JPH0358066B2 - - Google Patents
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- Publication number
- JPH0358066B2 JPH0358066B2 JP15464582A JP15464582A JPH0358066B2 JP H0358066 B2 JPH0358066 B2 JP H0358066B2 JP 15464582 A JP15464582 A JP 15464582A JP 15464582 A JP15464582 A JP 15464582A JP H0358066 B2 JPH0358066 B2 JP H0358066B2
- Authority
- JP
- Japan
- Prior art keywords
- ions
- acid
- titration
- sample
- solution
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- 239000002253 acid Substances 0.000 claims description 34
- 238000004448 titration Methods 0.000 claims description 30
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 28
- 229910052742 iron Inorganic materials 0.000 claims description 26
- -1 iron ions Chemical class 0.000 claims description 26
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 claims description 18
- 229910001447 ferric ion Inorganic materials 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 18
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 claims description 17
- 229910001448 ferrous ion Inorganic materials 0.000 claims description 17
- AKHNMLFCWUSKQB-UHFFFAOYSA-L sodium thiosulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=S AKHNMLFCWUSKQB-UHFFFAOYSA-L 0.000 claims description 13
- 235000019345 sodium thiosulphate Nutrition 0.000 claims description 13
- 238000004445 quantitative analysis Methods 0.000 claims description 7
- 239000003513 alkali Substances 0.000 claims description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 42
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 36
- 239000000243 solution Substances 0.000 description 33
- 239000003638 chemical reducing agent Substances 0.000 description 13
- 238000006243 chemical reaction Methods 0.000 description 11
- 238000005554 pickling Methods 0.000 description 10
- 238000005259 measurement Methods 0.000 description 9
- 229960002089 ferrous chloride Drugs 0.000 description 8
- NMCUIPGRVMDVDB-UHFFFAOYSA-L iron dichloride Chemical compound Cl[Fe]Cl NMCUIPGRVMDVDB-UHFFFAOYSA-L 0.000 description 8
- 238000006386 neutralization reaction Methods 0.000 description 7
- 239000012086 standard solution Substances 0.000 description 7
- 229910000831 Steel Inorganic materials 0.000 description 5
- 239000010959 steel Substances 0.000 description 5
- 229910021578 Iron(III) chloride Inorganic materials 0.000 description 4
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 3
- 150000007513 acids Chemical class 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- NLKNQRATVPKPDG-UHFFFAOYSA-M potassium iodide Chemical compound [K+].[I-] NLKNQRATVPKPDG-UHFFFAOYSA-M 0.000 description 3
