An automatic back titration method for microchemical analysis

An automatic back titration method for microchemical analysis is introduced, which is based on conventional volumetric analysis's principle and the use of flow injection analysis apparatus for the automation and microminiaturization of the process. The sample and a known, but excess amount of a calibrated reagent solution are injected and propelled into a titration cell, where their reaction takes place. The excess of the reagent is then titrated with a titrant containing an indicator and the end point is monitored photometrically. Since homogeneous mixing in the titration cell is obtained magnetically in the whole process, there is a linear relationship between the analyte's concentration and the volume of the titrant consumed. Nickel in the range of 10-70 g 1(-1) is determined by the above method, in which 30 microl of sample and 500 microl of EDTA are injected and the excess of EDTA is titrated with a standard zinc salt solution containing xylenol orange which could be blocked by nickel ion in a direct titration. This method is characteristic of low sample and reagent consumption, high sampling rate as high as 45 samples h(-1), negligible effect of sample's viscosity, small carry-over effect (lower than 0.14%), and very good precision, whose relative standard deviations are as small as 0.24%.     

Sorption–Desorption Photometric Determination of Trace Iron in Sodium, Potassium, and Ammonium Thiocyanates Using Polyurethane Foams

A reagent-free sorption photometric method for determining trace iron(III) in alkali-metal and ammonium thiocyanates was developed. The method consists in the adsorption of iron(III) thiocyanate complexes on polyurethane foams at pH 2–3 followed by the desorption of complexes with acetone and a measurement of the absorbance of solutions. The analytical range for iron was 0.5–20 g in a 0.2–2.5-g portion of salt. The determination limit and relative standard deviation were 2 × 10^–5% and 20–30%, respectively (n= 3; P= 0.95). The specific feature of the determination is that an additional photometric reagent is not introduced in the solution of the salt to be analyzed, because thiocyanate, that is, the matrix component of the test sample, acts as such a reagent.     

Slope comparison method (SCM) for the determination of trace amounts of silicate in ultrapurified water

A sensitive analytical method for the determination of trace amounts of silicate in ultrapurified water was developed. The method is based on the formation of an ion associate of molybdosilicate with malachite green (MG) and the collection of the ion associate on a tiny membrane filter (diameter: 5 mm, and effective filtering diameter: 1 mm). The ion associate formed on the membrane filter is dissolved together with the membrane filter in 1 ml of methyl cellosolve (MC) and the absorbance of MC solution is measured at 627 nm by a flow injection-spectrophotometric detection technique. In this method, silicate in the original sample (ultrapurified water) is concentrated as the ion associate into a small volume of MC to get high sensitivity. As sample concentration takes place, the small amounts of silicate contained in the reagents used also become concentrated as the ion associate into MC. The original sample volumes are varied and evaporated to an identical volume. Therefore, the reagent added is fixed to the same volume. The absorbance increase linearly with increase in the original sample volume will be due only to silicate in the original samples (ultrapurified water). The resulting slopes obtained by varying the sample volumes are compared with the slope of the calibration graph, and thus named the slope comparison method (SCM). The SCM facilitates a more sensitive and accurate evaluation of silicate concentration in the samples than either common calibration method (CCM) or standard addition method (SAM) because it compensates for the influence of trace amounts of silicate contained in chemicals, reagent solution and solvent used. The calibration graph was constructed from 0 to 0.25 ng ml⁻¹ of Si and the detection limit was 10 pg ml⁻¹ (ppt) when 30 ml of samples was used. The standard deviation and relative standard deviation from six measurements of the reagent blanks were 0.0012 and 3.5%, respectively.     

Flow-through sensor for the fluorimetric determination of cyanide

A fluorimetric method for the determination of cyanide, based on its reaction with pyridoxal-5-phosphate and the use of an anion-exchange resin (QAE Sephadex) located in the detector flow-cell, is proposed. The merging-zone flow-injection manifold used allows simultaneous injection of the sample and reagent, development of the reaction along the transport system, and retention of the reaction product in the flow-cell. The calibration graph for cyanide is linear over the range from 50 ng/ml to 3.0 mug/ml and the relative standard deviation and sampling frequency are 1.4% (for 2 mug/ml cyanide) and 10 per hr, respectively. The selectivity of the method is much better than that of the conventional fluorimetric and photometric flow-injection methods for cyanide.     

