Average Molar Absorption Research Articles

Optical Measurement of Molar Absorption Coefficient of HbA1c: Comparison of Theoretical and Experimental Results.

Diabetes can cause dangerous complications if not diagnosed in a timely manner. The World Health Organization accepts glycated hemoglobin (HbA1c) as a measure of diagnosing diabetes as it provides significantly more information on the glycemic behavior from a single blood sample than the fasting blood sugar reading. The molar absorption coefficient of HbA1c is needed to quantify the amount of HbA1c present in a blood sample. In this study, we measured the molar absorption coefficient of HbA1c in the range of 450 nm to 700 nm using optical methods experimentally. We observed that the characteristic peaks of the molar absorption coefficient of HbA1c (at 545 nm and 579 nm for level 1, at 544 nm and 577 nm for level 2) are in close agreement with those reported in previous studies. The molar absorption coefficient values were also found to be close to those of earlier reports. The average molar absorption coefficient values of HbA1c were found to be 804,403.5 M-1cm-1 at 545 nm and 703,704.5 M-1cm-1 at 579 nm for level 1 as well as 503,352.4 M-1cm-1 at 544 nm and 476,344.6 M-1cm-1 at 577 nm for level 2. Our experiments focused on calculating the molar absorption coefficients of HbA1c in the visible wavelength region, and the proposed experimental method has an advantage of being able to easily obtain the molar absorption coefficient at any wavelength in the visible wavelength region. The results of this study are expected to help future investigations on noninvasive methods of estimating HbA1c levels.

Development of a new highly sensitive and selective spectrophotometric method for the determination of cobalt at nanotrace levels in various complex matrices using N,N’-bis(salicylidene)-ethylenediamine

A new spectrophotometric reagent, N,N'-bis(salicylidene)-ethylenediamine (Salen), has been synthesized and characterized through novel reaction techniques. A very simple, ultrasensitive, and nonextractive spectrophotometric method has been developed for the determination of the picotrace amount of cobalt (II) using Salen. Salen undergoes a reaction in a slightly acidic solution (0.001-0.003 M H2S04) with cobalt in 20% ethanol to give a light orange chelate, which has an absorption maximum at 459 nm. The reaction is instantaneous, and the absorbance remains stable for over 24 hours. The average molar absorption co-efficient and Sandell’s sensitivity were found to be 6.04×105 L/mol.cm and 5.0 ng/cm2 of Co, respectively. Linear calibration graphs were obtained for 0.001-40 mg/Lof Co with a detection limit of 0.1 µg/L and RSD of 0-2 %. The stoichiometric composition of the chelate is 1:1 (Co:Salen). A large excess of over 60 cations, anions and some common complexing agents such as chloride, azide, tartrate, EDTA, SCN- etc. do not interfere in the determination. The developed method was successfully used in the determination of cobalt in several Certified Reference Materials (Alloys, steel, bovine liver, human hair, drinking water, sewage sludge, soil, and sediments) as well as in some environmental waters (Potable and polluted), biological fluids (Human blood, urine, and milk), soil samples, food samples (Vegetables, rice, and wheat) and pharmaceutical samples and solutions containing both cobalt (II) and cobalt (III) as well as complex synthetic mixtures. The results of the proposed method for assessing biological, soil, food and vegetable samples were comparable with ICP-OES and AAS were found to be in excellent agreement. The method has high precision and accuracy (s = ±0.01 for 0.5 mg/L).

Development of a new highly sensitive and selective spectrophotometric method for the determination of selenium at nano-trace levels in various complex matrices using salicylaldehyde-orthoaminophenol

