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Atomic absorption spectrometric determination of phosphorus in biological materials
Analytical Elsevier
Chimica Scientific
Acta, 131 (1981) 303-306 Publishing Company, Amsterdam
-
Printed
in The Netherlands
Short Communication
ATOMIC ABSORPTION SPECI’ROMETRIC DETERMINATION PHOSPHORUS IN BIOLOGICAL MATERIALS
F. J. LANGMYHR*
Department (Received
and I. M. DAHL
of Chemistry. 25th June
OF
University
of Oslo. Oslo 3 (Norway)
1981)
The phosphorus content in the National Bureau of Standards, Standard Reference Materials orchard and tomato leaves, bovine liver and oystir tissue is detcrmined by three atomic absorption spectromctric techniques: measurements of solid and liquid samples against liquid standards, and measurements based on standard additions. All methods gave results which agreed well with the certificate values. Compared to methods involving decomposition and atomization from solution, solid sampling offers the advantages of being direct and fast, and of requiring only small amounts of sample.
Summary.
Phosphorus is an important constituent of many inorganic and organic materials. Quantification of the element by atomic absorption spectrometry (aas.) cannot normally be achieved by measurements at the wavelengths of the resonance lines in the vacuum region; it is necessary to use the most sensitive nonresonance lines at about 214.9 nm, and the unresolved doublet at 213.6 nm. The small proportion of atoms populating these metastable energy levels gives rather poor sensitivity. The importance of temperature on the sensitivity has been stressed by various authors [ 1, 21, who advise that the determination be made by atomization from thermally stable phosphorus compounds at the maximum possible temperature. The use of lanthanum for thermal stabilization of phosphorus was introduced by Ediger [3]. Electrothermal aa.s. determinations of phosphorus in solid materials are based on atomization from the liquid state after dissolution of the sample. To the authors’ best knowledge, the solid sampling technique has not been applied previously. In the present communication, the solid sampling method is applied to the determination of phosphorus in orchard and tomato leaves, bovine liver and oyster tissue.
Experimental Apparatus.
The aas. measurements were made with a Perkin-Elmer 400s instrument equipped with two lamps for background correction and a PyeUnicam SP9-01 atomizer. The atomizer was modified by installing silica windows in both ends, and by introducing the purging gas at the ends; by this modification the smoke developed in the graphite tube was removed through the sample introduction port. Graphite tubes were of the profile type without pyrolytic coating. Solid samples, weighed on a microbalance, 0003-2670/81/0000-0000/$02.50
6 1981 Elsevier
Scientific
Publishing
Company
304
were placed in the middle of the graphite tube by means of a specially-made stainless steel injector by which the sample could bc introduced through the injection port. Liquids were transferred to the graphite tube by means of polytetrafluoroethylene-tipped micropipettes. It is important that the atomizer gives a high and reproducible temperature during the atomization step; to ensure this, a wattmeter was connected to one of the cables from the power supply. An electrodeless phosphorus lamp was employed as the radiation source. Reagents and standard solutions. Phosphorus standard solutions were prcpared from reagent-grade potassium dihydrogenphosphate. Lanthanum solutions were prepared from La,OJ (99.99%, Alfa Division, Danvers, U.S.A.). The nitric acid was of Suprapur quality and the hydrogen peroxide (30%) was of reagentgrade quality (both Merck). A 1% (w/v) standard solution of phosphorus was prepared by dissolving 43.94 g of the dried phosphate in water, adding 50 ml of concentrated nitric acid and diluting to 1 1. A 10% (w/v) solution of lanthanum was prepared by dissolving 29.32 g of the oxide in 40 ml of concentrated nitric acid, and diluting to 250 ml with water; a 1% lanthanum solution was prepared by appropriate dilution. Procedure for decomposition. Portions (0.3-0.5 g) of the plant materials were wet-ashed with 10 ml of concentrated nitric acid and 2 ml of hydrogen peroxide solution. After the decomposition, about 20 ml of water and 5 ml of 10% (w/v) lanthanum solution were added, and the solutions were diluted to 50 ml. Similarly, portions of about 0.1 g of bovine liver and of oyster tissue were attacked with 4 ml of concentrated nitric acid and about 5 drops of hydrogen peroxide solution; the further procedure was as described above for the plant materials. Blank solutions were