Cloud point extraction of some precious metals using Triton X-114 and a thioamide derivative with a salting-out effect

Peer review under responsibility of Mansoura University.

Figures & data

Table 1 Instrumental parameters for determination of Pd, Ag and Au using ETAAS.

A. Instrumental parameters
	Pd	Ag	Au
Wavelength (nm)	247.6	328.1	242.8
Slit width (nm)	0.2	0.7	0.2
Lamp current (mA)	30	15	15
B. Temperature program
Step	Temperature (°C)			Time (s)		Argon flow rate ml/min
	Pd	Ag	Au	Ramp	Hold
Drying 1	110			1	30	250
Drying 2	130			15	30	250
Pyrolysis	900	800	800	15	20	250
Atomization	2200	1700	1800	0	6	0
Cleaning	2500			1	5	250

Table 2 Microwave digestion program for the digestion of the geological samples.

Step	1	2	3	4
Power (%)	60	60	60	60
Pressure (psi)	100	130	160	170
T1^a (min)	30	30	30	30
T2^a (min)	15	10	5	5

T2: time the sample remains at the required pressure.

a T1: maximum time needed to reach the required pressure.

Fig. 1 Influence of the pH on the extraction recoveries of Pd, Ag and Au ions. Conditions: 20 μg L⁻¹ metal ion; 0.3 mol L⁻¹ Na₂SO₄; 50 ml aqueous solution; 5 × 10⁻⁵ mol L⁻¹ HCPTS; 0.05% w/v Triton X-114; 25 °C.

Fig. 2 Effect of the ligand concentration on the recovery of extraction for Pd, Ag and Au ions. Conditions: 20 μg L⁻¹ metal ion; 0.3 mol L⁻¹ Na₂SO₄; pH, 6.0; 50 ml aqueous solution; 0.05% w/v Triton X-114; 25°C.

Fig. 3 Effect of the surfactant concentration on the extraction recovery of Pd, Ag and Au ions. Conditions: 20 μg L⁻¹ metal ions; 0.3 mol L⁻¹ Na₂SO₄; pH, 6.0; 50 ml aqueous solution; 5 × 10⁻⁵ mol L⁻¹ HCPTS; 25 °C.

Fig. 4 Effect of the addition of different salts on the %recovery of Pd, Ag and Au ions. Conditions: 20 μg L⁻¹ metal ions; pH, 6.0; 50 ml aqueous solution; 5 × 10⁻⁵ mol L⁻¹ HCPTS; 25 °C.

Table 3 Analytical figures of merit for the proposed method.

Parameter	Pd(II)	Ag(I)	Au(III)
Limit of Detection (μg L^−1)	0.12	0.08	0.30
Limit of Quantification (μg L^−1)	0.45	0.29	1.13
Precision (% RSD, C = 20 μg L^−1, n = 10)	3.4	4.7	2.2
Linearity (μg L^−1)	0–125	0–50	0–100
Correlation Coefficient	0.998	0.997	0.995
Enrichment Factor (EF)	52	46	56

CPE conditions: 50 mL sample solution, pH 6, 5 × 10⁻⁵ mol L⁻¹ HCPTS, 0.05% (w/v) Triton X-114, 0.3 mol L⁻¹ Na₂SO₄ at 25 °C and centrifugation at 4000 RPM for 10 min.

Table 4 Tolerance limits of interfering ions.

External ion	Tolerable concentration ratio	%Recovery ± S.D.
		Pd(II)	Ag(I)	Au(III)
K^+	>1000	97.5 ± 2.0	96.0 ± 2.4	99.6 ± 1.0
Na^+	>1000	98.2 ± 1.8	96.2 ± 2.5	98.8 ± 2.0
Cs^+	1000	96.4 ± 2.1	98.0 ± 1.5	100.3 ± 2.4
Ca^2+	1000	97.5 ± 1.0	99.0 ± 2.1	101.3 ± 1.0
Mg^2+	1000	99.0 ± 1.5	96.2 ± 2.3	99.6 ± 1.2
Al^3+	700	100.5 ± 2.0	97.6 ± 1.6	99.5 ± 2.6
Bi^3+	400	96.0 ± 2.7	98.4 ± 1.0	98.0 ± 2.7
Fe^3+	300	97.2 ± 1.9	99.2 ± 2.1	96.9 ± 2.4
Fe^2+	1000	97.0 ± 1.8	100.0 ± 1.5	97.4 ± 1.5
Cr^3+	800	97.4 ± 2.3	96.3 ± 2.3	96.6 ± 1.8
Mn^2+	900	96.5 ± 2.0	98.3 ± 2.0	98.5 ± 1.0
Pb^2+	900	102.0 ± 1.8	97.6 ± 2.4	96.8 ± 2.8
Cd^2+	500	97.8 ± 2.2	103.0 ± 1.6	99.0 ± 2.0
Co^2+	300	97.2 ± 2.5	98.0 ± 2.0	95.1 ± 2.5
Ni^2+	500	99.2 ± 1.8	97.4 ± 3.0	103.5 ± 1.2
Zn^2+	500	96.5 ± 2.4	96.8 ± 1.9	95.7 ± 2.0
Hg^2+	400	96.8 ± 3.0	95.8 ± 2.5	95.8 ± 2.3
CrO4^2-	1000	101.5 ± 1.5	98.5 ± 2.0	99.5 ± 1.8
PO4^3-	1000	98.6 ± 2.0	96.4 ± 2.4	99.9 ± 1.4
SCN^−	1000	97.4 ± 2.3	98.0 ± 1.0	100.1 ± 2.1
CH3COO^−	1000	101.0 ± 1.0	96.4 ± 1.6	97.1 ± 1.6
NO3^−	1000	99.0 ± 1.8	97.0 ± 2.0	95.5 ± 2.0