A new spectrophotometric reagent, salicylaldehyde-orthoaminophenol (Sal-OAP) has been synthesized and characterized for the determination of selenium through novel reaction techniques. Also, a new highly selective, and sensitive spectrophotometric method for the nano-trace determination of selenium using salicylaldehyde-orthoaminophenol (Sal-OAP) has been developed. Sal-OAP undergoes reaction in a slightly acidic solution (0.0001-0.0002 M H2S04) with selenium (IV) to give an orange-red chelate, which has an absorption maximum at 379 nm. The reaction is instantaneous and absorbance remains stable for over 24 h. The average molar absorption co-efficient and Sandell’s sensitivity were found to be 6.4×105 L/mol.cm and 1.0 ng/cm2 of, respectively. Linear calibration graphs were obtained for 0.001-40.000 mg/Lof Se having detection limit of 0.1 µg/L and RSD 0-2 %. The stoichiometric composition of the chelate is 1:2 (Se:Sal-OAP). A large excess of over 60 cations, anions and some common complexing agents, such as chloride, azide, tartrate, EDTA, SCN¯etc., do not interfere in the determination. The developed method was successfully used in the determination of selenium in several Certified Reference Materials (Alloys, steels, human urine, bovine liver, drinking water, tea, milk, soil, and sediments) as well as in some environmental waters (Potable and polluted), biological fluids (Human blood, urine, hair, and milk), soil samples, food samples (Vegetables, rice, and wheat) and pharmaceutical samples (Tablet and syrup) and solutions containing both selenium (IV) and selenium (VI) as well as complex synthetic mixtures. The results of the proposed method for assessing biological, food and vegetables and soil samples were comparable with ICP-OES and AAS were found to be in excellent agreement. The method has high precision and accuracy (s = ±0.01 for 0.5 mg/L).

A highly sensitive and selective spectrophotometric method for the determination of vanadium at nanotrace levels in some environmental, biological, soil, food, and pharmaceutical samples using salicylaldehyde-benzoylhydrazone

A very simple, non-extractive and new spectrophotometric method for the swift determination of trace amount of vanadium using salicylaldehyde-benzoylhydrazone (Sal-BH) has been developed. Sal-BH undergoes a reaction in a slightly acidic solution (0.0016-0.0032 M H2S04) with vanadium to give a light greenish-yellow chelate, which has an absorption maximum at 392 nm. The reaction is instantaneous and absorbance remains stable for over 24 hrs. The average molar absorption co-efficient and Sandell’s sensitivity were found to be 2.5039×105 L/mol.cm and 1.0 ng/cm2 V, respectively. Beer’s law was obeyed for 0.001-30 mg/L of V, providing a detection limit of 0.1 µg/L of V and RSD 0-2 %. The stoichiometric composition of the chelate is 1:1 (V:Sal-BH). Interference study shows that a large excess of over 60 cations, anions, and some common complexing agents (such as chloride, azide, tartrate, EDTA and SCN‑, etc.) satisfy the tolerance limit. The developed method was successfully used in the determination of vanadium in several standard reference materials as well as in some environmental waters, biological fluids, soil, food and pharmaceutical samples and solutions containing both vanadium (IV) and vanadium (V). The results of the proposed method for assessing biological, food and vegetable samples were comparable with ICP-OES and AAS were found to be in excellent agreement. The method has high precision and accuracy (s = ±0.01 for 0.5 mg/L).

Development and validation of the HPLC method for quality control of radiolabelled DOTA-TATE and DOTA-TOC preparations

IntroductionThe information on the presence of cold metal complexes in radiolabeled DOTA-TATE or DOTA-TOC is important in assessing the cause of the radiolabeling failure, poor radiolabeling yield and/or low effective molar activity. DOTA-peptide complexes are detectable using UV–Vis detector. The main limitation in the quantitative analysis is the limited availability of standard substances and the lack of data on their molar absorption coefficients. The aim of our study was development and validation of HPLC method enabling RCP analysis and identification and quantification of metal complexes impurities in the radiopharmaceutical preparations of DOTA-chelated peptides. MethodsComplexes of DOTA-TATE and DOTA-TOC with several metals, were prepared. Their molar absorption coefficients at 220 nm were determined. The developed HPLC method has been validated in terms of quantitative determination of non-complexed DOTA-TATE and DOTA-TOC and their respective complexes with metallic individuals. ResultsGood chromatographic separation of the individual metal-DOTA-peptide complexes was achieved. The resolution between peaks of interest in radioactive preparations (complexes with: yttrium-90, lutetium-177, gallium-68) and metallic impurities was well above 1.5 (except gallium-68 DOTA-TOC preparations). Limits of detection and quantification were determined based on the parameters of the calibration curves. Based on the spectrophotometric and HPLC-DAD studies and statistical analysis of the results obtained, the average molar absorption coefficient was determined for studied DOTA-TATE and DOTA-TOC complexes, εHPLC-DAD = 48 × 103M−1 cm−1. With the use of the determined molar absorption coefficient the method enabled quantitative determination of non-labelled peptide in the radioactive preparation in the linearity range of 0.5–100 μg/mL for DOTA-TATE(net) and 0.5–100 μg/mL for DOTA-TOC(net). ConclusionThe developed HPLC method is suitable for RCP determination of radiolabelled DOTA-TATE and DOTA-TOC preparations. Determination of the average molar absorption coefficient for DOTA-TATE and DOTA-TOC complexes allows assessment of the total content of the peptide in radiopharmaceutical preparation regardless of its chemical form (free ligand, associated with radionuclide, in the form of a complex with metal ions being the impurity) using the HPLC method with UV detection.

