Determination of Ethyl Xanthate in Aqueous Solution by High Performance Liquid Chromatography–Inductively Coupled Plasma–Tandem Mass Spectrometry and Spectrophotometry

Figures & data

Table 1. Triple quadrupole ICP-MS operating conditions.

Parameter	Value
RF Power	1550 W
Gas flow rate
Nebulizer gas	0.52 mL min^−1
O2 optional gas	20% (∼0.2 L min^−1)
O2 reaction gas	15% (∼0.225 mL min^−1)
Sampling depth	10 mm
Integration time/mass	0.4 s
Monitored masses, MS/MS mode	^32S → ^32S^16O^+34S → ^34S^16O^+
Data acquisition mode	Time resolved analysis
Acquisition time	4 min

Figure 1. Schematic of the method for the determination of potassium ethyl xanthate (KEX). EX⁻ is ethyl xanthate anion and (EX)₂ is diethyl dixanthogen.

Figure 2. Typical chromatograms and absorption spectra for ethyl xanthate (EX⁻) in NH₄OH, diethyl dixanthogen (EX)₂ in hexane, and KEX sample after pretreatment in hexane. The initial KEX and (EX)₂ concentrations were 10 mg L⁻¹. The chromatograms employed ultraviolet-detection at 301 nm for EX⁻ and at 240 nm for (EX)₂ and the pretreated sample.

Figure 3. Optimization of ICP-MS/MS cell gas (O₂) flow rate. The flow rate is provided as percentage of its maximum value of 1.5 mL min⁻¹. A 50 µg L⁻¹ S standard in 80:20 methanol:H₂O (vol/vol) was used for optimization.

Table 2. Influence of mobile phase flow rate and composition on the retention time, resolution, and peak height of diethyl dixanthogen (EX)₂.

Mobile phase flow rate/mL min^−1	Mobile phase composition methanol-H2O % (vol/vol)	(EX)2 retention time/min	Resolution	Peak height/mAU
0.30	85:15	3.36	0.92	73
0.32	85:15	2.42	0.91	77
0.32	90:10	1.75	0.62	106
0.35	85:15	2.19	0.91	78
0.37	85:15	2.07	0.90	78
0.40	70:30	3.48	3.07	2.7
0.40	75:25	3.04	1.36	33
0.40	80:20	2.72	0.94	52
0.45	85:15	1.71	0.75	53

The resolution was evaluated by R = 2(t_(EX)2 − t_x)/w_(EX)2 + w_x where t is the retention time, w is the peak width at the baseline, and x is the peak eluting immediately before (EX)₂.

Figure 4. Chromatograms of blank, 1 and 10 mg L⁻¹ ethyl xanthate after pretreatment by HPLC-ICP-MS/MS. Intensities of blank and 1 mg L⁻¹ samples are shown in the left y-axis and 10 mg L⁻¹ in the right y-axis. The chromatograms were obtained in the MS/MS-mode using the mass-shift 32 → 48.

Table 3. Analytical figures of merit for the determination of potassium ethyl xanthate (KEX) and diethyl dixanthogen ((EX)₂).

		Peak height				Peak area
	Detection	Limit of detection (µg L^−1)	Limit of quantification (µg L^−1)	Linear equation	R^2	Limit of detection (µg L^−1)	Limit of quantification (µg L^−1)	Linear equation	R^2
KEX	ICP-MS/MS, 32 → 48	38	128	y = 5.57x +1513	0.998	88	294	y = 58.2 + 23720	0.990
	ICP-MS/MS, 34 → 50	71	236	y = 0.258x +80.36	0.993	98	328	y = 2.79x +903	0.988
	UV, 301 nm	52	175	y = 0.014x +0.16	0.998	77	258	y = 0.089 + 1.4	0.996
(EX)2	ICP-MS/MS, 32 → 48	26	86	y = 5.93x +93.45	0.9987	20	68	y = 60.0x −351	0.9992
	ICP-MS/MS, 34 → 50^a	93	311	y = 0.296x + 33.80	0.994	74	246	y = 2.97x−4.0	0.996
	UV, 301 nm	7.8	26	y = 0.010x + 0.01	0.9999	8.2	27	y = 0.068x + 0.07	0.9999

The linear ranges were from 100 to 1000 µg L⁻¹ for KEX and 50 to 1000 µg L⁻¹ for (EX)₂.

^a The linear range was from 250 to 1000 µg L⁻¹.

Table 4. Comparison of detection limits for xanthates.

Method		Detection limit (μg L^−1)	Reference
Spectrophotometry	Direct determination	160	Hao et al. 2008
	Flow injection	48	Fontenele et al. 2007
	Gas diffusion	38	Cordeiro et al. 2010
HS-GC-EDC		0.3	Li et al. 2015
CE		10	Sihvonen et al. 2014
Anion interaction chromatography		30	Hao, Silvester, and Senior 2000
HPLC	UV	8.2	This study
	ICP-MS/MS	20

Figure 5. Chromatograms of 500 µg L⁻¹ diethyl dixanthogen (EX)₂ and a tailings sample with a 500 µg L⁻¹ (EX)₂ spike by HPLC-ICP-MS/MS (mass-shift 32 → 48) following sample pretreatment.

Table 5. Linear equations and their confidence intervals (α = 0.05) for standard addition determination of (EX)₂ in ultra-pure water and a tailings sample by HPLC-ICP-MS/MS using peak area.

Sample matrix	Slope ± confidence interval	Intercept ± confidence interval	R^2
Ultra-pure water^a	42.04 ± 1.67	−486 ± 1576	0.994
Tailings^b	41.06 ± 1.47	143 ± 827	0.997

^aFour replicate measurements.

^bTwo replicate measurements.

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