JP2004361367A

JP2004361367A - Isotope-ratio analysis using plasma ion source mass analyzer

Info

Publication number: JP2004361367A
Application number: JP2003163454A
Authority: JP
Inventors: Hideyuki Sakamoto; 秀之坂元; Toshihiro Shirasaki; 俊浩白崎; Akira Yonetani; 明米谷; Kazuko Yamamoto; 和子山本; Hiromichi Kikuma; 裕道菊間
Original assignee: Hitachi High Technologies Corp; Hitachi Science Systems Ltd; Hitachi High Tech Corp
Current assignee: Hitachi Science Systems Ltd; Hitachi High Tech Corp
Priority date: 2003-06-09
Filing date: 2003-06-09
Publication date: 2004-12-24
Anticipated expiration: 2023-06-09
Also published as: JP4256208B2

Abstract

<P>PROBLEM TO BE SOLVED: To precisely correct isotope ratios in a plasma ion source mass analysis, where a quadruple mass spectrometer (QMS), such as a three-dimensional quadruple mass spectrometer (3DQMS), is mounted to a mass analyzer section. <P>SOLUTION: The plasma ion source mass analyzer performs measurement, by using the quadruple mass spectrometer (QMS), such as the three-dimensional quadruple mass spectrometer (3DQMS), for the mass analyzer section by using ICP or MIP, and other ion sources for the ion source. At least two standard substances, having different isotope ratios, are used to obtain the theoretical value to the measurement value for each isotope ratio for displaying on a screen, the interpolation relational expression between both of them is displayed on the screen, a measurement value for the measurement sample is measured, and the correction value of the isotope ratio is indicated on the screen from the measured measurement value and the interpolation relationship. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明はプラズマをイオン源にした質量分析装置に係わり、大気粉塵などのある元素の同位体比を測定するにあたり、信頼性高く分析することに関する。
【０００２】
【従来の技術】
鉛（Ｐｂ）の同位体比（^２０６Ｐｂ／^２０８Ｐｂ、^２０７Ｐｂ／^２０８Ｐｂ）の測定を例とする。従来のプラズマイオン源質量分析装置においてＰｂの同位体比分析を行う場合、予めＰｂの同位体存在度が既知である標準試料を用い、Ｐｂの同位体である^２０６Ｐｂ、^２０７Ｐｂ、^２０８Ｐｂのイオン信号強度Ｉ_２０６ｍ、Ｉ_２０７ｍ、Ｉ_２０８ｍを測定する。この測定値から算出した^２０６Ｐｂと^２０８Ｐｂ、^２０７Ｐｂと^２０８Ｐｂそれぞれの同位体比の実測値（Ｉ_２０６ｍ／Ｉ_２０８ｍ）、（Ｉ_２０７ｍ／Ｉ_２０８ｍ）と同位体比の理論値Ｌ_{２０６／２０８}、Ｌ_{２０７／２０８}から各同位体比の補正係数（Ｌ_{２０６／２０８}／（Ｉ_２０６ｍ／Ｉ_２０８ｍ））、（Ｌ_{２０７／２０８}／（Ｉ_２０７ｍ／Ｉ_２０８ｍ））を算出する。次に測定試料のＰｂの同位体である^２０６Ｐｂ、^２０７Ｐｂ、^２０８Ｐｂのイオン信号強度Ｉ_２０６Ｓ、Ｉ_２０７ｓ、Ｉ_２０８ｓを測定する。同位体比の実測値（Ｉ_２０６ｓ／Ｉ_２０８ｓ）、（Ｉ_２０７ｓ／Ｉ_２０８ｓ）に補正係数（Ｌ_{２０６／２０８}／（Ｉ_２０６ｍ／Ｉ_２０８ｍ））、（Ｌ_{２０７／２０８}／（Ｉ_２０７ｍ／Ｉ_２０８ｍ））をそれぞれ乗じ、補正された同位体比^２０６Ｐｂ／^２０８Ｐｂ＝（Ｉ_２０６ｓ／Ｉ_２０８ｓ）×（Ｌ_{２０６／２０８}／（Ｉ_２０６ｍ／Ｉ_２０８ｍ））、^２０７Ｐｂ／^２０８Ｐｂ＝（Ｉ_２０７ｓ／Ｉ_２０８ｓ）×（Ｌ_{２０７／２０８}／（Ｉ_２０７ｍ／Ｉ_２０８ｍ））を算出する。これにより分析装置による実測値との誤差を補正することができる。
