Fourier transform infrared determination of CO2 evolved from carbonate in carbonated apatites

A quantitative method based on FTIR has been developed to determine carbonate in synthetic apatites. The method measures the evolved CO2 after reaction of 50 mg apatite with 2 mL of hydrochloric acid (0.5 M) in a reaction vessel, heated to 40 degrees C. The CO2 evolved was swept by a carrier of nitrogen to a laboratory-made infrared gas cell of 39 mm pathlength and 490 microL volume. The signals were recorded as a function of time and the areas of the chemigram peaks obtained from the measurements in the wavenumber range of 2,500-2,150 cm(-1), were interpolated using a calibration curve. The method can be used to study apatites with carbonate contents below 0.2% with a sampling frequency of 8 h(-1).     

Fourier transform infrared spectrometric determination of Ziram

A procedure has been developed for vapour-phase Fourier transform infrared determination of Ziram, a dithiocarbamate pesticide. The method is based on the evolution of CS₂, after decomposition of the dithiocarbamate with diluted H₂SO₄ at 50°C. The CS₂ evolved was swept by a carrier flow of nitrogen to a laboratory-made infrared gas cell of 39 mm pathlength and 490 μl volume. The signals were registered as a function of time. The area of peaks obtained from absorbance measurement in the wavenumber range between 1600 and 1450 cm⁻¹ were interpolated in a calibration line established from Ziram standards treated in the same way as samples. The method provided an absolute limit of detection of 0.055 mg, a variation coefficient of the order of 6% for an analyte mass of 50 mg, and an analysis time of 3.5 min.     

Flow injection Fourier transform infrared determination of nicotine in tobacco

A fully automated procedure is proposed for the Fourier transform infrared (FTIR) determination of nicotine in tobacco. The method is based on the on-line extraction of nicotine with CHCl3. Samples, weighed inside empty extraction cartridges, were humidified with NH3 and the cartridges were installed in a flow manifold in which they were extracted with 2 ml CHCl3 for 2 min, then 400 microliters of the extract were introduced into a micro-flow cell using a carrier of CHCl3 and the IR spectrum was registered continuously. The absorbance, in the wavenumber range 1334-1300 cm-1, was measured, obtaining a peak as a function of time. The area of this peak was interpolated on a calibration line established from standard solutions of nicotine in chloroform treated in the same way as samples. The method provided a limit of detection of 0.1 mg ml-1 nicotine, an RSD lower than 2% and a sampling frequency of the whole procedure of 6 h-1. Results obtained for natural samples of cut tobacco and cigar compared well with those obtained by a batch FTIR procedure, involving an off-line extraction with a total time of 16 min. However, for yellow tobacco cigarette, an on-line extraction time of 10 min was required to obtain a good recovery of nicotine.     

Vapour phase Fourier transform infrared spectrometric determination of thiourea

A novel and precise procedure for the determination of thiourea based on vapour-generation Fourier transform infrared spectrometry is described. A 4 ml volume of 1.4% m/v iodine solution was injected into a glass vessel containing 5 ml of thiourea and 0.2 ml of 1 M sodium hydrogencarbonate solution. The CO2 evolved under these conditions was swept by a stream of nitrogen to an infrared gas cell. At 200 s after injection of the iodine solution, the vapour phase FTIR spectra were continously recorded, as a function of time, between 2500 and 2200 cm(-1), which includes the CO2 absorption band at 2350 cm(-1). From the absorbance data in the 2399-2284 cm(-1) range, integrated absorbance measurements were obtained providing transient recordings which correspond to the absorbance of CO2 in the selected wavenumber range. The method provided a limit of detection of 10 ppm of thiourea, a throughput of 14 samples h(-1) and an RSD of 1.1% for three independent analyses of a 500 ppm thiourea solution. Results obtained for a series of real samples compared well with those obtained using potentiometric titration as a reference method.     

Fourier transform infrared determination of caffeine in roasted coffee samples

A new procedure has been developed for the FT-IR determination of caffeine in roasted coffee samples. The method involves wetting the coffee samples with a 0.25 M aqueous NH₃ solution, extracting the caffeine with CHCl₃, and measuring absorbance at 1659 cm^–1 using a baseline established between 1900 and 830 cm^–1. The procedure proposed is fast, only requiring a total extraction time of 16 min for each sample, and provides a drastic reduction of the organic solvent consumed, from the 200 mL diethyl ether and 50 mL CHCl₃ required for each sample by the reference chromatographic UV-spectrometric determination to only 5 mL CHCl₃. The method provides a limit of detection of the order of 3 mg L^–1 caffeine and a relative standard deviation of 0.4% for 3 independent analyses of a sample containing 18.6%mg/g caffeine. The accuracy of the FT-IR procedure was evaluated from recovery experiments on spiked samples providing values from 94.4 to 100.1% and from the comparison of results found for a series of commercial samples, by both FT-IR and the official reference procedure. Received: 9 July 1999 / Revised: 23 September 1999 / /Accepted: 24 September 1999     

