Enzymatic reverse FIA method for total phenols determination in urine samples

A reverse flow injection spectrophotometric enzymatic method is proposed to quantify total phenols in urine samples. The polyphenol oxidase (PPO; EC 1.14.18.1) obtained as a crude extract from sweet potato root (Ipomoea batatas) was used as enzymatic catalyze. The detection limit, the sample throughput and relative standard deviation were 7.7 mg l⁻¹ of total phenols, 49 h⁻¹ and 0.9%, respectively. The method was applied to real samples and a recovery study was carried out in order to its validation.     

Fe analysis by the ferrozine method: Adaptation to FIA towards in situ analysis in hydrothermal environment

The target of this study is the adaptation of the ferrozine method to flow injection analysis (FIA) to perform iron analysis in situ using an in situ chemical analyser in hydrothermal environments. The adaptation of the method to FIA was followed by its optimisation using an experimental design screening method. The goals of the optimisation steps were to decrease the detection limit and to increase the measuring range to cope with the constraints of in situ analysis. The method allows the determination of iron in the mixing zone of hydrothermal fluid, enriched in iron, and seawater. A single manifold gives the possibility to analyse either Fe(II) or ΣFe [Fe(II) + Fe(III)] in situ, or ΣFe in the lab on hydrothermal seawater samples. The measuring range of the method was increased to up to 2000 μM, which is coherent with the study of the chemical environment of communities associated with deep-sea hydrothermal activity. Finally, the method was applied in situ using the chemical analyser Alchimist during the ATOS cruise on hydrothermal vent fields on the Mid Atlantic Ridge.     

A simple colorimetric method for the determination of ammonia in seawater

A method is proposed for the determination of trace amounts of ammonia in seawater. After calcium and magnesium have been chelated with CDTA, the blue colour obtained with hypochlorite and thymol-acetone is measured at 630 nm. The sensitivity is 1.3 ng NH₄⁺-N/cm².     

Application of factorial design to improve a FIA system for penicillin determination

A potentiometric FIA system for penicillin determination, employing penicillinase [E.C. 3.5.2.6] immobilized on silica gel, packed into a reactor, was improved by the use of statistically designed experiments. A two-level and three-factor factorial was used to find the best working conditions evaluating the influence of some parameters on the signal response of the system and the number of determinations per hour. These parameters were analyzed individually obtaining two level of the variables to be used in the factorial design: length of the reactor (1.5 and 2.0 cm), carrier flow rate (1.6 and 2.2 ml min⁻¹) and sample volume (100 and 150 μl). The pure error on the measurements was estimated by authentic repetitions. The ideal working conditions taking into account a compromise between the best response signal and the number of determinations per hour (with the same importance) being chosen the level of factors: length of reactor 1.5 cm, carrier flow rate 2.2 ml min⁻¹ and sample volume of 150 μl. Under these conditions the system allowed to analyze was about 45 samples per hour, during 73 days, with a standard deviation of 2.4% at concentration range between 10⁻¹ and 10⁻³ mol l⁻¹.     

Lead determination at the ppb level using stopped-flow FIA

A flow-injection-based kinetic method for the determination of lead ions was developed. In this method, resazurin was reduced to resorufin by sulfide and lead ions. The method has a detection limit of 1 ppb with a relative standard deviation of 5.2% at the 20 ppb level. Interferences can be removed by prior extraction.     

Photoelectro-synergistic catalysis combined with a FIA system application on determination of chemical oxygen demand

In this paper, photoelectro-synergistic catalysis oxidation of organics in the water on Ti/TiO₂/PbO₂ electrode was investigated. The prepared TiO₂ film was investigated with Atomic force micrograph (AFM). Furthermore, the results were compared with those obtained from electrocatalysis (EC) and electro-assisted photocatalysis (PC). The method proposed employed photoelectro-synergistic catalysis (PEC), together with flow injection analysis, to determine the chemical oxygen demand (COD) values. It was shown that the method of photoelectro-synergistic catalysis had lower detection limit (15.0 mg l⁻¹) and wider linear range (30.0–2500.0 mg l⁻¹) than the methods of electro-assisted photocatalysis and electrocatalysis. The results obtained by the proposed method and conventional one were compared by carrying out the experiment on 20 wastewater samples and also agreed well by high correlation (R = 0.9912).     