【０００３】
【発明が解決しようとする課題】
ある試料の同位体比を決定するには、既知の同位体比をもつ試料の信号強度をまず測定する。次に得られた同位体比と既知の同位体比の値から補正係数を算出し、この補正係数を用いて実試料の測定値を補正し、実試料の同位体比を決定する。同位体比の精度は、補正係数の精確さに依存するが、この精確さは結局測定値（イオン信号強度）の精度に依存することになる。すなわち、求める質量数における信号強度が十分大きく、かつ測定対象の同位体の信号強度が同じ程度のとき、同位体比の精度が最も良くなると考えられる。理想的には、実試料の同位体比に近い同位体比をもつ標準物質（同位体比既知の試料）にて、補正を行うのが最も良いと考えられるが、現実には困難で上記の理想的な条件での補正は行えない。従って、従来の技術では同位体比の補正が十分行えていたとは言い難い。
本発明は、簡便な方法によって、より同位体比の補正精度を向上させた質量分析装置および質量分析方法を提供することを目的とする。
【０００４】
【課題を解決するための手段】
２つの異なった同位体比を用いて補正式を作成し、より同位体比の補正精度を向上させることを考慮した本発明は、分析結果の信頼性を向上させる方法として、有用である。
【０００５】
本発明は、イオン源にＩＣＰ（ＩｎｄｕｃｔｉｖｅｌｙＣｏｕｐｌｅｄＰｌａｓｍａ）あるいはＭＩＰ（ＭｉｃｒｏｗａｖｅＩｎｄｕｃｅｄＰｌａｓｍａ）その他のイオン源を用い、質量分析部に三次元四重極質量分析計（３ＤＱＭＳ）などの四重極質量分析計（ＱＭＳ）を用いて、測定を行うプラズマイオン源の質量分析装置において、二つ以上の同位体比の異なる標準物質を用いてそれぞれ同位体比についての計測値に対する理論値による両者間の補間関係式に、測定試料についての測定値を計測し、該計測された測定値を適用して同位体比の補正計算を行うようにした質量分析装置を提供する。
【０００６】
また、本発明は、イオン源にＩＣＰあるいはＭＩＰその他のイオン源を用い、質量分析部に三次元四重極質量分析計（３ＤＱＭＳ）などの四重極質量分析計（ＱＭＳ）を用いて、測定を行うプラズマイオン源質量分析装置において、二つ以上の同位体比の異なる標準物質を用いてそれぞれ同位体比についての測定値に対する理論値を求めて画面に表示し、画面上に両者間の補間関係を表示し、測定試料についての測定値を計測し当該画面上に表示し、該計測された測定値と前記補間関係とから画面上に同位体比の補正値を指し示す質量分析装置を提供する。
【０００７】
また、本発明は、イオン源にＩＣＰあるいはＭＩＰその他のイオン源を用い、質量分析部に四重極質量分析計（３ＤＱＭＳ）などの四重極質量分析計（ＱＭＳ）を用いて、測定を行うプラズマイオン源の質量分析を用いた同位体比分析方法において、二つ以上の同位体比の異なる標準物質を用いてそれぞれ同位体比についての測定値に対する理論値を求めて画面に表示し、画面上に両者間の補正関係を表示し、測定試料についての測定値を計測して当該画面上に表示し、該計測された測定値と前記補間関係とから画面上に同位体比の補正値を指し示し、該補正値から同位体比を表示する同位体比分析方法を提供する。
【０００８】
【発明の実施の形態】
以下、本発明の実施例を図面に基づいて説明する。
本発明を実施するにあたり、使用するプラズマイオン源質量分析装置はイオン源にＩＣＰあるいはＭＩＰまたはその他のプラズマを用いたもので、例えば質量分析計はイオントラップタイプの三次元四重極質量分析計（３ＤＱＭＳ）を用いている。３ＤＱＭＳはイオンを閉じ込めるスペースを持ち、イオンを閉じ込める効率を高めるためＨｅガスなどのバッファーガスをそのスペース内に導入している。プラズマイオン源質量分析装置について図１に示した。試料１は導入用キャピラリーを通って試料導入系２に入り、霧化した後にイオン源であるＩＣＰ３へ運ばれて効率よくイオン化される。イオン化された目的元素はインターフェイス４を通過し、イオンレンズ６により軌道５のごとく軌道を描きながら、イオントラップタイプの質量分析計７へ入射する。ここで、イオンを質量数毎に分別してカウントすることにより目的とするイオンの情報を得る。得られた結果は操作・データ処理用のパソコン８に示される。
【０００９】
