fem/methcollectns.htm.

iii) ASTM American Society for Testing and Materials, Annual Book of ASTM Standards, Vol 11.01 and Vol 11.02.

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C4

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- End of Report -

Report No. 799 Waters Proficiency Testing Round 150...

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