- FVAUCKIRQBBSSJ-UHFFFAOYSA-M sodium iodide Chemical compound [Na+].[I-] FVAUCKIRQBBSSJ-UHFFFAOYSA-M 0.000 description 3
- 238000000954 titration curve Methods 0.000 description 3
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 2
- 239000012670 alkaline solution Substances 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- GPRLSGONYQIRFK-UHFFFAOYSA-N hydron Chemical compound [H+] GPRLSGONYQIRFK-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000011002 quantification Methods 0.000 description 2
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 description 2
- JYWKEVKEKOTYEX-UHFFFAOYSA-N 2,6-dibromo-4-chloroiminocyclohexa-2,5-dien-1-one Chemical compound ClN=C1C=C(Br)C(=O)C(Br)=C1 JYWKEVKEKOTYEX-UHFFFAOYSA-N 0.000 description 1
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 1
- MKYBYDHXWVHEJW-UHFFFAOYSA-N N-[1-oxo-1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propan-2-yl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(C(C)NC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 MKYBYDHXWVHEJW-UHFFFAOYSA-N 0.000 description 1
- 238000011481 absorbance measurement Methods 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 239000002585 base Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- FGRVOLIFQGXPCT-UHFFFAOYSA-L dipotassium;dioxido-oxo-sulfanylidene-$l^{6}-sulfane Chemical compound [K+].[K+].[O-]S([O-])(=O)=S FGRVOLIFQGXPCT-UHFFFAOYSA-L 0.000 description 1
- DUYAAUVXQSMXQP-UHFFFAOYSA-N ethanethioic S-acid Chemical class CC(S)=O DUYAAUVXQSMXQP-UHFFFAOYSA-N 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 150000004694 iodide salts Chemical class 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000007793 ph indicator Substances 0.000 description 1
- BHZRJJOHZFYXTO-UHFFFAOYSA-L potassium sulfite Chemical compound [K+].[K+].[O-]S([O-])=O BHZRJJOHZFYXTO-UHFFFAOYSA-L 0.000 description 1
- 235000019252 potassium sulphite Nutrition 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 235000009518 sodium iodide Nutrition 0.000 description 1
- 235000010265 sodium sulphite Nutrition 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- LSNNMFCWUKXFEE-UHFFFAOYSA-L sulfite Chemical class [O-]S([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-L 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/16—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using titration
- G01N31/162—Determining the equivalent point by means of a discontinuity
- G01N31/164—Determining the equivalent point by means of a discontinuity by electrical or electrochemical means
Landscapes
- Health & Medical Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Physics & Mathematics (AREA)