図２に三次元四重極質量分析計（３ＤＱＭＳ）の構造を示す。３ＤＱＭＳは一つのリング電極９と二つのエンドキャプ電極１０の合計三つの電極から構成されており、これらよりイオンを閉じ込める空間を作り、この空間にバッファーガス１１を導入する。このガスは３ＤＱＭＳ部に入るイオンと衝突しイオンの動きを失速させ、３ＤＱＭＳ内部への閉じ込め効率を高める効果がある。また、３ＤＱＭＳは電極に印加する電圧により特定の質量数のイオンだけを３ＤＱＭＳ内部に残すことができる。
【００１０】
次に、図３を参照して補間の手法について説明する。
本発明は質量分析部に３次元四重極質量分析計（３ＤＱＭＳ）を搭載したプラズマイオン源質量分析装置により同位体比分析を行った場合の同位体比の補正方法である。例として３ＤＱＭＳにおいてＰｂの同位体比分析を行う場合を始めにＰｂの同位体存在度が既知である標準物質で同位体存在度（同位体比）の異なる二つの標準物質ｍ／ｚ＝２０６、２０７、２０８のイオン信号強度を測定する。これらの値から二つの標準物質の同位体比（^２０６Ｐｂ／^２０８Ｐｂ、^２０７Ｐｂ／^２０８Ｐｂ）の実測値を算出する。縦軸に理論値、横軸に測定値を取り、補間関係式を作成する。
【００１１】
図３において、標準物質Ａおよび標準物質Ｂについてそれぞれ同位体比についての測定値と理論値とを求める。両者を結ぶ直線（あるいは曲線）が補間関係式となる。当該補間関係式は、直線に対して±５％程度の曲りは許容され、この程度の曲りについてもここでは直線として取り扱う。これらの測定値、理論値および補間関係式、すなわち補間関係状態をパソコン等の画面に表示することができる。
【００１２】
次に、測定物質について測定値を求め（Ｐ点）、Ｐ点から前述の補間関係式上に補正された値（Ｑ点）を求める。また、理論値（Ｔ点）が求まる。これらのＰ点、Ｑ点およびＴ点を画面上に表示することができる。
【００１３】
この場合の補正値を与える式は次のようになる。
【数１】

画面表示の場合、この補完関係式は標準物質Ａと標準物質Ｂを結ぶ線の傾きおよび切片として表示されるので、上式による厳密なる計算を要しない利点がある。
【００１４】
図４に鉛（Ｐｂ）についての実測例を示す（^２０６Ｐｂ／^２０７Ｐｂの場合）。例えば図４（ａ）に示すように標準物質Ａおよび標準物質Ｂについて同位体比としての測定値および理論値が、それぞれ１．０７７６、１．０９３４、および２．２４３５、２．１４０９として計算されたとすると傾きは０．８９８４で、切片は０．１２５３として計算され、求められる。画面上にあっては傾きおよび切片が表示される。
【００１５】
未知試料Ｃおよび未知試料Ｄについて測定値が１．２４２７、１．１１４６として計測されると、上述の補間関係から補正値は１．２４１８、１．１２６７として計算され、あるいは画面上に指し示され、すなわち表示される。
この場合に補間関係式は図４（ｂ）に示すように、
ｙ＝０８９８４ｘ＋０．１２５３
として表わされる。この式を使用すれば上述の補正値は未知試料Ｃおよび未知試料Ｄについての補正値は直ちに計算される。上述のように補正値は計算に代えて、画面表示点を読み取ることによっても求めることができる。
Ｒ^２は相関係数であり、直線性を示す。標準物質が２点の場合はＲ^２は常に１となる。
【００１６】
このように、次に測定試料のｍ／ｚ＝２０６、２０７、２０８のイオン信号強度を測定し、同位体比を算出する。作成した補正式から理論値を算出する。この値を補正値とする。つまり補正式を理論値について展開し、測定値を代入し、補正値としている。また図３は^２０６Ｐｂ／^２０８Ｐｂを例として挙げているが、^２０６Ｐｂ／^２０７Ｐｂなど同位体の関係にあるものについても同様に行うことができる。
【００１７】
図４に、前述したように^２０６Ｐｂ／^２０７Ｐｂの同位体比について実際に測定を行って結果を示す。同位体比が既知（同位体比の理論値を持つ）且つ同位体存在度（同位体比）の異なる標準物質Ａ、Ｂの測定値から補正式である補間関係式を作成した。画面において、プロット図は、縦軸に理論値、横軸に測定値を取っている。この補正式を利用して、未知試料Ｃ、Ｄの測定値から補正値を算出した。本実施例で得られた補正値の精度を検証するため従来法で同一の試料の測定を行った結果と比較した結果を図４（ｃ）に示す。従来法による測定値として、未知試料Ｃは文献値＿１、未知試料Ｄは文献値＿１、文献値＿２の２つの文献から引用した。本実施例の補正値と文献値が一致することから本実施例によれば、精度良く分析することができると言える。測定順番としては標準物質Ａ、未知試料Ｃ、未知試料Ｄ、標準物質Ｂとしたが、全ての試料を測定した後でも補正式作成は可能であるため、測定試料の順番はどのような順番でも良い。
【００１８】
多数の標準物質について予めデータベース化して記録として保留し、計測日における変動を考慮することによってデータベースから求めた値を補正し、標準物質の値とすることも可能である。
尚、本実施例は、その他の元素についても応用が可能である。
【００１９】
