Published on January 6, 2017
slide 1: International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-2 Issue-12 December- 2016 Page | 40 Determination of the total chromium in vegetable rice samples cultivated and marketed along Nhue River Khuat Quang Son 1 Dinh Thi Thu Hien 2 Dao Van Bay 3 1 PhD student 2 Graduate student Faculty of Chemistry Hanoi National University of Education 136 Xuan Thuy street Cau Giay Hanoi Corresponding author daobaydhsphnyahoo.com Abstract — The total chromium ions in vegetable and rice samples can be determined by spectrophotometric method using diphenylcarbazide reagent after their treatment. The treatment processes include: fresh sample treatment digestion and oxidation of CrIII to Cr VI. This oxidation was carried out very carefully using NH 2 S 2 O 8 AgNO 3 catalyst NaCl then combining with H 2 O 2 in alkaline media. The chromium contents in the root samples were higher than in the fresh stems samples for spinach. In the same locations if the chromium contents in the vegetable are high the chromium contents in the rice samples are high too. Keywords — Rice sample Vegetable sample Chromium oxidation Diphenylcarbazide. I. INTRODUCTION Rice and vegetables are daily used as food served as integral parts of a meal. So vegetables and rice constitute an important part of the human diet 1. In vegetables and rice there are carbohydrates proteins as well as vitamins and minerals 1. Vegetables can absorb metals from soil water as well as from waste deposits on the parts of the vegetables exposed to the air from polluted environments 2. As human activities are increasing especially combining with the application of modern technologies and fertilizers the pollution and contamination of the human food chain has become inevitable 3. Besides the number of elements such as chromium Cr lead Pb cadmium Cd nickel Ni cobalt Co copper Cu...in the high levels can be harmful to plants 4. The heavy metals in the small concentrations from environment can be accumulated in foods rice and vegetables. Heavy metals are one of a range of important types of contaminants that can be found on the surface and in the tissue of vegetables. For chromium there are two common oxidation states present in environments such as CrIII and CrVI. The form of CrIII is considered to be the trace element essential for proper functioning of living organisms 5.The chromium state of CrVI was reported to exert toxic effect on biological systems. Besides CrVI ions are the most mobile in environment of water and soil that are more available for living plants. Plants grow in the CrVI contaminated environment often show an accumulation particularly in root tissue 5. The mechanisms involved in the uptake and translocation of chromium in the plants is not understood at all. Because there is uncertainty about the ionic species present in different systems. There is however evidence that CrVI is reduced to CrIII at the plant root surface and the irrespective of the chromium is retained in the roots 67. This element at the concentrations exceeding the physiological demand of vegetables not only could cause toxic effect on them but also could enter food chains get biomagnified and pose a potential threat to human health 89. At present the problem of contamination food and clean safe food are of great interest 10. In this article the presence of chromium in rice and vegetable samples were analyzed. All samples were collected along Nhue river. The water of Nhue river is used to watering vegetables and rice. The water from Nhue River was identified as a water resource contaminated by heavy metals 11. The total chromium in the water spinach samples present in the roof and fresh stem part was analyzed. The presence of chromium in the rice and vegetable water spinach could allow an assessment of the safety levels of food rice and vegetables cultivated and marketed along Nhue River. slide 2: International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-2 Issue-12 December- 2016 Page | 41 II. MATERIALS AND METHODS 2.1 Sample Collections The rice and water spinach samples were collected from nine locations along Nhue River Figure 1. FIGURE 1. THE LOCATIONS OF COLLECTED SAMPLE ALONG NHUE RIVER The total samples include rice spinach samples collected from different locations in 2015 2016. Some vegetable samples were divided into fresh stem and root. All the vegetable samples about 2000 g were washed with tap water to remove dust particles then finally with distilled water. All vegetable samples then were chopped into small pieces using a knife and kept air – dried condition before digestion. 