Tolerance limits of investigated electrolytes is known as ion concentration causing a relative error < ±5% in the sensitivity of method.

Table 5 Analysis of Pd, Ag and Au ions in spiked water samples by the proposed method.

Sample	Ion	Added (μg L^−1)	Found (μg L^−1)	Recovery (%)	RSD (%)
Tape water	Pd(II)	–	N.D.	–	–
		5.0	4.95	99.0	2.5
		10.0	9.92	99.2	3.2
	Ag(I)	–	N.D.	–	–
		5.0	5.08	101.6	1.8
		10.0	9.87	98.7	2.2
	Au(III)	–	N.D.	–	–
		5.0	5.10	102.0	2.7
		10.0	9.85	98.5	1.7
River water	Pd(II)	–	N.D.	–	–
		5.0	4.88	97.6	3.1
		10.0	9.75	97.5	2.6
	Ag(I)	–	N.D.	–	–
		5.0	4.90	98.0	3.3
		10.0	9.92	99.2	1.9
	Au(III)	–	N.D.	–	–
		5.0	4.87	97.4	2.4
		10.0	9.84	98.4	3.0
Sea water	Pd(II)	–	N.D.	–	–
		5.0	5.02	100.4	2.5
		10.0	10.0	100.0	2.8
	Ag(I)	–	N.D.	–	–
		5.0	5.11	102.2	3.3
		10.0	9.90	99.0	1.5
	Au(III)	–	N.D.	–	–
		5.0	4.89	97.8	1.8
		10.0	9.66	96.6	2.3

Results of five determinations of each sample.

Table 6 Analysis of Pd, Ag and Au ions in geological samples by the recommended procedure.

Samples	The present procedure
	Pd(II)	Ag(I)	Au(III)
Road dust samples (ng g^−1)	29.0 ± 5.3	51.2 ± 5.9	35.5 ± 3.4
Rock samples (ng g^−1)	21.1 ± 4.7	73.8 ± 9.2	43.9 ± 6.5

Table 7 Comparison of the present method with previously reported ones.

Metal ion	Reagent	Instrument	Sample	LOD (μg L^−1)	EF	Reference
Pd, Au	1,8-diamino-4,5-dihyroxy anthraquinone	ICP-OES	Mine stones	0.3, 0.5	20.2, 8.6	[16]
Ag	Ligandless using PONPE 7.5 as a surfactant	ETAAS	Water	1.2	60	[17]
Ag	O,O-diethyl-dithiophosphate	ETAAS	Water and biological samples	7.8	35	[18]
Pd, Au	O,O-diethyldithiophosphate	ETV-ICP-MS	Biological samples	6.0, 0.8	40, 35	[19]
Pd, Au	Ammonium pyrolysine dithiocarbamate	FAAS	Soil samples	1.4, 1.2	21, 24	[20]
Ag	dithizone	FAAS	water	0.7	38	[21]
Pd, Ag	2-((2-((1H-benzo[d]imidazole-2-yl)methoxy)phenoxy)methyl)-1H-benzo[d]imidazol	FAAS	waste water, soil and catalyst samples.	25.0, 10.0	28, 35	[22]
Pd, Ag	bis((1H-benzo[d]imidazol-2-yl)ethyl) sulfane	FAAS	radiology waste, vegetable, blood and urine samples	1.6, 1.4	32, 42	[23]
Pd, Ag, Au	HPCTS	ETAAS	Water and geological samples	0.12, 0.08, 0.30	52, 46, 56	The present study