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Characterization and elimination of the interfering effects of foreign species in the atomic absorption spectrometry of chromium
Analytica Chimica Acta, 165 (1984)
105-111 Elsevier Science Publishers B.V., Amsterdam -Printed
in The Netherlands
CHARACTERIZATION AND ELIMINATION OF THE INTERFERING EFFECTS OF FOREIGN SPECIES IN THE ATOMIC ABSORPTION SPECTROMETRY OF CHROMIUM
A. M. ABDALLAH,
Department
M. M. EL-DEFRAWY*
and M. A. MOSTAFA
of Chemistry, Faculty of Science, University of Mansoum (Egypt)
(Received 22nd June 1983)
SUMMARY In the atomic absorption spectrometric determination of chromium(III), the interfering effects of different complexing agents can be completely eliminated by addition of excess of cyanide, boric acid or sulphosalicyclic acid. The effect of some complexing agents on the production of chromium atoms is discussed, and the mechanism of cyanide interaction is investigated in detail.
Although the sensitivity for chromium by atomic absorption spectrometry is greatest in a fuel-rich flame, interferences are also greater [ 11. The origin of many interferences is still speculative. A fundamental understanding of interfering effects in atomic absorption spectrometry depends largely on a knowledge of the mechanisms which control atomization processes in flames [2-51. The object of this paper is to investigate the feasibility of using a continuous titration technique [6-81 for studying the interfering effects of foreign species on the atomic absorption signal of chromium and thus establishing the possibility of using a simple method for eliminating such interferences. EXPERIMENTAL
A Unicam SP-9OA series 2 atomic absorption spectrometer was used with a Unicam chromium hollow-cathode lamp and a conventional 1Ocm slot burner head for an airacetylene flame. A continuous titration device [6] was attached to the instrument to conduct all the absorption and emission experiments; the titration plots were recorded with a Philips PM-8251 single-pen recorder at a chart speed of 30 cm min-‘. The evaluation of the titration plots was done by means of a Casio FX-502 type programmable pocket calculator. The instrumental parameters used were as follows: lamp current, 12 mA; wavelength, 357.9 nm; slit-width, 0.1 mm (monochromator dispersion 2.9 nm min-’ at 370 nm); air flow rate, 5 1 min-‘; fuel flow rate, 1.8 1 min-‘;
106
height in the flame, 6 mm. The emission study was done with the same equipment. All chemicals were of analytical-reagent grade. RESULTS
AND DISCUSSION
Effect of anions The effect of four anionic species as sodium or potassium salts on the absorbance from a chromium(II1) chloride solution is presented in Fig. 1. Each anion has a depressive effect, and at a definite stoichiometric ratio an inflection is observed, at mole ratios of interfering anion to chromium of 1:l for phosphate and 3:l for iodide, nitrite and nitrate, corresponding to the formation of CrP04, CrIJ, Cr(N02)3 and Cr(N03)3. The general trend is that the absorbance decreases during the first stages of the titration and after the stoichiometric ratio has been attained, the absorbance becomes constant, except for iodide. In this case, the absorbance is restored almost to its normal value at a ratio of 5:l. This phenomenon was exploited by Juhai et al. [ 91 who devised a procedure for the determination of chromium in steel, using iodide as a releasing agent for chromium. Effect of complexing agents The changes in the absorbance of 1.0 mM chromium(II1) caused by various ligands are shown in Fig. 2. There is an initial suppressive effect from sulphosalicyclic acid (SSA) which has a maximum effect at a mole ratio of 1:l. This is followed by a sharp enhancement by higher concentration of SSA, finally doubling the absorbance at a ratio of 5:l. The inflection at 1:l corresponds to the formation of a 1:l complex. To prove the formation of this complex, spectrophotometric measurements were conducted. Figure 3
Clnterferlnp amonl/CChmmwnl
0 0
2 6
4 12
6 16
6 24
10 30
24 CLlgondl/[chrom~uml 42 tCyumdel/Cchmrmuml
Fig. 1. Changes in the absorption signal of 1.0 mM chromium as a function of interfering anion:chromium ratio: (1) I-; (2) NO;; (3) NO;; (4) PO:-. Fig. 2. Changes of chromium (1.0 mM) absorption signal as a function of 1igand:chromium ratio: (1) sulphosalicyclic acid; (2) 4-amino&icy&c acid; (3) potassium cyanide.