以上のように、二つ以上の同位体比の異なる標準物質を用いてそれぞれ同位体比についての計測値に対する理論値による両者間の補間関係式に、測定試料についての測定値を計測し、該計測された測定値を適用して同位体比の補正計算を行うようにした質量分析装置が構成される。
【００２０】
また、イオン源にＩＣＰあるいはＭＩＰその他のイオン源を用い、質量分析部に三次元四重極質量分析計（３ＤＱＭＳ）などの四重曲質量分析計（ＱＭＳ）を用いて、測定を行うプラズマイオン源を用いた同位体比分析方法において、二つ以上の同位体比の異なる標準物質を用いてそれぞれ同位体比についての測定値に対する理論値による両者の補間関係式に、測定試料についての測定値を計測し、該計測された測定値を適用する同位体分析方法が構成される。
【００２１】
また、二つ以上の同位体比の異なる標準物質を用いてそれぞれ同位体比についての測定値に対する理論値を求めて画面に表示し、画面上に両者間の補正関係を表示し、測定試料についての測定値を計測して当該画面上に表示し、該計測された測定値と前記補間関係とから画面上に同位体比の補正値を指し示し、該補正値から同位体比を表示する同位体比分析方法が構成される。
【００２２】
次に本発明を用いた場合のＰｂ同位体比の測定例をフローチャート化し図５に示す。始めに同位体比が既知である標準物質Ａのｍ／ｚ＝２０６、２０７、２０８のイオン信号強度Ｉ_２０６Ａ、Ｉ_２０７Ａ、Ｉ_２０８Ａを測定し（Ｓ１）、同位体比（Ｉ_２０６Ａ／Ｉ_２０８Ａ）、（Ｉ_２０７Ａ／Ｉ_２０８Ａ）を算出する（Ｓ２）。次に測定試料のｍ／ｚ＝２０６、２０７、２０８のイオン信号強度Ｉ_２０６Ｘ、Ｉ_２０７Ｘ、Ｉ_２０８Ｘを測定し（Ｓ３）、同位体比（Ｉ_２０６Ｘ／Ｉ_２０８Ｘ）、（Ｉ_２０７Ｘ／Ｉ_２０８Ｘ）を算出する（Ｓ４）。次に同位体比が既知であり、標準物質Ａと同位体存在度（同位体比）の異なる標準物質Ｂのｍ／ｚ＝２０６、２０７、２０８のイオン信号強度Ｉ_２０６Ｂ、Ｉ_２０７Ｂ、Ｉ_２０８Ｂを測定し（Ｓ５）、同位体比（Ｉ_２０６Ｂ／Ｉ_２０８Ｂ）、（Ｉ_２０７Ｂ／Ｉ_２０８Ｂ）を算出する（Ｓ６）。尚Ｓ１、Ｓ３、Ｓ５の測定順番はどの順番でも良い。測定した標準物質Ａ、Ｂは同位体比が既知であるため、^２０６Ｐｂ／^２０８Ｐｂの同位体比の理論値Ｌ_{２０６／２０８Ａ}、Ｌ_{２０６／２０８Ｂ}とし、縦軸に理論値、横軸に測定値（Ｉ_２０６Ａ／Ｉ_２０８Ａ）、（Ｉ_２０６Ｂ／Ｉ_２０８Ｂ）をプロットし（Ｓ７）、補正式（図４（ｂ）参照）を求める（Ｓ８）。この補正式に測定試料の測定値を代入し、補正値Ｘ_{２０６／２０８}、Ｘ_{２０７／２０８}を算出する（Ｓ９）。これらの一連の測定により補正値を求めることができ、３ＤＱＭＳを搭載した質量分析装置を用いた場合においても、精度良く同位体比を求めることができる。本法は同位体存在度（同位体比）の異なる標準物質から検量線を作成し分析を行うことができることから、他の元素にも応用することができる。また、従来法では標準物質を一つで補正することから、その標準物質からかけ離れた試料については補正誤差が大きくなると考えられるが、本法では標準物質を二つ以上使うことから、補正範囲を広げることができる。
【００２３】
図６に、表示画面について提案する。サンプル名、標準物質の理論値を測定前後にて入力できるようにし、測定終了後に、標準物質の理論値と測定値をプロットする（図６（ａ））。この結果から補正式を算出し（図６（ｂ））、同一の画面に表示する（図６（ｃ））。順番を問わず、これらの情報を一画面に表示する。
【００２４】
【発明の効果】
本発明によれば、３ＤＱＭＳを搭載したプラズマイオン源質量分析装置において、生じる同位体比のずれを補正し、精度良く信頼性の高い同位体比分析を行うことができる。
【図面の簡単な説明】
【図１】本発明を適用したプラズマイオン源質量分析装置の概略構成を示す図。
【図２】本発明を適用した三次元四重極質量分析計（３ＤＱＭＳ）の構成を示す図。
【図３】本実施例での同位体比のプロット図と補正式を示す図。
【図４】本実施例を用いた実施例を示す図。
【図５】本発明の一連の方法を示すフローチャート。
【図６】測定結果の表示画面一例。
【符号の説明】
１…試料、２…試料導入系、３…プラズマイオン源、４…インターフェイス、５…イオンの軌道、６…イオンレンズ、７…質量分析計、８…操作・データ処理用ＰＣ、９…リング電極、１０…エンドキャップ電極、１１…バッファーガス。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a mass spectrometer using a plasma as an ion source, and more particularly to a method of measuring an isotope ratio of an element such as atmospheric dust with high reliability.