- Electrochemistry (AREA)
- Molecular Biology (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
Description
本発明は鋼材の酸洗液等のように酸及び鉄イオ
ンを含む試料をアルカリ滴定で定量する方法に係
り、殊に環元剤を添加して第二鉄イオンを第一鉄
イオンに還元することにより酸と全鉄イオンの量
又は濃度を測定する方法に関する。
鋼板等の鋼材製造において、酸洗処理は鋼材の
品質の良否を決定する重要な工程であるため、酸
洗液中の酸と全鉄イオンを最適濃度に制御する必
要がある。このため、従来から中和滴定、吸光度
測定、比重測定あるいはこれらの組合せにより定
量を行なつていたが、いずれも測定精度が悪く、
又、迅速性に劣り、実用性に欠けていた。又、酸
洗液等のように製造ライン中に組み込まれる工程
の試料の定量分析は簡便性、迅速性を要求される
ことから一般には用手法は不向きで機器を使用し
た自動計測法が最適とされている。そこで、近
年、酸洗液の定量に連続中和適定法を採用しガラ
ス電極と比較電極とによつて電位差測定を行なう
方法が開発された（特開昭56−33545号）。
かかる方法は試料に還元剤を加えて第二鉄イオ
ンを第一鉄イオンに還元した後にアルカリ滴定
（中和滴定）を行ない、酸及び第一鉄イオンの当
量点を測定して、消費されたアルカリ標準液の量
から酸又は全鉄イオンを算出するものである。こ
れは、酸洗液中には、鉄イオンとして第一鉄イオ
ンの他に第二鉄イオンが存在し、この第二鉄イオ
ンが酸との中和点以前に滴定液であるアルカリ標
準溶液と反応するため酸にプラス誤差が生じるこ
ととから、試料中の第二鉄イオンを予め第一鉄イ
オンに還元しておき、酸の定量の妨害を除去した
ものである。この方法をさらに詳しく述べる。酸
として通常、塩酸を含み、酸洗いの結果、鉄イオ
ンとして第一鉄イオン及び第二鉄イオンを含む酸
洗液にアルカリ標準溶液として所定濃度の水酸化
ナトリウム溶液を加えて、アルカリ滴定する場合
には以下の反応がおこる。
HCL＋NaOH→NaCl＋H2O ……(1)
FeCl2＋2NaOH→Fe（OH）2
＋2NaCl ……(2)
FeCl3＋3NaOH→Fe（OH）3
＋3NaCl ……(3)
このアルカリ滴定を連続して行ない、そのPHの
変化を第１図のようにグラフに表わすと、第二鉄
イオンはPH２〜３において水酸化ナトリウムと(3)
式の反応を起こして、(1)式の反応と併行して進行
する。このため、塩酸のみの中和点では当量とな
らずに、塩化第二鉄と塩酸の量を合した水酸化ナ
トリウム溶液の消費量はＰ点において当量とな
る。さらに滴定を続けると、次いで塩化第一鉄が
(2)式の反応をし、塩化第一鉄に相当する水酸化ナ
トリウム溶液の消費量が加算された点Ｑで当量点
が現われる。従つて、水酸化ナトリウム溶液と反
応した一部の第二鉄イオンが酸としてカウントさ
れ、酸全体としてプラス誤差が表われることか
ら、アルカリ滴定に際し、還元剤を加えて第二鉄
イオンを第一鉄イオンに還元せしめて、全鉄イオ
ンを第一鉄イオンとして定量するものである。こ
れにより、試料中の酸のプラス誤差は少なくなつ
たが、この方法によつても、依然として酸又は全
鉄イオンの正確な測定値が得られず、又、再現性
の悪いものであつた。
本発明者らは、この特開昭56−33545号公報の
定量分析方法を詳細に検討した結果、添加した還
元剤と試料中の酸とが反応し、このため酸が消費
されてマイナス誤差を生ずることを見い出し、還
元剤の選択と、その添加時期の採択を数多くの実
験から裏付け、本発明を完成するに至つた。
すなわち、滴定開始前の酸洗液は、嫁動状況に
よつてバラツキがあるが、通常PH1.2以下であり、
このPH1.2以下の状態で還元剤を投入すると酸と
還元剤が反応し、酸が還元剤により消費されて誤
差が生じるが、PHが1.3より中性側になると酸と
還元剤が反応せず、還元剤により酸が消費されな
いことを見い出し、本発明を完成させたものであ
る。
つまり本発明は、試料中の第二鉄イオンと第一
鉄イオンに還元した後、アルカリ滴定により試料
中の酸又は全鉄イオンを定量する方法において、
アルカリ滴定で試料のPH値を1.3から1.5の範囲に
調整してからチオ硫酸ナトリウムを添加して前記
還元を行ない、その後再びアルカリ滴定を行なう
こと、を特徴とするものである。
以下、本発明をさらに詳しく説明する。
本発明において、第二鉄イオンを還元する還元
剤として、チオ硫酸ナトリウムが使用される。他
の還元剤、例えば、チオ硫酸ナトリウム、チオ酢
酸カリウム等のチオ酢酸塩、亜硫酸ナトリウム、
亜硫酸カリウム等の亜硫酸塩、沃化ナトリウム、
沃化カリウム等の沃化物あるいはチオ硫酸カリウ
ム等は、還元力がチオ硫酸ナトリウムよりも劣
り、又、試料中の酸以外の他の物質と容易に反応
をおこしたり、分解したりして安定性にも劣るた
め、使用しても測定精度及び再現性が悪いものと
なる。
このように選択されたチオ硫酸ナトリウムはア
ルカリ滴定により試料のPH値が1.3から1.5の範囲
になつたとき添加される。PH1.5を越える水素イ
オン濃度においてはチオ硫酸ナトリウムの還元力
が弱くなり第二鉄イオンを十分に第一鉄イオンに
還元できず、このため既述のように塩酸の定量の
際に(3)式の反応が起つて塩酸の測定値にプラス誤
差が生じる。一方、PH1.3未満の水素イオン濃度
では試料中の塩酸とチオ硫酸ナトリウムとが次式
の反応をする。
Na2S2O3＋2HCl2NaCl＋H2O＋Ｓ＋SO2↑
……(4)
この反応は十分に酸性の場合は平衡が右に移行
し、二酸化イオウが揮散して失なわれるため、PH
1.3未満では塩酸が失なわれると同じこととなり
酸の測定値にマイナス誤差を生ずる。このPH値の
検知は、試料中に浸漬したガラス電極と比較電極
とにより電位差を計測してPH値に換算して行なつ
てもよく、又、PH指示薬を添加して行なつてもよ
いが、簡便性、正確度の点から電位差測定が好ま