107
0 Wavelength
(nm)
2
4
6
0
IO
Cyanide concentration
12
14
16
I8
( mM)
Fig. 3. Conventional absorption spectra for Cr-SSA mixtures: (1) SSA; (2) Cr’+; (3) 1:l at 60°C; (4) 1:l after boiling; (5) 1:2 after boiling; (6) 1:3 after boiling. Fig. 4. Changes of cyanide band emission intensity as a function of cyanide concentration in Cr solutions of the following concentrations: (1) 0.0; (2) 1.0; (3) 1.5; (4) 2.0 mM.
shows that the mole ratio is 1 :l irrespective of any increase in SSA concentration. Heating was required to speed up complex formation, and it seems probable that the required heating would occur during solvent evaporation in the flame. The marked increase in chromium absorbance is attributed to the efficiency of SSA in providing a reducing environment leading to increase in the chromium atom population in the area of measurement. Figure 2 shows that 4aminosalicylic acid has a similar but smaller effect. Cyanide forms stable complexes with chromium(II1) [lo]. Figure 2 indicates that the chromium absorbance generally decreases with increasing cyanide ion concentration, with a minimum at a ratio of 6:l; after which the absorbance increases and returns to the normal value at 225 mM. At such high cyanide concentrations, the reducing action of the excess of cyanide compensates for the effect of complex formation. The behaviour of cyanide towards chromium in the flame can be discussed on the basis that three main steps take place during a continuous increase in ligand concentration. Vaporization of the solid complex particles causes their decomposition and release of chromium atoms which react instantly with oxidising species in the flame to form chromium compounds, mainly oxides [ 111. After a particular stoichiometric ratio has been attained, the excess of the reducing species (CN radicals when potassium cyanide is used) in the flame reacts with chromium oxides Cr,O,
+mCN+nCr+1/2mNz+mC0
to increase the chromium atom population. The continuous increase in concentration of the reducing species in the flame overcomes the effect of the oxidising species and causes the complete restoration of the chromium atom concentration.
108
The behaviour of organic additives in the flame is quite diverse, because such agents are not decomposed equally in the flame; their oxidising and reducing properties differ under different flame conditions. In order to obtain more information on the reducing action of the ligands in the flames, the effect of potassium cyanide solution has been given particular attention because its decomposition products are only CN and K. The emission intensity of CN in the flame can easily be measured. Work is in progress to obtain and measure the emission signals of some of the decomposition products of sulphosalicylic acid and related compounds. The presence of cyanide radicals in the flame can be detected by measuring the emission intensity at 358 nm, no signal was detected when attempting to measure the absorbance of the cyanide radical at 358 nm, and the emission intensity of the cyanide band at the same wavelength does not effect the intensity of the line from a chromium hollow-cathode lamp. Moreover, the cyanide intensity at 358 nm is unaffected by the presence of chromium. Figure 4 indicates the initial existence of cyanide radicals in the flame at the start of the titration and in the absence of chromium. When the titration is conducted in the presence of 1.0, 1.5 and 2.0 mM chromium, Fig. 4 shows that the cyanide emission intensity is zero at the start of the titration and remains zero until the cyanide:chromium ratio reaches 6: 1. After this, the cyanide emission resumes its original trend of continuously increasing with increasing cyanide ion concentration. Thus the delay in appearance of the cyanide band emission is due to the complexing action of the cyanide ion on chromium. The reaction given above indicates that the reaction between chromium oxides and cyanide produces chromium, nitrogen and carbon monoxide. Figure 5 shows a progressive increase in the emission intensity of the carbon monoxide band when measured at 219 nm in solutions containing 1.0 mM chromium plus increasing amounts of cyanide. The increase is directly related to the concentration of the cyanide radical in the flame, after reaching the stoichiometric 6:l ratio. Such a result indicates that the excess of cyanide radicals removes from the flame volume under measurement unwanted oxidising species and restores the chromium signal to its original value. Interference 0 f cations Metal-metal interactions in the flame are complicated. Figure 6 shows that the chromium signal is considerably enhanced when aluminium, calcium or strontium is added to a chromium solution. Such metals may compete with chromium either for flame oxidizing species or for constituents of the nebulized solution so as to form metal monoxides. Dissociation energies Do, in kcsl mol-‘, for AlO, CaO, FeO, NiO, SrO and CrO are 106, 100, 99, 97, 97 and 101, respectively [ 121. In addition, monohydroxides of calcium (Do = 104 kcal mol-‘) and strontium (Do = 103 kcal mol-‘) are likely to be present in air-acetylene flames. These hydroxides and monoxides have very similar stabilities, and an appreciable proportion of each metal is present in these forms in the flame, particularly in the measurement zone.