[0002]
[Prior art]
The measurement of the isotope ratio of lead (Pb) ( ²⁰⁶ Pb / ²⁰⁸ Pb, ²⁰⁷ Pb / ²⁰⁸ Pb) is taken as an example. When performing Pb isotope ratio analysis in a conventional plasma ion source mass spectrometer, a standard sample whose Pb isotope abundance is known in advance is used, and ²⁰⁶ Pb, ²⁰⁷ Pb, and ²⁰⁸ Pb, which are Pb isotopes, are used. The ion signal intensities I _206m , I _207m and I _208m are measured. The actual measured values (I _206m / I _208m ) of the isotope ratios of ²⁰⁶ Pb and ²⁰⁸ Pb, ²⁰⁷ Pb and ²⁰⁸ Pb calculated from the measured values, (I _207m / I _208m ) and the theoretical value of the isotope ratio L _{206 / 208,} the correction coefficient of each isotope from _{_{_{_{L 207/208 (L 206/208 / (I}}}} 206m / I 208m)), calculates the _{_{(L 207/208 / (I 207m /}} I 208m)). Next, ion signal intensities I _206S , I _207s , and I _208s of ²⁰⁶ Pb, ²⁰⁷ Pb, and ²⁰⁸ Pb which are isotopes of Pb of the measurement sample are measured. I found isotopic _{_{_{(I 206s / I 208s),}}} (I 207s / I 208s) to the correction coefficient _{_{_{_{(L 206/208 / (I 206m /}}}} I 208m)), (L 207/208 / (I 207m / I _208m)) obtained by multiplying each corrected isotope ratios ^{^{_{206 Pb / 208 Pb = (I}}} 206s / I 208s) × (L 206/208 / (I 206m / I 208m)), 207 Pb / 208 Pb = (I _{_{_{207s / I 208s) × (L}}} 207/208 / (I 207m / I 208m)) is calculated. As a result, it is possible to correct an error with a value actually measured by the analyzer.
[0003]
[Problems to be solved by the invention]
To determine the isotope ratio of a sample, the signal intensity of a sample having a known isotope ratio is first measured. Next, a correction coefficient is calculated from the obtained isotope ratio and the value of the known isotope ratio, and the measured value of the actual sample is corrected using the correction coefficient to determine the isotope ratio of the actual sample. The accuracy of the isotope ratio depends on the accuracy of the correction coefficient, and this accuracy ultimately depends on the accuracy of the measured value (ion signal intensity). That is, when the signal intensity at the required mass number is sufficiently large and the signal intensity of the isotope to be measured is approximately the same, the accuracy of the isotope ratio is considered to be the best. Ideally, it is considered that it is best to perform correction using a standard substance (a sample with a known isotope ratio) having an isotope ratio close to the isotope ratio of the actual sample. Correction cannot be performed under ideal conditions. Therefore, it cannot be said that the correction of the isotope ratio was sufficiently performed by the conventional technique.
An object of the present invention is to provide a mass spectrometer and a mass spectrometry method in which the correction accuracy of the isotope ratio is further improved by a simple method.
[0004]
[Means for Solving the Problems]
The present invention, in which a correction formula is created using two different isotope ratios and consideration is given to further improving the correction accuracy of the isotope ratio, is useful as a method for improving the reliability of analysis results.
[0005]
According to the present invention, a quadrupole mass spectrometer such as a three-dimensional quadrupole mass spectrometer (3DQMS) is used as a mass spectrometer using an ion source such as ICP (Inductively Coupled Plasma) or MIP (Microwave Induced Plasma) as an ion source. In a mass spectrometer of a plasma ion source for performing measurement using (QMS), an interpolation relationship between the measured values of isotope ratios and theoretical values using two or more standard materials having different isotope ratios, respectively. Provided is a mass spectrometer that measures a measurement value of a measurement sample in a formula, and performs an isotope ratio correction calculation by applying the measured measurement value.
[0006]
In addition, the present invention uses an ion source such as ICP or MIP as an ion source and performs measurement using a quadrupole mass spectrometer (QMS) such as a three-dimensional quadrupole mass spectrometer (3DQMS) as a mass spectrometer. In the plasma ion source mass spectrometer that performs the above, using two or more standard materials with different isotope ratios, the theoretical value for the measured value of the isotope ratio is obtained and displayed on the screen, and the interpolation between the two is displayed on the screen Provide a mass spectrometer that displays a relationship, measures a measured value of a measurement sample, displays the measured value on the screen, and indicates a correction value of the isotope ratio on the screen from the measured value and the interpolation relationship. .