A Highly Selective and Simple Spectrophotometric Method for the Determination of Zinc at Nano-trace Levels in Some Environmental, Biological, Food, and Pharmaceutical Samples Using 2-hydroxynaphthaldehydebenzoylhydrazone

A simple, ultra-sensitive, and highly selective spectrophotometric method has been established for the trace quantification of zinc (Zn), using 2-hydroxynaphthaldehyde benzoylhydrazone (HNABH). Zn forms a pale yellowish-green complex (maximum absorption at 426 nm) with HNABH (1:1, v:v) in a marginally acidic solution (0.00005-0.00023 M H2SO4). The average molar absorption coefficient and Sandell’s sensitivity were found: 2.87×105 L/mol.cm and 12 ng/cm2 of Zn, respectively. The observed linearity range for Zn was 0.01-50 mg/Lwith a detection limit of 1 µg/L. The analysis of biological, food, and vegetable samples using the suggested method were found to be in tremendous accord with those acquired by Atomic Absorption Spectroscopy (AAS) and Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). The method has high precision and accuracy (s = ±0.01 for 0.5 mg/L). The limit of quantification of the proposed method was 10 µg/L.

A highly sensitive and rapid spectrophotometric method for the determination of molybdenum at nano-trace levels in some real, environmental, biological, food and soil samples using salicylaldehyde-benzoylhydrazone

A very simple, sensitive and highly selective non-extractive new spectrophotometric method has been developed for the determination of molybdenum at nano-trace levels using salicylaldehyde-benzoylhydrazone (Sal-BH). The method is based on the reaction of non-absorbent Sal-BH in a slightly acidic solution (0.0025-0.0075 M H2S04) with molybdenum (VI) to give a light yellowish chelate, which has an absorption maximum at 440 nm. The reaction is instantaneous and absorbance remains stable for over 24 h. The average molar absorption coefficient and Sandell’s sensitivity were found to be 4.32×105 L/mol.cm and 5 ng/cm2 of molybdenum, respectively. Linear calibration graphs were obtained for 0.01-60.00 mg/L of molybdenum having detection limit of 1 µg/L and RSD 0.0-2.0 %. The stoichiometric composition of the chelate is 1:1 (Mo:Sal-BH). A large excess of over 60 cations, anions and some common complexing agents (such as chloride, azide, tartrate, EDTA, SCN- etc.) do not interfere in the determination. The method was successfully used in the determination of molybdenum in several Certified Reference Materials (Alloys, steels, water, hair and bovine liver) as well as in some environmental waters (Potable and polluted), biological samples (Human blood, urine, nails, hair, food and vegetables), soil samples, and solutions containing both molybdenum(VI) and molybdenum(V) as well as complex synthetic mixtures. The results of the proposed method for assessing biological, food and vegetables samples were found to be in excellent agreement with those obtained by ICP-OES and AAS. The method has high precision and accuracy (s = ±0.01 for 0.5 mg/L).

