GC/MS衍生化法检测血中4-溴-2,5-二甲氧基苯乙胺

目的建立人体全血中4-溴-2,5-二甲氧基苯乙胺的衍生化GC/MS分析方法。方法血液样品经去离子水稀释4倍,8000r/min高速离心20min后,加入Na H2PO4缓冲溶液(p H值为6.0)2m L,混匀。将上述混合液加入用甲醇、Na H2PO4缓冲溶液(p H值为6.0)活化的Bond Elut Centify?固相萃取柱后,依次采用1.0M乙酸溶液、去离子水、甲醇、二氯甲烷/异丙醇/氨水(78/20/2,V/V/V)混合洗脱液进行提取、分离、净化处理,40℃空气流下挥干,三氟乙酸酐衍生化,GC/MS检测4-溴-2,5-二甲氧基苯乙胺和4-苯基丁胺衍生物。采用标准品衍生化产物的标准质谱图定性分析,选择m/z 242(4-溴-2,5-二甲氧基苯乙胺)、m/z 91(4-苯基丁胺)作为定量离子进行定量分析。结果血液中4-溴-2,5-二甲氧基苯乙胺的最低检出限为6ng/m L,在0.02~10μg/m L浓度范围内,线性关系良好(=0.9993),日内精密度和日间精密度均小于10%,平均提取回收率约为69%。结论该方法操作简便、灵敏度高,适用于全血中4-溴-2,5-二甲氧基苯乙胺检测。     

改革开放 40 年来中国企业员工集体离职机制的 典型案例研究

企业员工集体离职对相关组织和员工群体影响深远。本研究从 1978—2021 年中国知网（CNKI） 4 类论文数据库及报纸 1 类新闻数据库中，甄选出我国 102 个企业员工集体离职典型案例。研究发现：集体离 职集中发生在时代的热门行业、朝阳产业，其中制造业、IT 业的集体离职始终处于焦点；集体离职的主要原 因是个体自身因素、企业内部因素以及二者互动因素；集体离职的直接原因同样主要在内因，成为集体离职的 “导火索”或“催化剂”。研究提炼出企业员工集体离职影响因素和作用机制模型、企业员工集体离职主要原 因和直接原因作用模型。基于此，研究建议：预防集体离职需整体上更加关注企业的内部管理，化解集体离职 需避免主要原因的积累，缓解集体离职还需注意直接原因的作用。     

Organisational choices in public procurement: what can public management learn from the private sector?

ABSTRACT

In the public context, the efficient and effective management of procurement activities has a crucial impact on the achievement of operational and broader government objectives. In particular, the potential contribution of procurement within local governments has been broadly recognized, and organisational procurement choices represent a strategic aspect that must be managed to contribute to these objectives. Through the analysis of data on 371 Italian municipalities, this paper discusses how to design procurement organisation variables for local governments. Three possible organisational models are identified (i.e., authoritative procurement, silo procurement, and local procurement) and discussed from the perspective of internal and external contingencies that may affect organisational decisions.     

Affective blocs: Understanding affective polarization in multiparty systems

Research has suggested that affective polarization (AP)—the extent to which partisans view each other as a disliked out-group—has increased, especially in two-party political systems such as in the US. The understanding of AP in multiparty systems remains limited. We study AP in Finland, characterized by a strong multiparty system and a low level of ideological polarization, between 2007 and 2019. We find that AP has increased, driven mainly by voters evaluating their least favorite party more negatively. We also propose an approach that goes beyond earlier literature, which has mostly used a single aggregate metric to measure AP. Using latent profile analysis, we find that voters are grouped into blocs that view some parties positively and others negatively. This suggests that the complex dynamics of AP in multiparty democracies involve relationships between not just individual parties but between what we call affective blocs that span across party lines.     

Long‐Run Labor Market Effects of the Job Corps Program: Evidence from a Nationally Representative Experiment

Job Corps is the nation's largest and most comprehensive career technical training and education program for at‐risk youth ages 16 to 24. Using the sample from a large‐scale experiment of the program from the mid‐1990s, this article uses tax data through 2015 (20 years later) to examine long‐term labor market impacts. The study finds some long‐term beneficial effects for the older students, with employment gains of 4 percentage points, 40 percent reductions in disability benefit receipt, and 10 percent increases in tax filing rates in 2015. For these students, program benefits exceeded program costs from the social perspective. This study is the first to establish that a national program for disconnected youth can produce long‐term labor market gains, and can be a positive investment made for society. The results suggest that intensive, comprehensive services that focus on developing both cognitive and noncognitive skills are important for improving labor market prospects for this population.     