[0007]
Further, in the present invention, measurement is performed using an ICP or MIP or another ion source as an ion source, and using a quadrupole mass spectrometer (QMS) such as a quadrupole mass spectrometer (3DQMS) as a mass spectrometer. In an isotope ratio analysis method using mass spectrometry of a plasma ion source, a theoretical value for a measured value of the isotope ratio is obtained using two or more standard materials having different isotope ratios, and the theoretical value is displayed on a screen. The correction relationship between the two is displayed above, the measurement value of the measurement sample is measured and displayed on the screen, and the correction value of the isotope ratio is displayed on the screen from the measured measurement value and the interpolation relationship. An isotope ratio analysis method for pointing and displaying an isotope ratio from the correction value is provided.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In carrying out the present invention, the plasma ion source mass spectrometer used uses an ICP, MIP or other plasma as an ion source. For example, the mass spectrometer is an ion trap type three-dimensional quadrupole mass spectrometer ( 3DQMS). 3DQMS has a space for confining ions, and a buffer gas such as He gas is introduced into the space in order to increase the efficiency of confining ions. FIG. 1 shows a plasma ion source mass spectrometer. The sample 1 enters the sample introduction system 2 through the introduction capillary, is atomized, and then is carried to the ICP 3, which is an ion source, where it is efficiently ionized. The ionized target element passes through the interface 4 and enters the ion trap type mass spectrometer 7 while drawing a trajectory like the trajectory 5 by the ion lens 6. Here, information on the target ion is obtained by sorting and counting the ions for each mass number. The obtained result is shown on the personal computer 8 for operation / data processing.
[0009]
FIG. 2 shows the structure of a three-dimensional quadrupole mass spectrometer (3DQMS). The 3DQMS is composed of a total of three electrodes, one ring electrode 9 and two endcap electrodes 10. A space for confining ions is created from these electrodes, and a buffer gas 11 is introduced into this space. This gas collides with ions entering the 3DQMS part, stalls the movement of the ions, and has the effect of increasing the efficiency of confinement inside the 3DQMS. In 3DQMS, only ions having a specific mass number can be left inside 3DQMS by a voltage applied to the electrode.
[0010]
Next, an interpolation method will be described with reference to FIG.
The present invention is a method for correcting an isotope ratio when an isotope ratio analysis is performed by a plasma ion source mass spectrometer equipped with a three-dimensional quadrupole mass spectrometer (3DQMS) in a mass spectrometer. As an example, two standard substances having different isotope abundances (isotope ratios), m / z = 206, are standard substances in which the isotope abundance of Pb is known, including the case of performing the isotope ratio analysis of Pb in 3DQMS. The ion signal intensity of 207 and 208 is measured. From these values, the measured values of the isotope ratios ( ²⁰⁶ Pb / ²⁰⁸ Pb, ²⁰⁷ Pb / ²⁰⁸ Pb) of the two standard substances are calculated. Taking the theoretical value on the vertical axis and the measured value on the horizontal axis, an interpolation relational expression is created.
[0011]
In FIG. 3, measured values and theoretical values of the isotope ratios of the standard substance A and the standard substance B are obtained. A straight line (or curve) connecting the two is an interpolation relational expression. In the interpolation relational expression, a bend of about ± 5% with respect to a straight line is allowed, and such a bend is treated as a straight line here. These measured values, theoretical values and interpolation relational expressions, that is, interpolation relational states, can be displayed on a screen of a personal computer or the like.
[0012]
Next, a measured value of the measured substance is obtained (point P), and a value corrected from the point P on the above-mentioned interpolation relational expression (point Q) is obtained. Further, a theoretical value (point T) is obtained. These P point, Q point and T point can be displayed on the screen.
[0013]
The equation for giving the correction value in this case is as follows.
(Equation 1)

In the case of the screen display, this complementary relational expression is displayed as the slope and intercept of the line connecting the standard substance A and the standard substance B, and thus has an advantage that strict calculation by the above equation is not required.
[0014]
FIG. 4 shows an actual measurement example of lead (Pb) (in the case of ²⁰⁶ Pb / ²⁰⁷ Pb). For example, as shown in FIG. 4A, the measured value and the theoretical value as the isotope ratio of the standard substance A and the standard substance B are calculated as 1.0776, 1.0934, and 2.2435, 2.1409, respectively. For example, the slope is calculated as 0.8984, and the intercept is calculated as 0.1253. On the screen, the inclination and the intercept are displayed.
[0015]
When the measured values of the unknown sample C and the unknown sample D are measured as 1.2427 and 1.1146, the correction values are calculated as 1.2418 and 1.1267 from the above-described interpolation relationship, or are indicated on the screen. That is, it is displayed.