New simple spectrophotometric method for the specification of silver (i) in oil-water samples

A simple, highly selective and non-extractive spectrophotometric method for the specification of trace amounts silver (I) has been developed. In the water media 2,2’-di (2,3,4-trihydroxy-phenylazo) biphenyl reacts with the silver to give a highly absorbent greenish-yellow chelate in a molar ratio 2:1 (Ag:R). The reaction is instantaneous, the maximum absorption was obtained at 540 nm and remains stable for 24 hours. The average molar absorptivity and Sandell’s sensitivity were 4.3×104 l mol-1 cm-1 and 5.0 mkg cm-2 of silver (I), respectively. Linear calibration graphs were obtained for 0.1–30 mkgml−1 of silver (I), respectively. A large excess of over 30 cations, anions and complex agents do not interfere in the specification. The method is highly selective for silver and was successfully appliedin a number of oilwater samples. It has high precision and accuracy (s = ± 0.01 for 0.5 mkgl-1). Therefore, it may be used for monitoring to establish trace level of silver (I) in difficult matrices of oilwater samples.

A Highly Selective and Sensitive Spectrophotometric Method for the Determination of Lead at Ultra-trace Levels in Some Real, Environmental, Biological, Food and Soil Samples Using 5,7-Dibromo-8-Hydroxyquinoline

A very simple, ultra-sensitive and highly selective non-extractive spectrophotometric method for the determination of trace amounts of lead using 5,7-dibromo-8-hydroxyquinoline (DBHQ) has been developed. DBHQ reacts in a slightly acidic (0.0006-0.0025 M HCl) aqueous solution with lead (II) in 30% ethanolic media to produce highly absorbent a greenish-yellow chelate which has an absorption maximum at 390 nm. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption co-efficient and Sandal’s sensitivity were found to be 6.16 x 105 L mol-1cm-1 and 5 ng cm-2 of lead (II), respectively. Linear calibration graphs were obtained for 0.01- 60.0 mg L-1 of lead (II) having detection limit of 1.0 μg L-1 and RSD 0-2%. The stoichiometric composition of the chelate is 1:2 (Pb: DBHQ). A large excess of over 60 cations, anions and complexing agents (like, chloride, phosphate, azide, tartrate, oxalate, SCN- etc.) do not interfere in the determination. The developed method was successfully used in the determination of lead levels in several Standard Reference Materials (alloys, steels, natural water, bovine liver, human urine and hair) as well as in some environmental waters (potable and polluted), biological samples (human blood, urine and hair), soil samples, food samples (vegetables, rice, wheat) solutions containing both lead (II) and lead (IV) and complex synthetic mixtures. The results of biological and food analyses by the spectrophotometric method were found to be in excellent agreement with those obtained by AAS.

Thermostable gold nanoparticle-doped silicone elastomer for optical materials

When gold nanoparticles (AuNPs) are blended with matrix polymers for material engineering of a nanoparticle doped polymer matrix, one frequently observes nanoparticles’ aggregation due to their large interface energy. In this work, poly(dimethyl siloxane)-capped AuNPs (AuNP@PDMS) were successfully synthesized via hydrosilylation from alkenyl-terminated AuNPs and hydride-terminated PDMS polymer. The AuNP@PDMS particles have a well dispersed state after blending with polysiloxane elastomer prepolymer because the same component of the shell polymer to matrix polymer should decrease maximumly the interface influence between the nanoparticles and the polymer matrix. Therefore, uniform AuNP-doped silicone elastomer material with brilliant red color was obtained after vulcanization. The average molar absorption coefficient of doped AuNPs in silicone elastomer was deduced to be 3.06×107cm−1mol−1. Such AuNP-doped silicone elastomer showed good thermostability and obvious optical limiting performance. The intrinsic homogeneity of shell polymer on nanoparticles and matrix polymer is a remarkable advantage to diminish the interface influence in blending of nanoparticles with polymer matrix, thus could provide uniform nanoparticle-doped polymeric materials.