An automatic falling drop system based on multicommutation process for photometric chlorine determination in bleach

In this work an automatic photometric procedure for the determination of chlorine in bleach samples employing N,N′-diethyl-p-phenylenediamine (DPD) as chromogenic reagent is described. The procedure was based on a falling drop system where the analyte (Cl₂) was collected by a DPD solution drop (50 μL) after its delivery from the sample bulk that was previously acidified. The flow system was designed based on the multicommutation process assembling a set of three-way solenoid valves, which under microcomputer control afforded facilities to handle sample and reagent solution in order to control analyte delivering and solution drop generation. The analyte volatilization was improved by coupling online a little heating device. The detection system comprised a green LED (515 nm) and a phototransistor. Aiming to prove the usefulness of the proposed procedure a set of bleach samples was analyzed. Comparing the results with those obtained with reference method no significant difference at 95% confidence level was observed. Other profitable features such as a linear response ranging from 15 up to 100 mg L⁻¹ Cl₂ (R = 0.999); a detection limit of 4.5 mg L⁻¹ Cl₂ estimated based on the 3σ criterion; a relative standard deviation of 2.5% (n = 10) using a typical bleach sample containing 25.0 mg L⁻¹ Cl₂; a consumption of 55 μg of DPD per determination; and a analytical frequency of 20 determinations per hour were also achieved.     

An automatic flow injection analysis procedure for photometric determination of ethanol in red wine without using a chromogenic reagent

An automatic reagentless photometric procedure for the determination of ethanol in red wine is described. The procedure was based on a falling drop system that was implemented by employing a flow injection analysis manifold. The detection system comprised an infrared LED and a phototransistor. The experimental arrangement was designed to ensure that the wine drop grew between these devices, thus causing a decrease in the intensity of the radiation beam coming from the LED. Since ethanol content affected the size of the wine drop this feature was exploited to develop an analytical procedure for the photometric determination of ethanol in red wine without using a chromogenic reagent. In an attempt to prove the usefulness of the proposed procedure, a set of red wines were analysed. No significant difference between our results and those obtained with a reference method was observed at the 95% confidence level. Other advantages of our method were a linear response ranging from 0.17 up to 5.14 mol L⁻¹ (1.0 up to 30.0%) ethanol (R=0.999); a limit of detection of 0.05 mol L⁻¹ (0.3%) ethanol; a relative standard deviation of 2.5% (n=10) using typical wine sample containing 2.14 mol L⁻¹ (12.5%) ethanol; and a sampling rate of 50 determinations per hour.     

Determination of urea in serum by using naturally immobilized urease in a flow injection conductimetric system

A flow injection method was developed, aimed at the determination of urea in human serum. The system makes use of the naturally immobilized urease present in Canavalia ensiformis DC (jack bean). A column is filled with small pieces of this bean, and the sample (50 microliters) containing urea passes through it carried by a 1% NaCl solution. On leaving the column the stream is merged with an alkaline reagent (0.5 mol dm-3 NaOH; 0.5% disodium dihydrogen ethylenediaminetetraacetate). The ammonium ions, arising from the enzymatic reaction that occurs inside the column, are changed into the molecular form, which permeates a polytetrafluoroethylene membrane and is received in a de-ionized water acceptor stream. The ammonia ionizes causing an increase in the conductance, which is proportional to the urea content of the sample. About 40 samples can be processed in 1 h with negligible carry-over and with a relative standard deviation of 1% or less. The results are in agreement with those obtained by a standard spectrophotometric method.     

A rapid lateral flow test for the determination of total type B fumonisins in maize

A one-step lateral flow test was developed for the quantitative determination of total type B fumonisins in maize with a test range up to 4,000 μg/kg and a limit of detection of 199 μg/kg. The test presented gives a result within 4 min, including 1 min strip drying, and does not require any sample cleanup steps after a previous 3-min sample extraction. Quantitative readout with a compact photometric strip reader will also indicate the best suited measurement range when needed. The test is based on a competitive immunoassay format where a ready-to-use antibody–colloidal gold particle complex is mixed with 50 μL sample extract in a microwell and used as a signal reagent. The test strip is inserted into the well and the mixed content migrates onto the strip, which contains a test zone and a control zone. Mycotoxin–protein conjugate coated on the test zone captures free signal reagent, and colored particles concentrate, forming a visible line. The intensity of the test line is dependent on the total fumonisin concentration in the sample. Naturally contaminated quality-control maize material was used for matrix-matched calibration of photometric readout. The test presented is both quantitative and rapid, with no cross-reactivity to other mycotoxins. The applicability of the lateral flow test was shown by the screening of 23 naturally contaminated maize samples. Relative standard deviations ranged from 1.7 to 32.9%.     