Comparative Analysis of the HV1 and HV2 Regions of Human Mitochondrial DNA by Denaturing High-Performance Liquid Chromatography

Abstract:  Denaturing high-performance liquid chromatography (DHPLC) was evaluated as a sequencing-independent means of detecting the presence of sequence differences in pair-wise mixtures of nonconcordant amplicons of human mitochondrial DNA (mtDNA). A total of 920 pair-wise combinations of HV1 and HV2 mtDNA amplicons from 95 individuals were assayed by DHPLC for sequence concordance/nonconcordance. For the 72 combinations of amplicons from different individuals who shared identical DNA sequences, DHPLC assays consistently indicated sequence concordance between the samples. This was in 100% agreement with sequencing data. For the 849 combinations of amplicons which differed in sequence, DHPLC detected the presence of sequence nonconcordance in all but 13 assays to yield 98.5% concordance with sequencing. Thus, DHPLC can be used to detect a diversity of sequence differences (transitions, transversions, insertions, and deletions) in the mtDNA D-loop. Accordingly, DHPLC may have utility as a presumptive indicator of mtDNA sequence concordance samples, as a screen for heteroplasmy/situational mixtures, and as a means for the physical fractionation of the individual contributors to an mtDNA mixture prior to sequencing.     

Simple and Sensitive Method for Identification of Human DNA by Allele-Specific Polymerase Chain Reaction of FOXP2

Abstract:  The forkhead box P2 ( FOXP2 ) gene is specifically involved in speech and language development in humans. The sequence is well conserved among many vertebrate species but has accumulated amino acid changes in the human lineage. The aim of this study was to develop a simple method to discriminate between human and nonhuman vertebrate DNA in forensic specimens by amplification of a human-specific genomic region. In the present study, we designed an allele-specific polymerase chain reaction (PCR) using primers to amplify smaller than 70-bp regions of FOXP2 to identify DNA as being of human or nonhuman, including ape, origin. PCR amplification was also successfully performed using fluorescence-labeled primers, and this method allows a single PCR reaction with a genomic DNA sample as small as 0.01 ng. This system also identified the presence of human DNA in two blood stains stored for 20 and 38 years. The results suggested the potential usefulness of FOXP2 as an identifier of human DNA in forensic samples.     

Proteolytic‐Based Method for the Identification of Human Growth Hormone*

Abstract: Human growth hormone (HGH) is a relatively small protein consisting of 191 amino acids and has an average mass of 22,125 amu. The forensic analysis of proteins such as HGH must meet the analytical sufficiency requirements for the laboratory and consists of a binary approach. A suspected sample is analyzed as the whole protein for retention time and mass determination using high performance liquid chromatography equipped with a photodiode array and liquid chromatography mass spectrometry. Further fragmentation of the protein using a proteolytic enzyme adds another dimension to the specificity of the analysis. Porcine trypsin digests proteins in a very predictable manner and yields peptide fragments of the original protein that can be used as a means for fingerprinting the larger biomolecule. In silico, or theoretical, digestion of HGH by trypsin yields 21 peptides ranging in size from 1 to 23 amino acids in length. The larger fragments containing higher numbers of amino acids give more specificity to identifying a protein based on a fragment produced by the digestion of trypsin. Herein, the analysis of HGH using a proteolytic approach is presented that meets the Scientific Working Group for the Analysis of Seized Drugs (SWGDRUG) recommendations for the identification of unknown substances.     

Application of DNA Forensic Techniques for Identifying Poached Guanacos (Lama guanicoe) in Chilean Patagonia*

Abstract: Guanaco (Lama guanicoe) is a protected and widely distributed ungulate in South America. A poacher, after killing guanacos in Valle Chacabuco, Chilean Patagonia, transported and stored the meat. Samples were retrieved by local police but the suspect argued that the meat was from a horse. Mitochondrial cytochrome b gene (774 pb), 15 loci microsatellites, and SRY gene were used to identify the species, number of animals and their population origin, and the sex of the animals, respectively. Analysis revealed that the samples came from a female (absence of SRY gene) Patagonian guanaco (assignment probability between 0.0075 and 0.0282), and clearly distinguishing it from sympatric ungulates (E‐value = 0). Based on the evidence obtained in the field in addition to forensic data, the suspect was convicted of poaching and illegally carrying fire arms. This is the first report of molecular tools being used in forensic investigations of Chilean wildlife indicating its promising future application in guanaco management and conservation.     

Individual Camera Identification Using Correlation of Fixed Pattern Noise in Image Sensors

Abstract:  This paper presents results of experiments related to individual video camera identification using a correlation coefficient of fixed pattern noise (FPN) in image sensors. Five color charge-coupled device (CCD) modules of the same brand were examined. Images were captured using a 12-bit monochrome video capture board and stored in a personal computer. For each module, 100 frames were captured. They were integrated to obtain FPN. The results show that a specific CCD module was distinguished among the five modules by analyzing the normalized correlation coefficient. The temporal change of the correlation coefficient during several days had only a negligible effect on identifying the modules. Furthermore, a positive relation was found between the correlation coefficient of the same modules and the number of frames that were used for image integration. Consequently, precise individual camera identification is enhanced by acquisition of as many frames as possible.