Of course, if there were a means by which one could check the calibration with very great confidence, that means could itself serve as a calibration. Certainly none has come t o our attention. F o r the most part, confidence in the reliability of the calibration must be placed almost entirely in the reasonableness of the procedure. We believe such confidence is wellplaced, and our belief is reinforced by the agreement between our measurements (10) and those of Maloy and Bard (ZI) for the emission efficiency of the 9,lO-diphenylanthracene anioncation reaction. There are a few pitfalls in the operation of the apparatus that should perhaps be pointed out. Demas and Crosby ( I ) have recently described a pair of subtle effects which can alter the operation of integrating spheres. First, variations in the reflectivity of the sphere coating with wavelength can produce a strongly wavelength-dependent value for FSpllere. However, the sources of interest in our work emit in spectral regions in which the coating reflectance has been shown t o be quite constant (12); hence this effect was considered unimportant and its magnitude was not determined. Nevertheless, an assessment of the effect is worthwhile if short-wavelength sources are to be used, and it is conveniently carried out by comparing the spectrum from a continuous source recorded indirectly (10) R. Beznian and L. R. Faulkner, submitted for publication. ( 1 1 ) J. T. Malo) and A. J. Bard, J . A m v . C h m . Soc.. in press. (12) Eastman Kodak Co.. Rochester, N.Y., publications 5532 and 5533.
via the integrating sphere t o that obtained either directly or following one reflection from the Eastman paint. Demas and Crosby further indicated that if anything inside the sphere absorbs the source emission, the observed intensity can be greatly reduced because the light within the sphere is reflected so many times. This effect has not been a problem to us, but obviously it may be troublesome in certain instances. A third pitfall pertains to emitters having appreciable output at wavelengths longer than 610 nm. The fluorescent screen abruptly becomes transparent at about this wavelength ; hence long-wavelength light emerging from the sphere will register directly at the phototube, rather than being subjected t o the fluorescent scattering of the screen. This effect will appear as a n Fd value different from that obtained in the calibration procedure. We have encountered this problem in our studies of rubrene-containing systems (10), but in that case, the emission beyond 610 nm is small and a correction c a n be applied. Even recognizing problems like these, we nevertheless believe the present apparatus and calibration procedure represents a considerable improvement over the measurement methods ordinarily used in fields where they apply. RECEIVED for review June 28, 1971. Accepted August 23, 1971. The support of this research by the E. I. duPont de Nemours Company and the William F. Milton Fund of Harvard University is gratefully acknowledged. We are also indebted t o the National Science Foundation for a Graduate Fellowship awarded t o one of us (R. B.).
Fluorometric Determination of Submicrogram Quantities of Tin T. D. Filer Health Sercices Luhoratorj’, US.Atomic Energ!, Commission, Idaho Fulls. Idaho
A fluorometric procedure for the determination of tin using 3,4’,7-trihydroxyflavone (THF) has been developed that is much more sensitive than other common methods. After decomposition of the sample by a pyrosulfate fusion, the tin is extracted as the iodide into toluene from a sulfuric acid solution. The fluorescence of the tin(1V)-THF complex is measured in a sulfate buffer solution. The method has a detection limit of 0.007 pg, a precision to about 2% on 1 p g , and excellent tolerance to most common elements, antimony and tantalum being the only serious interferences.
FEWSENSITIVE PROCEDURES exist for the determination of microgram quantities of tin. Fluorometric procedures have been developed using the ammonium salt of 6-nitro-2 naphthylamine-8-sulfonic acid ( I ) , flavanol (2), and oxine-5sulfonic acid (3). The reaction of tin(I1) with the ammonium salt of 6-nitro-2-naphthylamine-8-sulfonic acid permits 0.1 pg/ml of tin t o be determined ( I ) . Since tin(I1) is the reactant species, reduction of tin and development of fluorescence must be carried out in a n inert atmosphere, and ions which are also capable of reducing the reagent will cause serious positive interferences in the procedure. The reaction of tin(IV) with Anderson and S . L. Lowy, Aim/. Chim. Actri. 15,246-53 (1956). ( 2 ) C. F. Coyle and C. E. White, ANAL.CHEM., 29, 1486-88 (1957). (3) B. K . Pal and D. E. Ryan, Auul. Chin?.Actu, 48, 227-31 (1969). (1) 5. R . A.
