AL (RhL2H2 2+) exhibited a maximum absorption at
624 nm, which is close to the wavelength of the He–Ne laser.
Effect of foreign species The effects of foreign species on the determina- tion of 2.5 ng/mL rhodium were investigated. Tolerance limit was defined as the amount of added species causing a ±5% variation in the thermal lens signal of the sample. Results of the interference study are shown in Table 1.
Figure 5 – Complexation of Rh(III) with 3,5-diCl-PADMA.
Table 1 – Effect of foreign ions on preconcentration/determination of rhodium Species Sr2+ Ca2+ SO4
2-
Cd2+ F-
K+ Ba2+
Mo(IV) I–
Mg2+ Zn2+ NO3- Mn2+ La3+
Foreign/Rh (w/w) 2500 2000 2000 1500 1000 1000 1000 800 800 600 500 500 400 300
*Masked with 100 µL 50 μg/mL Na4 O7 **Masked with 50 µL 50 μg/mL EDTA.
P2 .
Species NaF Br-
Na4 Al3+
P2 O7
EDTA Hg2+ As(V) Sb3+
Os(VIII) W(V) Fe3+ Cu2+ Ir(IV)
* ** Thiourea
Analytical features Using the optimized experimental condi- tions for preconcentration of rhodium, a calibration graph obtained by the proposed method showed linearity over the range of 0.2~5.0 ng/mL. The linear regression equation is Sc
= 0.7837c-0.0855, where Sc is the inten-
sity of thermal lens signal and c is the rhodium concentration in ng mL-1
, and the correlation
Foreign/Rh (w/w) 300 200 200 100 100 50 50 50 50 40 30 20 20 10
coefficient r was 0.9981. The detection limit (DL), calculated as three times the standard deviation of the blank solution (3σ), was 0.04 ng mL-1
3.0% (n = 11, c = 1.0 ng mL-1
. The relative standard deviation (RSD) was ). Compared with the
conventional spectrophotometric method,24 sensitivity of the method calculated as the ratio of the slopes of the calibration curves was enhanced 570 times. The enrichment factor, defined as the ratio of the volumes before and after CPE, was 22.
Table 2 compares the proposed method with previously reported methods using CPE prior to rhodium determination. As seen, the detec- tion limit of the new method is better than those given in the table, with the exception of CPE-ICP/MS.32,33
Analysis of real samples Method validation was performed by using the technique for the determination of rhodium in water samples. Five milliliters of each water sample was added to a 10-mL graduated coni- cal centrifuge tube, along with 100 µL 30 μg/ mL Na4
P2 O7 and 50 µL 50 μg/mL EDTA solution.
Recoveries (see Table 3) were within the range of 96.7–104%.
of the He–Ne laser. In the most commonly used solvents, ethanol can meet these requirements. Therefore, 2.67 mol L-1
HCl–ethanol solution
was used as the solvent medium for dissolving the remaining phase after CPE as well as for TLS measurement. In this medium, the complex
AMERICAN LABORATORY 29 MAY 2016
Conclusion TLS is a highly sensitive thermo-optical
analytical method that suffers from low se- lectivity. CPE is a powerful technique for the
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