Fourier transform infrared determination of caffeine in roasted coffee samples

A new procedure has been developed for the FT-IR determination of caffeine in roasted coffee samples. The method involves wetting the coffee samples with a 0.25 M aqueous NH3 solution, extracting the caffeine with CHCl3, and measuring absorbance at 1,659 cm(-1) using a baseline established between 1,900 and 830 cm(-1). The procedure proposed is fast, only requiring a total extraction time of 16 min for each sample, and provides a drastic reduction of the organic solvent consumed, from the 200 mL diethyl ether and 50 mL CHCl3, required for each sample by the reference chromatographic UV-spectrometric determination to only 5 mL CHCl3. The method provides a limit of detection of the order of 3 mg L(-1) caffeine and a relative standard deviation of 0.4% for 3 independent analyses of a sample containing 18.6%mg/g caffeine. The accuracy of the FT-IR procedure was evaluated from recovery experiments on spiked samples providing values from 94.4 to 100.1% and from the comparison of results found for a series of commercial samples, by both FT-IR and the official reference procedure.     

Fourier transform infrared spectrometric determination of Malathion in pesticide formulations

An environmentally friendly methodology has been developed for quality control analysis of emulsifiable concentrate pesticide formulations containing Malathion as active ingredient, using flow injection analysis (FIA)-Fourier transform infrared (FTIR) spectrometry. Five microlitres samples were directly injected into a 3 ml closed FIA manifold, in which 2 ml of CHCl₃ was re-circulated at 1.96 ml min⁻¹. After homogenisation and sample measurement, 2 μl volumes of a Malathion standard were injected, taking absorbance measurements after each injection. Peak height of the chemigrams, established from peak area values between 1027 and 1017 cm⁻¹, corrected with a baseline fixed from 1087 to 993 cm⁻¹ were employed for Malathion quantification using the standard addition approach, after reaching the steady state for every injection. A limit of detection of 12 μg ml⁻¹ was achieved. Results found by standard addition-FTIR in commercially available samples showed a good correlation with those obtained by the reference gas chromatography-flame ionisation detection procedure.     

Fourier transform infrared study of low-temperature CO adsorption on CuMgAl-hydrotalcite

Single-phase CuMgAl ternary hydrotalcite with (Cu+Mg)/Al atomic ratio of 3.0 and Cu/Mg atomic ratio of 1.0 was synthesized by coprecipitation. Thermoanalytical studies of this sample showed transformations in three stages in the temperature range up to ca. 900 K yielding mainly CuO phase. In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic measurements showed the presence of carbonates even after calcination of the sample at 973 K. The genesis of Cu+ sites during thermal treatment in vacuo at different temperatures for this sample was followed by IR spectroscopy of CO adsorbed at low temperature. Essentially no Cu+ sites are present on a sample calcined at 723 K, consistent with X-ray photoelectron spectroscopic (XPS) data. However, sample subjected to activation (1 h of O2 treatment at 723 K followed by 1 h of evacuation at the same temperature) upon CO adsorption at 85 K unambiguously showed the presence of Cu+ sites. 12CO-13CO coadsorption studies confirmed the presence of dicarbonyls, which are converted to linear Cu+-CO species during evacuation at 85 K. Concentration of the accessible Cu+ sites increased with the increase in activation temperature up to 873 K and decreased with a further temperature rise. The copper sites on the sample are heterogeneously distributed and their distribution depends on the activation temperature. Two routes of reduction of Cu2+ to Cu+ are proposed: (i) autoreduction during evacuation and (ii) reduction by CO.     