flavanol permits 0.1 pg/ml of tin to be determined, and only phosphate, fluoride, hafnium, and zirconium interfere. Close control of dimethylformamide concentration is necessary and satisfactory results are not obtained in the presence of chloride ion (2). The reaction of oxine-5-sulfonic acid with tin(I1) o r tin(1V) permits 0.001 pg,iml of tin t o be determined if the fluorescence is developed in a closely controlled concentration of ethanol, methanol, or p-dioxane; or 0.1 pg/ml of tin may be determined if the fluorescence is developed in water (3). Magnesium, cadmium, thorium, cobalt, fluoride, nickel, zirconium, hafnium, zinc, and aluminum are serious interferences in this procedure. The present procedure uses 3,4’,7-trihydroxyflavone (THF) which is 3 t o 15 times more sensitive to tin than the reagents listed above. Antimony, zirconium, hafnium, aluminum, gallium, tungsten, molybdenum, niobium, and tantalum interfere in the direct determination of tin. However, tin can be satisfactorily separated from most interfering ions by extracting the iodide from a sulfuric acid solution into toluene. EXPERIMENTAL
Apparatus. The instrumentation used was a Beckman DU spectrophotometer with a fluorescence accessory modified as described (4). A combination of Corning Filters with (4) C. W. Sill and C . P. Willis, ANAL.CHEM., 31,598 (1959).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
1753
color specification Nos. 3-74 and 5-58 having over 1 transmittance between 412 and 473 nm with a maximum of 27% transmittance was used for the primary. A combination of Corning Filters with color specification Nos. 3-71 and 4-97 having over 1 % transmittance between 463 and 680 nm with a maximum transmittance of 72 was used for the secondary. A tungsten source was used in the present work, but a mediumpressure mercury lamp can be used with the same filter combinations with similar results. Reagents. STANDARDTIN SOLUTIONS,1 mg/ml and 1 pg/ml. Dissolve 1.000 gram of metallic tin in 250 ml of concentrated hydrochloric acid and dilute to 1 liter. Dilute 1.00 ml of the stock solution and 250 ml of concentrated hydrochloric acid to 1 liter. The solutions contain 1 nig/ml and 1 pg/ml of tin, respectively. SULFATEBUFFERSOLUTION. Dissolve 110 ml of concentrated sulfuric acid in about 400 ml of water. Dissolve 120 grams of sodium hydroxide in about 400 ml of water. Carefully combine the solutions with cooling, add 20 grams of sulfamic acid, and dilute to 1 liter. Store in a glass-stoppered borosilicate glass bottle. “Reagent grade” sodium sulfate was found to be too impure t o use for the preparation of the buffer solution. 3,4’,7-TRIHYDROXYFLAVONE SOLUTION, 5 X %. The preparation of the flavone has been described (5-7). Transfer 5.0 mg to a 100-ml volumetric flask and dilute to volume with 95 ethanol. Sample Preparation. SOILSAND ROCKS. A procedure for the decomposition of the refractory silicates which involves a potassium fluoride fusion and a transposition to a mixed alkali pyrosulfate fusion has been described (8). Pretreatment of the sample with concentrated nitric acid will be necessary in cases where chlorides, bromides, or iodides are present t o eliminate loss of the tin halide by volatilization. In cases where silicates are known to be absent, the potassium fluoride fusion can be omitted and the sample treated initially with nitric acid followed by a pyrosulfate fusion. The solution is then diluted to any desired volume and a n appropriate aliquot is separated as described below. BIOLOGICALSAMPLES.Conventional wet-ash methods using nitric, sulfuric, and perchloric acids are used for the digestion of organic material. The residue is dissolved by a pyrosulfate fusion. Procedures for the decomposition of whole blood, tissue, bone, feces, and urine have been described (9). After the pyrosulfate fusion, the solution is diluted to any desired volume and a n appropriate aliquot is separated as described below. Separation of Tin. Although some samples can be analyzed directly following dissolution, tin must be separated from other elements whenever the sample is of unknown composition; whenever trace amounts of tin are present in a large excess of some interfering element; or whenever the sample is suspected of containing one or more of the particularly serious interferences, such as antimony, tungsten, tantalum, or aluminum. A convenient and very selective solvent extraction method in which tin is extracted as the tetraiodide from 9N sulfuric acid into toluene has been adapted to this procedure (IO,I I ) . After sample dissolution, a n appropriate aliquot is transferred to a 100-ml beaker. Add 1 ml of a 17% solution of sodium hydrogen sulfate and 10 drops of concentrated sulfuric acid and heat until all the sulfuric acid, including that
z
( 5 ) D. G. Roux and G. C . de Bruyn, Bioclzam. J . , 87, 439 (1963).
