Methylene blue a matsayin mai nuni: abin da sauyin launin yake nunawa a zahiri

Wata ma'aikaciyar fasaha ta ƙara methylene blue a cikin bikar, ta daidaita pH, sannan ta jira launin ya nuna yawan acidity. Ba a sami wani sauyi bayyananne ba. Sai ta ƙara ɗigon ruwan ascorbic acid a maimakon haka, kuma shuɗin ya ɓace. Ta girgiza flask ɗin a cikin iska, kuma shuɗin ya dawo. Rini ɗaya, amma halaye biyu masu bambanci sosai. Wannan ruɗani shi ne jigon wannan maƙala: methylene blue mai nuna redox ne wanda yake amsawa ga musayar elektron, ba mai nuna pH da yake amsawa ga proton ba. Da zarar an fahimci wannan bambanci, sauran bayanai duk suna shiga wurinsu.

Ana iya taƙaita ƙa'idar aiki a jumla ɗaya. Shuɗi yana nufin nau'in da aka yi wa oksidashan yana nan. Rashin launi yana nufin nau'in da aka yi wa ridiƙshan, leucomethylene blue, yana nan. Duk abin da yake motsa elektron zai iya sauya wannan yanayi. Acid da base su kaɗai ba za su iya ba, duk da cewa pH yana sauya ƙarfin lantarkin da sauyin yake faruwa a kansa.

Ma'auratan redox da ke haifar da launin

Methylene blue da aka yi wa oksidashan shi ne kation na methylthioninium, wani tsarin phenothiazinium mai zobe uku a shimfiɗe, wanda ake samarwa a matsayin gishirin chloride, kuma PubChem ya rubuta shi a matsayin methylthioninium chloride. A cikin ruwa mai ƙarancin taro, monomer ɗin yana shan haske kusa da 664 nm, kuma wannan shan hasken ne yake haifar da shuɗin da ido yake gani. Abokin ma'auratarsa da aka yi wa ridiƙshan, leucomethylene blue, yana da tsarin asali iri ɗaya, amma nitrogen na zoben tsakiya ya karɓi proton kuma chromophore ɗin ya katse, don haka kusan ba shi da launi, tare da ƙaƙƙarfan zangon shan haskensa a ɓangaren ultraviolet (bayanin PubChem na nau'in leuco).

Amsawar gaba ɗaya tana motsa elektron biyu, amma adadin proton yana dogara da pH saboda nau'in da aka yi wa ridiƙshan yana karɓar proton a cikin acid. Bayanin da ake amfani da shi a matsayin madogara a cikin bayyana sinadaran redox ta hanyar gani ya ba da ƙarfin lantarki na ma'auni kusa da +0.53 V a pH 0 da ƙarfin lantarki na sharadin gwaji kusa da +0.011 V a pH 7, idan aka auna su dangane da elektrod na hydrogen. Tsakanin waɗannan maki, ƙarfin lantarkin yana sauyawa da pH. Voltammetry na zamani a cikin binciken halayen redox da ƙarfin lantarkin rinaye ya gano kusan 29.5 mV a kowace raka'ar pH daga kusan pH 4 zuwa 10, wanda ya dace da tsarin elektron biyu da proton ɗaya, da kusan 88.5 mV a kowace raka'ar pH ƙasa da pH 4, wanda ya dace da tsarin elektron biyu da proton uku. Saboda haka, rahoton ƙarfin lantarki ba tare da pH ɗinsa ba ba shi da ma'ana. Koyaushe a tambayi wace karkatar sauyi da wane elektrod na madogara aka yi amfani da su wajen samun lambar, domin ba za a iya kwatanta ƙimomin da aka bayar dangane da madogarar azurfa kai tsaye da waɗanda aka bayar dangane da ma'aunin hydrogen ba. Tsari da kaddarorin da ke tushen sinadarin su ne suke ƙayyade chromophore ɗin, kuma wani shafi mai alaƙa kan tsara karatun redox ya faɗaɗa amfani da waɗannan ma'aurata zuwa zaɓuɓɓukan haɗa sinadarai.