しい。又、還元剤であるチオ硫酸ナトリウムは結
晶のままで添加してもよく、所定濃度の水溶液と
して添加してもよく、いずれにせよ、試料中の第
二鉄イオンを全て第一鉄イオンに還元するのに必
要な量が添加される。
前記アルカリ滴定（中和滴定）には、所定濃度
のアルカリ溶液を用いる。この場合、試料中の酸
が一般には強度である塩酸であることから濃度既
知の水酸化ナトリウム、水酸化カリウム等の強塩
基のアルカリ溶液を使用し、好ましくは、アルカ
リ標準溶液を用いて滴定を行なう。
このアルカリ滴定は測定当初から行ない、消費
されたアルカリの量を計測しておく。アルカリ滴
定でPH値が1.3から1.5の範囲に達したとき、一旦
滴定を中止し、所定濃度あるいは所定量のチオ硫
酸ナトリウムを試料に添加して、第二鉄イオンの
全てが第一鉄イオンに還元されるまで放置する。
この時間は試料中の第二鉄イオンの濃度によつて
も異なるが60〜90秒で十分である。又、この際、
還元を促進するため、試料を撹拌するのが好まし
い。第二鉄イオンの還元が終了した後は試料中の
鉄イオンは全て第一鉄イオンとなつており、酸定
量の際に(3)式の反応がおきず(1)式の反応のみであ
るから、その後、再びアルカリ滴定を行なうこと
により第１段の当量点では酸のみの測定が正確に
でき、又、第１段の当量点以降の滴定では第一鉄
イオンが(2)式の反応をするだけであるから、第２
段の当量点で全鉄イオンの測定が正確にできる。
第２図は試料中に塩酸、第一鉄イオン及び第二
鉄イオンを含有せしめたものを本発明の方法によ
りアルカリ標準溶液として1N水酸化ナトリウム
を使用して滴定した場合の滴定曲線である。第１
段のPH急変点Ｒが塩酸の中和点であり、第２段の
PH急変点Ｓは還元されて第一鉄イオンとなつた全
鉄イオンの当量点である。従つてPH急変点Ｒまで
のアルカリ標準溶液の消費量ａは塩酸の量に匹敵
し、第２段のPH急変点Ｓまでのアルカリ標準溶液
の消費量ｂからａを差し引いたｂ−ａは全鉄イオ
ンの量に匹敵するから、正確な測定が可能とな
る。
以上のように、本発明によると、還元剤チオ硫
酸ナトリウムの添加時期をその還元力が十分に維
持でき、かつ、酸との反応をおこさない範囲に選
択したから、酸及び全鉄イオンの測定が正確とな
る。又、酸と全鉄イオンの各当量点は明確に分離
されて現われるから再現性もよく、操作も簡便で
あり、迅速性にも優れている。さらに、以下の実
施例に示すように、酸と全鉄イオンの配合比の変
化にもかかわらず正確な測定ができるから酸が高
濃度で全鉄イオンが低濃度の場合から、酸が低濃
度で全鉄イオンが高濃度の場合に致る広い範囲に
使用できる。
以下、実施例により本発明を具体化して説明す
る。
実施例 １
濃度20.48ｇ／（0.562N）の塩酸溶液４mlと
濃度152.31ｇ／（2.403N）の塩化第一鉄溶液４
ml及び濃度31.48ｇ／（0.582N）の塩化第二鉄
溶液４mlを混合して約PH0.9の試料を調整した。
この試料に窒素ガスを用いて空気酸化を防止しな
がら1N水酸化ナトリウム溶液で滴定し、PH1.4に
達したとき滴定を中止し、濃度2mol／チオ硫
酸ナトリウム溶液２mlを加えて撹拌しながら90秒
放置した。その後、再びアルカリ滴定を行ない、
第１段のPH急変点までに消費された水酸化ナトリ
ウム溶液の量及び第１段のPH急変点から第２段の
PH急変点までに消費された水酸化ナトリウム溶液
の量を計測し、それぞれを塩酸相当滴定量と全鉄
イオン相当滴定量とした。
比較例１として、濃度15.78ｇ／（0.433N）
の塩酸溶液２mlと濃度152.36ｇ／（2.404N）の
塩化第一鉄溶液２ml及び濃度34.04ｇ／
（0.630N）の塩化第二鉄溶液２mlを混合した約PH
1.0の試料を、前記と同濃度のチオ硫酸ナトリウ
ムを添加したのち1N水酸化ナトリウム溶液で滴
定し、同様に第１段及び第２段のPH急変点までの
水酸化ナトリウム溶液消費量を計測した（前記特
開昭56−33545号の分析方法）。
以上の結果を第１表に表わす。
The present invention relates to a method for quantifying a sample containing acid and iron ions, such as a pickling solution for steel materials, by alkaline titration, and in particular, it involves adding a ring agent to reduce ferric ions to ferrous ions. In particular, it relates to a method for determining the amount or concentration of acids and total iron ions. In the production of steel materials such as steel plates, pickling treatment is an important process that determines the quality of steel materials, so it is necessary to control the acid and total iron ions in the pickling solution to an optimal concentration. For this reason, quantitative determination has traditionally been carried out by neutralization titration, absorbance measurement, specific gravity measurement, or a combination of these, but all of these methods have poor measurement accuracy.