Highly sensitive spectrophotometric method for the determination of vanadium in environmental, biological, food and soil samples using orthoaminophenol

A simple, ultra-sensitive and highly selective non-extractive spectrophotometric method for the determination of trace amount of vanadium(V) using orthoamino phenol (OAP) has been developed. OAP reacts in highly acidic (0.005-0.015 mol/L H 2 SO 4 ) and aqueous media with vanadium(V) to give a chocolate color chelate which has an absorption maximum at 405 nm. The reaction was instantaneous and absorbance remains stable for over 72 h. The average molar absorption co-efficient and Sandell’s sensitivity were found to be 6.7×10 5 L/mol.cm and 10 ng/cm 2 of vanadium(V), respectively. Linear calibration graphs were obtained for 0.02-50.00 mg/L having detection limit 1 µg/L and quantification limit of the reaction were found to be 10 µg/L and RSD 0-2%. The stoichiometric composition of the chelate is 1:3 (Vanadium(V):OAP, v : v ). Large excess of over 60 cations, anions and complexing agents (Like tartrate, EDTA, oxalate, chloride, phosphate, thiourea, SCN - etc .) do not interfere in the vanadium determination. The method was successfully used in the determination of vanadium in several standard reference materials (Alloys and steels) as well as in some environmental waters(Potable and polluted), biological samples (Human blood and urine), food samples, soil samples, solution containing both vanadium(IV) and vanadium(V) and complex synthetic mixtures. The results of the proposed method for biological analyses were found to be in excellent agreement with those obtained by AAS. The method has high precision and accuracy (s = ±0.01 for 0.5 µg/mL).

A simple and rapid spectrophotometric method for the determination of iron in environmental, biological, pharmaceutical, food and soil samples using 1,2-dihydroxybenzene-3,5-disulfonic acid

An ultra-sensitive and highly selective non-extractive spectrophotometric method is presented for the rapid determination of iron (III) at trace levels using 1,2-dihydroxybenzene-3,5-disulfonic acid (Tiron) as a new spectrophotometric reagent (l max = 665 nm) in slightly acidic aqueous (2×10 -6 - 2×10 -5 mol/L H 2 SO 4 ) solution. The reaction is instantaneous and absorbance remains stable for over 24 h. The average molar absorption coefficient and Sandell’s sensitivity and detection limit were found to be 6.0×10 5 L/mol.cm, 10 ng/cm 2 , and 1 µg/L, respectively. Linear calibration graphs were obtained for 0.02-70.00 mg/L of Fe(III). The stoichiometric composition of the chelate is 2:3 (Fe(III):Tiron). Large excesses of over 50 cations, anions and complexing agents (e.g. Tartrate, oxalate, citrate, phosphate, thiourea, and thiocyanate) do not interfere in the determination. The method was successfully used in the determination of iron in several standard reference materials (Alloys and steels) as well as in some environmental waters (portable and polluted), biological samples (Human blood and urine), food, pharmaceutical and soil samples, solution containing iron (II) and iron (III) and some complex synthetic mixtures. The method has high precision and accuracy (s = ±0.01 for 0.5 mg/L).

A Simple Spectrophotometric Method for the Determination of Trace Level of Cadmium in Real, Environmental, Biological, Tobacco, Fertilizer and Soil Samples Using 2⁄, 3, 4⁄, 5, 7 Pentahydroxyflavone

A very simple, ultra-sensitive and highly selective non-extractive spectrophotometric method for the determination of trace amount of cadmium using 2, 3, 4, 5, 7pentahydroxyflavone (morin) has been developed. Morin reacts in a slightly acidic (0.000001-0.000012M H2SO4) in 50% ethanolic solution with cadmium to give a deep greenishyellow chelate which has an absorption maximum at 422 nm. The reaction is instantaneous and the absorbance remains stable for over 24 h. The average molar absorption co-efficient and Sandell’s sensitivity were found to be 4.09 × 10 L molcm and 4.0 ng cm of cadmium, respectively. Linear calibration graphs were obtained for 0.01 25 mg L of cadmium with a correlation co-efficient value 0.9996 for Cd-morin complex. The stoichiometric composition of the chelate is 1:2 (Cd:morin). The detection limit and quantification limit of the reaction system were found 1μg L and 10μg L, respectively. A large excess of over 50 cations, anions and complexing agents (like, chloride, tartrate, azide, citrate, EDTA, SCN etc.) do not interfere in the determination. The developed method was successfully used in the determination of cadmium in several Standard Original Research Article American Chemical Science Journal, 4(4): 481-503, 2014 482 Reference Materials (alloys and steels) as well as in some environmental waters (inland and surface), biological samples (human blood, urine and hair), tobacco, fertilizer, soil samples and complex synthetic mixtures. The results of the proposed method for biological samples were comparable with AAS and were found to be in good agreement. The method has high precision and accuracy (s = ±0.01 for 0.5 mg L).