硫酸铵中氮含量的电位滴定检测

建立一种酸碱电位滴定法直接测定硫酸铵中氮含量的方法。样品溶解后,可直接用氢氧化钠标准滴定溶液进行滴定。为了保证检测的准确度,分别使用硫酸铵高纯试剂和邻苯二甲酸氢钾基准试剂对氢氧化钠标准滴定溶液进行标定,并对标定结果进行比较,两种方法基本无差异。同时,通过适量硫酸的加入避免了样品中游离硫酸对检测结果的影响。该方法检测速度快、检测精度高、绿色环保、易于控制,非常适合于硫酸铵中氮含量的检测。将本方法与蒸馏后滴定法(仲裁法)检测结果进行比较,两种方法无显著性差异。采用本方法测得氮含量的加标回收率为99.9 %-100.3 %,相对标准偏差(RSD,n=5)为0.03 %-0.05 %。分别使用实验方法和蒸馏后滴定法测定不同样品的氮含量,结果相吻合。     

一种自动微量滴定新方法

本文依据传统滴定分析原理，利用流动注射装置提出一种新的自动微量滴定方法，它不仅具有流动注射滴定分析法简便快速，试剂和试样消耗少，仪器装置简单等优点，而且测定信号怀被测组分的浓度直接成线性关系，结果的准确度和精度优于一般流动注射滴定方法。通过用盐酸滴定氢氧化钠进行验证，相关系数为０．９９９９，相对标准偏差（ＲＳＤ）为０．４％。     

Flow-injection photometric determination of mercaptans in light oil products with chromatomembrane extraction

A procedure was developed for the flow-injection photometric determination of mercaptans in light oil products. The use of sodium nitroferricyanide as the photometric reagent at 540 nm provides a detection limit of mercaptan sulfur of 0.3 mg/L at a volume of the sample of 3 mL; the analytical range is from 1 to 50 mg/L.     

Synthesis and characterization of an ion-imprinted polymer for selective solid phase extraction of thorium(IV)

A new surface ion-imprinted composite polymer containing 3-methyl-1-phenyl ?4-(cis-acylbutenoic acid)-2-pyrazolin-5-one as the functional reagent is presented that is capable of extracting and preconcentrating traces of Th(IV) ion prior to its photometric determination. Parameters affecting the recovery of Th(IV) such as acidity, shaking time, initial concentration of Th(IV), elution condition, sample flow rate, and influence of potentially interfering ions were investigated. The maximum uptake capacity of this material and that of the non-imprinted polymer at pH 4.5 are 56.8 and 26.3?mg?g^?1, respectively. Recovery exceeds 95% and is complete within 5?min. A Langmuir isotherm fits the experimental data. The relative selectivity factor for Th(IV)/U(VI), Th(IV)/La(III), and Th(IV)/Ce(III) are 50.8, 78.3, and 82.6, respectively. The relative standard deviation is <2.5%, the detection limit is 0.54???g?L^?1 (3??). The imprinted polymer was coupled to spectrophotometry to separate and determine trace levels of Th(IV) in a soil standard material with satisfactory results.

Turbidimetric determination of sulphate in plant digests and natural waters by flow injection analysis with alternating streams

An improved flow injection system with alternating streams of reagents is described for the turbidimetric determination of sulphate. Samples are injected into an inert carrier stream which is mixed with barium chloride to form a barium sulphate suspension. The range of the method can be extended to low concentrations by continuously adding sulphate to the sample carrier stream. System performance is improved by automatic alternate pumping of the reagent stream and an alkaline EDTA solution at high flow rate. All operations are controlled by an electronically-operated proportional injector-commutator. Even after routine analysis of 3000 samples of natural waters and plant digests, baseline drift was not observed. The proposed method is suitable for 120 samples per hour with a relative standard deviation less than 1% for sulphate concentrations in the range 1–30 ppm (waters) or 5–200 ppm (plant digests). The results compare well with those obtained by standard manual procedures.     