A simple and green analytical method for determination of iron based on micro flow analysis

A simple, inexpensive and reagent-less colorimetric micro flow analysis (μFA) system was implemented in a polymethyl methacrylate (PMMA) micro fluidic manifold. A T-shaped micro channel on a PMMA chip was fabricated by laser ablation and topped with molded polydimethylsiloxane (PDMS). The fabricated μFA system was integrated with the optical components as detector and applied to the determination of iron in water samples. It is based on the measurement of Fe(III)-nitroso-R salt complex at 720 nm formed by the reaction between Fe(III) and nitroso-R salt in an acetate buffer solution pH 5. The proposed μFA consumed very small amount of reagent and sample, it released waste of less than 2.0 mL h⁻¹. The relative standard deviation (R.S.D.) was less than 2% (n = 11) with the recovery of 98.7 ± 0.12 (n = 5). The linear range for the determination of iron in water samples was over the range of 0.05-4.0 μg mL⁻¹ with a correlation coefficient (r²) of 0.9994. The limit of detection (3σ) and limit of quantitation (10σ) were 0.021 μg mL⁻¹ and 0.081 μg mL⁻¹, respectively with a sample throughput of 40 h⁻¹.     

A colorimetric method for the determination of nitrazepam

A simple colorimetric method for the determination of nitrazepam is described. Nitrazepam dissolved in ethyl alcohol (95%) produces a yellow anion on addition of aqueous sodium hydroxide, and this is measured spectrophotometrically. The method has been applied to pharmaceutical formulations containing nitrazepam.     

流动注射-电化学氧化法测定水体化学需氧量

采用硼掺杂金刚石(Boron-doped diamond,BDD)薄膜电极为工作电极,利用流动注射分析方法测定水体化学需氧量(COD),根据水样中有机物组分在工作电极表面氧化消耗的电量(Qoxidation)测定样品的COD值。考察了一些基本参数包括载液、工作电位、流速对检测信号的影响并选定了最佳检测条件。在最佳检测条件下,本法检测COD的线性范围为2.5~120 mg/L,检出限为1 mg/L。用该法测定化工厂和食品厂废水的COD值,相对标准偏差和回收率分别在2.4%~4.8%和96%~106%之间,且检测结果与国家标准方法(CODcr法)有良好的一致性。     

A simple colorimetric method for the assay of penicillin G salt and penicillamine by oxidation with iodate

A simple colorimetric procedure is described for determination of penicillin G salt and penicillamine. It is based on oxidation with potassium iodate at room temperature and measurement of the liberated iodine at 520 nm after extraction with carbon tetrachloride. Compared with other procedures, this method proved to be more rapid, highly reproducible and reasonably accurate. The relative standard deviation did not exceed 0.9% and 0.4% for penicillin and penicillamine, respectively. The procedure has been successfully applied to pharmaceutical preparations containing either of the two compounds.     

Syntheses,supramolecular structures and properties of six coordination complexes based on 5-sulfosalicylic acid and bipyridyl-like chelates

Six new complexes constructed by 5-sulfosalicylic acid and bipyridyl-like ligands (2,2′-bipy and 1,10-phen), namely [Cu₄(OH)₂(ssal)₂(phen)₄ · 7H₂O] (1), [Cu₄(OH)₂(ssal)₂(bipy)₄ · 2H₂O] (2), [Cd(Hssal)(bipy)] (3), [Cd(HL)₂(phen)₂] (4), [Cr(ssal)(bipy)(H₂O)₂ · 2H₂O] (5) and [Cr(ssal)(phen)₂] (6) (H₃ssal = 5-sulfosalicylic acid, H₂L = p-hydroxybenzenesulfonic acid, bipy = 2,2′-bipy, phen = 1,10-phen) were prepared under hydrothermal conditions and their structures were determined by single-crystal X-ray diffraction. Complexes 1 and 2 are both tetranuclear copper complexes with a stepped topology. In complex 3, a new coordination mode of the Hssal²⁻ group is reported in this work. During the synthetic process of complex 4, in situ decarboxylation of 5-sulfosalicylic acid into p-hydroxybenzenesulfonic acid is involved. Two chromium 5-sulfosalicylates (5 and 6) are reported for the first time. These new complexes display different supramolecular structures by O–H?O, C–H?O hydrogen bonds as well as π?π, C–H?π and O?π interactions. The results of magnetic determination show that ferromagnetic interactions exist in complex 1, however, antiferromagnetic interactions exist in 2.     

A colorimetric method for the determination of carboxylic acids

A new colorimetric method for the determination of carboxylic acids using bromocresol green reagent is established. The formed color follows Beer's Lambert law and is stable for 24 hr. The method is successfully applied for measuring the disappearance of volatile fatty acids in P. oxalicum culture media. The method is reproducable and is used also for the quantitative determination of carboxylic acids in Dowex 1-X8 eluates. A linear relationship between the pK₁ of different carboxylic acids and the calculated molar extinction coefficients of the color formed at 440 nm is demonstrated.     