(6) K. Yamaguchi, Nippon Kagnka Zasslii, 1963, 148. (7) Z . I. Jerzmanowska and M. Michalska, Rocz. Clim., 35, 353 (1961). (8) C. W. Sill, ANAL. CHEM., 33, 1684 (1961). (9) C. W. Sill and C. P. Willis, ibid., 36, 622-30 (1964). (10) E. J. Newman and P. D. Jones, Analysr, 91, 406-10 (1966). (11) K. Tanaka and N. Takagi, Anal. Chitti. Acra, 48, 357-66 (1969).
1754
condensed on the beaker walls, has been volatilized and fuming has ceased. Add 2 ml of water, cover the beaker with a watch glass, and boil the solution until the volume has been reduced to about 0.5 ml. Rinse the cover glass with a few drops of 9N sulfuric acid. Add 10 m l of 9N sulfuric acid and transfer the solution quantitatively t o a 60-ml separatory funnel using three 5-ml aliquots of the 9N sulfuric acid to wash the beaker. Add 2.5 ml of freshly prepared 5 M potassium iodide and mix thoroughly. Extract the solution with 10 ml of toluene for 2 minutes and discard the aqueous phase. The toluene layer will be colored pink with extracted iodine. Add 15 ml of 9N sulfuric acid and shake for 5 seconds. Add 3 ml of 5 M potassium iodide, extract for 1 minute, and discard the aqueous phase. Add 5 ml of water t o the toluene extract and then add 5M sodium hydroxide dropwise with shaking until the toluene layer is colorless. Add 2 drops in excess (usually a total of 8 to 10 drops is required). Stopper and shake the funnel for 30 seconds and run the aqueous layer into a 100-ml beaker. Shake the toluene layer with two 3-ml portions of 0.1M sodium hydroxide for 30 seconds and add each of the wash solutions t o the contents of the 100-ml beaker. Add 1 ml of 17% sodium hydrogen sulfate, 10 drops of concentrated sulfuric acid, and 5 drops of concentrated nitric acid t o the combined extracts and continue as described below. Procedure. The procedure given below for preparation and measurement of the fluorescence is that used in the development of the procedure with pure tin solutions and is to be followed when tin has been separated from interfering elements. However, some applications of this procedure can be made without separations, provided the sample size is chosen so that the heavy metal content does not exceed the permissible levels described below. Place the tin standard or other tin solution in a 100-ml beaker. Add 1 ml of a 17% solution cf sodium hydrogen sulfate, 5 drops of concentrated nitric acid, and 10 drops of concentrated sulfuric acid and evaporate the solution until fumes of sulfuric acid appear. Cool, add 1 ml of water and 5 drops of concentrated nitric acid, and evaporate the solution again until fumes of sulfuric acid appear. Repeat this step and heat to a pyroculfate fusion. The nitric acid treatment can be omitted if halides are known to be absent. Cool the residue and add 2 ml of water and 3 drops of 25 % hydroxylammonium sulfate. Cover the beaker with a watch glass and boil the solution until the volume has been reduced t o about 0.5 ml. Rinse the cover glass with a few drops of water. Pipet 10 ml of the sulfate buffer solution into the beaker. Transfer the ~ o l u t i o nquantitatively to a 25-ml volumetric flask using about 5 ml of water. Add 1.00 ml of T H F solution, mix, and dilute t o volume. Mix thoroughly and place in a constant-temperature bath for 20 minutes. Measure the fluorescence using the technique described previously ( 4 , 12). A 2 X solution of quinine sulfate can be used as a standard t o reproduce the same instrumental sensitivity from day to day. The time of measurement after addition of the T H F is very important and should be kept within 3 or 4 minutes of the recommended value of 20 minutes for blanks, standards, and samples for highest precision. Also, the temperature of the water bath should be within 1 or 2 “C of the prevailing room temperature to minimize temperature effects while handling the cell. Place 1 ml of water for a blank and 1 ml of the l-pg/ml standard tin solution in separate 100-ml beakers and add 2 drops of concentrated sulfuric acid and 1 ml of 1 7 z sodium hydrogen sulfate solution. Evaporate carefully to dryness o n an asbestos-covered hot plate until evolution of sulfuric acid fumes has ceased and treat as described above. Subtract the blank reading from that of the standard and express the (12) C. W. Sill, C. P. Willis, and J. K. Flygare, Jr., ANAL. CHEM., 33, 1671 (1961).
