Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.Phân tích Auramin O, Sundan I, Sudan II trong thực phẩm bằng phương pháp RPHPLC sử dụng vật liệu nanosilica để xử lý mẫu.
MINISTRY OF EDUCATION OF TRAINING HANOI NATIONAL UNIVERSITY OF EDUCATION PHAM THI CHUYEN ANALYSIS OF AURAMINE O, SUDAN I, SUDAN II IN FOOD BY RP-HPLC METHOD USING NANOSILICA MATERIAL FOR SAMPLE TREATMENT Major: Analytical Chemistry Code: 9.44.01.18 PhD THESIS ABSTRACT Hanoi - 2022 Place: Department of Analytical Chemistry – Faculty of Chemistry Hanoi National University of Education Advisors: Assoc Prof PhD Dang Xuan Thu Hanoi National University of Education PhD Nguyen Bich Ngan Hanoi National University of Education Reviewer 1: Assoc Prof PhD Pham Thi Ngoc Mai University of Science, Vietnam National University Hanoi Reviewer 2: Assoc Prof PhD Huynh Van Trung Institute for Technology of Radioactive and Rare Elements Reviewer 3: Assoc Prof PhD Duong Thi Tu Anh Thai Nguyen University of Education The thesis is completed in Hanoi National University of Education in 2022 The thesis can be found at: - National Library of Vietnam - Library of Hanoi National University of Education INTRODUCTION Urgency and reason of the thesis According to Circular No.24/2019/TT-BYT issued on August 30, 2019, in Vietnam, there are 57 colorants allowed to be used in food, including natural extracted colorants and synthetic colorants Thus, compared with Decision 3742/2001/QD-BYT issued in 2001 (which allowed the use of 21 colors), the number of color products in the list increased significantly, so the demand for chemical products has increased significantly Food colorings are becoming more and more popular However, there are production facilities that ignore food safety conditions to use toxic synthetic colors that are not allowed to be used on food to color food These dyes have the advantage of being inexpensive, standard and fast, and colorfast, but most of them contain toxic substances that can cause disease, which are classified as potentially carcinogenic substances according to International Agency for Research on Cancer (IARC) such as Sudan, Auramine O, Rhodamine B, and Ponceau 3R In fact, controlling the use of synthetic food colorings is difficult in Vietnam because they are used privately and on a small scale Many food products on the market have been found to contain dyes that are not allowed for food In Vietnam, Auramine O and Sudan dyes are not present in the National technical regulation on Food Additives - Colours QCVN 410:2010/BYT, which means banned substances for food coloring In addition, Circular No.21/2019/TT-BNNPTNT of the Ministry of Agriculture and Rural Development on “Guiding a number of articles of the Law on Animal Husbandry regarding animal feed” clearly stipulates in Appendix V: Prohibition of using Use of Auramine O and Auramine O derivatives in animal feed Currently, in Vietnam, there is only one certified method for determining Auramine O in food and animal feed, which is the Vietnam Standards TCVN 12267:2018 on “Foodstuffs - Determination of auramine - Liquid chromatography with tandem mass spectrometric (LC-MS/MS) method” However, for diverse food samples with different matrix, applying the same procedure for extraction and analysis can lead to low recovery efficiency and low accuracy In order to find solutions for extraction and separation suitable for different food samples, and develop a method to quantify toxic artificial dyes with a simple system of equipment suitable for laboratory conditions, we conducted the project “Analysis of Auramine O, Sudan I, Sudan II in food by RP-HPLC method using nanosilica material for sample treatment” Goals and main research contents of the thesis Goal of the study: Developing a process to analyze Auramine O in food samples: bamboo shoots, arrowroot vermicelli noodles, pickled mustard greens, pollen, dried fish and noodles Developing a process to analyze the mix of Sudan I and Sudan II in food samples: dried meat and snack samples Contents of the study: Auramine O: o Study to find optimal conditions for determination of Auramine O by HPLC method o Study on adsorption conditions of Auramine