Improved mole ratio method by dual-wavelength spectrophotometry
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Abstract:
An improved mole ratio method for the dual-wavelength spectrophotometric determination of the equilibrium concentration of a chromogenic ligand L in an aqueous binary system is proposed. Techniques involving the k factor and isoabsorbance points can be used to mask instrumentally the absorbance of the product formed. By varying x, the concentration of the metal ion M, and fixing y, that of L, added in excess to ensure virtual completion of the reaction under study, a set of AL values, the absorbance of free L, can be measured under conditions free from any side reaction. As AL=εLl(y – xn/m), where ε is the molar absorptivity, l is the optical pathlength and n/m is the mole ratio of M and L in the reaction product MmLn, a linear graph can be plotted with AL as the ordinate and x as the abscissa. By extrapolation it intersects the abscissa at x0(x=x0 when AL= 0). Once x0 has been found, the mole ratio n/m can be readily obtained from the above equation as y is known and AL= 0. This is an absolute method. Its special features are as follows. (1) A linear plot gives more reliable results. (2) Dispensation with the use of a reference solution ensures a precise correction for any concomitant interfering absorbance possibly present in the same solution. (3) It is feasible to determine AL, one of the two interdependent variables of absorption under the specified conditions, hence it is applicable also to systems in which the absorption spectra of L and MmLn cross or overlap each other.Keywords:
Molar absorptivity
Absorbance
Mole fraction
Spectrophotometry
Ordinate
Under the buffer medium of HAc-NaAc pH=5,Fe(Ⅱ) and 2,2'-bipyridine formed a colored complex which can be quantitatively absorbed on the strong acidic cation exchange resin,and the amount of trace Fe(Ⅱ) was determined by spectrophotometry.The maximum absorption wavelength is at 522 nm,the apparent molar absorptivity is 9.12×104L·mol-1·cm-1,which is about 11 times than water phase method.The Beer's law is obeyed in the range of 0—1.5mg·L-1 for Fe(Ⅱ).The proposed method has been applied to the determination of trace Fe(Ⅱ) in Mongolian medicine Hasu-12 with satisfactory results.The relative standard deviation is 2.3% and recovery is 98.4%—100.3%,respectively.
Molar absorptivity
Spectrophotometry
Ion-exchange resin
Buffer solution
Trace Amounts
Relative standard deviation
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Green compound of Cu with CAS in the presence of CTMAB are studied under the condition of pH=7.5~9.0.The absorption maximum of reagen and its complex are at 420nm and 624nm respectively.The apparent molar absorptivity of the complex for the dual-wavelength spectrophotometry is 1.12×10~5.Beer's law is obeyed in the range of 0~20mg/L.The method is applied to the determination of copper in steel and the result is satisfactory.
Molar absorptivity
Spectrophotometry
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The method for the determination of light rare earth elements based on the color reaction of RE(Ⅲ) with DBM-MSA in 0.24～0.72 mol/L HCl by double-wavelength(spectrophotometry) was(proposed.) The(maximum)(absorption)(wavelength) are all 640 nm.Beer′s law is(obeyed) in the (concentration) range of 0～500 μg/L for RE(elements.) Their apparent molar absorptivity are between 0.8×10~5 and 1.5×10~5 L·mol·cm~(-1).In(double-)(wavelength)(condition,) the(apparent) molar(absorptivity) is 1.5～2.6×10~5 L·mol~(-1)·cm~(-1) and its(sensitivity)(increases) 75%(compared) with that of the(single)(wavelength.) The(method) (was)(applied) to the(determination) of(light) rare earth(elements) in steels with satisfactory results.
Molar absorptivity
Spectrophotometry
Color reaction
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The content of hesperidins in peels of citrus has been determined by spectrophotometry.The maximum wavelength of color system is in 422nm. The apparent molar absorptivity is 4.21×10 4L· mol -1·cm -1.Beer's law is obeyed in the range of 0-60μg/mL. The method is convenient and reliable,with satisfactory results.