Wannan matsayi na tsakiya a ma'aunin ƙarfin lantarki shi ne yake sa rinin ya zama mai amfani. A pH 7 yana cikin masu yin oksidashan masu sauƙi: yana da isasshen ƙarfi don karɓar elektron daga masu bayarwa masu kyau kamar ascorbate ko NAD(P)H, amma ba ya riƙe su da ƙarfin da zai hana miƙa su ga oxygen da ya narke ko wuraren ƙarfe na ferric. Saboda haka yana zagayawa maimakon makalewa a yanayi ɗaya. Ridiƙshan yana kawar da launinsa. Iska tana sake yi masa oksidashan. Hanyar ɗaya ce a ɓangarorin biyu.

Dalilin da ya sa tambayoyin pH suke yawan tasowa

Abubuwa uku da ke haifar da ruɗani suna maimaituwa a dakunan gwaje-gwaje da azuzuwa, kuma kowannensu yana da takamaiman gyara.

Na farko, pH yana sauya ƙarfin lantarki, wanda yake kama da amsawa ga pH. Idan aka ƙara pH, zai fi sauƙi a yi wa ma'auratan ridiƙshan a wani tsayayyen karatun elektrod, don haka mai bayar da elektron ɗin nan ɗaya zai kawar da launin rinin da sauri. Amma babu wani matakin karɓar proton shi kaɗai da yake haifar da sauyi bayyananne daga shuɗi zuwa rashin launi a cikin zangon da aka saba. Wani bita mai nazari na 2025 kan kaddarorin methylene blue ya ruwaito cewa mafi girman shan haske a 665 nm kusan bai sauya ba daga pH 2 zuwa 12, sai ƙananan sauye-sauye a adadin shan haske. Proton suna daidaita ƙarfin lantarki. Elektron suna sauya launi.

Na biyu, lakabin tsarin rarraba bayanai yana ruɗarwa. A halin yanzu PubChem yana shigo da rukunin amfani daga ChEBI wanda yake kiran rinin mai nuna acid-base. Bai kamata a ɗauki wannan lakabi a matsayin shaida cewa methylene blue yana aiki kamar phenolphthalein ko methyl red ba. A aikin ruwa na yau da kullum, ba haka yake ba.

Na uku, haɗin Tashiro yana aro sunan. Mai nuna Tashiro haɗin methyl red da methylene blue ne, inda methyl red yake samar da amsawar acid-base, methylene blue kuma yake samar da shuɗin bango na gani, yana mayar da sauyin ja zuwa rawaya zuwa sauyin haɗaɗɗen launi mafi bayyana. Wani haɗin Tashiro na kasuwa ya bayar da pH 4.4 zuwa 6.2, yayin da wani takamaiman haɗin ITW Reagents ya ƙayyade ja-shunayya a pH 4.4 zuwa kore a pH 5.8. Babu ɗaya daga cikin waɗannan zanguna da yake zangon sauyin methylene blue shi kansa. Rinin mai samar da launin bango ne, ba mai ganowa ba.

Akwai wani yanayi na musamman da ya cancanci gargaɗi. Kusa da pH 13, yanayin alkaline mai ƙarfi na iya samar da sinadarai masu launin ja zuwa ruwan hoda na nau'in methylene-violet ta hanyar hydrolysis da ba a iya juyawa. Wannan ruwan hodar lalacewa ne, ba ƙarshen sauyin mai nuni ba. A ɗauke shi a matsayin alamar zubar da ruwan, ba alamar da za a karanta ba.

