1. UNDP/GEF Yellow Sea Project Inter-Calibration Exercises for Metals Analysis
Zhifeng Zhang
Division of Marine Environmental Chemistry
National Marine Environmental Monitoring Center, SOA
Dalian, China,

2. Contents Sample Preparation and Storage Instrumentation and Reagents
Operating Procedure
Quality Control
Results and Discussion
NMEMC

3. 1. Sample Preparation and Storage
Moisture content determination
1.0g(0.0001g) of a separate subsample (not used for analysis) was weighed, and dried at 105℃ (~24h) until a constant weight was obtained.
Storage
The biota and sediment samples (solid samples) were stored in a desiccator in the dark and kept below 25℃;
The Standard solution was stored in a refrigerator at 4 ℃.
NMEMC

4. 2. Instrumentation and Reagents
Atomic Absorption Spectrophotometer
Flame AAS for Zn
Graphite Furnace AAS for Cu, Pb, Cr, Cd
The following matrix modifiers were used:
Pd and Mg(NO3)2 for Cu
Mg(NO3)2 and NH4H2PO4 for Pb, Cd
Mg(NO3)2 for Cr
Atomic Fluorescence Spectrometer
Hydride Generation technique was used for As
Cold Vapor technique was used for Hg
NMEMC

5. CV-AAS (SP-II, Rigaku, Japan)
Instrumentation and Method Detection Limits (MDL) for Metals
Instrumentation
MDL (mg/kg)
Instrument
Technique Zn
FAAS (WFX-110, BJ, China)
0.162 Cu
GF-AAS (4110ZL, PE, US)
Matrix modifier
0.008 Pb
0.029 Cd
0.004 Cr
0.066 As
AFS (XGY 1011A, LF, China)
Hydride Generation
0.047 Hg
CV-AAS (SP-II, Rigaku, Japan)
Cold Vapor
0.005
NMEMC

6. Other Lab-wares Microwave Digester (CE Corp., US): for biota samples
Heating Plate (Lab-Tech Corp., US): for sediments
Pipettes and flasks
PTFE vessels
Rinsed thoroughly by 1:1 HNO3
All the lab wares were calibrated and accredited by:
Chinese General Administration of National Quality and Technology Supervision
NMEMC

7. Reagent water Acid Other Reagents
Pure water (Millipore, Resistivity > 18 M)
Acid
Nitric acid, HNO3 (sub-boiling distillation)
Hydrofluoric acid, HF (GR)
Perchloric acid, HClO4 (GR)
Sulphuric acid, H2SO4 (GR)
Hydrogen peroxide, H2O2 (30%)
Other Reagents
At least Analytical Reagent Grade of purity
Reagent blanks were checked for each batch.
Tin dichloride
NMEMC

8. Standard Stock Solution
All the stock standard solutions are freshly prepared.
Expiration: Cu, Zn, Pb, Cr, Cd, As, two weeks;
Hg prepared freshly when used.
Working solutions
Prepared daily, including reagent and standard solutions
NMEMC

9. 3. Operating Procedure
Acid Digestion for sediment and biological samples
Sediment samples were digested on a hotplate
Biological samples were digested with microwave digester.
The samples were specially digested for the determination of Hg
Detection of digested solutions by various instrumental techniques.
NMEMC

10. Schematic operating procedures
Sediment Sample
Biota Sample
HNO3, r.t.
HNO3:H2O2, r.t.
Initial Digestion overnight
Initial Digestion: 30 min
Rising to 120℃
in 6 min
HNO3, 180℃
Reflux for 3~4 h
Digestion for 6 min
Rising to 180℃
in 6 min
HNO3:HF:HClO4,
Complete Digestion: 3~4 h
Digestion for 15 min
Transfer to PTFE vessel after cooling
200℃, for <2 h
Potassium permangnate
Remove of excess acids
1:1 HNO3
Dissolve and Dilution
Zn, Cd, Cr, Cu As
Detection by AAS
Detection by HG-AFS
NMEMC