O in solution onto Nanosilica made from rice husk (RHNS) o Investigation of optimal conditions for extraction of Auramine O from laboratory food samples o Application of the studied procedure for the determination of Auramine O in real samples Sudan I and Sudan II: o Study to find optimal conditions for determination of the mix of Sudan I and Sudan II by HPLC method o Study on adsorption conditions of the mix of Sudan I and Sudan II onto RHNS o Investigation of optimal conditions for extraction of Sudan I and Sudan II from laboratory food samples o Application of the studied procedure for the determination of Sudan I and Sudan II in real samples Objects, research scope and research methods Research object and scope - Sudan I, Sudan II dyes in food samples: dried meat, snack samples - Auramine O in bamboo shoots, vermicelli, pollen, pickles, dried fish and noodles Research Methods - Method of liquid-liquid extraction of food samples with organic solvents - Dyes adsorption method on nanosilica - Analytical method HPLC quantitative dyes, using detector Diode Array (PDA) - Molecular absorption spectroscopy method UV-Vis to determine the maximum absorption wavelengths of dyes solutions The thesis uses modern physicochemical methods to evaluate and identify the characteristics of the adsorbent: FTIR, SEM, EDX, BET spectroscopy, etc Use statistical methods to process results, evaluate experimental data Scientific significance, practicality and new contributions - The thesis has proposed a general procedure for the analysis of dyes (Auramine O and mixture of Sudan I, Sudan II) in food samples The process comprises two main stages: sample processing and sample quantitative analysis by HPLC method Sample processing is performed in two ways, with different sample types Method 1: Extraction with organic solvents Method 2: Extraction with organic solvents - Adsorption of dyes in the extract by Nanosilia made from rice husks - Desorption by HPLC mobile phase This is a procedure for analyzing food dyes that has not been proposed before in any scientific research - Sample processing by extraction method with organic solvents is evaluated as a fast, simple, easy to implement and lowcost method An important point of the thesis is to provide a method for extracting dyes by ethanol solvent (extracting auramine O with a mixture of ethanol: water (v/v 70:30, extracting a mixture of Sudan I and Sudan II by absolute ethanol) With the amount of sample, volume of extract, extraction times, temperature, and time, using an extraction solvent containing ethanol for high extraction efficiency for many types of food samples (over 90%) while still ensuring the following factors: non-toxic to the analyst and the environment, low cost, simple steps and can extract many types of samples at the same time - Using Nanosilica made from rice husks to adsorb dyes from food sample extracts is also a new point of the thesis This is an important step in sample processing towards the “green chemistry” Using nanosilica to adsorb Sudan dyes at an isoelectric point while Sudan is hydrophobic is research that has not been proposed before (dyes adsorption studies by RHNS have only focused on hydrophilic dyes such as Methylene Blue, Rhodamine B, ) - The thesis has given the quantitative analysis results of AO, Sudan I and Sudan II in many food samples, valuable data regarding the selection of safe foods for consumers Layout thesis The layout of thesis includes 147 pages, introduction pages; overview 40 pages; experimental 27 pages; results and discussion 56 pages; conclusion pages The thesis has 56 figures and 42 tables; reference 11 pages with 13 Vietnamese and 63 English documents There are also Appendixes with pages CHAPTER - OVERVIEW Chapter introduces information about the issues under the research scope of the thesis, including: 1.1 Introductions of dyes 1.2 Binding mechanism of dyess with materials 1.3 Auramine O 1.4 Sudan compounds 1.5 Introduction to high-performance liquid chromatography, focusing on factors that influence the method, such as mobile phase composition, symmetry coefficient of chromatographic peaks, peak problems, limit of linearity, limit