prepared_ Spectrometric procedures. In all cases, peak heights were measured; for the decomposed samples of liver and oyster tissue, peak areas were also measured. The determinations were made as follows: Method A_ Solid samples measured wainst liquid standards. Solid samples (0.2-0.4 mg) were transferred to the graphite tube by means of the injector, and 5 ~1 of 1% lanthanum solution was added. It is important that the lanthanum solution is soaked up by the sample, and the addition should therefore be observed through a mirror. The instrumental parameters pertaining to the measurements are listed in Table 1. For each sample, 4-8 portions were atomized. The calibration curve was found to be linear up to about 1200 ng of phosphorus; in those instances where the sample signal was outside the linear range, the curve was extended by measuring more-concentrated standard solutions. Method B. Liquid samples measured against liquid standards. From the solutions of the decomposed samples, lo-111portions were transferred to the atomizer, and the procedure described above for Method A was followed,
305 TABLE
1
Instrumental
parameters
and
programs
for the atomic
absorption
spcctrometry
of
solid
and liquid samples Parameter
Solids
Liquids
Lamp power (w) Wavelength (nm) Spectral bandwidth
8 214.9 0.7
8 213.6 2
(nm)
Heating program: Drying FJfrOlYsiS Atomization Tube
20 5.100”c 50 s, 165O’C 8 s, 2800°C
8 s. 2SOO”C
cleaning
with the exceptions aliquot
portions
were
apparent
from Table
15 s, 100°C 35 s, 1350°C 8 s, 2800°C
8 s. 2900°C
1. For each sample solution,
four
atomized.
Method C. Standard additions. Three 12-ml portions of each sample solution were transferred to 25ml volumetric flasks. To two of the flasks, 2 and 5 ml of phosphorus standard solution (50 ppm) were added, to all flasks 2.5-ml portions of 10% lanthanum solution were added, and the solutions were made up to the mark. A blank solution was prepared. The solutions were measured in triplicate and in the same way as for Method B. Results and discussion The methods described above were applied to the following Standard Reference Materials (SRM) from the National Bureau of Standards (NBS), Washington, D-C.: Orchard Leaves SRM 1571, Tomato Leaves SRM 1573, Bovine Liver SRM 1577, and Oyster Tissue SRM 1566. The two former samples are certified for phosphorus, while for the other two materials only tentative values arc given. The samples were dried as specified by NBS and the results listed in Table 2 refer to the dried materials_ For those samples (liver and oyster tissue) where both peak heights and peak areas were measured the results were in close agreement, and only the averages are tabulated As is apparent from Table 2, the accuracy and precision of the present methods are satisfactory_ The small amounts of sample taken for the direct determination in solid materials do not seem to introduce any serious sampling errors. In a critical compilation of data on elemental concentrations in NBS biological and environmental standard reference materials, Gladney [4] has listed the following averages (in percent) and standard deviations for the phosphorus values reported in the literature: orchard leaves 0.198 f 0.019 (13); tomato leaves 0.334 + 0.012 (3); bovine liver 1.05 + 0.16 (9). (The numbers in parentheses refer to the number of values represented in the average.) No data were given for the recently issued sample of oyster tissue. The averages
306 TABLE
2
Determination
of phosphorus
in some
biological
materials
NBS certificate value (W)
Content (90) by Method’
Sample
A
B
Orchard leaves Tomato leaves Bovine leaves
0.33 r 0.02
Oyster
0.76 I 0.04
tissue
0.19 1.04
: 0.02b : 0.06
0.20
C z 0.01
0.20
% 0.01
0.21
0.32 2 0.02
0.35 I 0.02
1.10
n.d.
l.lC
n-d.
O.Bl=
t 0.02
0.78 2 0.03
z 0.01
0.34 t 0.02
aThe letters refer to the procedures described above. bThe average and the standard deviation of the present methods. =Tentative data.
listed by Gladney are in excellent agreement with the NBS certificate values and the data obtained by the present methods. From results reported previously in the literature and from the results of the present work, it is evident that the content of phosphorus in dissolved samples of biological materials can be conveniently determined by electrothermal a_a.s. It is as effective, however, to use the solid sampling technique, which has the significant advantages of being fast and direct and of requiring only small amounts of sample. REFERENCES 1 B. V. L’vov
and L. A. Pclicva,
Zh. Anal.
Khim.,
33 (1978)
2 J.-A. Persson and W. Frech, Anal. Chim. Acta. 119 (1980) 3 R. D. Ediger, At. Absorpt. Newsl., 15 (1976) 145. 4 E. S. Gladney. Anal. Chim. Acta, 118 (1980) 385.
