Abstract Chromatography is an important technique enabling the separation, identification, and purification of the components of a mixture for qualitative and quantitative analysis.

Abstract Persistent organic pollutants (POPs) are organic chemicals capable of persisting in the environment, being transported over long distances, bioaccumulating and biomagnifying in ecosystems. The harmful effects of these compounds on the environment and the health of living beings are of concern. In particular, humans can come into contact with POPs when consuming contaminated food of animal origin with a high fat content. In the Dominican Republic these compounds have been widely used and generated. However, the levels of POP exposure to which the population is exposed are unknown. Therefore, the objective of this study was to determine the presence of 34 POPs in five main brands of nationally produced cow's milk. The samples were prepared using the QuEChERS extraction method and the analytical technique used was GC/MS. The results obtained indicated that no POPs were present in the samples. The results obtained indicated that there is no presence of the POPs evaluated in any of the cow's milk samples, which suggests that their consumption does not represent a threat to the health of consumers. In addition, this study contributes to the knowledge on the evaluation of POPs in the Dominican Republic.

Abstract The career of Chemical Engineering presents among the areas studied several analytical techniques in common within the laboratory field with the field of Criminalistics, these techniques are used for the detection of foreign components within samples of biological and non-biological origin that alter the behavior of an individual or end with the death of the same, the results are analyzed by comparison with established patterns that allow to give a reliable interpretation to be presented to a judge. The objective of this study is to collect information to determine the areas within the criminalistic and forensic field where a chemical engineer can be of support, taking advantage of his knowledge in the different analytical techniques and helping in the interpretation of the results of these, thus allowing to contribute to the legal procedures that are carried out in the cases presented before the law.

Abstract The evaluation of contaminants present in the environment is a recurring theme at the international level, which is why it is imperative to develop new methodologies for the extraction of analytes from matrices such as surface water, with a low impact on the environment. Chlorpyrifos (CP) is an organophosphate compound widely used for pest control, toxic to living organisms, which can be mobilized from soils to different water sources. Dispersive liquid-liquid microextraction (DLLME) can be considered as a methodology with green analytical chemistry characteristics, due to its low solvent and time consumption. The objective of this work was to optimize DLLME for the analysis of CP in water samples. For the extraction, methanol was used as dispersing agent and CS2 as extracting agent, and five extraction times were evaluated: 5, 10, 15, 15, 20 and 25 minutes. The extracts were analyzed by gas chromatography with electron microcapture detector (GC- μECD). The results of the shaking time evaluation showed that, for the shaking times of 10 and 15 minutes, a CP recovery percentage of 108 and 88 % was obtained, respectively, with a detection and quantification limit of 18.3 and 22.4 μg/L, respectively, and a precision expressed as relative standard deviation of less than 14.2 %, which is acceptable for this type of extraction. It can be concluded that the DLLME methodology associated with GC-μECD is a suitable alternative for the quantification of CP in aqueous matrices with a low environmental impact.

Abstract Ambient ionization mass spectrometry(AIMS)is a mass spectrometry technology which could be used to analyze target analytes in samples under atmospheric pressure without or with simple sample pretreatment. With the advantages of simplicity, rapidness, non-destructiveness and wide application range, it is widely used in forensic toxicological analysis. This article gives a brief over- view on the ambient ionization(AI)technique, and the samples are divided into two types: in vivo test materials and in vitro test materials. The application of AIMS in the poison analysis of different types of test materials is summarized, and its application direction in forensic toxicological analysis is prospected.

Abstract In order to accurately determine the content of vitamin A (vitamin A 1 , vitamin A 2 ) in fish liver, sample pretreatment methods (water bath saponification, room temperature saponification, direct extraction) and detection methods (normal phase chromatography, reversed phase chromatography) were screened and applied to the determination of vitamin A in the liver of nine economic fish species. The results showed that vitamin A 1  and vitamin A 2  were separated effectively by reversed phase chromatography and showed good linear relationship within their respective linear ranges( R 2  > 0.99); the content of vitamin A extracted by water bath saponification was significantly higher than that by room temperature saponification and direct extraction (p <0. 05), and its average recoveries of vitamin A 1  and vitamin A 2  were 104. 52% and 90. 94%, respectively. Except for the freshwater snakehead and big mouth bass, the total content of vitamin A in the livers of other freshwater fishes and marine fishes was more than 200μg/100 g, and the total content of vitamin A in the liver of marine giant grouper was the highest, reaching 14 413.78μg/100 g. The water bath saponification method combined with reversed phase chromatography has good precision and is suitable for the determination of vitamin A in fish liver.

Abstract Objective : To establish a pre⁃column derivatization liquid chromatography method and a post⁃column derivatization liquid chromatography method for the determination of residual amount of free formaldehyde in vaccines. Consistency of the results of two methods was investigated. Methods : The pre⁃column derivatization liq⁃ uid chromatography was performed on a Shimadzu LC⁃20AT liquid chromatograph (SPD⁃20A UV detector). Sepa⁃ ration was accomplished on a Kromasil 100⁃5⁃C 18 (250mm×4.6mm) column with a mobile phase of 60% acetoni⁃ trile solution at a flow rate of 0. 8 mL·min -1  at 40℃ and the detection wavelength was 360 nm. The post⁃column derivatization liquid chromatography was performed on a Shimadzu LC⁃20AT liquid chromatograph (SPD⁃M20A diode array detector and vector derivative device). Separation was accomplished on a Chrom Core AQ⁃C 18  (250mm ×4.6mm) column with a mobile phase of 0.2% (V/V) phosphoric acid solution at a flow rate of 1.0 mL·min -1  at 25℃ and the detection wavelength was 412 nm. The derivatization solution was acetate buffer, the flow rate was 0. 5 mL·min -1 , and the temperature was 100℃. The precision, repeatability and sample recovery of the two methods were investigated, and the experiment results were tested for significance by F⁃test and t⁃test. Results : The precolumn derivatization liquid chromatography had good linearity in the range of 0. 025 -100μg· mL -1 ( R  =0. 999 9, n  =12). RSD values of precision and repeatability were 0. 06 % and 0.3%-1.4%, respectively. The average recoveries were 97. 3%-104. 8 % with RSD of 0. 7%-2. 9 %. The limit of quantitation was 0. 02μg·mL -1 , and the limit of detection was 0. 01μg·mL -1 . The post⁃column derivatization liquid chromatog⁃ raphy had good linearity in the range of 0.025-100μg·mL -1  ( R  =0. 9999, n =12). RSD values of precision and repeatability were 0. 02% and 0. 0.7%-3.5 %, respectively. The average recoveries were 105. 6%-114. 6% with RSD of 0.3% - 1.9%. The limit of quantitation was 0. 02μg·mL -1 , and the limit of detection was 0. 006μg·mL -1 . The F⁃test and the t⁃test results showed there was no significant difference between two methods. Conclusion:  Two methods are simple and accurate with high sensitivity and good specificity, which can be applicable to the determination of free formaldehyde residues in vaccines.