Molar absorptivity
Spectrophotometry
Content (measure theory)
Beer–Lambert law
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A new determination method of chromium(Ⅵ) was astablished with spectrophotometry based on the reaction of KI and chromium(Ⅵ) in a solution of H 2SO 4,which gets iodine and turns starch solution into blue.The linear range of the determination is 0.09—1.04mg/L.The detection limit for chromium(Ⅵ) is 0.088mg/L.An apparent molar absorptivity is 4.94×10 4L·mol -1·cm -1.This method is simple and very sensitive,it is used for the determination of chromium(Ⅵ) synthetic sample with satisfactory results.
Molar absorptivity
Spectrophotometry
Linear range
Color reaction
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The conditions of color reaction of Mn(II) with O-CIPF in the presence of CTMAB were strdied. In the PH8. 00-10. 00 Na2B4O7-HCI buffer solution,a stable complex of Mn(II) with O-CIPF and CTMAB is formed. The complex has maximum absorption at 570nm,and its molar absorptivity is 9. 6 ×104L Mol-1cm-1. Beer's Law is obeyed in the concentration range of O-2ug/ml for Mn(II). The method has been applied to the determination of Mn(II) in the steel product with satisfactory ruslts.
Molar absorptivity
Spectrophotometry
Buffer solution
Color reaction
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A sensitive method for the determination of Bi by spectrophotomctry was developed.Chlorophosphonazo Ⅲ can react with bismuth to form a stable red complex.The results showed that the maximum absorption of the complex is at 510 nm,the molar absorptivity is 1.567×105 L·mol-1·cm-1.Beer′s law was obeyed in the range of 0～0.60 μg/mL.The method was applied to direct determination of Bi in Al alloys and satisfactory results were achieved.
Molar absorptivity
Bismuth
Spectrophotometry
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In a hexamine-HCl buffer solution of pH 6.0～6.3, a stable complex is formed between pyrocatechol violet (PCV) and Al(Ⅲ) in the presence of CTMAB, exhibiting an absorption peak at 580nm and a negative absorption peak at 448nm. Based on this phenomenon, a method of determination of aluminum(Ⅲ) by DW-spectrophotometry using 580nm as λ_1 and 448nm as λ_2. Beer′s law is kept between ΔA(A_(580)-A_(448)) and concentration of Al(Ⅲ) in the range 0 to 6μg per 25ml of color solution. Molar absorptivity of the DW-spectrophotometric method is found to attain a value of 9.51×10~4L·mol~(-1)·cm~(-1) which is about 66% higher than the value of e (5.73×10~4L·mol~(-1)·cm~(-1)) found by the conventional spectrophotometry. In its application to the analysis of bush feed samples, consistent results were obtained in checking with the CAS photometric method, and the recoveries obtained were in the range 96.0%～106.0%.
Molar absorptivity
Spectrophotometry
Buffer solution
Color reaction
Ultra violet
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A new method for the determination of trace iron by resin phase spectrophotometry is introduced. Fe(II) ion reacts with 5 NO 2 phen, a stable complex compound is formed. Then it is enriched on a cation exchange resin.The absorbance of resin phase is determined at wave length 520?nm,pH=4-9,the apparent?molar absorptivity is 5.1×10 6 L·mol -1 ·cm -1 . This method has been applied to water sample with satisfactory sensitivity and precision.
Molar absorptivity
Spectrophotometry
Absorbance
Ion-exchange resin
Trace Amounts
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This paper makes a systematic study on application of negative absorption spectrophotometry in add colour photometry about chromogenic agent by colour compound and establishes dual wavelength spectrophotometry of positive and negative absorption that can determine real and signal absorbance of real absorption peak.This method applies in the field of this type photometric analysis,molar ratio determination of composition for chelate,and judgement of situation in chemical reaction and so on,the effect clearly superior to the traditional method and it can solve many questions which the latter fails to do,so it is of value both in theory and practive.In the samples of determining Fe 3+and Zn 2+ on contrast degree of wavelength 160 and 49nm respectively,the real absorption peak wavelengths of chelat formed are 560 and 461nm,the real absorption molar absorptivity(e r)are 1 70×104 and 2 10×105L.mol -1.cm -1,the signal molar absorptivity(e s)are 3 10×104 and 2 86×105L.mol -1.cm -1,the dates are 1 26,1 98,2 23 and 2 71 times than traditional method do.
Molar absorptivity
Spectrophotometry
Absorbance
Chromogenic
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