Moreover, it was inferior in speed and lacked practicality. In addition, quantitative analysis of process samples such as pickling solutions that are incorporated into the manufacturing line requires simplicity and speed, so manual methods are generally unsuitable and automatic measurement methods using equipment are optimal. has been done. Therefore, in recent years, a method has been developed in which a continuous neutralization adjustment method is adopted for quantifying the pickling solution and the potential difference is measured using a glass electrode and a reference electrode (Japanese Patent Application Laid-open No. 33545/1983). In this method, a reducing agent is added to the sample to reduce ferric ions to ferrous ions, and then alkaline titration (neutralization titration) is performed to measure the equivalence point of acid and ferrous ions, and the amount of consumed ferrous ions is measured. This method calculates acid or total iron ions from the amount of alkaline standard solution. This is because in addition to ferrous ions, ferric ions are present in the pickling solution, and these ferric ions are mixed with the alkaline standard solution, which is the titrant, before the point of neutralization with the acid. Because the reaction causes a positive error in the acid, the ferric ions in the sample are reduced to ferrous ions in advance to eliminate any interference with acid quantification. This method will be described in more detail. When performing alkaline titration by adding a sodium hydroxide solution of a predetermined concentration as an alkaline standard solution to a pickling solution that usually contains hydrochloric acid as the acid and contains ferrous and ferric ions as iron ions as a result of pickling. The following reaction occurs. HCL + NaOH → NaCl + H 2 O ...(1) FeCl 2 +2NaOH→Fe(OH) 2 +2NaCl ...(2) FeCl 3 +3NaOH→Fe(OH) 3 +3NaCl ...(3) Continuously perform this alkaline titration and When the change in pH is expressed graphically as shown in Figure 1, ferric ions interact with sodium hydroxide at pH 2 to 3 (3)
The reaction of formula (1) occurs and proceeds in parallel with the reaction of formula (1). Therefore, the amount of sodium hydroxide solution consumed, which is the sum of the amounts of ferric chloride and hydrochloric acid, does not become equivalent at the neutralization point of only hydrochloric acid, but becomes equivalent at point P. Continuing the titration, ferrous chloride then
The equivalence point appears at point Q where the reaction of equation (2) is carried out and the amount of sodium hydroxide solution consumed corresponding to ferrous chloride is added. Therefore, some ferric ions that react with the sodium hydroxide solution are counted as acids, and a positive error appears for the entire acid. Therefore, when performing alkaline titration, a reducing agent is added to convert ferric ions to The total iron ions are reduced to iron ions and quantified as ferrous ions. As a result, the positive error of the acid in the sample was reduced, but even with this method, accurate measurements of acid or total iron ions could not be obtained, and the reproducibility was poor. As a result of a detailed study of the quantitative analysis method disclosed in JP-A-56-33545, the inventors found that the added reducing agent reacts with the acid in the sample, and as a result, the acid is consumed and a negative error occurs. They discovered that this phenomenon occurs, confirmed the selection of the reducing agent and the timing of its addition through numerous experiments, and completed the present invention. In other words, the pickling solution before titration starts usually has a pH of 1.2 or less, although it varies depending on the dynamic conditions.
