Determination of trace anions in G2-grade phosphoric acid using two-dimensional ion-exclusion-ion-exchange chromatography with valve-switching technology

doi:10.3724/SP.J.1123.2024.04010

Abstract

Abstract:

This study established a method for determining trace anions in G2-grade phosphoric acid under ultra-clean conditions that used two-dimensional ion-exclusion-ion-exchange chromatography coupled with valve-switching technology. The optimal flow rate of ultrapure water through the ion-exclusion column in the first dimension was determined to be 0.5 mL/min through comparative experiments. The valve-switching window was optimized to minimize enriching PO₄^3- on the anion-enrichment column and reduce interference from the phosphoric-acid matrix. The use of external water mode for the suppressor led to lower baseline noise, and optimizing the elution program of the second dimension enabled target trace anions to be well separated, thereby avoiding the risk of a false positive for NO^3-. The anions of Cl^-, Br^-, NO^3-, and SO₄^2- exhibited good linearities within the 0.5-20 μg/kg, with correlation coefficients ≥0.999. The limits of detection (LODs) and quantification (LOQs) were 0.09-0.29 μg/kg and 0.29-0.97 μg/kg, respectively. The spiked recoveries of each anion at four spiked levels ranged from 91.7% to 103.6%, with RSDs of 0.1%-4.9%. The developed method demonstrated excellent stability through repeated injections, and low detection limits; it is highly precise and accurate, and meets the detection requirements for trace anions in G2-grade phosphoric acid. Additionally, retention-time comparisons with single standard substances led to the discovery of other phosphorus-related anions and anion clusters, such as hypophosphite (HPO₃^-) and hexametaphosphate (PO₃^-)₆, in G2-grade phosphoric acid, in addition to conventional anions. This finding is theoretically and practically significant for the future development of purification processes for higher-purity phosphoric acid.

Key words: electronic grade phosphoric acid, trace anions, valve switching, two-dimensional ion chromatography (2D-IC)

CLC Number:

O658

WANG Jiading, TANG Gao, LU Yan, LU Hengjun, YE Tao. Determination of trace anions in G2-grade phosphoric acid using two-dimensional ion-exclusion-ion-exchange chromatography with valve-switching technology[J]. Chinese Journal of Chromatography, 2025, 43(3): 237-244.

Figures/Tables 9

Fig. 1 Structure diagram of 2D-IC valve-switching system Solid line indicates the load state, dashed line indicates the inject state.

Table 1 Analytical system eluent gradient and valve-switching operation procedure table

Time/min	c(OH^-)/(mmol/L)	Valve 1	Event of 1D system	Valve 2	Event of IC system
-9.0	8.0	inject	/	inject	analyzing system balance
-2.0	8.0	inject	matrix separation window start	load	target anion enrichment
0	8.0	inject	matrix separation window end	inject	target ion analysis
5.0	8.0	load	preparing a new sample for injection	inject	target ion analysis
10.0	8.0	load	equilibrium exclusion column	inject	target ion analysis
60.0	60.0	load	equilibrium exclusion column	inject	target ion analysis
63.0	60.0	load	equilibrium exclusion column	inject	target ion analysis
63.1	8.0	load	equilibrium exclusion column	inject	target ion analysis

Fig. 2 Elution profiles of anionic mixed solution and phosphoric acid solution at different flow rates on the ion exclusion column Detector connected after ion exclusion column.

Fig. 3 Chromatograms of anionic phosphoric acid mixed solution at different flow rates in the first dimension a. 0.3 mL/min (10.5-16.5 min in Fig. 2a); b. 0.4 mL/min (8-12.5 min in Fig. 2b); c. 0.5 mL/min (7-10 min in Fig. 2c); d. 1 mL/min (3.5-5.5 min in Fig. 2d). Elution gradient: 0-8 min, 8 mmol/L KOH, 8-30 min, 8-60 mmol/L; sample: 100 μg/kg anionic mixed standard solution in 33% (v/v) phosphoric acid solution.

Fig. 4 Chromatograms of continuous analysis of 33% (v/v) phosphoric acid solution under two valve switching windows a. valve switching window of 7-10 min, first injection; b. valve switching window of 7-10 min, second injection; c. valve switching window of 7-9 min, first injection; d. valve switching window of 7-9 min, fifth injection. Elution gradient: 0-8 min, 8 mmol/L KOH, 8-30 min, 8-35 mmol/L KOH; suppressor curren: 87 mA; sample: 33% (v/v) phosphoric acid solution.

Fig. 5 False positive interference of NO3- caused by unknown ion (possibly HPO3-) a. 20 μg/kg anionic mixed standard solution in 1% (v/v) phosphoric acid solution; b. 1% (v/v) phosphoric acid solution; c. 20 μg/kg anionic mixed standard solution in pure water matrix. Elution gradient: 0-8 min, 8 mmol/L KOH, 8-35 min, 8-60 mmol/L KOH, 35-38 min, 60 mmol/L KOH.