11. Schematic operating procedures for Hg
Sediment Sample
Biota Sample
HNO3, 90±5℃
HNO3, r.t.
Initial Digestion overnight
Water-bath Digestion: 30 min
HNO3, 90±5℃
H2O2, 90±5℃
Water-bath Digestion: 1.5 h
Water-bath Digestion: 30 min
H2O2, 90±5℃
KMnO4
Water-bath Digestion: 30 min
Stabilization of Hg2+
KMnO4
NH2OH.HCl
Stabilization of Hg2+
Pre-reduction of Hg2+
NH2OH.HCl
Pre-reduction of Hg2+
SnCl2
SnCl2
Detection by CV-AAS
Detection by CV-AAS
NMEMC

12. The acid digestion procedure for sediment samples:
Mix the sample thoroughly to achieve homogeneity by shaking
Weigh 0.1g (0.0001g) sample (dry weight) to the PTFE vessel, add 5.0mL of concentrated nitric acid (HNO3), and cover with a lid, place at room temperature overnight.
Heat the sample on a hotplate to 180℃±1℃ and reflux for 3~4h, then add 1.0mL of concentrated nitric acid (HNO3), 1.0mL of hydrofluoric acid (HF) and 2.0mL of perchloric acid (HClO4) to the digestion vessel, replace the lid, and reflux for 3~4h.
Open the vessel to evaporate the hydrofluoric and percholric acid when the solution was dried, transfer the solution into a 50mL PET sample bottle after the addition of 1.0mL of (1+1) nitric acid solution to dissolve the solids, and dilute to 30g with Milli-Q water for determination.
NMEMC

13. Microwave digestion procedure for biological samples:
Mix the sample thoroughly to achieve homogeneity by shaking
Weigh 0.2g (0.0001g) sample (dry weight) to the PTFE vessel, add 8.0mL of concentrated nitric acid (HNO3) and 2.0mL hydrogen peroxide (30%), place at room temperature for 30min.
Seal the vessels tightly, heat the samples to 120℃ in approximately less than 6min and remaining at 120±5℃ for 6min, and then rise the temperature to 180℃ in approximately less than 6min and remaining at 180±5℃ for 15min.
After cooling, transfer the solution into the PTFE vessel for evaporating, when the solution was dried, transfer the solution into a 50mL PET sample bottle by 1.0mL of (1+1)nitric acid solution was added, and diluted to 30g with Milli-Q water for determination.
NMEMC

14. 4. Quality Control Laboratory Reagent blanks
Laboratory Reagent blanks (LRB) were processed with samples at a frequency of at least 5% to assess contamination from the lab environment. The results of the laboratory Reagent blank should be lower than 30% of the lowest analyte concentration.
Laboratory Fortified Sample Matrix (LFM)
Definition
sample to which know quantities of the analyte standard were added in the lab;
To assess the effects of sample matrix;
Requirements
LFM replicates for one set of samples;
The recovery of the added standard should be in the range of 80~120%.
NMEMC

15. Data Validation Calibration
Data was obtained by calculating the signal intensity of the seawater samples with the regression equation, and the calibration should be verified at a frequency of every 10 samples with the initial calibration solution. The results of the initial calibration verification solution must agree within ± 5% of the expected value. If not, terminate the analysis, correct the problem, and recalibrate the instrument. Any sample analyzed under an out-of-control calibration must be reanalyzed.
For low concentrations
An additional set of calibration solutions were prepared for the determination of nutrients at low concentration.
NMEMC

16. Replicates measured
One duplicate sample in a batch at a frequency of one matrix duplicate for every 20 samples. A control limit of 20% relative percent difference (RPD) should not be exceeded for analyte values greater than 100 times the instrumental detection limit. The RPD can be calculated as follows
Where: RPD= relative percent difference
D1 = first sample value
D2 = second sample value (duplicate)
NMEMC

