ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2015, том 70, № 5, с. 490-496
ОРИГИНАЛЬНЫЕ СТАТЬИ =
УДК 543
SPECTROPHOTOMETRIC DETERMINATION OF TIN(II) BY REDOX REACTION USING 3,3',5,5-TETRAMETHYLBENZIDINE DIHYDROCHLORIDE AND N-BROMOSUCCINIMIDE
© 2015 X. Wei*, G. Jang**, D.K. Roper*, 1
*Ralph E. Department of Chemical Engineering, 3202 Bell Engineering Center, University of Arkansas
Fayetteville, AR 72701, USA 1E-mail: dkroper@uark.edu **Bioscience Division, Oak Ridge National Laboratory (ORNL) Oak Ridge, TN 37831, USA Received 13.09.2013; in final form 29.05.2014
A rapid, straightforward spectrophotometric method based on the redox reaction of tin(II) with a mixture of N-bromosuccinimide (NBS) and 3,3',5,5'-tetramethylbenzidine dihydrochloride (TMB) was developed for determining low concentrations of tin(II). The redox method improved sensitivity by 2.3-fold relative to the existing spectrophotometric methods by titrating tin(II) into an equimolar solution of colorimetric reagent TMB and oxidant NBS buffered with acetate to pH between 4.0 and 4.4 at 25°C. The spectral absorption at 452 nm was linear with respect to tin(II) concentration between the limit of quantitation (LOQ, 10ст) of 0.05 and 0.34 p,g/mL over which a response curve was generated (R2 = 0.9981, n = 7). The limit of detection (LOD) was calculated (3ст) at 0.01 p.g/mL. Deviation between actual and measured concentrations varied from 0.014 ^g/mL near the LOQ to 0.042 at 0.255 ^g/mL.
Keywords: tin(II) quantification, spectrophotometric method, TMB, NBS, redox.
DOI: 10.7868/S0044450215050175
Tin(II) compounds are important in 99mTc radiopharmaceutical kits as stabilizing agents [1], in dental gels and food as preservatives [2—4], and in electroless plating as electrochemical catalysts [5—8]. Common methods to determine tin(II) are limited by some combination of the range and/or limit of detection, ease of application, reproducibility, and inability to distinguish tin(II) from tin(IV). A need to rapidly quantitate tin(II) concentration in an electroless plating sensitization solution at concentrations less than 0.3 ^g/mL to evaluate its effectiveness motivated the development of the present colorimetric approach. A spectrophotometric approach was selected which complements the existing spectrophotometric methods for quantification of boron [9], vanadium(IV) [10], and mercury(II) [11].
Common methods for determining tin(II) concentration are summarized in Table 1. These methods are: electrochemistry [1—4, 12—19], membrane sensor [18], inductively coupled plasma—optical emission spectrometry (ICP—OES) [19], flame atomic absorption spectrometry (FAAS) [20], fluorescence [21], and spectrophotometry [22—29]. The electrochemical method, which includes anodic stripping voltam-metry (ASV) [1—4, 12] and differential pulse polarog-
raphy (DPP) [13—17], has been widely used because of selective determination of tin(II) in the presence of tin(IV). The ASV method has a low LOD. For example, a LOD equal to 0.00026 |g/mL was achieved by Hutton et al. by using the ASV method with a bismuth film electrode [3]. However, the limitation of the ASV method is that it requires either formation of a tin(II) complex such as a tin(II)—oxine [1] or a tin(II)— tropolone [2], or use of a modified electrode such as an epoxy-carbon electrode or the BiFE [3, 4, 12]. The DPP method does not require a tin(II) complex or a modified electrode but it is limited by the detection range and the LOD. Decristoforo et al. [14] reported a DPP method with a LOD of0.005 |g/mL but the concentration range was from 10 to 15 |g/mL. Similarly, using the DPP method, Sebastian et al. [15] quantified tin(II) within the concentration range 0 to 10 |g/mL but the LOD was 0.5 |g/mL.
