Evaluation of Anionic Interferences During Cyanide Determination Using 2,2-Dihydroxyindane-1,3-Dionechromophore

International Journal of Advanced Technology & Science Research Volume 02 Issue 04 April 2021

Evaluation of anionic interferences during cyanide determination using 2,2-dihydroxyindane-1,3-dionechromophore

Dr. Nyasha Makuve

PhD University of Johannesburg

Abstract – The toxicity of cyanide ion in waste waters has been of great concern due to accidental pollution. The determination of cyanide ion in the presence of 2,2-dihydroxyindane-1,3-dione (ninhydrin) chromophore has been one of the recommended methods with a detection limit of 1.5 ng ml-1. However, this method has limitations due to interference errors. Therefore, this work reports the effect of nitrite, ascorbic acid, glucose, sulphite and bromide ion interferences in order to increase the method effectiveness and robustness. Cyanide was determined with ninhydrin chromophore at 590 nm without any colour interference.

Key words: cyanide, interferences, ninhydrin

1. Introduction

Cyanide is highly toxic and can enter the environment as a result of both natural and industrial processes.1–3 The chemical composition of cyanide in environmental samples is dependent upon the matrix of the samples and is predominantly a function of pH, temperature and trace metal content.4 Methods have been developed to measure and analyze various cyanide species in the environment such as wastewaters however, this has been challenging due to interferences.5,6 These interferences cause the concentration of cyanide to be suppressed or enhanced, thus not giving the actual results. Potential interferences are anions such as metal sulphides, aldehydes, oxidants, carbonates, nitrates and any other reactive compounds in the environment.Nitrateshave been reported to react with cyanide during cyanide detection thus causing a positive bias whilst sulfide can cause positive or negative bias depending on the method of analysis employed.

The widespread detection of cyanide in disinfected effluent continues to be a major concern for wastewater utilities due widely use of cyanide salts in electroplating, organic chemical industries, steel manufacturing and gold extraction process.7 Cyanide waste solutions are harmful to aquatic life, bacteria and other microorganisms in the environment thus disturbs the ecosystem. Due to these pronounced environmental impacts of cyanide, there is need to www.ijatsr.org Copyright © IJATSR 2021, All Right Reserved Page 226 International Journal of Advanced Technology & Science Research Volume 02 Issue 04 April 2021

determine the effect of interferences during cyanide analysis. This work evaluated cyanide relative absorbance in the presence of interferences using ninhydrin chromophore.

Experimental

All chemicals were of analytical reagent grade and all solutions were prepared with milliQ grade water with R = 18.2 Ω. Standard cyanide solution of 1 000 ppm was prepared by dissolving 2.1568 g of KCN in 1 000ml of deionized. Aqueous solution of 1 % ninhydrin in 5 % sodium carbonate were prepared and Argon was bubbled to release the interfering oxygen. Argon HP/zero -grade (> 99%) cylinder was purchased from Afrox Gases. Sodium hydroxide(Aldrich, >99%), potassium cyanide (Aldrich, >99%), potassium nitrite (Aldrich, >99%), sodium carbonate (Aldrich, >99%), sodium sulphite (Aldrich, >99%), glucose (Aldrich, >99%), potassium bromide (Aldrich, >99%), ascorbic acid (Aldrich, >99%) and ninhydrin (Aldrich, >99%). Several solutions of these interferences were made and introduced both in the ninhydrin reagent and cyanide solutions up to the desired concentrations.UV-Vis spectra were performed on a Shimadzu UV1800 UV-Vis spectrophotometerwith a temperature controller at 590 nm. The pH values were measured with HANNA PH 211 microprocessor pH meter.

Procedure

After the working solutions were made, appropriate volumes in ml (0, 0.4, 0.8, 1.0, 1.2 ,1.4, 1.6 ,2.0) were transferred into a series of 100ml volumetric flask to which 16ml 1% ninhydrin and 16ml of 5% sodium carbonatewere added to each 100ml volumetric flask. The solutions were diluted to the mark with 2M NaOH and blue colour was developed instantaneously. The absorbance was measured at 590nm and a graph was plotted. 50 ppm of the respective interferences (sodium sulphite, potassium bromide, ascorbic acid, potassium nitrite and glucose) were added to the respective flasks whilst the cyanide concentration was kept constant.The absorbance was measured at 590nm and a graph was plotted.

Results and Discussion

The effect of ninhydrin on the determination of cyanide was studied by reacting 0.2 ppm cyanide (25 ml) with1% ninhydrin in the range of 1-6ml to achieve optimum colour intensity. According to Table 1, 4ml of ninhydrin in 25 ml cyanide was the optimum volume with dark blue colour intensity obtained.

Table 1:Ninhydrin optimization in the presence of 0.2 ppm KCN

Volume (ml) 1 2 3 4 5 6

Colour Faint blue Light blue Blue Dark blue Dark blue Dark blue

According to Scheme 1, ninhydrin (I) reacts with KCN in a two-equivalence molar ratio and similar results have been reported in literature.8 The addition of the first molecule of KCN forms an intermediate complex II. Elimination of OCN- forms a 2H indene, hydrindantin intermediate III. Addition of the second KCN molecule forms the blue visible complex IV.

Scheme 1: Proposed reaction mechanism for the reaction of ninhydrin in the presence of KCN to form the visible blue colour.

The effect of nitrite, ascorbic acid, glucose, sulphite and bromide ion interferences on the determination of cyanide was analyzed using UV-vis. According to Figure 1 pure cyanide was analyzed, and the absorbance was reported. The interferences were the compared with the results of the pure cyanide. As shown from Figure 1, some interferences enhance the absorbance signal whilst other interferences suppress the absorbance signal of cyanide.All results were based on cyanide absorbance ranging from 0.208 to 1.819 within a concentration range of 0.04ppm to 0.2ppm. The presence of nitrite enhanced absorbance ranges with 1.999 being the highest absorbance observed.Ascorbic acid and glucose absorbance ranges from 0.150 to 1.689 and 0.017 to 0.884 respectively thus suppresses cyanide absorbance. Sulphite and bromide ranges from 0.125 to 1.521 and 0.126 to 1.346respectively thus suppresses cyanide absorbance signal. Effects of interferenceson cyanide determination showed that nitrite enhances cyanide absorption signal whilst ascorbic acid, glucose, sulphite and bromide ion suppresses cyanide absorption signal. At 0.2 ppm cyanide can be accurately determined in the presence of these interferences by finding the ratio of their negative and positive bias towards cyanide absorbance signal. The calculated absorbance ratios could be used as a correction factor when determining cyanide in the presence of these interferences. www.ijatsr.org Copyright © IJATSR 2021, All Right Reserved Page 228 International Journal of Advanced Technology & Science Research Volume 02 Issue 04 April 2021

UV-vis Absorbance vs Concentration of cyanide in the presence of interferences pure cyanide cyanide+nitrite cyanide+ ascorbic acid cyanide+glucose cyanide +sulphite cyanide + bromide

1.5

1 Absorbance

0.5

0 0 0.05 0.1 0.15 0.2 Cynanide concentration (ppm)

Figure 1: Graph of UV-vis Absorbance vs Concentration of cyanide in the presence ofinterferences.

Conclusion

Conclusively the results showed that nitrite enhances cyanide absorption signal while sulphite, ascorbic acid, glucose and bromide ion suppresses cyanide absorption signal. However, there is also need to analyze the extent at which lower concentration of interferences affect cyanide analysis because the analysis were done when the concentration of interference was at their maximum polluting levels.

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