2.2 Digestion of sample for total chromium determination The rice and vegetable samples were weighed to determine the fresh weight and dried in a drying cabinet at 1000 C until the weigh being constant to determine their dry weight. The dry samples were crushed in a mortar to obtain uniform powder. The resulting powder digested by weighing 2.0 g for the spinach samples and 10.0 g for rice samples into an acid washed porcelain crucible few drops of concentrated added then placed in a muffle furnace for four hours at the range of 650 – 700 o C to ash. The crucibles with ash were removed from the furnace and cooled. Taken 5 mL for vegetable sample and 10 mL for rice samples 65 concentrated HNO3 were added into crucibles covered and heated on a steam bath to dissolve completely samples. The obtained solutions were used for to determine the total concentration in the samples of rice and vegetable. 2.3 Analysis of chromium in samples The analysis of chromium in the samples was carried out using diphenylcarbazide reagent DPC based on measuring the absorbance of color compound being proportional to chromium at 541 nm. By our experimental study and combining with the work 12 a procedure of chromium determination was suggested as following Figure 2. slide 3: International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-2 Issue-12 December- 2016 Page | 42 FIGURE 2. SCHEMA OF CHROMIUM ANALYSIS As suggested in Figure 2 the oxidation of CrIII to CrVI was carried out with NH 4 2 S 2 O 8 AgNO 3 catalyst combining with H 2 O 2 in alkaline NaOH 8M. The obtained sample solutions in a glass beaker were heated on a steam bath adding AgNO 3 solution about 4 mLfor rice samples 6 mL for spinach samples enough to remove Cl - ions in precipitated AgCl. Adding 10 mL of NH 4 2 S 2 O 8 solution and the samples continued heating on the steam bath to oxidize CrIII to CrVI pink color solution appeared. Adding 4 mL H 2 O 2 30 in the samples and then quickly add 10 mL NaOH 8M waiting until a black precipitation appeared and remove this precipitation by filtration. The pH in the obtained samples was adjusted by HNO 3 65 about 0.1 mL to obtain pH 1.65 before adding 0.8 mL DPC reagent. The obtained color solution with PDC was used for determination of chromium concentration in the samples by measurement of absorbance at the wave of 541 nm. This measurement was carried out using UV-Vis Biochrom S60 spectrophotometer USA. The determination of chromium in the samples based on the standard conditions described in the work 1314. The sample without chromium should be used as a blank. The chemicals and solutions used for determination of chromium including K 2 Cr 2 O 7 5 mg/L HNO 3 65 NaOH 8M NH 4 2 S 2 O 8 0.01M AgNO 3 0.01M NaCl 1 and diphenylcarbazide C 6 H 6 NHNH 2 CO 0.021M were selected from Merck company. III. RESULTS AND DISCUSION 3.1 Standard plot used for determining chromium By experiment at the standard conditions the standard plot was established and was presented by the equation as follows: Cr A 08576 ± 00411096C + 002615 ± 003420906 1 After calculation with student- t distribution the standard equation has became: Cr A 088 ± 003C 2 Basing on the standard equation the LOD limit of detection and LOQ Limit of quantification were determined as follows: LOD 0.010 mg/L LOQ 0.034 mg/L So that the obtained standard equation let’s determine chromium concentrations in vegetable and rice samples. slide 4: International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-2 Issue-12 December- 2016 Page | 43 3.2 Concentration of chromium in water spinach samples 3.2.1 Determination the ratio of dried samples per fresh samples The weight of fresh and dried samples was presented in the Tables 1 and Table 2. The obtained results showed that the fresh stems of spinach contained more water than the roots. This is consistent with reality. TABLE 1 RATIO BETWEEN DRIED SAMPLES AND FRESH SAMPLES FOR FRESH STEMS Samples Fresh stem spinach samples m NR g Dried stem spinach samples m NR g Avarage weight NR m