Modified CUPRAC spectrophotometric quantification of total polyphenol content in beer samples using Cu(II)/neocuproine complexes

Cu(II)/neocuproine (2,9-dimethyl-1,10-phenanthroline) complexes were utilized for spectrophotometric determination of total polyphenol content in beers. This procedure is based on the reduction of Cu(II) by polyphenols in hydroethanolic medium (pH 7.0) in the presence of neocuproine, yielding Cu(I)/complexes with maximum absorption at 454nm. The sensitivity of the proposed method was compared with the AOAC method using tannic and gallic acid as standards. The average apparent molar absorptivity, in Lcm−1mol−1, of tannic acid (3.50±0.20)×105 and gallic acid (5.12±0.21)×104, was twice as high for the proposed method. A lower limit of detection (LOD) (2.9×10−1mgL−1) was found when tannic acid was used in the proposed method. Additionally, less interference from the most common additives in beers was noticed. Total content of polyphenols was analyzed in 17 Brazilian samples. Results ranged from 35.5 to 556mgL−1 of tannic acid, with higher values for recovery rates (45.4–118%, mean 85.0%) than for gallic acid. Although tannic acid is a mixture of polygalloyl glucoses, the total polyphenol content found in the samples suggests that tannic acid should be used as a standard. This is the first attempt to use this particular copper complex to quantify total polyphenol content in beer samples.

Spectrophotometric determination of cobalt (ii) in low concentrations using hydroxytriazene as selective chelating agents.

The present work describes a selective, rapid and simple spectrophotometric method for the determination of cobalt (II) at trace levels using some selected hydroxytriazene. The method is based on the reaction of hydroxytriazene at pH 5.5 to 6.2, 6.0 to 6.8, 7.1 to 7.35, 7.3 to 7.9, 6.75 to 7.25 and 7.2 to 7.75 for hydroxytriazenes no (i), (ii), (iii), (iv), (v) and (vi) respectively and ethanol media with cobalt (II) to produce a highly absorbent yellow coloured chelate product with an absorption maximum at 393,397,417,406,410 and 412 nm for hydroxytriazenes no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The reaction is instantaneous and the absorption remains stable for 24 Hrs. The average molar absorption coefficient were 1.1 x 104, 1.2 x 104,1.8 x 104, 2.5 x 104, 2.1 x 104, 1.9 x 104mol-1 dm3 cm-1 for hydroxytriazene no (i), (ii), (iii), (iv), (v), (vi) respectively and Sandell’s sensitivity in ng/cm2 were 5.4, 4.9, 3.3, 2.4, 2.9 and 3.1 for hydroxytriazene no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The stoichiometric composition of the chelate is 1:3 for hydroxytriazene no (i), (iv), (v), (vi), 1:2 for (ii) and 1:1 for (iii). A large excess of over 30 cations, anions and complexing agent do not interfere in the determination at equivalent amounts. The method was successfully used in Mussaenda arcu. The method has high precision and accuracy. Key words: Spectrophotometry, Mussaenda arcu, hydroxytriazene, cobalt, interference.