热解齐化-原子吸收光谱法测定红土镍矿中汞含量

经过条件试验,建立了热解齐化-原子吸收光谱法直接测定红土镍矿中汞含量的方法。样品中汞含量在57～1752μg／kg,重复测定的相对标准偏差（RSD）在1．6％～5．3％（n=11）,回收率在92．79％～94．77％,与冷原子吸收光谱法的方法间相对偏差为5．18％～11．93％。方法准确、快速、样品用量少、无试剂污染,适合于批量样品的测试,有应用和推广价值。     

Quantitative analysis of an oligomeric hindered amine light stabilizer in polypropylene by matrix-assisted laser desorption/ionization mass spectrometry using a solid sampling technique

A small amount of an oligomeric hindered amine light stabilizer (HALS) (Adekastab LA-68LD) in polypropylene (PP) materials was directly determined by solid sampling matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) using an internal standard method. First the matrix reagent (dithranol), 20 mg, and the empirically selected internal standard, angiotensin I (MW = 1296.5), 5 microg, were premixed in the solid state. The matrix mixture was then co-ground with the PP sample containing the HALS in liquid nitrogen using a freezer mill. The powdered sample mixture was spotted on the sample plate, suspended in ion-exchanged water, dried to adhere on the plate, and subjected to MALDI-MS. Three series of the HALS components accompanied by the oxidized species were clearly observed as their molecular ions (M*+)) along with that of the internal standard in the mass spectra. A fairly good linear relationship (R2 = 0.9991) with a relative standard deviation of ca. 11% was observed between the relative peak intensities of the HALS components and the HALS contents ranging from 0.1-2.5 wt%, which could be used as the calibration line to determine the HALS content in PP composites directly by MALDI-MS. The UV-exposed PP composite samples were evaluated by this method to interpret the photostabilizing action of HALS in the PP materials based on the observed change in the relative abundances of the original and oxidized HALS components as a function of UV-exposure time.     

Comparison of pyrolysis-mass spectrometry with high performance liquid chromatography for the analysis of vancomycin in serum

Mass spectrometry coupled with a pyrolysis inlet system (Pyr-ms) is compared with high performance liquid chromatography (HPLC) for the determination of vancomycin and its crystal degradation products (CDP-Is) in human serum. Quantitative analysis of Pyr-ms was performed by selected ion monitoring (SIM) method at 108 mass:charge (m/z) of pyrolysis product of vancomycin. 3-Nitroaniline (138 m/z) was used as an internal standard. A mu-Bondapak C(18) column and the gradient mobile phase of triethylamine buffer (pH 6.2), acetonitrile and tetrahydrofuran and a photometric detection at 205 nm are found to be the optimum conditions for the HPLC determination of vancomycin and CDP-Is. The limit of detection (LOD=1 ng ml(-1)), linearity (1 ng ml(-1)-10 mg ml(-1)), relative standard deviation (R.S.D.=1%), time analysis (1/2 h) and sample volume (50 mul) of Pyr-ms are far better than of the HPLC method. However, the HPLC method can individually determine the concentration of vancomycin and its degradation products.     

脂肪醇聚醚产品及脂肪醇羟值的快速测定

以4-二甲氨基吡啶为催化剂,过量乙酸酐为乙酰化试剂,吡啶为溶剂,用电位滴定法快速测定脂肪醇聚醚产品及脂肪醇羟值,并对催化剂、反应条件、系统的适应性进行了探讨。用该方法对5种不同羟值的脂肪醇聚醚及脂肪醇样品进行了测定,测定结果的相对标准偏差小于0.5%(n=6),且测定结果与国标法测定结果相符合,相对误差在±1%之内。     

Photometric determination of cobalt with nitroso-R-salt

The chelate is quantitatively formed only in the pH range 6.5-7.5. Despite the large stability constant, a large excess of reagent is required to suppress interferences. The most suitable wavelength for the photometric measurement is 500 nm, where the molar absorptivity is 1.607 x 10(4) 1.mole(-1). cm(-1). The procedure given allows determination of 8 x 10(-4)% Co in a l-g sample. The standard deviation for cobalt is 2.1 mug/100 ml (f = 19). Applications to analysis of iron and steel, nickel, copper, ores and silicates are given.     

Detection and determination of phenylhydrazine

Cacotheline has been employed successfully as a new qualitative and quantitative reagent for phenylhydrazine. The spot-test is performed at pH 4.5-5.5 with a limit of detection of 0.5 mug ml in the sample solution. The method can be extended to the colorimetric estimation and photometric titration of phenylhydrazine with cacotheline. Beer's law is obeyed over the range 0.1-2 mg.