109
60 40. 2cI
0
6
I2
I6
24
Cyomde concentmtlon
30 (mM)
36
42
I 0
/ 2
i&
1
4 Clnterfermg
EY
6
1
20
catnnl/tchromwml
Fig. 5. Effect of potassium cyanide in the presence of 1.0 mM chromium band emission intensity at 219 nm.
on the CO
Fig. 6. Change in the absorption signal of 1.0 mM chromium as a function of interfering metal ion:chromium ratio: (1) Al*; (2) Cal? (3) SP+; (4) Fe’+; (5) Nil+. (May be due to formation of CrNi, with low melting point and high volatility [ 151.)
When iron or nickel is present in aspirated solution of chromium, the experimental observations are in agreement with the theory that relatively non-volatile compounds are formed between chromium and iron or nickel. These compounds dissociate only slowly in the measurement zone. The severity of the depressive effect is decreased when the measurements are made in the higher regions of the flame, and has disappeared 1.2 cm above the flame base. Control 0 f interferences The action of boron in an airacetylene flame as a promising universal flame buffer was discussed in earlier papers [ 13,141. Its action in the flame, when present in excess, is to interact with the matrix components to form relatively stable, unreactive species, leaving the analyte atoms free. Table 1 indicates that boric acid is a powerful releasing agent and acts very effectively on oxidising species such as nitrate or chlorate and possible reducing species such as nitrite. Moreover, it removes from the area of measurement interfering distintegration products of organic chelating agents. In addition, formation of metal borides of the interferents leads to release of chromium without affecting the atomization process. However, the data in Table 1 help to reach the conclusion that boron can efficiently level the flame conditions to obtain signals identical to samples to which boron but no interferent has been added.
110 TABLE 1 Interference of various species on the absorbance of 1.0 x lo-’ M chromium(II1) effect of different releasing agents Addes substance(s) (200 mg 1-l each)
Chromium recovery (%)” No releasing agent
Boric acid (1.85 x lo-’ M)
NO; NO; Iso:ClO; PO:- + NO; PO:- + NO; + BrPO:- + so:-
60 83 68 93 85 138 33 88 69
EDTA CDTA NTA EDTA + PO;EDTA + PO:- + BrA13’ Caz+ Sr” Fe3+ Nia+ AP+ + Cut+ + Pb=+ Cal+ + Mn’+ + EDTA Sra+ + Cdl+ + Fe3+ SrN + Ba’+ + In” + NO-3
PO:-
and the
SSA (2.0 x lo-’ M)
KCN (5.0x
100 98 100 100 100 100 100 100
100 100 99 100 100 100 100 100 100
100 99 100 100 100 105 100 100
82 80 82 122 100
100 100 100 100 100
100 99 100 102 100
100 99 100 105 105
170 154 130 68 110 150 150 94 83
100 100 100 98 100 100 100 100 100
100 100 100 99 100 100 100 95 95
b b b b b b b b b
98
1O-1 M)
99
aRecovery with respect to the chromium absorbance signal in the presence of the releasing agent alone (= 100%). bPrecipitation of the metal cyanide.
While boric acid acts upon the interferents and their disintegration products, it does not enhance the absorption signals of the analytes. Sulphosalicylic acid (SSA), however, plays a unique role in reacting with the analyte to cause simultaneous enhancement and normalization of the recovered signal, when it is present in large amounts in both samples and standards. Differences in chromium from samples containing diverse ions completely disappear in the presence of 0.02 M SSA. Moreover, SSA doubles chromium signals compared to a chromium chloride solution. The general usefulness of cyanide addition to chromium solutions of samples and standards is quite clear; its precipitating action on a variety of cations can be exploited by filtering off interfering species and the filtrate can be nebulized directly in order to determine chromium.