In this case, the interpolation relational expression is as shown in FIG.
y = 09884x + 0.1253
It is represented as Using this equation, the above-described correction values are immediately calculated for the unknown sample C and the unknown sample D. As described above, the correction value can be obtained by reading the screen display point instead of the calculation.
R ² is the correlation coefficient, indicating the linearity. If standard is two points R ² is always 1.
[0016]
As described above, next, the ion signal intensities of m / z = 206, 207, and 208 of the measurement sample are measured, and the isotope ratio is calculated. The theoretical value is calculated from the created correction formula. This value is used as a correction value. In other words, the correction formula is developed with respect to the theoretical value, and the measured value is substituted to obtain a correction value. Although FIG. 3 shows ²⁰⁶ Pb / ²⁰⁸ Pb as an example, the same can be applied to those having an isotope relation such as ²⁰⁶ Pb / ²⁰⁷ Pb.
[0017]
FIG. 4 shows the results obtained by actually measuring the isotope ratio of ²⁰⁶ Pb / ²⁰⁷ Pb as described above. An interpolation relational expression, which is a correction expression, was created from the measured values of the standard substances A and B having different isotope ratios (having a theoretical value of the isotope ratio) and different isotope abundances (isotopic ratios). In the screen, the plots indicate theoretical values on the vertical axis and measured values on the horizontal axis. Using this correction equation, a correction value was calculated from the measured values of the unknown samples C and D. FIG. 4C shows a result of comparison with a result obtained by measuring the same sample by the conventional method in order to verify the accuracy of the correction value obtained in this embodiment. As the measurement values by the conventional method, the unknown sample C was cited from the literature value_1, and the unknown sample D was quoted from the literature value_1 and the literature value_2. Since the correction value of this embodiment matches the literature value, it can be said that the analysis can be performed with high accuracy according to this embodiment. The measurement order was standard substance A, unknown sample C, unknown sample D, and standard substance B. However, since the correction formula can be created even after all the samples have been measured, the order of the measurement samples may be any order. good.
[0018]
It is also possible to make a database of many standard substances in advance and hold them as records, and to correct the values obtained from the database by taking into account fluctuations on the measurement date to obtain the values of the standard substances.
The present embodiment can be applied to other elements.
[0019]
As described above, using two or more different isotope ratio standard materials, the measured value of the measurement sample was measured by an interpolation relational expression between the measured value of the isotope ratio and the theoretical value with respect to the measured value of the isotope ratio. A mass spectrometer is configured to perform correction calculation of the isotope ratio by applying the measured value.
[0020]
In addition, a plasma ion is measured using an ion source such as ICP or MIP as an ion source and a quadrupole mass spectrometer (QMS) such as a three-dimensional quadrupole mass spectrometer (3DQMS) as a mass spectrometer. In the isotope ratio analysis method using a source, two or more standard materials having different isotope ratios are used to calculate the measured values for the measured sample by using the theoretical relationship to the measured values for the isotope ratios. Is measured, and an isotope analysis method for applying the measured value is configured.
[0021]
In addition, using two or more isotope ratios of different reference materials, the theoretical value for the measured value of the isotope ratio is obtained and displayed on the screen, the correction relationship between the two is displayed on the screen, and the Is measured and displayed on the screen, the corrected value of the isotope ratio is indicated on the screen from the measured value and the interpolation relationship, and the isotope is displayed based on the corrected value. A ratio analysis method is configured.
[0022]
Next, FIG. 5 is a flowchart showing an example of measuring the Pb isotope ratio when the present invention is used. First, the ion signal intensities I _206A , I _207A , I _208A of m / z = ₂₀₆ , ₂₀₇ , ₂₀₈ of the standard substance A whose isotope ratio is known are measured (S1), and the isotope ratio (I _206A / I _208A). ) And (I _207A / I _208A ) are calculated (S2). Next, the ion signal intensities I _206X , I _207X and I _208X of the measurement sample at m / z = 206, ₂₀₇ and ₂₀₈ are measured (S3), and the isotope ratios (I _206X / I _208X ) and (I _207X / I _208X) ) Is calculated (S4). Next, the ion signal intensities I _206B , I _207B , and I _208B of m / z = ₂₀₆ , ₂₀₇ , and _{208 of the} standard substance B having a known isotope ratio and having a different isotope abundance (isotope ratio) from the standard substance A. Is measured (S5), and the isotope ratio (I _206B / I _208B ) and (I _207B / I _208B ) are calculated (S6). The measurement order of S1, S3, and S5 may be any order. Since the measured standard substances A and B have known isotope ratios, the theoretical values of the isotope ratio of ²⁰⁶ Pb / ²⁰⁸ Pb are L _{206 / 208A} and L _{206 / 208B} , and the vertical axis indicates the theoretical value and the horizontal axis indicates the measured value. The values (I _206A / I _208A ) and (I _206B / I _208B ) are plotted (S7), and a correction formula (see FIG. 4B) is obtained (S8). The measured values of the measurement sample are substituted into this correction formula to calculate correction values X _206/208 and X _207/208 (S9). A correction value can be obtained by a series of these measurements, and the isotope ratio can be accurately obtained even when a mass spectrometer equipped with 3DQMS is used. This method can be applied to other elements because it can make a calibration curve from standard substances with different isotope abundances (isotopic ratios) and perform analysis. Also, in the conventional method, since the standard material is corrected by one, the correction error is considered to be large for samples far from the standard material.However, in this method, the correction range is limited because two or more standard materials are used. Can be spread.