of detection LOD, limit of quantitation LOQ 1.6 Food sample processing methods are also studied through the following contents: classification of sample treatment methods, liquid-liquid extraction techniques, application of sample treatment, trends in application of green sample preparation techniques 1.7 Overview of nanosilica materials including the following contents: physical and chemical characteristics of the material, the basis of statistical processing of adsorption data, applications of nanosilica materials made from rice husks in adsorption and enrichment CHAPTER – EXPERIMENTAL 2.1 Materials, chemicals, tools and equipment 2.2 Research content 2.2.1 Preparation of samples 2.2.1.1 Analytical Sample Auramine O Fresh bamboo shoots have just been dug up, removed the hard and old parts, washed, thinly sliced, soaked in diluted salt water, taken out, boiled, drained, then soaked with vinegar for days, when smelling bamboo shoots with a characteristic sour smell, take it out, cut it into pieces, weigh the initial weight - m (g), add a predetermined amount of Auramine O - mAO (g) Dry to constant weight in a vacuum oven, weigh m2 g, then grind and sieve finely With arrowroot vermicelli noodles samples, which are handmade in Son La province, the process is strictly controlled so as not to use any dyes or bleach in the in the production process Take a quantity of arrowroot vermicelli noodles and dry it to constant weight (weigh initial weight m1 g), soak in warm water until soft, mix AO of predetermined mass (mAO g), stir and grind until homogenous, dried to constant weight (m g), crushed, sifted finely, dry powder in a vacuum oven for about hours, product stored in sealed jars, stored in a dark refrigerator 2.2.1.2 Mixed analysis sample Sudan I and Sudan II To determine the optimal conditions for the extraction of food samples, two dried meat samples, denoted A and B, were used Fresh pork was purchased from a VinMart supermarket in Hanoi city Only lean meats were used for the experiments Lean meat is minced to a maximum size of mm 12 Figure 2.3: Sample processing of arrowroot vermicelli noodles, pickled mustard greens, dried meat Figure 2.4: Sample processing of pollen, dried fish, noodles, snack (*) : Depending on whether the analyte is AO or a mixture of Sudan I and Sudan II, appropriate optimal extraction conditions will be applied 13 CHAPTER - RESULTS AND DISCUSSION 3.1 HPLC system and analytical conditions of AO The suitable parameters of quantitative analysis of AO by HPLC method are presented in Table 3.4 Table 3.4: Optimal conditions for AO analysis by HPLC Conditions for the analysis Column Value C18-RP (150 mm × 4,6 mm, 100Å, µm) Waters Column 40°C temperature Injector volume 20 µL Wavelength 432 nm detector Mobile phase PBS (pH=3; 0,2% triethylamine) : ACN Mobile phase 65:35 (v/v) composition Speed of mobile 1,0 mL/min phase The results of the repeatability of determining AO standard sample (40 µg/L) after HPLC measurements: the RSD% standard deviation values of peak area and retention time of 2,415% and 0,474%, respectively, are small, showing that the method has good repeatability Thus, the HPLC method to quantify AO with the above optimal conditions has high sensitivity, good repeatability, and it is suitable for the analysis of AO at tiny concentration (µg/L or ppb) 14 Ext ract io n efciency(%) 3.2 Optimal extraction conditions 100 80 60 40 20 Ext ract io n so lvent s MMT MIT Figure 3.7: Variation of average AO extraction efficiency according to extraction solvent Experiments showed that when extracting MMT and MIT samples, a sample mass to solvent volume ratio of about 0,1 g/10 mL is acceptable (equal extraction efficiency over 95%) Other research results on optimal extraction conditions include: the number of extractions is times, each time using 5,00 mL of solvent mixture for 30 minutes/time at a maintained extraction temperature of 60°C The results of determining AO recovery in MIG and MAG samples showed that the recovery of the extraction method was under AOAC and according to the European council (from 80% to 110%), so the extraction method was concluded: suitable for extraction of AO from