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1 9 7 1
I
I
I
I
I
I
1
io0
90
80
70
P 60 ._ 0 Q
-
[z
50
i
-2
- 40 30
-1
2c
2
0
3,4:7
Figure 1.
-
4
6
Trihydroxyflovone Concentration ( x
0
ic
%I
Effect of 3,4‘,7-trihydroxyflavone concentration 1. 1 pg Sn standard 2. Blank 3. 1 pg Sn standard corrected for blank
C
1 1
3
0
2
i
3
2
0.5 M_
H 2 S 0 4 , ml
1 M_
NoOH,rni
Figure 2. Effect of acidity
sensitivity as micrograms of tin per net scale division. Correct the samples for a n appropriate blank carried through the entire procedure including separations, if any, and calculate the tin content from the sensitivity value obtained from the standard. RESULTS AND DISCUSSION
Erratic results were obtained during the development of this procedure because of the ease with which quadrivalent tin hydrolyzes to form metastannic acid (13, 14). Several times during the preparation of the sample for fluorescence measurement, conditions prevail that are certain t o cause the formation of metastannic acid-e.g., the removal of the halides in the sample by fuming with concentrated nitric and sulfuric acids. Failure t o redissolve the metastannic acid causes low results on the immediate sample and high results on subsequent samples due t o contamination of the glassware. Therefore, a pyrosulfate fusion is always used t o dissolve the original sample and is also used during the procedure at points where conditions might exist that are likely t o form metastannic acid. The excellent precision and reliability of the present procedure clearly shows the effectiveness of pyrosulfate fusions in eliminating any solubility problems due t o the formation of metastannic acid. Effect of 3,4 ’,7-Trihydroxyflavone Concentration. Figure 1 shows the relationship between T H F concentration and fluorescence intensity. Curve 1 shows that the intensity of the fluorescence of 1 pg of tin increases with increasing flavone (1 3) H. Remy, “Treatise on Inorganic Chemistry,” Elsevier,
Houston, Texas, 1956. Chap. 12. (14) G. E. Collins and J. K. Wood, J. Chem. SOC.(Lo~zdon), 121, 441-49 (1922).
1. 1 pg Sn standard 2. Blank
concentration. If the highest precision is desired, the highest concentration of flavone should be used because the maximum fluorescence signal is produced at this level and the instrument can be operated in the range of maximum stability. Also, at the higher concentration of flavone, small changes in concentration will not produce significant variations in the fluorescence readings. However, the concentration of flavone can be adequately controlled so that it will not significantly affect the precision even on the steeper portion of Curve 1. On the other hand, the ratio of the net tin fluorescence to the blank fluorescence (signal t o noise) is greater at lower concentrations of the flavone and reaches a maximum at 2 X If the instrumental sensitivity can be increased so that the relatively weak fluorescence obtained at lower flavone concentrations can be used without significant loss of precision, smaller quantities of tin can be detected. The minimum detectable quantity of tin and the proper concentration of the flavone to be used are dependent on the value of the blank, and the stability and sensitivity of the instrument. A concentration of 2 X lOd4XT H F was used in this work, a ratio of 22 moles of T H F for 1 mole of tin. Effect of Acidity. The effect of changes in acidity o n the fluorescence of the tin-THF complex was studied. Various amounts of 1M sodium hydroxide or 0.5M sulfuric acid were added to the volumetric flask before the addition of the flavone. The excellent buffering capacity of the system is indicated by the data shown in Figure 2. The arrows mark the points o n the buffer curves that result under the recommended conditions. Spectral Characteristics. The excitation and emission spectra for the reagent and its tin complex were obtained
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
1755
2. c .-
In
0 C c
-c 0 0 E v)
E
-a lL
I
I
300
400
I 500
I 600
Wavelength, nrn
Figure 3. Excitation and emission spectra of reagent and tin complex in 1Mperchloric acid A.