[0023]
FIG. 6 proposes a display screen. The sample name and the theoretical value of the standard substance can be input before and after the measurement. After the measurement, the theoretical value of the standard substance and the measured value are plotted (FIG. 6A). A correction formula is calculated from the result (FIG. 6B) and displayed on the same screen (FIG. 6C). The information is displayed on one screen regardless of the order.
[0024]
【The invention's effect】
According to the present invention, in a plasma ion source mass spectrometer equipped with 3DQMS, a deviation in the isotope ratio that occurs can be corrected, and an accurate and reliable isotope ratio analysis can be performed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of a plasma ion source mass spectrometer to which the present invention is applied.
FIG. 2 is a diagram showing a configuration of a three-dimensional quadrupole mass spectrometer (3DQMS) to which the present invention is applied.
FIG. 3 is a diagram showing a plot of an isotope ratio and a correction formula in the present embodiment.
FIG. 4 is a diagram showing an embodiment using this embodiment.
FIG. 5 is a flowchart showing a series of methods of the present invention.
FIG. 6 is an example of a display screen of a measurement result.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... sample, 2 ... sample introduction system, 3 ... plasma ion source, 4 ... interface, 5 ... ion orbit, 6 ... ion lens, 7 ... mass spectrometer, 8 ... operation / data processing PC, 9 ... ring electrode , 10 ... end cap electrode, 11 ... buffer gas.

Claims

An ICP (Inductively Coupled Plasma) or MIP (Microwave Induced Plasma) or other ion source is used as an ion source, and a quadrupole mass spectrometer (QMS) or a three-dimensional quadrupole mass spectrometer (3DQMS) is used as a mass spectrometer. In a plasma ion source mass spectrometer,
Using two or more different isotope ratio standard materials, the measured value of the measurement sample is measured by an interpolation relational expression between the measured value of the isotope ratio and the theoretical value for the measured value of the isotope ratio. A mass spectrometer characterized in that correction calculation of the isotope ratio is performed by applying the formula.

In a plasma ion source mass spectrometer using an ICP or MIP or another ion source as an ion source and a quadrupole mass spectrometer or a three-dimensional quadrupole mass spectrometer as a mass spectrometer,
Using two or more standard materials with different isotope ratios, obtain the theoretical value for the measured value of the isotope ratio, display it on the screen, display the interpolation relationship between the two on the screen, and measure the measured sample A mass spectrometer characterized in that a value is measured and displayed on the screen, and a corrected value of the isotope ratio is indicated on the screen from the measured value and the interpolation relationship.

In an isotope ratio analysis method using a plasma ion source mass spectrometer using an ICP or MIP or another ion source as an ion source and a quadrupole mass spectrometer or a three-dimensional quadrupole mass spectrometer as a mass spectrometer,
By using two or more different isotope ratio standard substances, the interpolation relation between the two by a theoretical value for the measured value of the isotope ratio, the measured value of the measured sample is measured, and the measured value is calculated. An isotope analysis method characterized by being applied.

In an isotope ratio analysis method using a plasma ion source mass spectrometer using an ICP or MIP or another ion source as an ion source and a quadrupole mass spectrometer or a three-dimensional quadrupole mass spectrometer as a mass spectrometer,
Using two or more standard materials with different isotope ratios, obtain the theoretical value for the measured value of the isotope ratio, display it on the screen, display the correction relationship between the two on the screen, and measure the measurement sample Measuring the value and displaying it on the screen, indicating the correction value of the isotope ratio on the screen from the measured measurement value and the interpolation relationship, and displaying the isotope ratio from the correction value. Isotope ratio analysis method.

In an isotope ratio analysis method using an ICP or MIP or other ion source as an ion source and a quadrupole mass spectrometer or a three-dimensional quadrupole mass spectrometer as a mass spectrometer,
The ion signal intensities I _206A , I _207A , and I _208A of the lead standard material A at m / z = ₂₀₆ , ₂₀₇ , and ₂₀₈ were measured, and the standard material B having a different isotope abundance (isotopic ratio) from the standard material A was measured. The ion intensity signals I _206B , I _207B , and I _208B of m / z = ₂₀₆ , ₂₀₇ , and ₂₀₈ are measured, and the measurement of the measurement sample is performed by an interpolation relational expression between the two based on the theoretical value with respect to the measured value of the isotope ratio. Measuring the value and providing the measured value.