g NR m / m NR .100 1 460.00 39.80 39.81 86.54 2 39.82 3 39.82 4 39.79 5 39.85 6 39.76 7 39.81 TABLE 2 RATIO BETWEEN DRIED SAMPLES AND FRESH SAMPLES FOR FRESH ROOT Samples Fresh root spinach samples m RR g Dried root spinach samples m RR g Avarage weight RR m g RR m / m RR .100 1 770.00 73.28 73.26 95.14 2 73.24 3 73.26 4 73.25 5 73.26 6 73.27 3.2.2 Determination of chromium in the spinach samples The result of the total chromium concentration in the water spinach samples presented in Table 3 and in Figure 2. slide 5: International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-2 Issue-12 December- 2016 Page | 44 TABLE 3 THE TOTAL CHROMIUM CONCENTRATIONS IN THE FRESH STEM Nr. Symbols Absorbance A at 541nm C Cr mg/L C Cr in 2 g of dried spinach stem samples mg/2g C Cr in fresh spinach sample mg/kg 1 NR 2 0.077 0.088 0.0022 0.095 2 NR 3 0.072 0.085 0.0022 0.095 3 NR 4 0.079 0.090 0.0022 0.097 4 NR 5 0.086 0098 0.0024 0.106 5 NR 6 0.126 0.143 0.0036 0.155 6 NR 7 0.079 0.090 0.0022 0.097 7 NR 8 0.221 0.251 0.0063 0.272 8 NR 9 0.063 0.072 0.0018 0.077 1 2 3 4 5 6 7 8 0.00 0.05 0.10 0.15 0.20 0.25 0.30 Crmg/kg Locations along Nhue river FIGURE 3. PLOT OF CHROMIUM CONTENT FRESH STEM VEGETABLE VERSUS LOCATIONS OF SAMPLES ALONG NHUE RIVER The chromium contents in the fresh stem vegetable samples along Nhue river varied from the location 1 to the location 8. In the location 8 the chromium content was highest. This might due to the polluted environment around Nhue river. Here chromium content of the rice sample G8 sample is high too reaches to 1.9716 mg/kg. The experimental data of chromium contents in the fresh stem samples were smaller than in International/national standards for heavy metals in food 12. TABLE 4 THE TOTAL CHROMIUM CONCENTRATIONS IN THE ROOT SAMPLES Nr Symbols Absorbance A at 541nm C Cr mg/L C Cr in 2 g of dried samples mg/2g C Cr in fresh sample mg/kg 1 RR 4 0.174 0.198 0.0049 0.235 2 RR 5 0.103 0.117 0.0029 0.139 3 RR 6 0.529 0.601 0.0150 0.715 4 RR 7 0.168 0.191 0.0048 0.227 5 RR 8 0.431 0.490 0.0122 0.582 6 RR 9 0.116 0.132 0.0033 0.157 slide 6: International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-2 Issue-12 December- 2016 Page | 45 The results of chromium in the water spinach samples showed that for the same spinach samples the chromium concentrations in the fresh stem and in the root were different see Table 5. TABLE 5 THE CHROMIUM CONCENTRATIONS IN STEM AND ROOT IN THE SAME SAMPLES Nr Symbols C Cr /mg/kg in fresh spinach stem samples C Cr /mg/kg in fresh root samples 1 NR 4 RR 4 0.097 0.235 2 NR 5 RR 5 0.106 0.139 3 NR 6 RR 6 0.155 0.715 4 NR 7 RR 7 0.097 0.227 5 NR 8 RR 8 0.272 0.582 6 NR 9 RR 9 0.077 0.157 The experimental data in Table 4 showed that the chromium in the root samples was much higher than in the stem. These results are consistent with the works 89. 3.3 Concentration of chromium in rice samples The chromium concentrations in the rice samples presented in Table 6 and Figure 3. TABLE 6 CHROMIUM CONCENTRATION IN RICE SAMPLES Nr. Symbols Absorbance A at 541nm C Cr mg/L C Cr in 10 g of dried samples mg/10g C Cr in fresh rice sample mg/kg 1 G 4 0.204 0.237 0.0058 0.498 2 G 7 0.475 0.552 0.0135 1.160 3 G 8 0.789 0.917 0.0224 1.927 4 G 9 0.524 0.609 0.0149 1.280 1 2 3 4 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Cr mg/kg Locations along Nhue river FIGURE 4. PLOT OF CHROMIUM CONTENTS OF RICE SAMPLES ALONG NHUE RIVER The chromium contents in these samples are smaller than in the work 2 reported from Malaysia. slide 7: International Journal of Engineering Research Science IJOER ISSN: 2395-6992 Vol-2 Issue-12 December- 2016 Page | 46 IV. CONCLUSION Chromium ion from environment of water and soil can be absorbed by water spinach and rice plants. This is a problem needed to be carefully studied. A spectrophotometric measurement method used DPC reagent allowed determining chromium content in spinach samples fresh stems and roots and in rice samples collected from different locations along the Nhue River. Based on the standard curve concentrations of chromium in the samples after treatment oxidation CrIII to Cr VI by NH 2 S 2 O 8 combining with H 2 O 2 were determined. The chromium contents in the root samples were higher than in the fresh stems samples for spinach. 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