111 REFERENCES 1 J. C. Van Loon, Analytical Atomic Absorption Spectroscopy, Selected Methods, Academic Press, New York, 1980. 2 I. Rubeska and B. Moldan, Anal. Chim. Acta, 37 (1967) 421. 3 I. Rubeska, Can, J. Spectrosc., 20 (1975) 166. 4 J. Y. Marks and G. G. Welcher, Anal. Chem., 42 (1970) 1033. 5 C. B. Boss and G. M. Hieftje, Anal. Chem., 51(1979) 895. 6 D. Stojanovic, J. Bradshaw and J. D. Winefordner, Anal. Chim. Acta, 96 (1978) 45. 7 J. Posta and J. Lakatos, Magy. Kern. Foly., 86 (1980) 284. 8 M. M. El-Defrawy, J. Posta and M. T. Beck, Anal. Chim. Acta, 115 (1980) 155. 9 E. Juhai, K. Szivos, V. Izekov, T. Kantor and E. Pungor, Magy. Kern. Foly., 86 (1980) 650. 10 A. G. Sharpe, The Chemistry of Cyano-Complexes of Transition Metals, Academic Press, London, 1976. 11 H. Remy, Treatise on Inorganic Chemistry, Vol. 2, Elsevier, Amsterdam, 1956. 12 A. G. Gaydon, Dissociation Energies and Spectra of Diatomic Molecules, 3rd edn., Chapman and Hall, London, 1968. 13 A. M. Abdailah and M. A. Mostafa, Ind. J. Chem., 19A (1980) 1112; Annali di Chimica, 70 (1980) 1. 14 A. M. Abdallah, M. M. El-Defrawy, M. A. Mostafa and A. B. Sakla, Paper presented at the 9th Int. Symp. Microchemical Techniques and Trace-Analysis, Amsterdam, 1983. 15 P. M. Hansen, Constitution of Binary Alloys, 2nd edn., McGraw-Hill, London, 1958.
105-111 Elsevier Science Publishers B.V., Amsterdam -Printed
in The Netherlands
CHARACTERIZATION AND ELIMINATION OF THE INTERFERING EFFECTS OF FOREIGN SPECIES IN THE ATOMIC ABSORPTION SPECTROMETRY OF CHROMIUM
A. M. ABDALLAH,
Department
M. M. EL-DEFRAWY*
and M. A. MOSTAFA
of Chemistry, Faculty of Science, University of Mansoum (Egypt)
(Received 22nd June 1983)
SUMMARY In the atomic absorption spectrometric determination of chromium(III), the interfering effects of different complexing agents can be completely eliminated by addition of excess of cyanide, boric acid or sulphosalicyclic acid. The effect of some complexing agents on the production of chromium atoms is discussed, and the mechanism of cyanide interaction is investigated in detail.