Fig. 6 Final elution gradient and sample spiked test plot a. 1% (w/w) phosphoric acid solution; b. 20 μg/kg anionic mixed standard solution in 1% (w/w) phosphoric acid solution.

Table 2 Linear equations, linear ranges, correlation coefficients (r), limits of detection (LODs) and limits of quantification (LOQs) for the four anions

Anion	Linear equation	Linear range/ (μg/kg)	r	LODs/(μg/kg)		LOQ/(μg/kg)
Anion	Linear equation	Linear range/ (μg/kg)	r	This study	Literature	LOQ/(μg/kg)
Cl^-	y=0.005x-0.0003	0.5-20	0.99974	0.09	3^[5], 60^[14], 12^[15], 7^[19]	0.29
Br^-	y=0.0024x-0.0003	0.5-20	0.99978	0.29	/	0.97
N	y=0.0031x+0.0004	0.5-20	0.99978	0.15	4^[5], 40^[14], 19^[15], 3^[19]	0.50
S	y=0.0043x+0.0148	0.5-20	0.99978	0.16	90^[5], 680^[14], 30^[15], 3^[19]	0.54

Table 3 Spiked recoveries of anions in phosphoric acid samples at four levels (n=5)

Anion	Background/ (μg/kg)	Spiked/ (μg/kg)	Recovery/ %	RSD/ %
Cl^-	0	0.52	91.7	4.9
	0	4.07	99.6	1.1
	0	10.18	100.0	0.4
	0	16.33	99.3	0.1
Br^-	0	0.52	93.3	2.3
	0	4.13	93.2	2.0
	0	10.34	95.6	0.4
	0	16.59	99.3	0.2
N	0	0.52	94.0	2.8
	0	4.10	103.6	2.3
	0	10.28	101.2	0.4
	0	16.48	99.4	0.3
S	3.19	0.48	98.1	4.3
	3.12	3.76	96.2	1.3
	3.17	9.42	97.2	0.3
	3.17	15.11	98.9	0.2

References

[1]	Yu L Y, Liu S B, Jia S Z, et al. Journal of Chemical Industry and Engineering, 2024, 75(1): 2
[1]	余留洋, 刘书博, 贾晟哲, 等. 化工学报, 2024, 75(1): 2
[2]	Xiao L H, Zeng B. Yunnan Chemical Industry, 2007, 34(6): 4
[2]	肖立华, 曾波. 云南化工, 2007, 34(6): 4
[3]	Fan X H, Zhou C, Yuan J, et al. Adhesion, 2019, 40(5): 4
[3]	范相虎, 周聪, 袁军, 等. 粘接, 2019, 40(5): 4
[4]	Zhang D Z, Long H, Lu W X, et al. Chemical Fertilizer Design, 2022, 60(4): 4
[4]	张大洲, 龙辉, 卢文新, 等. 化肥设计, 2022, 60(4): 4
[5]	SEMI C36-1213
[6]	Liu Y X, Yu N S, Liu W, et al. Phosphate & Compound Fertilizer, 2016, 31(11): 40
[6]	刘永秀, 于南树, 刘伟, 等. 磷肥与复肥, 2016, 31(11): 40
[7]	GB/T 2091-2008
[8]	Zhang L X, Wang C W, Wang W G, et al. Inorganic Chemicals Industry, 2009, 41(3): 56
[8]	张岚欣, 王存文, 王为国, 等. 无机盐工业, 2009, 41(3): 56
[9]	Yoon S H, Jo D H, Kim H J, et al. JAST, 2016, 29(5): 219
[10]	Siriraks A, Stillian J. J Chromatogr A, 1993, 640(1/2): 151
[11]	Vanatta L E, Coleman D E, Woodruff A. J Chromatogr A, 2003, 997(1/2): 269
[12]	Gao Y M, Hao P, Tian Y P, et al. Shanghai Measurement and Testing, 2021, 48(3): 6
[12]	高一鸣, 郝萍, 田玉平, 等. 上海计量测试, 2021, 48(3): 6
[13]	Geng P L, Cheng H P. Shandong Chemical Industry, 2020, 49(12): 69
[13]	耿平兰, 程化鹏. 山东化工, 2020, 49(12): 69
[14]	Stover F S. J Chromatogr A, 2002, 956(1/2): 121
[15]	Zhou F Q, Zhao M. Physical Testing and Chemical Analysis(Part B: Chemical Analysis), 2016, 52(9): 1062
[15]	周富强, 赵明. 理化检验(化学分册), 2016, 52(9): 1062
[16]	Ye M, Nesterenko P N, Yan Z, et al. J Chromatogr A, 2019, 1588: 169
[17]	ISO 14644-1: 2015
[18]	Corbridge D E C. Phosphorus: Chemistry, Biochemistry and Technology. 6th ed. Boca Raton: CRC Press, 2013
[19]	GB/T 28159-2011