1572.
75.
Chimica Scientific
Acta, 131 (1981) 303-306 Publishing Company, Amsterdam
-
Printed
in The Netherlands
Short Communication
ATOMIC ABSORPTION SPECI’ROMETRIC DETERMINATION PHOSPHORUS IN BIOLOGICAL MATERIALS
F. J. LANGMYHR*
Department (Received
and I. M. DAHL
of Chemistry. 25th June
OF
University
of Oslo. Oslo 3 (Norway)
1981)
The phosphorus content in the National Bureau of Standards, Standard Reference Materials orchard and tomato leaves, bovine liver and oystir tissue is detcrmined by three atomic absorption spectromctric techniques: measurements of solid and liquid samples against liquid standards, and measurements based on standard additions. All methods gave results which agreed well with the certificate values. Compared to methods involving decomposition and atomization from solution, solid sampling offers the advantages of being direct and fast, and of requiring only small amounts of sample.
Summary.
Phosphorus is an important constituent of many inorganic and organic materials. Quantification of the element by atomic absorption spectrometry (aas.) cannot normally be achieved by measurements at the wavelengths of the resonance lines in the vacuum region; it is necessary to use the most sensitive nonresonance lines at about 214.9 nm, and the unresolved doublet at 213.6 nm. The small proportion of atoms populating these metastable energy levels gives rather poor sensitivity. The importance of temperature on the sensitivity has been stressed by various authors [ 1, 21, who advise that the determination be made by atomization from thermally stable phosphorus compounds at the maximum possible temperature. The use of lanthanum for thermal stabilization of phosphorus was introduced by Ediger [3]. Electrothermal aa.s. determinations of phosphorus in solid materials are based on atomization from the liquid state after dissolution of the sample. To the authors’ best knowledge, the solid sampling technique has not been applied previously. In the present communication, the solid sampling method is applied to the determination of phosphorus in orchard and tomato leaves, bovine liver and oyster tissue.
Experimental Apparatus.
The aas. measurements were made with a Perkin-Elmer 400s instrument equipped with two lamps for background correction and a PyeUnicam SP9-01 atomizer. The atomizer was modified by installing silica windows in both ends, and by introducing the purging gas at the ends; by this modification the smoke developed in the graphite tube was removed through the sample introduction port. Graphite tubes were of the profile type without pyrolytic coating. Solid samples, weighed on a microbalance, 0003-2670/81/0000-0000/$02.50
6 1981 Elsevier
Scientific
Publishing
Company
304
were placed in the middle of the graphite tube by means of a specially-made stainless steel injector by which the sample could bc introduced through the injection port. Liquids were transferred to the graphite tube by means of polytetrafluoroethylene-tipped micropipettes. It is important that the atomizer gives a high and reproducible temperature during the atomization step; to ensure this, a wattmeter was connected to one of the cables from the power supply. An electrodeless phosphorus lamp was employed as the radiation source. Reagents and standard solutions. Phosphorus standard solutions were prcpared from reagent-grade potassium dihydrogenphosphate. Lanthanum solutions were prepared from La,OJ (99.99%, Alfa Division, Danvers, U.S.A.). The nitric acid was of Suprapur quality and the hydrogen peroxide (30%) was of reagentgrade quality (both Merck). A 1% (w/v) standard solution of phosphorus was prepared by dissolving 43.94 g of the dried phosphate in water, adding 50 ml of concentrated nitric acid and diluting to 1 1. A 10% (w/v) solution of lanthanum was prepared by dissolving 29.32 g of the oxide in 40 ml of concentrated nitric acid, and diluting to 250 ml with water; a 1% lanthanum solution was prepared by appropriate dilution. Procedure for decomposition. Portions (0.3-0.5 g) of the plant materials were wet-ashed with 10 ml of concentrated nitric acid and 2 ml of hydrogen peroxide solution. After the decomposition, about 20 ml of water and 5 ml of 10% (w/v) lanthanum solution were added, and the solutions were diluted to 50 ml. Similarly, portions of about 0.1 g of bovine liver and of oyster tissue were attacked with 4 ml of concentrated nitric acid and about 5 drops of hydrogen peroxide solution; the further procedure was as described above for the plant materials. Blank solutions were prepared_ Spectrometric procedures. In all cases, peak heights were measured; for