If a reducing agent is added when the pH is below 1.2, the acid and reducing agent will react and the acid will be consumed by the reducing agent, causing an error, but if the pH is more neutral than 1.3, the acid and reducing agent will not react. First, they discovered that the acid was not consumed by the reducing agent, and completed the present invention. In other words, the present invention provides a method for quantifying acid or total iron ions in a sample by alkaline titration after reducing the sample to ferric ions and ferrous ions.
The method is characterized in that the PH value of the sample is adjusted to a range of 1.3 to 1.5 by alkaline titration, sodium thiosulfate is added to perform the reduction, and then alkaline titration is performed again. The present invention will be explained in more detail below. In the present invention, sodium thiosulfate is used as a reducing agent to reduce ferric ions. Other reducing agents, such as sodium thiosulfate, thioacetates such as potassium thioacetate, sodium sulfite,
Sulfites such as potassium sulfite, sodium iodide,
Iodides such as potassium iodide or potassium thiosulfate have lower reducing power than sodium thiosulfate, and may easily react with other substances other than acids in the sample or decompose, resulting in unstable stability. Therefore, even if used, the measurement accuracy and reproducibility will be poor. The sodium thiosulfate thus selected is added when the pH value of the sample is in the range of 1.3 to 1.5 by alkaline titration. At hydrogen ion concentrations exceeding PH 1.5, the reducing power of sodium thiosulfate becomes weak and ferric ions cannot be sufficiently reduced to ferrous ions. ) reaction occurs and a positive error occurs in the measured value of hydrochloric acid. On the other hand, at a hydrogen ion concentration below PH1.3, hydrochloric acid and sodium thiosulfate in the sample react as shown below. Na 2 S 2 O 3 ＋2HCl2NaCl＋H 2 O＋S＋SO 2 ↑
...(4) If this reaction is sufficiently acidic, the equilibrium will shift to the right and sulfur dioxide will be volatilized and lost, so the pH will change.
If it is less than 1.3, it will be the same as hydrochloric acid being lost, resulting in a negative error in the acid measurement value. The PH value may be detected by measuring the potential difference between a glass electrode and a reference electrode immersed in the sample and converting it into a PH value, or by adding a PH indicator. Potential difference measurement is preferred from the viewpoint of simplicity and accuracy. In addition, sodium thiosulfate, which is a reducing agent, may be added in the form of crystals or as an aqueous solution at a predetermined concentration; in any case, all ferric ions in the sample are reduced to ferrous ions. The amount necessary to do so is added. For the alkaline titration (neutralization titration), an alkaline solution of a predetermined concentration is used. In this case, since the acid in the sample is generally strong hydrochloric acid, an alkaline solution of a strong base such as sodium hydroxide or potassium hydroxide with a known concentration is used, and preferably an alkaline standard solution is used for titration. Let's do it. This alkali titration is performed from the beginning of the measurement to measure the amount of alkali consumed. When the pH value reaches a range of 1.3 to 1.5 during alkaline titration, the titration is temporarily stopped and a specified concentration or amount of sodium thiosulfate is added to the sample to convert all ferric ions to ferrous ions. Leave it alone until it is restored.
