海南4+1

单聚焦扇形磁场质谱仪
来源/作者:中国标准物质网  日期:2014-7-23 15:04:10

ZHIPUYIDEZHONGLEIHENDUO,CHANGYONGDEYOU:

1.SHANXINGCICHANGZHIPUYI(magnetic sector mass spectrometer)

ZHEIZHONGLEIXINGDEYIQIZAIZAOQIYINGYONGZUIWEIPUBIAN,YOUFENWEIDANJUJIAOHESHUANGJUJIAOLIANGZHONGLEIXING。

(1)DANJUJIAOZHIPUYI

①原理 在离子源中产生的总离子束,经加速电压加速后,其动能与位能的关系为:

1/2mv2=zeV

式中,m为离子质量,单位为道尔顿(dalton,以C一12为12.000 dalton作标准);v为加速后的离子速度;z为电荷数;e为单位电荷;v为加速电压。

JINGJIASUHOUDELIZIJINRUYUQIYUNDONGFANGXIANGXIANGCHUIZHIDEQIANGDUWEIHDEJUNYUNCICHANGSHI,JIANGSHOUDAODIANCILI(zevh)DEZUOYONGERZUOYUANZHOUYUNDONG,YUNDONGDEQULVBANJINGWEIr。LIZIYUNDONGDELIXINLImv2/rYUGAIDIAN

磁力大小相等,方向相反。

zevH=mv2/r

因此, v=zerH/m

m/ze=r2H2/2V

在实践中,并不考虑e的绝对值,而是作为一个单位,故式简化为

m/z=r2H2/2V

YOUCIKEJIAN,KEYONGSANZHONGFANGSHIJILUZHIPUTU,RUHHEVGUDINGSHI,ZEBUTONGm/zDELIZIQIYUNDONGDEQULVBANJINGBUTONG,YINERZONGLIZISHUFENSANCHENGGEBIEDELIZISHU,JICICHANGJUYOUZHILIANGSESANZUOYONG。ZAIYIDINGDEJIASUDIANYAHECICHANGQIANGDUXIA,ZHIYOUm1,LIZIKEDAODAJIANCEQI,ERJIAOZHONGDELIZIm2JIANGYUFEIXINGDAOGUANDEGUANBIXIANGZHUANG。RUYIQIDErGUDING,ZEKEYONGSAOMIAOCICHANGHUODIANCHANGFANGSHIDEDAOZHIPUTU。DANSHI,YOUYULIZIDEJUJIAODENGWENTIYUJIASUDIANYAYOUGUAN,GUYIBANZHIPUYIDOUSHIZAIZUIJIAJIASUDIANYAXIAJINXINGCICHANGSAOMIAO。

②XINGNENGXIANZHIDANJUJIAOZHIPUYISHIYIZHONGDIFENBIANLVDEYIQI。ZHIPUYIDEFENBIANLVYOURUOGANZHONGBUTONGDEDINGYI,XIANZAI,CHANGYONGm/mBIAOSHI,ERQIEGUIDINGmWEIZHIDINGFENGDEm/zZHI,△mWEIGAIFENGFENGGAOYIBANCHUDEFENGKUAN(BANFENGKUAN,YIZHILIANGDANWEIBIAOSHI)。CIZHONGFENBIANLVBIAOSHIFANGFACHENGFWHM(full width at half maximum)。DIFENBIANZHIPUYIDEFENBIANLVXIAOYU1000,ZHINENGFENBIANDANWEIZHILIANG。YOUJIZHIPUFACHANGCHANGYAOQIUDEDAOGAOFENBIANDEZHIPUSHUJUJIZHUNQUEDEZHILIANGCEDINGJIEGUO,JIYAOQIUYIQINENGFENBIANMINGYIZHILIANG(nominal mass)XIANGTONGERZHUNQUEZHILIANG(exact mass)BUTONGDELIZIBINGJICHUJU6WEIYOUXIAOSHUZIDEZHILIANGCEDINGJIEGUO。ZHEIJIUXUYAOXINGNENGGENGHAODEYIQI,RUSHUANGJUJIAOZHIPUYI。

SHANXINGCICHANGZHIPUYIDELINGYIGEBUZUZHICHUSHISAOMIAOSULVBUGAO。DANGZHIPUYIYUSEPUYILIANYONGSHI,YAOQIUZHIPUYIJUYOUGAOSAOMIAOSULV。CIZHIPUYIDESAOMIAOSULVSHOUDIANCITIEDECIZU(reluctance)XIANZHI。CIZUSHIDIANCITIEDEYIZHONGDUOXING,XIANZHICICHANGQIANGDUDEBIANHUA。XIANDAICICHANGZHIPUYICAIYONGDIEPIANCITIE(1aminated magnets),SAOMIAOSULVKEDA0.1 sec/decade。decadeZAIZHIPUFAZHONGCHENGWEISHIBEICHENG,RU50~500ZHILIANGDANWEIJIWEIYIGESHIBEICHENG。

另一种影响扫描速率的问题是:如扫描速率超过了一定限度,在离子迁移过程中磁场发生明显变化,则将造成离子迁移轨道的变形,导致分辨率和灵敏度的下降。
此外,扫描过程是低效率的。因为在此过程中的某一瞬间,只有满足式的离子可以通过狭缝到达检测器,其他离子均与器壁碰撞消失,而且扫描速率与分辨率和灵敏度是相互矛盾的,高扫描速率将牺牲仪器的分辨率和灵敏度。

(2)SHUANGJUJIAOZHIPUYI

WEILETIGAOYIQIDEFENBIANLV,XUCAIYONGSHUANGJUJIAOZHIPUYI,ZAICICHANGFENXIQIQIAN,WAIJIAJINGDIANFENXIQI。WEIYIZHONGLEIXINGDESHUANGJUJIAOZHIPUYISHIYITU,JINGDIANCHANGDEZUOYONGSHINENGLIANGFENSAN,LIZIANNENGLIANGDAXIAODEDAOFENLIHOU:JINGFANGXIANGJUJIAOJINRUCICHANG,ZAICICHANGZUODONGLIANGFENLI,JIANGSUDUXIANGDENGERm/zBUTONGDELIZIFENKAI,SHIXIANLIZISHUDEFANGXIANGHENENGLIANGDESHUANGJUJIAO,DADAOGAOFENBIANDEXIAOGUO。

双聚焦质谱仪的分辨率在10000以上,高分辨率质谱可给出原子质量单位至少四位小数的精确度,用以测定离子的元素组成。但是这种仪器的装置复杂,需要处理的数据庞大,所以一般结构分析多用低分辨质谱完成,仅在个别问题需要时,再补作高分辨质谱数据。