the decomposed samples of liver and oyster tissue, peak areas were also measured. The determinations were made as follows: Method A_ Solid samples measured wainst liquid standards. Solid samples (0.2-0.4 mg) were transferred to the graphite tube by means of the injector, and 5 ~1 of 1% lanthanum solution was added. It is important that the lanthanum solution is soaked up by the sample, and the addition should therefore be observed through a mirror. The instrumental parameters pertaining to the measurements are listed in Table 1. For each sample, 4-8 portions were atomized. The calibration curve was found to be linear up to about 1200 ng of phosphorus; in those instances where the sample signal was outside the linear range, the curve was extended by measuring more-concentrated standard solutions. Method B. Liquid samples measured against liquid standards. From the solutions of the decomposed samples, lo-111portions were transferred to the atomizer, and the procedure described above for Method A was followed,
305 TABLE
1
Instrumental
parameters
and
programs
for the atomic
absorption
spcctrometry
of
solid
and liquid samples Parameter
Solids
Liquids
Lamp power (w) Wavelength (nm) Spectral bandwidth
8 214.9 0.7
8 213.6 2
(nm)
Heating program: Drying FJfrOlYsiS Atomization Tube
20 5.100”c 50 s, 165O’C 8 s, 2800°C
8 s. 2SOO”C
cleaning
with the exceptions aliquot
portions
were
apparent
from Table
15 s, 100°C 35 s, 1350°C 8 s, 2800°C
8 s. 2900°C
1. For each sample solution,
four
atomized.
Method C. Standard additions. Three 12-ml portions of each sample solution were transferred to 25ml volumetric flasks. To two of the flasks, 2 and 5 ml of phosphorus standard solution (50 ppm) were added, to all flasks 2.5-ml portions of 10% lanthanum solution were added, and the solutions were made up to the mark. A blank solution was prepared. The solutions were measured in triplicate and in the same way as for Method B. Results and discussion The methods described above were applied to the following Standard Reference Materials (SRM) from the National Bureau of Standards (NBS), Washington, D-C.: Orchard Leaves SRM 1571, Tomato Leaves SRM 1573, Bovine Liver SRM 1577, and Oyster Tissue SRM 1566. The two former samples are certified for phosphorus, while for the other two materials only tentative values arc given. The samples were dried as specified by NBS and the results listed in Table 2 refer to the dried materials_ For those samples (liver and oyster tissue) where both peak heights and peak areas were measured the results were in close agreement, and only the averages are tabulated As is apparent from Table 2, the accuracy and precision of the present methods are satisfactory_ The small amounts of sample taken for the direct determination in solid materials do not seem to introduce any serious sampling errors. In a critical compilation of data on elemental concentrations in NBS biological and environmental standard reference materials, Gladney [4] has listed the following averages (in percent) and standard deviations for the phosphorus values reported in the literature: orchard leaves 0.198 f 0.019 (13); tomato leaves 0.334 + 0.012 (3); bovine liver 1.05 + 0.16 (9). (The numbers in parentheses refer to the number of values represented in the average.) No data were given for the recently issued sample of oyster tissue. The averages
306 TABLE
2
Determination
of phosphorus
in some
biological
materials
NBS certificate value (W)
Content (90) by Method’
Sample
A
B
Orchard leaves Tomato leaves Bovine leaves
0.33 r 0.02
Oyster
0.76 I 0.04
tissue
0.19 1.04
: 0.02b : 0.06
0.20
C z 0.01
0.20
% 0.01
0.21
0.32 2 0.02
0.35 I 0.02
1.10
n.d.
l.lC
n-d.
O.Bl=
t 0.02
0.78 2 0.03
z 0.01
0.34 t 0.02
aThe letters refer to the procedures described above. bThe average and the standard deviation of the present methods. =Tentative data.
listed by Gladney are in excellent agreement with the NBS certificate values and the data obtained by the present methods. From results reported previously in the literature and from the results of the present work, it is evident that the content of phosphorus in dissolved samples of biological materials can be conveniently determined by electrothermal a_a.s. It is as effective, however, to use the solid sampling technique, which has the significant advantages of being fast and direct and of requiring only small amounts of sample. REFERENCES 1 B. V. L’vov
and L. A. Pclicva,
Zh. Anal.
Khim.,
33 (1978)
2 J.-A. Persson and W. Frech, Anal. Chim. Acta. 119 (1980) 3 R. D. Ediger, At. Absorpt. Newsl., 15 (1976) 145. 4 E. S. Gladney. Anal. Chim. Acta, 118 (1980) 385.
1572.
75.