Although the sensitivity for chromium by atomic absorption spectrometry is greatest in a fuel-rich flame, interferences are also greater [ 11. The origin of many interferences is still speculative. A fundamental understanding of interfering effects in atomic absorption spectrometry depends largely on a knowledge of the mechanisms which control atomization processes in flames [2-51. The object of this paper is to investigate the feasibility of using a continuous titration technique [6-81 for studying the interfering effects of foreign species on the atomic absorption signal of chromium and thus establishing the possibility of using a simple method for eliminating such interferences. EXPERIMENTAL
A Unicam SP-9OA series 2 atomic absorption spectrometer was used with a Unicam chromium hollow-cathode lamp and a conventional 1Ocm slot burner head for an airacetylene flame. A continuous titration device [6] was attached to the instrument to conduct all the absorption and emission experiments; the titration plots were recorded with a Philips PM-8251 single-pen recorder at a chart speed of 30 cm min-‘. The evaluation of the titration plots was done by means of a Casio FX-502 type programmable pocket calculator. The instrumental parameters used were as follows: lamp current, 12 mA; wavelength, 357.9 nm; slit-width, 0.1 mm (monochromator dispersion 2.9 nm min-’ at 370 nm); air flow rate, 5 1 min-‘; fuel flow rate, 1.8 1 min-‘;
106
height in the flame, 6 mm. The emission study was done with the same equipment. All chemicals were of analytical-reagent grade. RESULTS
AND DISCUSSION
Effect of anions The effect of four anionic species as sodium or potassium salts on the absorbance from a chromium(II1) chloride solution is presented in Fig. 1. Each anion has a depressive effect, and at a definite stoichiometric ratio an inflection is observed, at mole ratios of interfering anion to chromium of 1:l for phosphate and 3:l for iodide, nitrite and nitrate, corresponding to the formation of CrP04, CrIJ, Cr(N02)3 and Cr(N03)3. The general trend is that the absorbance decreases during the first stages of the titration and after the stoichiometric ratio has been attained, the absorbance becomes constant, except for iodide. In this case, the absorbance is restored almost to its normal value at a ratio of 5:l. This phenomenon was exploited by Juhai et al. [ 91 who devised a procedure for the determination of chromium in steel, using iodide as a releasing agent for chromium. Effect of complexing agents The changes in the absorbance of 1.0 mM chromium(II1) caused by various ligands are shown in Fig. 2. There is an initial suppressive effect from sulphosalicyclic acid (SSA) which has a maximum effect at a mole ratio of 1:l. This is followed by a sharp enhancement by higher concentration of SSA, finally doubling the absorbance at a ratio of 5:l. The inflection at 1:l corresponds to the formation of a 1:l complex. To prove the formation of this complex, spectrophotometric measurements were conducted. Figure 3
Clnterferlnp amonl/CChmmwnl
0 0
2 6
4 12
6 16
6 24
10 30
24 CLlgondl/[chrom~uml 42 tCyumdel/Cchmrmuml
Fig. 1. Changes in the absorption signal of 1.0 mM chromium as a function of interfering anion:chromium ratio: (1) I-; (2) NO;; (3) NO;; (4) PO:-. Fig. 2. Changes of chromium (1.0 mM) absorption signal as a function of 1igand:chromium ratio: (1) sulphosalicyclic acid; (2) 4-amino&icy&c acid; (3) potassium cyanide.
107
0 Wavelength
(nm)
2
4
6
0
IO
Cyanide concentration
12
14
16
I8
( mM)
Fig. 3. Conventional absorption spectra for Cr-SSA mixtures: (1) SSA; (2) Cr’+; (3) 1:l at 60°C; (4) 1:l after boiling; (5) 1:2 after boiling; (6) 1:3 after boiling. Fig. 4. Changes of cyanide band emission intensity as a function of cyanide concentration in Cr solutions of the following concentrations: (1) 0.0; (2) 1.0; (3) 1.5; (4) 2.0 mM.
shows that the mole ratio is 1 :l irrespective of any increase in SSA concentration. Heating was required to speed up complex formation, and it seems probable that the required heating would occur during solvent evaporation in the flame. The marked increase in chromium absorbance is attributed to the efficiency of SSA in providing a reducing environment leading to increase in the chromium atom population in the area of measurement. Figure 2 shows that 4aminosalicylic acid has a similar but smaller effect. Cyanide forms stable complexes with chromium(II1) [lo]. Figure 2 indicates that the chromium absorbance generally decreases with increasing cyanide ion concentration, with a minimum at a ratio of 6:l; after which the absorbance increases and returns to the normal value at 225 mM. At such high cyanide concentrations, the reducing action of the excess of cyanide compensates for the effect of complex formation. The behaviour of cyanide towards chromium in the flame can be discussed on the basis that three main steps take place during a continuous increase in ligand concentration. Vaporization of the solid complex particles causes their decomposition and release of chromium atoms which react instantly with oxidising species in the flame to form chromium compounds, mainly oxides [ 111. After a particular stoichiometric ratio has been attained, the excess of the reducing species (CN radicals when potassium cyanide is used) in the flame reacts with chromium oxides Cr,O,
+mCN+nCr+1/2mNz+mC0
to increase the chromium atom population. The continuous increase in concentration of the reducing species in the flame overcomes the effect of the oxidising species and causes the complete restoration of the chromium atom concentration.