Inda yake aiki a matsayin mai nuna redox

Sanannen amfaninsa na gargajiya shi ne titration na Lane-Eynon don sukari mai yin ridiƙshan. Ana yin titration na ruwan Fehling mai zafi kuma alkaline da sukari, sannan a ƙara methylene blue kusa da ƙarshen titration; shuɗin da ya rage yana ɓacewa da zarar ƙarfin ridiƙshan na sukarin ya wuce abin da ake buƙata don copper(II). Hanyar AOAC Lane-Eynon tana ci gaba da tafasa haɗin domin tururin da yake fita ya rage sake oksidashan daga iska, yawanci tare da ɗan ɗigogi na ruwan rini. Sauyin launin yana nuna cewa babu sauran copper da za a iya yi wa ridiƙshan, wanda yake bayani ne na redox game da abin da ke cikin flask, ba bayani na pH ba.

Titrimetry na da ya yi amfani da wannan dabara a wasu wurare. Rini mai ƙarancin taro zai iya maye gurbin sitaci a wasu titration na iodimetry inda barasa ta sa sitaci bai dace ba, da taron aiki kusa da 0.05 g a kowace lita, ko da yake yawan rini fiye da kima yana iya samar da haɗaɗɗen sinadarin iodine da rini kamar yadda Sinnatt ya nuna a 1912. Littattafan tattara bayanai kuma suna lissafa rinin don titanometry da iodometry. Hanyar ascorbic acid ta Gal ta 1936 ta yi wa rinin ridiƙshan da ruwan da aka tsamo vitamin C, sannan ta yi titration na baya na rinin da ya rage da titanium trichloride. Yanzu wannan hanyar ta tarihi ce maimakon ta aikin yau da kullum, amma tana nuna tsarin: mai bayar da elektron yana yi wa shuɗi ridiƙshan ya zama marar launi, kuma ɓacewar shuɗin ita ce alamar ƙarshen titration.

Hanyoyin auna oxygen da ya narke suna amfani da waɗannan ma'aurata a kishiyar hanya. Wata hanyar da aka wallafa tana fara yi wa rinin ridiƙshan da glucose a cikin ethanol mai ruwa kuma alkaline, sannan ta bar oxygen da ya narke ya yi wa nau'in leuco marar launi oksidashan ya koma shuɗi kusan nan take, ana yin karatu kusa da 600 nm har zuwa kusan 13 micrograms a kowace milliliter, kamar yadda Okumura da Hashitani suka bayyana. Kada a ruɗa wannan da titration na gargajiya na Winkler don oxygen da ya narke, wanda yake amfani da sitaci a ƙarshensa; SOP na NOAA Winkler ya ƙayyade kusan 1 bisa ɗari na sitaci. Hanyoyin oxygen na methylene blue rukuni ne dabam, inda sauyin launin yake tafiya a kishiyar hanya.

Gwajin kwalbar shuɗi na aji yana amfani da waɗannan ma'aurata a ƙaramin sikeli: glucose a cikin ruwa mai alkaline yana yi wa rini mai shuɗi ridiƙshan ya koma marar launi idan aka bar shi a tsaye, sannan girgizawa tana narkar da oxygen wanda yake sake yi masa oksidashan ya koma shuɗi. Cikakkiyar hanyar gwajin da abubuwan sarrafa ta suna cikin gwajin nuna kwalbar shuɗi, kuma wuraren zangon shan haske da sauye-sauyen da taruwar ƙwayoyin sinadari ke haifarwa suna cikin shafin bakan haske da tasirin taro. Wannan maƙala tana riƙe da tsarin amsawar ne kawai, domin hanyar gwaji da bakan haske kowannensu yana buƙatar nasa sharuddan.

Jadawalin yanayin launi: yanayi, sharudda, iyakoki

Wannan tebur shi ne tushen bayanan madogara na maƙalar. A karanta layi gaba ɗaya kafin a amince da kowace alamar ƙarshe.

