Trivalent chromium solubility and its influence on quantification of hexavalent chromium in ambient particulate matter using EPA method 6800

Figures & data

Figure 1. The IC-ICPMS chromatogram of 1.0 ppb Cr standard.

Figure 2. The IC-ICPMS chromatogram of a typical Teflon field sample that was extracted with DI-H₂O.

Table 1. The concentrations of Cr³⁺ that equilibrate with Cr(OH)_3(s) under differential pH in solution

Equilibrium:	Cr(OH)3(s) ↔ Cr^3+ + 3OH^− Ksp = [Cr^3+][OH^−]^3 = 6.3 × 10^−31 M^4 (25ºC)
pH	0	1	2	3	4	5	6	7	8	9	10	11	12	13	14
[Cr^3+] (ng/mL)	3 × 10^19	3 × 10^16	3 × 10^13	3 × 10^10	3 × 10^7	3 × 10^4	30	3 × 10^−2	3 × 10^−5	3 × 10^−8	3 × 10^−11	3 × 10^−14	3 × 10^−17	3 × 10^−20	3 × 10^−23

Figure 3. The Eh–pH diagram of chromium (Huang et al., 2014).

Figure 4. The concentrations of Cr(VI) in ambient air determined by EPA method 6800 (SIDMS) and the external standard curve.

Table 2. Chromates and their solubility products (25°C)

Name	Chemical form	Solubility product
Mercury(I) chromate	Hg2CrO4	2.0 × 10^−9 M^3
Strontium chromate	SrCrO4	2.2 × 10^−5 M^2
Silver chromate	Ag2CrO4	1.1 × 10^−12 M^3
Barium chromate	BaCrO4	1.17 × 10^−10 M^2
Lead(II) chromate	PbCrO4	3 × 10^−13 M^2
Thallium(I) chromate	Tl2CrO4	8.67 × 10^−13 M^3
Ammonium chromate	(NH4)2CrO4	75.7 M^3
Calcium chromate	CaCrO4	7.1 × 10^−4 M^2
Copper(II) chromate	CuCrO4	3.6 × 10^−6 M^2
Potassium chromate	K2CrO4	136 M^3
Sodium chromate	Na2CrO4	626 M^3

Note: Solubility product data are from Lide (2004).

Huang, L., C. H. Yu, P. K. Hopke, P. J. Lioy, B. T. Buckley, J.Y. Shin, and Z. Fan. 2014. Measurement of soluble and total hexavalent chromium in the ambient airborne particles in New Jersey. Aerosol and Air Quality Research. doi:10.4209/aaqr.2013.10.0312.

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Lide, D.R. 2004, CRC Handbook of Chemistry and Physics. Boca Raton, FL: CRC Press

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