108
The behaviour of organic additives in the flame is quite diverse, because such agents are not decomposed equally in the flame; their oxidising and reducing properties differ under different flame conditions. In order to obtain more information on the reducing action of the ligands in the flames, the effect of potassium cyanide solution has been given particular attention because its decomposition products are only CN and K. The emission intensity of CN in the flame can easily be measured. Work is in progress to obtain and measure the emission signals of some of the decomposition products of sulphosalicylic acid and related compounds. The presence of cyanide radicals in the flame can be detected by measuring the emission intensity at 358 nm, no signal was detected when attempting to measure the absorbance of the cyanide radical at 358 nm, and the emission intensity of the cyanide band at the same wavelength does not effect the intensity of the line from a chromium hollow-cathode lamp. Moreover, the cyanide intensity at 358 nm is unaffected by the presence of chromium. Figure 4 indicates the initial existence of cyanide radicals in the flame at the start of the titration and in the absence of chromium. When the titration is conducted in the presence of 1.0, 1.5 and 2.0 mM chromium, Fig. 4 shows that the cyanide emission intensity is zero at the start of the titration and remains zero until the cyanide:chromium ratio reaches 6: 1. After this, the cyanide emission resumes its original trend of continuously increasing with increasing cyanide ion concentration. Thus the delay in appearance of the cyanide band emission is due to the complexing action of the cyanide ion on chromium. The reaction given above indicates that the reaction between chromium oxides and cyanide produces chromium, nitrogen and carbon monoxide. Figure 5 shows a progressive increase in the emission intensity of the carbon monoxide band when measured at 219 nm in solutions containing 1.0 mM chromium plus increasing amounts of cyanide. The increase is directly related to the concentration of the cyanide radical in the flame, after reaching the stoichiometric 6:l ratio. Such a result indicates that the excess of cyanide radicals removes from the flame volume under measurement unwanted oxidising species and restores the chromium signal to its original value. Interference 0 f cations Metal-metal interactions in the flame are complicated. Figure 6 shows that the chromium signal is considerably enhanced when aluminium, calcium or strontium is added to a chromium solution. Such metals may compete with chromium either for flame oxidizing species or for constituents of the nebulized solution so as to form metal monoxides. Dissociation energies Do, in kcsl mol-‘, for AlO, CaO, FeO, NiO, SrO and CrO are 106, 100, 99, 97, 97 and 101, respectively [ 121. In addition, monohydroxides of calcium (Do = 104 kcal mol-‘) and strontium (Do = 103 kcal mol-‘) are likely to be present in air-acetylene flames. These hydroxides and monoxides have very similar stabilities, and an appreciable proportion of each metal is present in these forms in the flame, particularly in the measurement zone.
109
60 40. 2cI
0
6
I2
I6
24
Cyomde concentmtlon
30 (mM)
36
42
I 0
/ 2
i&
1
4 Clnterfermg
EY
6
1
20
catnnl/tchromwml
Fig. 5. Effect of potassium cyanide in the presence of 1.0 mM chromium band emission intensity at 219 nm.
on the CO
Fig. 6. Change in the absorption signal of 1.0 mM chromium as a function of interfering metal ion:chromium ratio: (1) Al*; (2) Cal? (3) SP+; (4) Fe’+; (5) Nil+. (May be due to formation of CrNi, with low melting point and high volatility [ 151.)
When iron or nickel is present in aspirated solution of chromium, the experimental observations are in agreement with the theory that relatively non-volatile compounds are formed between chromium and iron or nickel. These compounds dissociate only slowly in the measurement zone. The severity of the depressive effect is decreased when the measurements are made in the higher regions of the flame, and has disappeared 1.2 cm above the flame base. Control 0 f interferences The action of boron in an airacetylene flame as a promising universal flame buffer was discussed in earlier papers [ 13,141. Its action in the flame, when present in excess, is to interact with the matrix components to form relatively stable, unreactive species, leaving the analyte atoms free. Table 1 indicates that boric acid is a powerful releasing agent and acts very effectively on oxidising species such as nitrate or chlorate and possible reducing species such as nitrite. Moreover, it removes from the area of measurement interfering distintegration products of organic chelating agents. In addition, formation of metal borides of the interferents leads to release of chromium without affecting the atomization process. However, the data in Table 1 help to reach the conclusion that boron can efficiently level the flame conditions to obtain signals identical to samples to which boron but no interferent has been added.
