液相色谱/串联质谱法测定芹菜中甲拌磷及其代谢物残留

建立了芹菜中甲拌磷及其代谢物(甲拌磷亚砜和甲拌磷砜)残留的液相色谱/串联质谱检测方法。样品以乙腈提取,采用电喷雾正离子源(ESI+)和多重反应监测(MRM)模式测定,基质匹配标准曲线定量。结果表明:芹菜基质中甲拌磷、甲拌磷亚砜和甲拌磷砜在0.01~0.1mg/L范围内线性关系均较好(r0.995),方法检出限和定量限分别为0.42~1.10μg/kg和1.4~3.6μg/kg;在5、50和100μg/kg三个添加水平下,甲拌磷、甲拌磷亚砜和甲拌磷砜的回收率为71.9%~90.2%,相对标准偏差为5.8%~9.9%。该法简单、准确、快速、灵敏,符合法规残留限量监测要求。     

QuEChERS-气相色谱/质谱法测定牛奶中氟虫腈及其代谢物的残留量北大核心CSCD

建立了QuEChERS-气相色谱/质谱法测定牛奶中氟虫腈及其代谢物氟甲腈、氟虫腈砜、氟虫腈硫醚残留量。样品经QuEChERS法提取净化,采用DB-5MS柱进行分离,选择离子模式下同时测定,外标法定量。结果表明,氟虫腈及其代谢物在0.01~0.50μg/mL质量浓度范围内均呈良好的线性关系,相关系数R^(2)>0.997,该方法检出限为0.30~0.68μg/kg,定量限为0.90~1.20μg/kg。在加标水平分别为0.01、0.10、0.50 mg/kg下,4种化合物的回收率范围为83.7%~112.6%,相对标准偏差范围为1.8%~4.2%。该方法简单快捷、准确可靠,适用于牛奶中氟虫腈及其代谢物的同时测定。     

气相色谱串联质谱法测定蔬菜中甲拌磷和克百威及其代谢物的残留量

建立气相色谱–三重四级杆串联质谱法(GC–MS/MS)测定蔬菜中甲拌磷及其代谢产物甲拌磷砜、甲拌磷亚砜,克百威及其代谢产物3-羟基克百威。蔬菜样品经乙腈提取、Qu ECh ERS法净化,GC–MS/MS采用选择反应监测模式(SRM)采集数据后进行分析。5种化合物的含量在检测范围内与色谱峰面积均呈良好的线性,相关系数r2为0.998 0~0.999 6。在0.02,0.05 mg/kg的添加水平下,平均回收率在73.6%~118.2%范围内,测定结果的相对标准偏差小于8.5%(n=6),方法定量限为5~10μg/kg。该方法可用于蔬菜中甲拌磷和克百威及其代谢物的常规检测。     

超高效液相色谱-串联质谱法测定荔枝花粉花蜜中吡唑醚菌酯及其代谢物

采用改进的Qu ECh ERS方法结合超高效液相色谱-串联质谱技术,建立了荔枝花粉和花蜜中吡唑醚菌酯及其主要代谢物BF 500-3的分析方法。样品经乙腈提取,分别由乙二胺-N-丙基硅烷(PSA)和十八烷基键合硅胶吸附剂(C_(18))净化、浓缩后进样分析,正离子扫描、多反应监测模式下,对基质匹配标准溶液定量分析,考察了前处理和质谱分析条件。结果表明,吡唑醚菌酯及其代谢物在1~100μg/L浓度内,基质匹配标准溶液线性关系良好,相关系数(R~2)为0.991~0.999。花粉和花蜜基质中的平均回收率为87.0%~97.8%,相对标准偏差(RSD)为1.3%~3.7%,检出限(LOD)为0.08~0.20μg/kg,定量限(LOQ)为0.20~0.50μg/kg。本方法简便、快速、灵敏度高,适于荔枝花粉和花蜜样品中吡唑醚菌酯及其代谢物的快速测定。     

高效液相色谱-串联质谱法测定蜂蜜中的红霉素及其代谢物

建立了高效液相色谱-串联质谱法检测蜂蜜中红霉素及其代谢物红霉素A烯醇醚和脱水红霉素A的测定方法。以pH 7.0的磷酸盐缓冲液为提取剂,经HLB小柱净化富集后,采用高效液相色谱串联质谱法测定蜂蜜中红霉素及其代谢物的含量。该方法前处理简单,采用内标法定量,方法的线性范围为2.0~100.0μg/L,相关系数大于0.996,红霉素及其两种主要代谢物的检出限和定量下限分别为0.5μg/kg和2.0μg/kg,回收率范围为70.5%~109.2%,RSD小于10%。方法的回收率稳定且重现性较好,可用于蜂蜜中红霉素及其代谢物的检测。     

