background and overview[1]
diphenylcarbazide, also known as diphenylamine urea and carbonyldiphenylhydrazine, is a white or light yellow crystalline powder with a melting point of 168 to 173°c. it is soluble in ethanol and insoluble in water, ether and chloroform. it dissolves in the air. will gradually turn red. it is produced by reacting urea and aniline as raw materials. diphenylcarbazide (c13h14n4o) is obtained from the reaction of phenylhydrazine and urea and must be stored away from light. diphenylcarbazide can complex with metal ions such as hexavalent chromium ions and copper ions to form a purple-red substance, and then use a spectrophotometer to measure its absorbance, and calculate the concentration of the measured substance through lambert-beer’s law.
apply[1]
1 determination of hexavalent chromium
chromium is one of the essential trace elements for organisms. the lack of chromium can cause metabolic system disorders such as sugar and fat, but excessive levels are harmful to organisms and humans. chromium exists in trivalent and hexavalent forms in water. trivalent chromium is less toxic, while hexavalent chromium is highly toxic (100 times more toxic than trivalent chromium). if it is irritating to the skin, it can cause skin ulcers. the harmful mass concentration ranges from 5 to 170 mg/l and has been confirmed as a carcinogen. the detection of hexavalent chromium in water is very strict. commonly used measurement methods include diphenylcarbazide spectrophotometry, flame atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and ferrous ammonium sulfate titration.
spectrophotometry is a standard method commonly used in my country and other countries. mo jiangmin et al. used diphenylcarbazide spectrophotometry to determine trace amounts of hexavalent chromium in ferric nitrate. the results showed that in high-concentration ferric iron solutions, there is no need to separate and remove ferric ions. hydrazine is used as a color developer and forms a colored complex with hexavalent chromium. it has a maximum absorption peak at a wavelength of 540 nm. the degree of color development is proportional to the hexavalent chromium content. the hexavalent chromium content is in the range of 0 to 10 μg/ml. good linear relationship, the molar absorption coefficient is 4.0 ×105 l·mol-1·cm-1. six parallel measurements were performed, with a relative standard deviation of 4.06% and a standard recovery rate between 91.5% and 105.2%. it is suitable for the determination of trace amounts of chromium in industrial ferric nitrate.
zhang dongyun studied how to appropriately adjust the acidity of the color developing solution in the process of measuring hexavalent chromium in water using diphenylcarbazide spectrophotometry. instead of adding sulfuric acid and phosphoric acid mixed acid, only sulfuric acid was added. the results show that the relative standard deviations determined by the improved method are less than 5%, and the recovery rate reaches 99.9% to 102%. the diphenylcarbazide spectrophotometric method for determination of hexavalent chromium in water is simple to operate, has strong anti-interference performance, and has a large measurement range; however, the specific operating steps are somewhat cumbersome. the improved method has simplified the steps and has stable measurement results. research shows that: when pretreating water samples, a single acid can be used to adjust the ph or an appropriate amount of sulfuric acid and phosphoric acid can be added when preparing diphenylcarbazide chromogen to simplify the experimental steps and the measurement effect is equivalent to or even higher than the standard method. to standard methods.
2 determination of total chromium
zhou pei et al. used diphenylcarbazide reagent to react with hexavalent chromium under acidic conditions to generate chromium diphenylcarbazide. the compound is purple-red and has a maximum absorption peak at a wavelength of 540 nm, which is very important for refrigeration. the total chromium in the lithium bromide solution in the machine was measured. the experimental determination range of chromium was 0.020~0.20 mg/l, with a precision of ±5%. the sample recovery rate is 98%~102%.
zhang hui used potassium persulfate instead of potassium permanganate as the oxidant for the colorimetric analysis of diphenylcarbazide of chromium. the recovery rate was 94.9% and the relative standard deviation was 0.65%. it is easy to operate and with the characteristics of fast speed, high precision and good reproducibility, satisfactory results can be obtained when analyzing water samples. when measuring total chromium using diphenylcarbazide spectrophotometry, potassium permanganate is first used as an oxidant under acidic conditions to oxidize trivalent chromium to hexavalent chromium. excess potassium permanganate is treated with nitrous acid. sodium is decomposed, and excess sodium nitrite is decomposed into urea. if this method is not used properly, excess sodium nitrite can reduce trivalent chromium to hexavalent chromium under acidic conditions. using potassium persulfate instead of potassium permanganate can avoid the above problems.
3 determination of trace amounts of copper
copper is an essential trace element for the human body. copper deficiency can cause anemia, diarrhea and other illnesses, and excessive copper intake can lead to poisoning. therefore, it is necessary to detect the copper content in water. the main measurement methods include atomic absorption spectrometry, sodium diethylamidodithiocarbamate spectrophotometry, oscillographic polarographic analysis, etc. under alkaline conditions, diphenylcarbazide can form a purple-red complex with copper ions that is insoluble in water but soluble in chloroform and can be quantitatively extracted by chloroform, thereby being measured. yan chao studied the determination of the trace element copper content in different water samples using diphenylcarbazide spectrophotometry in the ph range of 6 to 7. copper ions and diphenylcarbazide form a red complex with a maximum absorption wavelength of 545 nm and an apparent molar absorption coefficient of ε = 1.297 ×104 l·mol -1·cm– 1, the copper ion content obeys lambert-beer’s law within the measurement range, the relative standard deviation rsd of 7 measurement results = 2.86%, and the recovery rate is between 98% and 102%. diphenylcarbazide spectrophotometry can accurately determine the total trace copper in a solution. it is simpler to operate, more sensitive, and consumes less water than traditional methods. it is a new method for determining trace copper and has certain application prospects.
main reference materials
[1] pan zhongcheng, lai na. research progress on the application of diphenylcarbazide spectrophotometry[j]. yunnan chemical industry, 2014,41(01):34-37.