Nitroprusside and methylene blue methods for silicone membrane differentiated flow injection determination of sulfide in water and wastewater

Abstract

Hydrogen sulfide evolved from an acidified sample is pre-concentrated by permeation in a stationary alkaline acceptor solution enclosed in a silicone rubber sample loop. Depending on the sample volume pre-concentrated, the applicable analytical range spans low micrograms/L to tens of mg/L for both methods. The methylene blue method is more sensitive by a factor of approximately 30 and actually permits practical determinations in the sub-micrograms/L levels. The limit of detection (LOD) for the nitroprusside method ranges from 20 micrograms/L for a 20 microL sample by conventional flow-injection determination (no membrane, throughput 30 samples/h) to less than 2 micrograms/L for 12 mL sample pre-concentrated in the membrane system (throughput 5 samples/h). The membrane is highly resistant to fouling and permits analysis of untreated wastewater samples bearing suspended solids, oil, grease, etc. without any pretreatment. No significant interference is observed with either chemistry. Although the nitroprusside chemistry is less sensitive, it does not involve the use of concentrated aggressive reagents and is recommended unless ultratrace determinations are essential. Viable reaction mechanisms are proposed for both of these chemistries.

Métodos de amostragem e análise para compostos reduzidos de enxofre atmosférico

“…86,94,95 Espectrofotometria molecular O método mais comum, que utiliza espectrofotometria molecular UV/Vis para análise de sulfeto em matrizes gasosas, é o método do azul de metileno. 39,106,107 É baseado no acoplamento oxidativo de duas moléculas de N,N-dimetilfenileno-1,4-diamina (DMPD) com sulfeto, na presença de pequenas quantidades de íon férrico, produzindo o corante azul de metileno, cuja absorção máxima ocorre a 670 nm.…”

“…Neste método é necessário um controle rígido do pH do meio (10)(11)(12)5), visto que a velocidade da reação de formação do complexo colorido e a sensibilidade do método diminuem bastante em valores de pH menores que 10; em valores de pH maiores que 12,5 o reagente se decompõe, diminuindo a quantidade do produto obtido. 107 Shanthi e Balasubramanian 108 também usaram a espectrofotometria molecular UV/Vis para determinação de H 2 S após sua fixação em solução alcalina de citrato-acetato de zinco. O método baseia-se na reação do sulfeto com bromato para gerar bromo, que, posteriormente, reage com a diclorofluoresceína.…”

Micellar-Mediated Extractive Spectrophotometric Determination of Hydrogen Sulfide/Sulfide through Prussian Blue Reaction: Application to Environmental Samples

“…Among the several spectrophotometric methods, methylene blue method is the most popular and standard procedure for the determination of sulfide at trace level. [12][13][14][15][16] Several modifications have been reported based on the same principle with different degrees of sensitivity for sulfide quantification. Among them, multi syringe flow injection analysis, solid-phase extraction and solid phase reflectometry techniques are significant ones in recent years.…”

Exploiting iminoquinone free radical production for thiol based drugs determination in pharmaceutical formulations

“…1,2 The reaction between sulfide and DMPD to yield methylene blue dye is presented in Scheme 1a. The same reagents (DMPD and Fe 3+ ) used for sulfide determination were employed for spectrophotometric determination of alkyl thiols 3,4 as well as to produce electroactive species from thiol aminoacids. 5 Some other bioactive species, such as synthetic and natural drugs, have thiol functional groups in their molecular structures and reactions analogous those observed in the derivatization of alkyl thiols (Scheme 1b) and thiol aminoacids (cysteine and monocysteine) with an aromatic p-substituted amine are expected.…”