Although this time varies depending on the concentration of ferric ions in the sample, 60 to 90 seconds is sufficient. Also, at this time,
It is preferable to agitate the sample to promote reduction. After the reduction of ferric ions is completed, all of the iron ions in the sample become ferrous ions, and when quantifying acid, the reaction of equation (3) is omitted, and only the reaction of equation (1) occurs. Then, by performing alkaline titration again, it is possible to accurately measure only the acid at the first stage equivalence point, and in the titration after the first stage equivalence point, ferrous ions undergo the reaction of equation (2). The second
Total iron ions can be measured accurately at the equivalence point of the stage. FIG. 2 is a titration curve obtained by titrating a sample containing hydrochloric acid, ferrous ions, and ferric ions using 1N sodium hydroxide as an alkaline standard solution according to the method of the present invention. 1st
The pH sudden change point R of the stage is the neutralization point of hydrochloric acid, and the pH of the second stage is
The sudden pH change point S is the equivalence point of all iron ions that have been reduced to ferrous ions. Therefore, the consumption amount a of the alkaline standard solution up to the sudden PH change point R is comparable to the amount of hydrochloric acid, and b - a, which is the consumption amount b of the alkaline standard solution up to the second stage sudden PH change point S minus a, is the total amount. Since the amount is comparable to that of iron ions, accurate measurements are possible. As described above, according to the present invention, the timing of addition of the reducing agent sodium thiosulfate is selected within a range that can sufficiently maintain its reducing power and does not cause any reaction with the acid, so that acid and total iron ions can be measured. becomes accurate. In addition, since each equivalence point of acid and total iron ion appears clearly separated, reproducibility is good, operation is simple, and speed is excellent. Furthermore, as shown in the example below, accurate measurements can be made despite changes in the mixing ratio of acid and total iron ions. It can be used in a wide range of applications when the total iron ion concentration is high. Hereinafter, the present invention will be concretely explained with reference to Examples. Example 1 4 ml of hydrochloric acid solution with a concentration of 20.48 g/(0.562 N) and 4 ml of ferrous chloride solution with a concentration of 152.31 g/(2.403 N)
ml and 4 ml of ferric chloride solution with a concentration of 31.48 g/(0.582 N) were mixed to prepare a sample with a pH of about 0.9.
This sample was titrated with a 1N sodium hydroxide solution using nitrogen gas to prevent air oxidation. When the pH reached 1.4, the titration was stopped, and 2 ml of a 2 mol/sodium thiosulfate solution was added to the sample, and the solution was heated to 90° C. with stirring. I left it for seconds. After that, perform alkaline titration again.
The amount of sodium hydroxide solution consumed up to the sudden pH change point of the first stage and the amount of sodium hydroxide solution consumed from the sudden pH change point of the first stage to the second stage
The amount of sodium hydroxide solution consumed up to the sudden pH change point was measured, and these were defined as the hydrochloric acid equivalent titre and the total iron ion equivalent titer, respectively. As Comparative Example 1, concentration 15.78g/(0.433N)
2 ml of hydrochloric acid solution and 2 ml of ferrous chloride solution with concentration of 152.36 g/(2.404 N) and 2 ml of ferrous chloride solution with concentration of 34.04 g/
Approximate pH of 2 ml of ferric chloride solution (0.630N)
After adding sodium thiosulfate at the same concentration as above, a sample of 1.0 was titrated with 1N sodium hydroxide solution, and the amount of sodium hydroxide solution consumed up to the sudden pH change point in the first and second stages was similarly measured. (Analysis method of JP-A No. 56-33545). The above results are shown in Table 1.
【表】
実施例 ２
濃度157.56ｇ／（4.323N）の塩酸溶液４mlと
濃度7.70ｇ／（0.121N）の塩化第一鉄溶液４ml
及び濃度2.69ｇ／（0.0497N）の塩化第二鉄溶
液４mlを混合して約PH0.4の試料とし、実施例１
と同様の処理及び滴定をして、塩酸相当滴定量と
全鉄イオン相当滴定量とを計測した。
比較例２として、濃度157.82ｇ／（4.330N）
の塩酸溶液２mlと濃度5.06ｇ／（0.080N）の塩
化第一鉄溶液２ml及び濃度2.60ｇ／（0.032N）
の塩化第二鉄溶液２mlを混合して約PH0.3の試料
とし、比較例１と同様の処理及び滴定を行なつ
た。
この結果を第２表に表わす。[Table] Example 2 4 ml of hydrochloric acid solution with a concentration of 157.56 g/(4.323 N) and 4 ml of ferrous chloride solution with a concentration of 7.70 g/(0.121 N)
Example 1
The same treatment and titration as above were carried out to measure the titer equivalent to hydrochloric acid and the titer equivalent to total iron ion. As comparative example 2, concentration 157.82g/(4.330N)
2 ml of hydrochloric acid solution and 2 ml of ferrous chloride solution with concentration of 5.06 g/(0.080N) and 2 ml of ferrous chloride solution with concentration of 2.60 g/(0.032N)
A sample having a pH of about 0.3 was prepared by mixing 2 ml of a ferric chloride solution, and the same treatment and titration as in Comparative Example 1 were carried out. The results are shown in Table 2.