Solid sampling Fourier transform infrared determination of Mancozeb in pesticide formulations

A series of approaches have been assayed for FTIR determination of Mancozeb in several solid commercial fungicides using different calibration strategies. The simplest procedure was based on the use of the ratio between the absorbance of a characteristic band of Mancozeb and that of a KSCN internal standard measured in the FTIR spectra obtained from KBr pellets. It was employed the quotient between peak height absorbance values at 1525 cm⁻¹ for Mancozeb and 2070 cm⁻¹ for KSCN. In these conditions a precision as relative standard deviation (RSD) of 0.6% and a relative accuracy error of 0.8% (w/w) were found. For complex formulations, containing other compounds with characteristic absorption bands at different wavenumbers than Mancozeb, one of them was used as internal reference being employed the standard addition approach. In this case, the Mancozeb bands at 1525 cm⁻¹ or at 1289 cm⁻¹ were employed, being used the ferrocyanide band at 2075 cm⁻¹ as internal reference. RSD values between 0.7-1.4% and a relative accuracy error of 3% (w/w) were found. A third strategy was based on the use of partial least squares (PLS) calibration. A reference set was prepared mixing Mancozeb, Kaolin, Cymoxanil and KBr, being predicted the Mancozeb concentration in pesticide formulations by using the quotient between absorbance bands of Mancozeb and those of Cymoxanil. In these conditions a relative accuracy error of 0.6% (w/w) and a relative standard deviation of 1.3% were found.     

Seafood freshness determination through vapour phase Fourier transform infrared spectroscopy

A new vapour-phase manifold has been developed to determine trimethylamine (TMA) in fish and cephalopod samples by Fourier transform infrared (FT-IR) spectroscopy. Samples were treated off-line for 1 h with trichloroacetic acid (TCA), filtered and washed. The obtained extracts were aspirated and alkalinized with NaOH 2.0 M, in an on-line system. TMA was separated from the solution in a gas phase separator and then transported by means of a nitrogen carrier into a home made 10 cm pathlength IR gas cell, where the corresponding FT-IR spectra were acquired by accumulating 30 scans per spectrum with 2 cm⁻¹ nominal resolution. The method was applied to the determination of TMA in natural samples providing concentration values statistically comparables with those obtained by a head space gas chromatography (HS-GC) reference procedure. The sample throughput by FT-IR is increased by a factor of 6 as compared with HS-GC.     

Vapour phase Fourier transform infrared spectrometric determination of L-cysteine and L-cystine

A novel and selective procedure for the determination of l-cysteine and l-cystine based on vapour-generation Fourier transform infrared spectrometry is described. Potassium iodate solution was injected into a glass vessel containing l-cysteine and/or l-cystine. The evolved CO was swept by a stream of nitrogen to an infrared gas cell. The vapour phase FTIR spectra were continuously recorded, as a function of time, between 2240 and 2000cm(-1), which includes the CO absorption band. The maximum absorbance at 2170cm(-1) was selected as a measurement criterion. The calibration curve was linear over the range 6-300mgL(-1). The method provided a limit of detection of 2mgL(-1) of l-cysteine, a throughput of 12samples h(-1) and an R.S.D. of 1.76% for five independent analyses of a 75mgL(-1)l-cysteine solution. For the measurement of l-cysteine and l-cystine separately, after measuring total concentration of l-cysteine and l-cystine, l-cysteine was masked with p-benzoquinone at a pH of 3 and individual l-cystine was determined. The amount of l-cysteine was obtained by difference. The method was applied to the determination of l-cysteine and l-cystine in pharmaceutical and urine samples. Results obtained for real samples compared well with those obtained by a reference spectrometric method.     

Ultra-rapid-scanning Fourier transform infrared spectrometry

Several applications of Fourier transform infrared (FT-IR) spectrometry are discussed where both conventional rapid-scanning interferometers and step-scan interferometers are unable to provide the needed information. A new interferometer is described by which it is possible to acquire interferograms with 0.25 cm optical path difference (4 cm⁻¹ spectral resolution) in less than 1 ms. The moving element of this interferometer is a tilted mirror that continuously rotates at a speed of up to 500 Hz. The performance of this spectrometer is demonstrated by examining the spark-initiated combustion of ethane and methane in air. The formation of vibrationally excited CO₂ and H₂O, with lifetimes approaching 50 ms, was observed.     

Fourier transform infrared spectroscopic study of water-in-supercritical CO2 microemulsion as a function of water content

Fourier transform infrared (FT-IR) spectrum of water-in-supercritical CO(2) microemulsion was measured at 60 degrees C and 30.0 MPa over a wide range of water/CO(2) ratio from 0.0 to 1.2 wt % to study the distribution of water into CO(2), interfacial area around surfactant headgroup, and core water pool. The microemulsion was stabilized by sodium bis(1H,1H,2H, 2H-heptadecafluorodecyl)-2-sulfosuccinate [8FS(EO)(2)] equimolarly mixed with sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-hexanesulfonate [FC6HC4] or with poly(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether [TMN-6]. The signal area of the O-H stretching band of water suggested that the number of water molecules in the microemulsion increases linearly with the water/CO(2) ratio, except for a slow initial increase below 0.4 wt % due to a part of water dissolved in CO(2). The amount of water in CO(2) was evaluated by decomposing the bending band of water into two components, one at lower frequency ascribed to water in CO(2) and the other at higher frequency to water in the microemulsion. The decomposition confirmed that CO(2) is saturated with water at the water content of 0.4 wt %. It was also revealed, from the symmetric SO stretching frequency of the surfactant, that the sulfonate headgroup is completely hydrated at the water/CO(2) ratio of 0.4-0.5 wt %. The results demonstrated that water is introduced preferentially into CO(2) and the interfacial area at small water content, and then is loaded into the micelle core after the saturation of CO(2) with water and the full hydration of the surfactant headgroup.     