液液萃取柱-液相色谱-串联质谱法测定乳制品中硝基呋喃类代谢物残留

采用液液萃取柱-超高效液相色谱-串联质谱技术建立了乳制品中硝基呋喃类代谢物的快速测定方法。硝基呋喃类代谢物衍生化反应后,利用EXtrelut NT液液萃取小柱进行净化富集,采用正离子多反应监测模式,内标法定量。硝基呋喃类代谢物在0.10~10.0μg/L范围内线性关系良好,检出限为0.04~0.10μg/kg,回收率范围为71.5%~109.4%,相对标准偏差(RSD)范围4.6%~9.8%。方法适用于乳制品中硝基呋喃类代谢物的快速检测。     

QuEChERS-四极杆/静电场轨道阱高分辨质谱测定动物性食品中氟虫腈及其代谢物残留

基于低温处理和QuEChERS方法,采用超高效液相色谱-四极杆/静电场轨道阱高分辨质谱建立了动物性食品中氟虫腈及其代谢物残留的分析检测方法。样品采用乙腈提取,经低温处理,N-丙基乙二胺(PSA)和C18粉分散固相萃取(d-SPE)净化,以BEH C18色谱柱为分析柱,乙腈-0.1%乙酸溶液为流动相进行梯度洗脱分离,外标法定量。采用高分辨质谱平行反应监测(PRM)扫描模式,以负离子采集进行定性筛查和定量分析。氟虫腈及其代谢物在0.02~2μg/L和0.2~20μg/L质量浓度范围内均呈良好的线性关系,相关系数(r2)大于0.992。对液体或半液体样品(如牛奶和鸡蛋)和固体样品(如鸡肉),方法的定量下限分别为0.1μg/kg和0.2μg/kg。在不同浓度的加标水平下,氟虫腈及其代谢物在鸡蛋中的平均回收率为81.6%~96.9%,相对标准偏差(RSD)为1.3%~11.5%;在鸡肉中的平均回收率为81.2%~96.0%,RSD为3.4%~11.4%;在牛奶中的平均回收率为79.1%~100.1%,RSD为1.5%~10.7%。该方法简单、灵敏、准确,适用于动物性食品中氟虫腈及其代谢物的快速筛查和定量检测,方法的灵敏度满足欧盟的残留限量要求。     

液相色谱-串联质谱法测定猪肉中咪唑类药物及其代谢物

建立了高效液相色谱-串联质谱同时测定猪肉中29种咪唑类药物及其代谢物残留的检测方法。样品采用乙酸乙酯提取,浓缩复溶后加入乙腈饱和正己烷净化除脂,以0.3%(体积分数)甲酸水溶液和乙腈为流动相,反相C_(18)色谱柱梯度洗脱分离,采用电喷雾正离子(ESI+)源多反应监测(MRM)模式进行检测。29种化合物在0.05~20.0μg/L范围内线性关系良好,相关系数r~20.99。在1.0~5.0μg/kg添加范围内,平均回收率为65.4%~103%,相对标准偏差(RSD)为1.3%~6.8%。方法检出限为0.02~0.3μg/kg,定量限为0.1~1μg/kg。该方法简便、快速、灵敏,适用于猪肉中咪唑类及其代谢物残留的检测。     

低温液液萃取/超高效液相色谱-串联质谱法快速测定鲜枣中氟虫腈及代谢物

采用低温液液萃取技术,对鲜枣中的氟虫腈及其代谢物残留进行提取和净化,并利用超高效液相色谱-串联质谱法(UPLC-MS/MS)进行定性和定量分析。鲜枣样品以乙腈作为提取溶剂,-25℃低温液液萃取后,直接进样分析,采用负离子多反应监测(MRM)模式,外标法定量。结果表明,在优化条件下,氟虫腈及其代谢物在0.02~10μg/L范围内线性关系良好,相关系数(r2)大于0.999,检出限为0.005~0.02μg/kg,在不同加标浓度下的平均回收率为78.5%~95.8%,相对标准偏差(RSD)为3.4%~6.9%。该方法快速、简便、灵敏,适用于鲜枣中氟虫腈及其代谢物的快速测定。     

气相色谱-三重四极杆质谱法测定鸡蛋中氟虫氰及其代谢残留

建立了QuEChERS快速提取和净化样品,气相色谱-三重四级杆质谱联用法测定鸡蛋中氟虫腈及其代谢物氟甲腈、氟虫腈砜、氟虫腈亚砜的方法。水和乙腈萃取、C_(18)和PSA净化样品,气相色谱分离,多反应离子监测模式测定。氟虫腈及其3种代谢物在5~400μg/L范围内线性关系良好,方法的检出限为1.0~2.5μg/kg;定量限为3.0~7.5μg/kg。在两个浓度水平进行加标,上述4种测定物的回收率为72.5%~95.3%,相对标准偏差为3.7%~7.5%。本方法可满足鸡蛋中氟虫腈及其代谢物氟甲腈、氟虫腈砜、氟虫腈亚砜残留检测的实际需要。     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.