B. C. D.
+ +
Sn reagent. Sn reagent. Reagent alone. Reagent alone
Excitation at 427 nm Emission at 473 nm Excitation at 377 nm Emission at 485 nm
with a Cary 14 recording spectrophotometer with a model 1412 fluorescence attachment. The fluorescence of THF exhibits its excitation maximum at 377 nm and a fluorescence emission maximum at 485 nm as shown in Figure 3. The tin complex shows its excitation maximum at 427 nm and fluorescence emission maximum at 473 nm. All values are uncorrected for emission characteristics of the light source or the response of the detector. Detection Limit and Precision. The detection limit and determination limit as defined by Currie (15) were determined for this procedure. To determine the precision obtained with larger quantities of tin, 12 blanks and twelve 1-pg tin standards were analyzed starting with the evaporation of tin solutions t o dryness in the presence of sulfuric acid. The mean for the 1-pg tin standards was 103.7 scale divisions with a standard deviation of 1 0 . 9 scale division. The mean for the blanks was 13.9 scale divisions with a standard deviation of i 0 . 2 scale division. The results indicate a detection limit of 0.007 pg of tin. The minimum quantity of tin that can be determined with a precision of 10% is 0.02 pg. Linearity. The effect of tin concentration on the fluorescence was investigated at a THF concentration of 2 X t o determine the linearity under analytical conditions. The instrument response for samples containing up t o 6 pg of tin is linear within the precision of the procedure-Le., about 2%'. As the quantity of tin is increased beyond 6 pg, deviation from linearity toward the concentration axis becomes more pronounced. Effect of Time. The effect of time of development o n the fluorescence of a 1-pg tin standard was studied under the rec(15) L. A. Currie, ANAL.CHEM., 40, 586-93 (1968). 1756
ommended conditions. The fluorescence increases by about 5 between 5 and 15 minutes after addition of THF, remains constant during the next 10 minutes, and decreases by about 3 %' during the next 2 hours. Blanks reach maximum fluorescence in about 5 minutes after addition of THF and remain constant for at least 2 hours. Therefore, a standing time of 20 minutes is recommended since it is sufficiently long for full fluorescence development and allows a tolerance of 3 t o 4 minutes in either direction without affecting precision. Effect of Temperature. The effect of temperature on the fluorescence of a 1-pg tin standard was studied in the range of 15 to 35 "C. The tin-THF complex was found t o have a temperature coefficient of about - 1%' per "C. Therefore, the temperature should be controlled t o within 1 or 2 "C. Effects of Other Substances. A detailed investigation was made of the effect of many other substances on both blanks and 1-pg tin standards. The element o r compound investigated was added before fuming with sulfuric acid t o determine its effect under the recommended conditions. The following substances produced no error on blanks and less than 2 % error o n 1-pg tin standards: 1 mg of chloride, bromide, iodide, lithium, potassium, rubidium, cesium, magnesium, zinc, iron, cobalt, copper, lutetium, manganese, vanadium, and yttrium; or 0.1 mg of titanium, platinum, cadmium, mercury, boron, nickel, calcium, silver, lead, scandium, lanthanum, thorium, selenium, uranium, gadolinium, and thallium. Errors produced by other substances are shown in Table I. The effectiveness of the separation procedure for the more serious interferences is also shown in Table I. FLUORESCENT COMPLEXES. Antimony (16), zirconium (17), hafnium, aluminum, gallium, indium, thallium, beryllium, arsenic, germanium, tungsten, and molybdenum also form fluorescent complexes with the flavone under the given conditions. A fluorometric procedure for tungsten is presently being investigated. The extraction procedure increases the tolerance of the method t o most of these interferences by at least a factor of ten. The lone exceptions are beryllium and arsenic which appear to follow tin through the extraction. HALIDES. Iodide, bromide, and, in some cases, chloride can be serious interferences in this procedure if they are present during strong heating of the sample because of the volatility of the tin halides. Oxidation of the halide to the halogen with nitric acid before such treatment eliminates this interference. The presence of fluoride in the final solution used for fluorometric determination produces serious negative interference, probably due t o the complexation of tin. Fortunately, fluoride will be eliminated from the original sample by the pyrosulfate fusion. However, the pyrosulfate fusion should be carried out in platinum rather than glass in the presence ofluoride because hydrogen fluoride will dissolve enough zirf conium from the glass to give a positive interference. Chromium, nioCHROMIUM, NIOBIUM,AND TANTALUM. bium, and tantalum are particularly serious interferences because of their strong absorption of both the emitted tinT H F fluorescence and the exciting radiation and because of the insolubility of anhydrous chromic sulfate, niobic acid, and tantalic acid. The extraction procedure separates tin from niobium and tantalum but not effectively from chromium. Chromium can be removed easily from sulfuric-perchloric acid solutions by volatilization with hydrogen chloride gas. PHOSPHATE.As seen from Table I, phosphate is a very (16) T. D. Filer, ANAL.CHEM., 43,725 (1971) (17) Ibid., pp 469-73.
