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Table 2017.02B. Preparation of working standards

Final working std concn, mg/L

Intermediate std, G ( l ), mL

Stock std, G ( m ), mL

HNO a , G ( b ), mL 3

HCl a , G ( c ), mL

Std

Final vol., mL

Blank

0

0 5

0

0

90 45

30 15

1000

1

0.1 A/0.5 B

500

2

0.5 A/1 B

25

45

15

500

3

1 A/3 B

50

90

30

1000

4

5 A & B

5

90

30

1000

5

10 A & B

5

45

15

500

6

30 B

3

90

30

1000

7

50 B

5

90

30

1000

8

80 B

4

45

15

500

9

100 B

10

90

30

1000

10

200 B

10

45

15

500

11

300 B

15

45

15

500

12

400 B

20

40

15

500

30

40

15

500

13

600 B

14

10 A

5

45

15

a  Since commercial stock standards are often stored or preserved in acids, the volume of HNO 3

and HCl added to the calibration standards should be adjusted to

and/or HCl from the commercial stock standard source.

include any contribution of HNO 3

of white/white, 1.02 mm id sample pump tube, and orange/white, 0.64 mm id internal standard pump tube. If the test solutions and internal standard solutions are mixed in different proportions by the instrument’s peristaltic pump, then adjust the reagent concentrations to meet concentration requirements of mixed solution nebulized by the instrument, as outlined in F . Note that sample and internal standard solution mixing ratio is proportional to pump tube flow rates, not proportional to pump tube IDs.) ( j )  Stock standard solutions, As, Cd, Co, Cr, Pb, Mo, Ni, and Se .—Working standards can be prepared from ICP grade 1000 mg/L commercial stock standard solutions for As, Cd, Co, Cr, Pb, Mo, Ni, and Se. A number of companies provide this stock standard service. ( k )  Stock standard solutions, Ca, Cu, Fe, Mg, Mn, and Zn .— Working standards can be prepared from 10 000 mg/L individual element ICP grade commercial stock standard solutions for Ca, Cu, Fe, Mg, Mn, and Zn. However, it is also acceptable to use commercially prepared custom blended stock standard mixtures containing some or all elements at stock concentrations. Anumber of companies provide this stock standard service. ( l )  10 mg/L intermediate standard solution for preparation of low-level working standards for As, Cd, Co, Cr, Pb, Mo, Ni, and Se .—Dilute 5.0 mL of stock 1000 mg/L standard solution, G ( j ), to 500 mL. Prepare fresh each time standards are prepared, and use immediately after preparation. ( m )  50 mg/L intermediate standard solution for preparation of low-level working standards for Ca, Cu, Fe, Mg, Mn, and Zn .— Dilute 5.0 mL of stock 10 000 mg/L standard solution to 1000 mL. Prepare fresh each time standards are prepared, and use immediately after preparation. ( n )  Working standard solutions (see Table 2017.02B ) for Ca, Cu, Fe, Mg, Mn, and Zn .—Standards should have the same acid concentration as digested test solutions. Date all calibration solutions whenmade, which are stable at roomtemperature for 60days.Monitor

standard curve fit and intensity for signs of change and degradation over time. ( Note : Based on instrumentation, the calibration standards may be adjusted to fit the manufacturer guidelines regarding standard curve requirements. However, linear curves should have correlation coefficients of at least 0.999 and a standard error of no more than 10%. Quadratic calibrations should have a correlation coefficient of at least 0.999, a standard error of less than 10%, a curvature of no more than 25%, and an upward curvature of no more than 400%.) ( 1 )  10 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 100.0 mL intermediate standard solution, G ( m ), into a 500 mL acid-washed volumetric flask. Add 45 mL trace metal grade HNO 3 and 15 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to acid-washed polypropylene bottle. ( 2 )  5 mg/L Ca, Cu, Fe, Mg, Mn, and Zn. —Pipet 100 mL of combined 50 mg/L element stock solution into a 1000 mL acid-washed volumetric flask. Add 90 mL trace metal grade HNO 3 and 30 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 3 )  1 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 50.0 mL of 10 mg/L intermediate stock solution into a 500 mL acid-washed volumetric flask. Add 45 mL trace metal grade HNO 3 and 15 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 4 )  0.5 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 25.0 mL of 10 mg/L intermediate stock solution into a 500 mL acid-washed volumetric flask. Add 45 mL trace metal grade HNO 3 and 15 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle. ( 5 )  0.1 mg/L Ca, Cu, Fe, Mg, Mn, and Zn .—Pipet 5.0 mL of 10 mg/kg intermediate stock solution into a 500 mL acid-washed volumetric flask. Add 45 mL trace metal grade HNO 3 and 15 mL trace metal grade HCl, dilute to volume with H 2 O, mix, and transfer to an acid-washed polypropylene bottle.

© 2017 AOAC INTERNATIONAL

03/10/2019