Recently published methods based on membrane sensor, ICP, FAAS, and fluorescence quenching improved the detection concentration range and the LOD, but the constraints in the methods limit their usage. The tin(II) selective potentiometric membrane sensor method was reported to have a concentration range of 0.013 to 1190 |g/mL and a low LOD of
Table 1. Methods for determining tin(II)
Method
Principle
Concentration range, (ag/ml
LOD, (j.g/ml
Conditions
Reference
S
H
s
A
tu o
o s
X
s s s s
£
Anodic stripping voltammetry
Differential pulse polarography
Potentiometric membrane sensor Inductively coupled plasma—optical emission spectrometry Flame atomic absorption spectrometry
Quenching fluorescence method
Spectrophotometry, iodine, 520 nm
Spectrophotometry, molybdenum-thio-cyanate complex, 460 nm Spectrophotometry, iron(II)—ferrozine complex, 562 nm
Spectrophotometry, triiodide ion (I3 ), 350 nm
Spectrophotometry,
palladium(II)—tin(II) complex, 410 nm Spectrophotometry, rhenium(IV)—SCN~ complex, 353 nm Spectrophotometry, tin(II)— DMPHBH complex, 430 nm Spectrophotometry, pyrocatechol violet (PCV), 550 nm
Tin(II)—8-hydroxyquinoline (oxine) complex
Tin(II)—tropolone complex Bismuth film electrode (BiFE) BiFE
Epoxy-carbon powder composite—8-hydroxyquinoline composite electrode Static mercury drop electrode (SMDE) Dropping mercury electrode (DME)
Hanging mercury drop electrode
SMDE
DME
Polyvinyl chloride membrane electrode Combine ICP—OES and solid phase extraction
Combine FAAS and cloud point extraction
Tin(II) quenches fluorescence of carbon Nano dots
Reduce iodine monochloride, I CI, to iodine
Reduce molybdenum(VI) to molybde-num(V) and molybdenum(III) Reduce iron(III) to iron(II)
Reduce sodium periodate to iodine
Complex with palladium chloride
Reduce rhenium(VII) to rhenium(IV)
Complex with diacetylmonoxime p-hy-droxybenzoylhydrazone (DMPHBH) Rate of complex reaction of tin(II) with PCV
0.03—2.38a
0.03—2.38a 0.001-0.1 0.01-0.15 0.0006-0.119b
10—15e 0-5
0-10c 2.0-6.0 >0.1309b 0.013—1190b 0.0-0.200
0.01-1.3
0—476d
8-80
0.5-5.0
0.2-3.2
0.91-3.33f
3.33-150 1.6-6.4 0.25-2.76 0.10-1.80
0.012a
0.012a 0.00026 0.00026 5.5 x 10-5b
0.005e
0.5e 0.21
0.06545b
0.002b
0.0007
0.00286
0.043d
0.20e
0.2
0.242
0.03
Acetate buffer, 0.01 M, pH 6
Acetate buffer, 0.05 M, pH 5.5 Acetate buffer, 0.1 M, pH 4.5 HC1 and NH4C1, pH~1.4 Acetate buffer, 0.1 M, pH 5.8
Methanol and perchloric acid 0.7 M NaF, 0.1 MNaN03, and 0.1 M HEPES6, pH 8.0 3 M H2S04 and 3 M HC1 3 M H2S04 and 3 M HC1 0.1 M NaOH and 0.1 M kno3 HC1 and NaOH, pH 2.0-8.5 HC1, pH 2.0
nh3/nh4ci buffer, pH 8.0
Water and pH 8 buffer
6 M HC1 and carbon tetrachloride
3MHC1
1-1.5 MHC1
Sodium acetate and glacial acetic acid, pH 2.2-4.7
1.5MHC1 3MHC1
Ascobic acid, HC1 and cetylpyri-dinium chloride
Acetic acid-acetate buffer, 1.0 M, pH 4.0
' 1 (amol/L equals 0.119 (ag/mL; b 1.00 x 10 6 M equals 0.119 (ag/mL; e 1 ppm equals 1 \xg/mL; d 1 mM equals 119 (ag/mL; eHEPES represents N-2-hydroxyethylpiperazine-N'-2-
ethane sulphonic acid; f the conversion is based on the total amount tin(II) added to the acetate buffer.
vo
492
WEI и др.
0.0025 |g/mL, but preparation of the membrane electrode was work-intensive [18]. ICP—OES was used to quantify trace amounts of tin(II) by separating tin(II) from tin(IV) with a biosorbent. However, recovery of tin(II) in solution was less than 90% [19]. Cloud point extraction (CPE) followed by FAAS is another method that can quantify tin(II and IV) in a low concentration range (0.01—1.3 |g/mL), but the CPE procedure is complicated (including pH and temperature adjustment, centrifugation, and cooling in an ice bath) [20]. Quenching the fluorescence of carbon nano-dots (C-dots) by tin(II) was found to enable detection of tin(II) concentrations between 0 to 476 |g/mL. However, synthesis of the C-dots with a specific size distribution was difficult to repeat [21].
Spectrophotometry is widely employed for the determination of tin(II) (Table 1). Linear correlation is observed between absorbance and concentration (Beer—Lambert law) [22—29]. However, existing spec-trophotometric methods are limited by various constraints. Reducing iodine monochloride [21] or sodium periodate [25] to iodine and extracting iodine with chloroform is a toxic, insensitive (LOD = 0.20 |g/mL) method. Using complexes of molybdenum [23], fer-rozine [24], palladium [26], and rhenium [27] is expensive, and these chemicals did not improve the LOD. Synthesized chemical diacetylmonoxime ^-hydroxy-benzoylhydrazone was reported to determine tin(II) concentration from 0.25 to 2.76 |g/mL, but synthesizing DMPHBH was time consuming and the LOD was high (0.24 |g/mL) [28]. A spectrophotometric method that showed improvement in both the concentration range and the LOD using the mean centering of ratio kinetic profiles was reported by Madrakian et al. [29]. This method was operated at a concentration range of 0.10 to 1.80 |g/mL and a LOD of 0.03 |g/mL. However, the detection concentration range and the LOD must be lowered in order to provide sensitivity competitive with the other methods.
The present work introduces a spectrophotometric method using TMB as a color indicator for quantitative measurement of tin(II) in aqueous solution. This approach follows a recent report by Jang and Roper [30] regarding a simple, rapid and accurate method for determining Au(I) using TMB. In that work, the absorption coefficient of the reagent was reported at 2.75 x 105 L/mol cm [30], 3 times higher than iron— ferrozine complex (5.56 x 104 L/mol cm) [24]. Reduction of the fully oxidized TMB (diimine) by tin herein resulted in a measurable, proportional decrease in absorption at 452 nm under selected conditions. A linear correlation between absorption and tin(II) concentration was generated in concentration range of 0.049 (LOQ) to 0.340 |g/mL. The LOD (which represented the sensitivity of the method) was calculated at 0.013 |g/mL (3a) [1—3]. This new method allowed quantification of tin(II) without use of complexation agent, at a lower LOD and concentration range when
compared with the other spectrophotometric methods. To date, the lowest published tin(II) LOD and concentr
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