Spectrophotometric determination of cobalt (ii) in low concentrations using hydroxytriazene as selective chelating agents

The present work describes a selective, rapid and simple spectrophotometric method for the determination of cobalt (II) at trace levels using some selected hydroxytriazene. The method is based on the reaction of hydroxytriazene at pH 5.5 to 6.2, 6.0 to 6.8, 7.1 to 7.35, 7.3 to 7.9, 6.75 to 7.25 and 7.2 to 7.75 for hydroxytriazenes no (i), (ii), (iii), (iv), (v) and (vi) respectively and ethanol media with cobalt (II) to produce a highly absorbent yellow coloured chelate product with an absorption maximum at 393,397,417,406,410 and 412 nm for hydroxytriazenes no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The reaction is instantaneous and the absorption remains stable for 24 Hrs. The average molar absorption coefficient were 1.1 x 104, 1.2 x 104,1.8 x 104, 2.5 x 104, 2.1 x 104, 1.9 x 104mol-1 dm3 cm-1 for hydroxytriazene no (i), (ii), (iii), (iv), (v), (vi) respectively and Sandell’s sensitivity in ng/cm2 were 5.4, 4.9, 3.3, 2.4, 2.9 and 3.1 for hydroxytriazene no. (i), (ii), (iii), (iv), (v) and (vi), respectively. The stoichiometric composition of the chelate is 1:3 for hydroxytriazene no (i), (iv), (v), (vi), 1:2 for (ii) and 1:1 for (iii). A large excess of over 30 cations, anions and complexing agent do not interfere in the determination at equivalent amounts. The method was successfully used in Mussaenda arcu. The method has high precision and accuracy. Key words: Spectrophotometry, Mussaenda arcu, hydroxytriazene, cobalt, interference.

Spectrophotometric Determination of Toxic Elements (Cadmium) in Aqueous Media

Trace amount of toxic element (Cadmium) was determined by spectrophotometer method using 1, 2-dihydroxy anthraquinone-3-sulphonic acid, sodium salt. (Alizarin red S) as a new spectrophotometer reagent. Alizarin red S reacts in slightly acidic solution (0.005 - 0.05M H2SO4) with cadmium to give a deep greenish yellow chelate which has an absorption maximum at 422 nm. The reaction is instantaneous and absorbance remains stable for over 24hrs. The average molar absorption co-efficient and sandell's sensitivity were found to be 2.24 103L mol-1 cm-1 and 20 ng cm 2 of Cd respectively. Linear calibration graphs were obtained for 0.1 - 40μg mL-1 of Cd. The stoichiometric composition of the chelate is 1 : 2 (Cd : Alizarin red S). Large excess of over 50 cations, anions, and some common complexing agents (e.g EDTA, oxalate, citrate phosphate, thio-urea, SCN-) do not interfere in the determination. The method was successfully used in the determination of cadmium in Several Standard Reference Materials (alloys, steels and water) as well as in some environmental waters (In land and surface), biological samples (human blood and urine), soil samples and complex synthetic mixtures. The method has high precision and accuracy. (S = ±0.01 for 0.5 μg mL-1. Keywords spectrophotometry; cadmium determination; 1, 2-dihydroxy anthraquinone-3-sulphonic acid; sodium salt (Alizarin red S); alloy; steel; environmental; biological; samples; soil samplesDOI: 10.3329/jce.v25i0.7233Journal of Chemical Engineering, IEB Vol. ChE. 25, No. 1, December 2010 pp.1-12

A Simple and Rapid Spectrophotometric Determination of Trace Level Simple and rapid spectrophotometric determination of trace level chromium using bis (salicylaldehyde) orthophenylenediamine in nonionic micellar media

Bis(salicylaldehyde)orthophenylenediamine (BSOPD) has been proposed as new analytical reagent for the direct spectrophotometric determination of chromium. It reacts with chromium(VI) in slightly acidic (0.1 -- 0.3 M H_2SO_4) micellar medium to form a yellow - orange chelate with a molar ratio 2:3. The most remarkable point of this method is that the molar absorptivities of the Cr^{VI} -- BSOPD complex formed in the presence of nonionic TritonX -- 100 surfactant are almost 10 times higher than the value observed in aqueous solution. This results in enhancing the sensitivity and selectivity of the method. The reaction is instantaneous and the maximum absorbance was obtained at 482 nm and remains constant for over 24h. The average molar absorption coefficient and Sandell's sensitivity were found 3.5 \times 10^5 L mol^{-1} cm^{-2} and 5 ng cm^{-2} of Cr(VI), respectively. Linear calibration graphs were obtained for 0.01 -- 12.0 mgL^{-1} of Cr(VI) with correlation coefficient value 0.9987 for Cr -- BSOPD complex. Large excess of over 50 cations, anions and complexing agents do not interfere in the determination. The method was successfully used in the determination of chromium(VI) from synthetic mixture and certified reference materials to test the validity of the method and the results of analyses were found to be in excellent agreement with those of certified values. The developed method was also used for the determination of chromium in some environmental waters (potable and polluted), biological samples (blood and urine) and to determine chromium species. The results of the biological analyses by the proposed method were in good agreement with those of by AAS.