17. Control sample Quality Control chart Data source
Certified Reference Material (CRM) was employed as the laboratory quality control sample along with the inter-comparison samples
Quality Control chart
Data source
Laboratory determined recoveries of LFM in one month
Application
Recoveries of LFM in this study should not be out of the control limits of the QC chart.
NMEMC

18. 5. Results and Discussion
Results of sediment samples
Moisture content(%):
Average weight of sample (g): 0.1
Certified Reference Material used for Quality Assurance: IAEA-433
Inter-comparison Sample Number: SD YSLME /TM-1
NMEMC

19. Results for sediment sample SD YSLME /TM-1
Elements
Unit
Mean value
Standard
Deviation
Detection limit As
mg·kg-1
24.78
2.02
0.047 Cd
0.82
0.03
0.004 Cr
82.60
4.20
0.066 Cu
43.52
1.90
0.008 Hg
0.954
0.027
0.005 Pb
71.45
1.28
0.029 Zn
265.00
12.78
0.162
NMEMC

20. Results for CRM sample IAEA-433
Elements
Unit
Mean value
Standard
Deviation
Certified
Value As
mg·kg-1
19.13
1.08
18.4 ~ 19.4 Cd
0.152
0.005
0.145 ~ 0.161 Cr
134.85
3.58
134 ~ 138 Cu
29.24
0.42
30.2 ~ 31.4 Hg
0.168
0.004
0.164 ~ 0.172 Pb
25.94
0.38
25.4 ~ 26.6 Zn
101.53
1.79
99 ~ 103
NMEMC

21. Results of biological samples
Moisture content(%): 8.5
Average weight of sample (g): 0.2
Certified Reference Material used for Quality Assurance: ERM-CE278
Inter-comparison Sample Number: MA YSLME /TM-1
NMEMC

22. Results for Biological samples MA YSLME /TM-1
Elements
Unit
Mean value
Standard Deviation
Detection limit As
mg·kg-1
14.47
1.15
0.008 Cd
0.76
0.02
0.002 Cr
0.45
0.03
0.017 Cu
3.54
0.11
0.005 Hg
0.085
0.004
0.01 Pb
1.01
0.05
0.003 Zn
148.53
7.10
0.097
NMEMC

23. Results for CRM sample ERM-CE278
Elements
Unit
Mean value
Standard
Deviation
Certified
Value As
mg·kg-1
5.73
0.18
5.94 ~ 6.20 Cd
0.343
0.015
0.341 ~ 0.355 Cr
0.75
0.05
0.72 ~ 0.84 Cu
9.33
0.19
9.32 ~ 9.58 Hg
0.196
0.005
0.187 ~ 0.205 Pb
2.02
0.09
1.96 ~ 2.04 Zn
83.10
1.88
81.4 ~ 84.8
NMEMC

24. Quality Control Chart Zn: 703 g/L Cu: 5.00.4 g/L Cr: 5.00.4 g/L
Cd: 1.00.06g/L
NMEMC

25. Results for Standard Solution (g/L)
Elements
Replicates Cr Cu Zn As Cd Pb Hg 1
5.96
8.26
9.71
4.83
0.849
3.58
0.811 2
6.06
8.42
9.87
5.31
0.864
3.65
0.808 3
6.16
7.99
9.16
5.26
0.897
3.37
0.810 4
5.90
7.90
8.94
4.78
0.868
3.28
0.818 5
6.24
7.85
10.98
4.82
0.873
3.68
0.802 6
8.08
9.73
5.00
0.870
3.51
0.807
Average
0.809 SD
0.12
0.22
0.71
0.24
0.016
0.16
0.005
NMEMC

26. 6. Problems
The prevention of contamination during the sample pre-treatment and determination process
Possibility for simultaneous determination of As, Hg and other metals?
NMEMC

27. Thank you! zfzhang@nmemc.gov.cn http://www.nmemc.gov.cn
National Marine Environmental Monitoring Center