ANALYTICAL CHEMISTRY, VOL. 43, NO. 13, NOVEMBER 1971
Element Sb
Quantity, mg
Ce
1 .o 1 .o 0.1
Ceb F
1 .o
1 .o
$15.9 +0.6 132.2 +1.2 +18.5 +0.8 +3.5 $0.4 +1.6 +0.9 $11.4 +1.4 +3.2 +2.7 +7.6 +9.7 -0.1 $3.0 0.0 +3.4 - 1 .o +2.0 +0.7 -0.5 +0.4 $14.3 +3.0 -2.0 15.5 t4.2 -0.8 -3.1 -0.7 +0.9 +1.2 +I .2 +6.0
Feh
10.0
-0.5
Sbb Zr Zrb Hf Hfb AI
AIb Ga Gab I I1
T1
Be As
Ge W Wb
Mo Mob
Nb N b" Ta Tat' Bi Bi"
Cr Ba Sr Si Au A Ub P P Pb
0.001 0.001 0.001 0.1
Table I. Effect of Other Substances Error, scale divisionBlank 1 Pg Sn
0.001
0.1 0.01 0.1
0.001 0.01 1 .O 1 .O
0.1 1 .o 0.1 0.01 0.01 0.01 1 .o 0.01 0.01 0.01 0.001 0.1 0.I 0.1 0.1 0.1 1 .o 0.1 I .o 1 .o
>+IO -0.3 >+lo 0.0 >+IO 0.0 +I .6 $2.1 +3.6 -2.3 +6.0 +1 .o +6.0 +3.0 +3.1 +2.6 +2.4 -3.1 0.0 -20.6 -0.2 -42.2 $0.6 -9.8 +0.7 -46.4 -0.6 +0.5 -2.4 -1
.o
-0.2 -90.3 -3.5 -1.5 +I .2 - 1.o +6.4
Remarks Fluor. ; 0.06 pg/scale div Fluor. ; 0.03 pg/scale div Fluor. ; 0.05 pykcale div
Fluor.; 3 pgiscale div Fluor. ; 0 . 6 pg/scale div Fluor.; Fluor.; Fluor.; Fluor.; Fluor. ; Fluor.;
88 pgiscale div 715 pgjscale div 31 pg/scale div 370 pg/scale div 13 pg/scale div 1 pglscale div
Fluor.; 3 pgjscale div Yellow complex with flavone Yellow complex with flavone Yellow complex with flavone Anhydrous Cr2(S04).,precipitates Tyndall effect due to BaS04 Tyndall effect due to SrSO( Flocs of Si02 Elemental gold precipitates Added as NanHPOI before fuming Added as Na?HPOI after fuming Slight turbidity due to NaCe(SOr)t! Added as NaF before fuming. Fluoride dissolves zirconium from glass
-0.8
Blank, 13.9 scale divisions: 1 pg Sn standard, 103.7 scale divisions; sensitivity, 0.011 1 pg/scale division. Differences larger than &0.4 scale division on blanks or 1 2 . 0 scale divisions on standards probably indicate significant effect of added substance. Carried through the separation procedure as described.
Sample Soil Soil Tissue Tissue
Weight, g 0.5 0.5 100 100
Table 11. Recovery of Tin Tin in sample weight Tin added, pg taken, pg 10.0 100 10.0 100
31.2 31