sample matrices However, when analyzing other types of real samples including: pollen, dried fish, noodles sample, it was found that for the studied optimal HPLC extraction and analysis procedure, these types of samples gave the extract a suspension when mixed in the 15 HPLC mobile phase and could cause chromatographic column clogging Therefore, the method of using nanosilica from rice husk to adsorb AO in the extract is proposed, then AO is desorbed by mobile phase and quantified by HPLC 3.3 Optimized adsorption conditions of AO on RHNS A concentration of mM KCl was selected for further adsorption studies The dependence of the AO adsorption efficiency on the pH of the solution is shown in Figure 3.10 pH=4,0 was chosen as the optimal pH value of the adsorbent solution The adsorption equilibration time was chosen to be 150 Based on experimental data based on Langmuir adsorption isotherm Adsorpton efciency (%) Ce/qe in Figure 3.12, the maximum adsorption 100 capacity of AO on RHNS 100 80 Adsorpton Adsorptonefciency(%) efciency (%) 100 60 the adsorption constant was determined to be qm = 0,371 mg/g, and 80 75 60 KL = 1,843 40 50 Figure 20 3.9: Effect of KCl concentration on AO 25 0.010.1 10 100 adsorption KCl (mM) 10 60 120 150 C = 0.05 (µg/mL) C = 1.00 (µg/mL) Time (min) 3.11: Adsorption CFigure = 10.00 (µg/mL) 40 20 35 f(x) = 2.7x + 1.46 283.10: Figure Effect of pH on 3R² =4 21AO 10 adsorption pH values 14 0 10 12 Ce (mg/L) Figure3.12: Linear Langmuir efficiency according to AO initial concentration and adsorption equilibrium time plots of AO adsorption on nanosilica 3.4 Results of analysis of AO content in real samples Results of analysis of AO concentration in the samples presented in Table 3.19 Comment: The AO retention time of real samples is relatively 16 stable (from 3,74 minutes to 3,83 minutes) The concentration of AO in sample MA1 was determined by the standard addition method, because if the extract is concentrated, the baseline is not smooth and that affects the accuracy of the method For the MA6 chromatogram of the original extract, there was a peak occurring at 3,56 minutes, however this was not the peak of AO, showing that when AO standard was added, the peak of AO appeared later (at 3,97 minutes) Thus, the composition of substances in the real sample influences the retention time of the analyte 17 Table 3.19: AO content in dried fish, pollen, and noodles samples Numbe Sample r s AO Numbe Sample r s content (µg/g) AO content (µg/g) PH1 ND CK3 ND PH2 ND MT1 ND PH3 MT2 ND CK1 ND MT3 ND CK2 ND 0,82 ± 0,19 Analytical results on chromatograms of the original PH3 sample without AO standard added by HPLC appeared peak at 3,758 min, however the peak was very obtuse, it can be assumed that there is peak overlap, in there is one peak of AO, the remaining peaks can be a salt with similar structural formula AO The determination of AO content in the PH3 sample is relative with the assumption that the peak at 3,758 minutes in Figure 3.22 is AO, using the standard addition method, repeated measurement times (Figure 3.23), giving the results of AO content in the PH3 sample was 0,82 ± 0,19 (µg/g) 3.6 Conditions for the HPLC analysis of Sudan I and II Chose wavelength of 490 nm for further study We used different mobile phases to investigate the appearance of the Sudan dyes and found that a mobile phase of MeOH, H2O, and ACN in a volume ratio of 77: 3: 20 achieved the best peak shape and separation HPLC measurements were performed with a PDA detector The manual injector valve had a 20 µL sample injection ND : Not detection 18 volume A SunFire C18 column (100 , àm, 4,6 mm ì 150 mm) was used to separate Sudan I and II Limit of linearity, standard curve, LOD and LOQ Thus, the data were sufficiently reliable for use to construct a calibration curve The data related to the standard curve are presented in Table 3.24 Table 3.24: Method performance and validation parameters with standard samples Chemica l Linear range (µg/L) Sudan I Sudan II LOD LOQ (µg/L (µg/L ) ) 0,9991 2,73 9,11 0,9991 2,99 9,96 Linear Coefficient equations R2 2÷ S = (69,50 ± 10000 0,32).C 5÷ S = (76,03 ± 10000 0,39).C The Sudan I and II standards were