Matsalolin da suke sa ƙarshen titration ya kasa bayyana

Iska ita ce abin zargi na farko duk lokacin da alamar ƙarshen titration take sauyawa. Nau'in leuco yana samun sake oksidashan cikin sauƙi, musamman a tsarin alkaline, don haka titration da ya zama marar launi na iya sake komawa shuɗi idan aka bar shi a tsaye ko aka juya shi da ƙarfi. A hana iska idan dorewar yanayin tana da muhimmanci, a daidaita yadda ake girgizawa, kuma a yi karatu a ƙayyadadden lokaci.

Haske shi ne abin zargi na biyu. Rinin yana shiga amsawar sinadarai ta haske, kuma fallasa shi ga haske idan akwai masu bayar da elektron na iya kawar da launinsa ta hanyoyin da suka haɗa da sinadaran da aka cire wa ƙungiyoyin methyl. A adana ruwan rini na nazari a duhu kuma kada a tantance ƙarshen titration a ƙarƙashin fitilun tebur masu ƙarfi.

Taro shi ne na uku. Kation da aka yi wa oksidashan yana taruwa a matsayin dimer da manyan gungu tare da zangon shan haske da ya matsa kusa da 610 zuwa 615 nm, don haka ruwan da yake da taro mai yawa yana iya nuna sauyin kololuwar shan haske ba tare da ya ƙunshi ƙazantar sinadarai ba. A tsarma shi har ya kai yanayin monomer kafin tantance bakan haske ko ƙarshen titration.

Wasu karkacewar sakamako biyu da ba su cika bayyana ba sun cancanci a ambace su domin musamman suna shafar aikin da ake yi da ƙarancin taro. Rinin yana manne wa saman iyakar gilashi da ruwa da adadin da za a iya aunawa, wanda yake karkatar da sakamakon ruwan ma'auni mai ƙarancin taro da ma'aunin saurin amsawa; kwantena ko cuvettes na polymer su ne mafita idan daidaito yana da muhimmanci. Haka kuma rinin kasuwa na iya ɗauke da ƙazantattun sinadaran thiazine masu alaƙa, ciki har da Azure B, waɗanda binciken tsarkakewa na tarihi ya cire musamman, don haka aikin nazari ya kamata ya ƙayyade darajar tsarkin rinin maimakon ɗauka cewa kowace kwalba da aka rubuta methylene blue a jikinta iri ɗaya ce a sinadarance. Da gangan aka bar cikakken bayanin bakan haske na sauyin taruwar ƙwayoyin sinadari a shafin bakan haske.

Taƙaitaccen jerin dubawa a teburin gwaji

A yi amfani da buffer don daidaita pH na ruwan kuma a rubuta pH kusa da kowane ƙarfin lantarki da kowace alamar ƙarshen titration. A tsayar da yanayin oxygen: tafasawa tare da rufin tururi don aikin irin Lane-Eynon, rufin iskar da ba ta shiga amsawa ko ƙayyadadden lokaci a sauran ayyuka. A yi aiki da taro mai ƙaranci da zai ba da damar ganin monomer, a kare ruwan daga haske, a fi amfani da kayan polymer idan taro ya yi ƙasa, kuma a rubuta darajar tsarkin rinin. Idan ainihin manufar ita ce pH, a ɗauki mai nuna acid-base na gaske ko takamaiman haɗin Tashiro, sannan a ambaci zangon haɗin a matsayin zangon haɗin, ba a matsayin zangon methylene blue ba.

Wannan tsari na aiki yana kiyaye ma'anar daidai. Methylene blue yana nuna yanayin oksidashan da bayyananniyar alama ta musamman saboda yanayinsa biyu suna da bambanci sosai wajen shan hasken da ido yake gani. A ɗauki launin a matsayin karatun redox a wani pH da aka bayyana, a ƙarƙashin yanayin oxygen da haske da aka bayyana, tare da darajar tsarkin rini da aka bayyana, kuma zai cancanci matsayinsa a titration. A ɗauke shi a matsayin litmus kuwa, zai ruɗar ba tare da kasawa ba.