A sensitive flow-injection method for determination of trace amounts of nitrite

A new sensitive colour reaction for nitrite determination is presented. In acidic medium, nitrite was reacted with safranine to form a diazonium salt which caused the reddish-orange dye colour of the solution to change to blue. The carrier stream, into which the sample solution was injected, was doubly distilled water. The reagent solution stream, which contained safranine dye, hydrochloric acid and potassium chloride, was mixed with the carrier in a 3-m length of silicon tubing (bore 0.5 mm) maintained at 30°C in a thermostatic bath. The absorbance intensity was measured at 520 nm. The detection limit was 20 ng ml⁻¹ and the RSD% of 20 injections of 1 μg ml⁻¹ of nitrite was 0.65%. Analysis can be done at a rate of up to 30 h⁻¹. Under the optimum conditions in the concentration range of 30–4000 ng ml⁻¹ of nitrite ion, a linear calibration graph was obtained (r=0.9999). The method was applied successfully to the determination of nitrite in sausages.     

流动注射-电化学氧化荧光法测定叶酸

提出了一种流动注射在线电化学氧化荧光分析新方法,并用于叶酸的测定。该方法将电化学氧化与流动注射荧光光度法很好的结合起来,通过在流路中的流通电氧化池将弱荧光物质叶酸氧化成为具有较强荧光的蝶呤-6-羧酸,并进行测定。在0.02 mol/L,pH 8的NaH2PO4-Na2HPO4缓冲溶液中,电解质NaCl浓度为0.01 mol/L,氧化电位为1.100 V时,氧化产物蝶呤-6-羧酸的最大λex和λem分别为370和460 nm。在此条件下,叶酸的浓度和荧光信号的增强强度在1.0×10-7~1.0×10-5g/mL的范围内有很好的线性关系,检出限为4.2×10-8g/mL(3σ)。已用于B族复合维生素及奶粉中叶酸的测定。     

Spectrophotometric FIA methods for determination of hydrogen peroxide: Application to evaluation of scavenging capacity

The determination of hydrogen peroxide (H₂O₂) and the evaluation of scavenging capacity against this species were performed using five colorimetric reactions, which were adapted to flow injection analysis. The reactions chosen were based on the oxidation of iodide (I⁻ method), on the formation of titanium-peroxide complex (TiP method), on the formation of titanium-xylenol orange-peroxide complex (TiXoP method), on the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB method) and on the co-oxidation of phenol-4-sulfonic acid and 4-aminoantipyrine (PSA/4-AAP method). The operational conditions were studied in order to improve the sensitivity of each method. Concerning to the method sensitivity, the ranking order was TMB method > I⁻ method > TiXoP method ∼PSA/4-AAP method > TiP method. All methods showed an excellent repeatability (RSD < 2%) and, except for I⁻ method, relative deviations from the reference method were <1.9%. The FIA manifolds were adapted to perform the determination of scavenging capacity against H₂O₂ and glutathione (GSH) was applied as model compound. TiP and TiXoP methods were not suitable as no inhibition or an increase of analytical signal was attained. PSA/4-AAP method was chosen for further application to dietary phenolics and pharmaceutical compounds, providing IC₅₀ values for those compounds that are fast reacting antioxidants.     

A simple method for the colorimetric and spectrophotometric determination of ferric iron in a large concentration range

Summary A method is described for the colorimetric or spectrophotometric determination of ferric iron based upon the measurement of the colour produced by hydrochloric acid. Concentrations within the range of 3 · 10^–5 M to 1.6 M may be determined by changeing the wave-lengthappropriately. Though the method is of lower sensitivity than other ones it offers the advantage of being simple and less time consuming. The errors amount to 4% in spectrophotometry and to 10% in colorimetry. If interfering ions are present the transmittance may be determined at two or more wave-lengths and results are obtained by appropriate calculation.

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Zusammenfassung Zur colorimetrischen oder spektralphotometrischen Bestimmung von dreiwertigem Eisen wird die Färbung mit Salzsäure verwendet. Es lä\t sich ein Konzentrationsbereich von etwa 3 · 10^–5 bis 1,6 m erfassen, wenn man zur Messung jeweils die geeignete Wellenlänge benutzt. Wenn das Verfahren auch weniger empfindlich als andere Methoden ist, so bietet es doch den Vorteil des geringen Zeitbedarfs und der einfachen DurchfÜhrung. Die Fehler betragen bis zu 4% (spektralphotometrisch) bzw. 10% (colorimetrisch). Störungen durch andere Ionen können durch Messung bei zwei oder mehreren Wellenlängen und entsprechende Berechnung umgangen werden.

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Contribution No. 120 from the Laboratory of Physical Chemistry, Faculty of Science, University of Zagreb.     

A simple colorimetric assay for muramic acid and lactic acid

The Barker and Summerson method of assaying lactic acid colorimetrically is modified to provide a simple and fast method of measuring lactic acid and other compounds such as muramic acid and glyceraldehyde that will release acetaldehyde on incubation in hot sulfuric acid. The assay can be done with open tubes and no more complicated equipment than a spectrophotometer. A further modification allows a relatively specific determination of formaldehyde.