Spatial and seasonal changes in optical properties of autochthonous and allochthonous chromophoric dissolved organic matter in a stratified mountain lake

In this study, we present results on seasonal and spatial changes in CDOM absorption and fluorescence (fCDOM) in a deep mountain lake (Salto Lake, Italy). A novel approach was used to describe the shape of CDOM absorption between 250-700 nm (distribution of the spectral slope, S(lambda)) and a new fluorescence ratio is used to distinguish between humic and amino acid-like components. Solar ultraviolet irradiance, dissolved organic carbon (DOC), DOM fluorescence and absorption measurements were analysed and compared to other physicochemical parameters. We show that in the UV-exposed mixed layer: (i) fluorescence by autochthonous amino acid-like CDOM, (ii) values of S(lambda) across UV-C and UV-B wavebands increased during the summer months, whereas (i) average molar absorption coefficient and (ii) fluorescence by allochthonous humic CDOM decreased. In the unexposed deep layer of the water column (and in the entire water column in winter), humic-like CDOM presented high values of molar absorption coefficients and low values of S(lambda). UV attenuation coefficients correlated with both chlorophyll a concentrations and CDOM absorption. In agreement with changes in CDOM, minimal values in UV attenuation were found in summer. The S(lambda) curve was used as a signature of the mixture between photobleached and algal-derived CDOM with respect to the unexposed chromophoric dissolved compounds in this thermal stratified lake. Furthermore, S(lambda) curves were useful to distinguish between low and high molecular weight CDOM.

Comparison of 3 Spectrophotometric Methods for Carotenoid Determination in Frequently Consumed Fruits and Vegetables

Carotenoids are C-40 tetraterpenoid compounds with potential health beneficial effects. Major dietary sources include a variety of fruits and vegetables. Rapid screening methods are therefore desired, but their accuracy varies depending on the carotenoid profile and the matrix of the plant food. In the present study, 3 different methods were compared, all based on a rapid extraction protocol and spectrophotometric measurements to determine the total amount carotenoids present in fruits and vegetables (n = 28), either with or without chlorophyll. Published methods (a) Lichtenthaler and (b) Hornero-Méndez and Mínguez-Mosquera were compared with a newly developed method (method c) based on the average molar absorption coefficient (135310 Lcm(-1)mol(-1)) and wavelength (450 nm in acetone), for the 5 predominant carotenoid species (beta-carotene, zeaxanthin, lycopene, lutein, beta-cryptoxanthin) in the investigated foods. All results were compared to HPLC (method d). To avoid overestimating carotenoid concentrations due to chlorophyll A and B presence, the effect of saponification was studied for all methods. Overall, saponification led to significant carotenoid losses (12.6 +/- 0.9%). Methods a, b, c, and d yielded 5.1 +/- 0.4 mg/100 g, 4.6 +/- 0.5 mg/100 g, 4.3 +/- 0.5 mg/100 g, and 4.2 +/- 0.5 mg/100 g total carotenoids, respectively, with method a leading to significant higher mean concentrations compared to all other methods (P < 0.001, Bonferroni) with methods b and c being not significantly different and highly correlated compared to HPLC (> r = 0.95). Similar results were found when stratifying for chlorophyll content and fruits compared with vegetables, however, accuracy varied for individual fruits, highlighting the limitation to use the same method for all plant foods. This study presents a comparison of various rapid spectrophotometric measurements to determine total carotenoid content in various fruits and vegetables and could aid in the selection of the appropriate method for individual plant foods with different carotenoid profile and matrices.