110 TABLE 1 Interference of various species on the absorbance of 1.0 x lo-’ M chromium(II1) effect of different releasing agents Addes substance(s) (200 mg 1-l each)
Chromium recovery (%)” No releasing agent
Boric acid (1.85 x lo-’ M)
NO; NO; Iso:ClO; PO:- + NO; PO:- + NO; + BrPO:- + so:-
60 83 68 93 85 138 33 88 69
EDTA CDTA NTA EDTA + PO;EDTA + PO:- + BrA13’ Caz+ Sr” Fe3+ Nia+ AP+ + Cut+ + Pb=+ Cal+ + Mn’+ + EDTA Sra+ + Cdl+ + Fe3+ SrN + Ba’+ + In” + NO-3
PO:-
and the
SSA (2.0 x lo-’ M)
KCN (5.0x
100 98 100 100 100 100 100 100
100 100 99 100 100 100 100 100 100
100 99 100 100 100 105 100 100
82 80 82 122 100
100 100 100 100 100
100 99 100 102 100
100 99 100 105 105
170 154 130 68 110 150 150 94 83
100 100 100 98 100 100 100 100 100
100 100 100 99 100 100 100 95 95
b b b b b b b b b
98
1O-1 M)
99
aRecovery with respect to the chromium absorbance signal in the presence of the releasing agent alone (= 100%). bPrecipitation of the metal cyanide.
While boric acid acts upon the interferents and their disintegration products, it does not enhance the absorption signals of the analytes. Sulphosalicylic acid (SSA), however, plays a unique role in reacting with the analyte to cause simultaneous enhancement and normalization of the recovered signal, when it is present in large amounts in both samples and standards. Differences in chromium from samples containing diverse ions completely disappear in the presence of 0.02 M SSA. Moreover, SSA doubles chromium signals compared to a chromium chloride solution. The general usefulness of cyanide addition to chromium solutions of samples and standards is quite clear; its precipitating action on a variety of cations can be exploited by filtering off interfering species and the filtrate can be nebulized directly in order to determine chromium.
111 REFERENCES 1 J. C. Van Loon, Analytical Atomic Absorption Spectroscopy, Selected Methods, Academic Press, New York, 1980. 2 I. Rubeska and B. Moldan, Anal. Chim. Acta, 37 (1967) 421. 3 I. Rubeska, Can, J. Spectrosc., 20 (1975) 166. 4 J. Y. Marks and G. G. Welcher, Anal. Chem., 42 (1970) 1033. 5 C. B. Boss and G. M. Hieftje, Anal. Chem., 51(1979) 895. 6 D. Stojanovic, J. Bradshaw and J. D. Winefordner, Anal. Chim. Acta, 96 (1978) 45. 7 J. Posta and J. Lakatos, Magy. Kern. Foly., 86 (1980) 284. 8 M. M. El-Defrawy, J. Posta and M. T. Beck, Anal. Chim. Acta, 115 (1980) 155. 9 E. Juhai, K. Szivos, V. Izekov, T. Kantor and E. Pungor, Magy. Kern. Foly., 86 (1980) 650. 10 A. G. Sharpe, The Chemistry of Cyano-Complexes of Transition Metals, Academic Press, London, 1976. 11 H. Remy, Treatise on Inorganic Chemistry, Vol. 2, Elsevier, Amsterdam, 1956. 12 A. G. Gaydon, Dissociation Energies and Spectra of Diatomic Molecules, 3rd edn., Chapman and Hall, London, 1968. 13 A. M. Abdailah and M. A. Mostafa, Ind. J. Chem., 19A (1980) 1112; Annali di Chimica, 70 (1980) 1. 14 A. M. Abdallah, M. M. El-Defrawy, M. A. Mostafa and A. B. Sakla, Paper presented at the 9th Int. Symp. Microchemical Techniques and Trace-Analysis, Amsterdam, 1983. 15 P. M. Hansen, Constitution of Binary Alloys, 2nd edn., McGraw-Hill, London, 1958.