【表】
以上の実施例によれば、本発明は塩酸濃度が小
さく全鉄イオン濃度が大きい場合（実施例１）で
も、塩酸濃度が大きく全鉄イオン濃度が小さい場
合（実施例２）でも、正確に酸又は全鉄イオンの
定量が可能である。
なお、本発明は上記した鋼材の酸洗液の定量分
析のみならず、酸及び鉄イオンを含むあらゆる試
料の酸又は全鉄イオンの定量分析に使用ができ
る。又、自動滴定法によらず用手法により行なつ
てもよい。[Table] According to the above examples, the present invention can be applied both when the hydrochloric acid concentration is low and the total iron ion concentration is high (Example 1), and when the hydrochloric acid concentration is high and the total iron ion concentration is low (Example 2). Accurate quantification of acid or total iron ions is possible. Note that the present invention can be used not only for quantitative analysis of the above-mentioned pickling solution for steel materials, but also for quantitative analysis of acid or total iron ions in any sample containing acid and iron ions. Alternatively, the titration may be carried out manually instead of using the automatic titration method.
第１図は従来の方法によつて定量分析した場合
の滴定曲線を表わしたもの、そして第２図は本発
明によつて定量分析した場合を表わしたものであ
り、いずれも縦軸にPH値を、横軸に消費されたア
ルカリの量をプロツトしてある。
Figure 1 shows the titration curve when quantitative analysis was performed using the conventional method, and Figure 2 shows the titration curve when quantitative analysis was performed using the present invention. In both cases, the vertical axis shows the PH value. The amount of alkali consumed is plotted on the horizontal axis.
Claims (1)
した後、アルカリ滴定により酸又は全鉄イオンを
定量する方法において、アルカリ滴定を行なつて
試料のPH値を1.3から1.5の範囲に調整してからチ
オ硫酸ナトリウムを添加して前記還元を行ない、
その後再びアルカリ滴定を続行することを特徴と
する酸又は全鉄イオンの定量分析方法。1 In the method of quantifying acid or total iron ions by alkaline titration after reducing ferric ions in a sample to ferrous ions, alkaline titration is performed to adjust the pH value of the sample to a range of 1.3 to 1.5. and then adding sodium thiosulfate to carry out the reduction,
A quantitative analysis method for acid or total iron ions, characterized in that alkali titration is then continued again.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15464582A JPS5944657A (en) | 1982-09-07 | 1982-09-07 | Quantitatively analyzing method of acid or total iron ion |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15464582A JPS5944657A (en) | 1982-09-07 | 1982-09-07 | Quantitatively analyzing method of acid or total iron ion |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPS5944657A JPS5944657A (en) | 1984-03-13 |
| JPH0358066B2 true JPH0358066B2 (en) | 1991-09-04 |
Family
ID=15588746
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP15464582A Granted JPS5944657A (en) | 1982-09-07 | 1982-09-07 | Quantitatively analyzing method of acid or total iron ion |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPS5944657A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103091450A (en) * | 2013-01-02 | 2013-05-08 | 河北钢铁股份有限公司承德分公司 | Method for rapidly determining content of total iron in nitrided ferrovanadium |
| CN104101683A (en) * | 2014-06-30 | 2014-10-15 | 武汉钢铁(集团)公司 | Method for measuring content of ferric ion in iron plating liquid |
| CN106404996A (en) * | 2016-09-06 | 2017-02-15 | 国网天津市电力公司 | Method for measuring ferrous oxide in corrosion product |
| CN113607878B (en) * | 2021-07-29 | 2024-06-07 | 北京首钢股份有限公司 | Assay method and application of free acid and ferrous ion concentration in pickling waste hydrochloric acid |
-
1982
- 1982-09-07 JP JP15464582A patent/JPS5944657A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5944657A (en) | 1984-03-13 |
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