added to blank extracts (MTA) The concentration of Sudan I and II was added incrementally The results of statistical processing of the obtained data are in Table 3.25 Table 3.25: Method performance and validation parameters with blank samples Chemica l Sudan I Sudan II Linear range (àg/L) Linear equations 2ữ1000 S= (69,17 0,59).C 5÷1000 S= (75,70 ± 0,37).C Coefficient R 0,9994 0,9991 MDL MQL (µg/g) (µg/g) 0,002 0,007 0,002 0,009 19 3.7 Optimal extraction conditions for the mixture of Sudan I and Sudan II The results of the investigation of mixed extraction conditions of Sudan I and Sudan II are as follows: - Ultrasonic vibration extraction method - Extraction solvent: 100% EtOH solvent because the extraction efficiency when using this solvent is the highest (97,26% with Sudan I and 93,79% with Sudan II) - Extraction temperature 60°C, optimum extraction time 120 minutes, number of extractions: 2, solvent volume 10 mL, the most suitable sample mass/solvent volume ratio is about 0,1000g sample/ 10 mL solvent 3.8 Optimal conditions for adsorbing mixture of Sudan I and Sudan II on RHNS mM KCl was selected for further study The pH of the solution affects the surface charge of the nanosilica and the dissociation of the Sudan dyes The dye adsorption between pH and pH = is the optimal pH value chosen for the adsorption of Sudan dyes on RHNS because the adsorption efficiency is biggest We choose to investigate the adsorption with the concentration of Sudan dyes less than 1000 µg/L Langmuir adsorption isotherms were plotted to get the maximum adsorption capacities The coefficient of determination (R2) for the linear fit of the data was greater than 0,99, showing that the dyes are adsorbed by monolayer physical adsorption, and the 20 adsorption centers on the surface are homogeneous The maximum adsorption capacity (qm) and adsorption constant (KL) for Sudan I were 0,619 mg/g and 2,132, respectively, whereas those for Sudan II were 0,699 mg/g and 1,573, respectively 3.9 Uncertainty of the Sudan mixed analytical method Sudan I: UR%=tα,f RSDR %= t0,05;19 RSDR %=1,73.3,62=6,26% Sudan II: UR%=tα,f RSDR %= t0,05;19 RSDR %=1,73.4,53=7,84% Thus, at the content of Sudan I and Sudan II from 10÷100 g/L, the measurement uncertainty of the extraction - adsorption desorption process is 6,26% and 7,84%, respectively, with a confidence level of 95 % 3.10 Analysis of real samples Optimal extraction and adsorption conditions applied to the analysis of three dry meat and five snack samples The results showed that Sudan I and II were below the LOD in the samples (BK1, BK3, MBB4) Even after getting rich, there is no sign of Sudans All remaining samples contained Sudan I and Sudan II at concentrations above the limit of detection (Table 3.28) 21 Table 3.28: Quantification of Sudan I and II in food samples (mean±confidence, n = 3) Sampl e Add Add Found Found Sudan Sudan Recovery Recovery Sudan I Sudan II I II of Sudan of Sudan (µg/L) (µg/L) (µg/L (µg/L (%) II (%) ) ) 82,76±1,13 83,64±0,81 BK1 ND ND 50,00 50,00 BK2 26,72±1,48 47,68±1,39 50,00 50,00 BK3 ND ND 50,00 50,00 84,32±2,25 83,90±2,40 MBB1 17,59±0,80 44,43±2,57 50,00 50,00 77,31±1,06 81,73±2,07 MBB2 26,85±0,45 40,78±2,20 50,00 50,00 82,13±1,03 82,20±1,24 MBB3 15,97±0,38 28,46±0,43 50,00 50,00 86,82±0,83 91,22±1,46 MBB4 ND ND 50,00 50,00 84,98±0,99 86,90±2,31 20,39±1,10 50,00 50,00 80,22±1,34 84,76±1,31 MBB5 13,23±0,18 101,53 ±1,23 93,24±0,78 Based on the results of quantification of Sudan I and Sudan II from the extraction and desorption solutions by HPLC, the ND : Not detecton After desorption, the solution was diluted times with PB5-S because the Sudan II content in the extract was outside the linear range of the calibration curve After desorption, the solution was diluted times with PB5-S because the Sudan I and Sudan II contents in the extract were outside the linear range of the calibration curve 22 concentrations (µg/g) of Sudan I and Sudan II in the original dried food samples are given in Table 3.30 23 Table 3.30: Contents of Sudan I and Sudan II in the primary dry food sample Sample Sudan I content Sudan II content (µg/g) (µg/g) BK1 ND ND BK2 19,55 ± 1,08 34,88 ± 1,01 BK3 ND ND MBB1 11,86 ± 0,54 29,37 ± 1,02 MBB2 17,46 ± 0,29 26,53 ± 1,43 MBB3 45,59 ± 1,08 67,81 ± 1,22 MBB4 ND ND MBB5 7,38 ± 0,10 11,38 ± 0,61 24 CONCLUSION After researching and implementing the project "Analysis of Auramin O, Sundan I, Sudan II in food by RP-HPLC method using nanosilica material for sample treatment", some results have been obtained: HPLC method using reversed phase chromatography with C18-RP column and PBS mobile phase (pH = 3.0; add 0.2% triethylamine): Acetonitrile (ACN) ratio v/v = 65:35 is suitable for quantification of AO at 432 nm When changing the mobile phase as MeOH:H2O:ACN ratio v/v = 67:3:20, the method can quantify Sudan I and Sudan II when present simultaneously in solution at measuring wavelength 490 nm Reliable analysis results with high sensitivity: LOD and LOQ of AO are 1.2 µg/L, 3.9 µg/L and Sudan I are 2.7 µg/L, 9.1 µg/L, respectively.; of Sudan II are 3.0 µg/L and 10.0 µg/L The proposed method of handling food samples through two diagrams (Figure 3.9 and Figure 3.10) is appropriate and ensures novelty AO was extracted from food samples with the extraction solvent EtOH:H2O (ratio v/v = 70:30), the Sudan in food samples was extracted with absolute ethanol solvent, which is a safe solvent for environment and user, for high recovery efficiency and simple extraction process that can be carried out in large quantities at the same time Dyes in some solutions after extraction can use nanosilica materials made from rice husks to adsorb, enrich and eliminate the influence of other factors in the extract on the determination of dyes by HPLC The use of RHNS to adsorb synthetic dyes AO and the 25 mixture of Sudan I and Sudan II in food sample extracts is suitable, giving high adsorption efficiency This is an important stage in the treatment of food samples with dyes for quantitative analysis of dyes by HPLC method, highly selective adsorbents shown in clear, lownoise chromatographic signals RHNS has a low point of zero charge (PZC), so it is suitable for adsorbing hydrophobic dyes such as Sudan I and Sudan II electrostatic interaction of RHNS with AO in aqueous solution also plays a role in increasing the solubility AO adsorption under suitable conditions Good sample handling prolongs the life of the analyzer, increases selectivity, and above all, this sample handling process is non-toxic to the analyst and to the environment, and requires less solvent Out of the total of 30 analyzed samples, up to 11 samples contained AO or Sudan (accounting for 36.7%) which are synthetic color compounds banned for use in food in Vietnam This is a worrying result about the current food safety situation in Vietnam LIST OF PUBLISHED PAPERS Pham Thi Chuyen, Dang Xuan Thu, Nguyen Bich Ngan, Pham Thi Thuyen (2020), Study on auramine - O extraction produce from foods and quantify samples by high perfomance liquid chromatography, Journal of Analytical Sciences, Volume 25, issue 3, pp 108-113 Vu Thi Tinh, Nguyen Bich Ngan, Pham Thi Chuyen (2020), Optimization of extraction process of Sudan i from foodstuffs, Journal of Analytical Sciences, Volume 25, issue 3, pp 180-184 Pham Thi Chuyen, Dang Xuan Thu, Nguyen Bich Ngan (2021), Study on absorption of auramine o by silica extracted from rice husk and application in analysis, Journal of Science, Volume 74, pp 16-27 Thi Chuyen Pham, Bich Ngan Nguyen, Xuan Thu Dang, and Thi Tinh Vu (2021), Determination of Sudan I and II in Food by High-Performance Liquid Chromatography after Simultaneous Adsorption on Nanosilica, Journal of Analytical Methods in Chemistry, Volume 2021, ID 6664463, pp.1-9 ... of Sudan I and II in food samples (mean±confidence, n = 3) Sampl e Add Add Found Found Sudan Sudan Recovery Recovery Sudan I Sudan II I II of Sudan of Sudan (µg/L) (µg/L) (µg/L (µg/L (%) II (%)... determination of Sudan I and Sudan II in real samples Objects, research scope and research methods Research object and scope - Sudan I, Sudan II dyes in food samples: dried meat, snack samples - Auramine... for laboratory conditions, we conducted the project “Analysis of Auramine O, Sudan I, Sudan II in food by RP-HPLC method using nanosilica material for sample treatment” Goals and main research