Observation of CO(2) in Fourier transform infrared spectral measurements of living Acholeplasma laidlawii cells

In monitoring the time course of conformational disorder by Fourier transform infrared spectroscopy for intact Acholeplasma laidlawii cells grown at 37 degrees C on binary fatty acid mixtures containing oleic acid and for cells grown on pure palmitic acid, an absorption band at 2343 cm(-1) was observed. The band intensity was found to increase with time. This band was not observed in the spectra for isolated membranes. It is suggested that the 2343 cm(-1) band is due to CO(2) dissolved in water, most likely produced at the final point of fermentation of amino acid by this microorganism.     

Fourier transform infrared spectrometric strategies for the determination of Buprofezin in pesticide formulations

Two different strategies for Buprofezin determination, an off-line extraction and stopped-flow determination and an automated procedure, based on the on-line extraction of Buprofezin samples with chloroform and flowing action analysis-fourier transform infrared (FIA-FT-IR) spectrometric measurement of the extracts, have been developed. For the treatment of the off-line extraction mode, data a three-factor partial least squares (PLSs) calibration was developed, using the region from 1465.7 to 1342.3 cm⁻¹ with a single point baseline defined at 2051.9 cm⁻¹ and based on the use of chloroform solutions of Buprofezin. The method provides a R.S.D. <0.1%, recoveries of the order of 100% and generates 25 ml of CHCl₃ waste for each sample.On the other hand, the recommended FIA method provided a 3 s limit of detection of 20 μg ml⁻¹, which corresponds to 0.12% (w/w) in the solid sample, a repeatability of 0.8% as R.S.D., and a maximum sampling frequency for the whole procedure of 6 h⁻¹.The waste generation, being lower than the off-line strategy, is only 3 ml of CHCl₃ per sample.     

Factors stabilizing the paramagnetic radicals CO 2 - , CO 3 - , and CO 3 3- in natural carbonated apatites

Carbon radicals in natural magmatic, sedimentary, biological, and synthetic carbonated apatites are studied by ESR. The thermal and radiation behavior of the radicals is studied. The effect of composition on spectrum intensity and the ratio of radicals on their stabilization in a matrix are investigated; this made it possible to establish two positions and two forms of carbon as well as two variants of its location in the structure: in the form of CO ₃ ^2- on the PO ₄ ^3- site, in the form of CO₂ on the surface, as a complex with structurally bound water and without it It is established that bound water in molecular form H₂O affects the observed ESR spectra, the dynamic characteristics of carbonate radicals, and their quantitative relations. Translated fromZhumal Strukturnoi Khimii, Vol. 39, No. 5, pp. 821–842, September–October, 1998. This work was supported by RFFR grants No. 94-05-16537 and 97-05-65305.     

Fourier transform infrared spectroscopic determination of cypermethrin and deltamethrin in emulsifiable concentrate formulations

Fourier tranform infrared (FT-IR) spectroscopic method has been developed for determination of cypermethrin and deltamethrin in emulsifiable concentrate formulations. The known concentration of formulation was subjected to preparative thin layer chromatography and the active ingradient zone was scrapped from the plate. Pyrethroids were eluted from the adsorbent with chloroform and estimated by measuring the ester carbonyl absorption band at 1749 cm(-1) in cypermethrin and at 1743 cm(-1) in deltamethrin using base line technique. Recoveries of cypermethrin and deltamethrin from commercial and laboratory prepared formulations were 90 to 97% in both the cases. The validity of FT-IR method was confirmed by comparing the results with standard HPLC method.     

Trends in Fourier transform infrared spectroscopic imaging

Fourier transform infrared (FTIR) spectroscopic imaging is a relatively new method that has received great attention as a new field of analytical chemistry. The greatest benefit of this technique lies in the high molecular sensitivity combined with a spatial resolution down to a few micrometers. Another advantage is the ability to probe samples under native conditions, which allows new insights into samples without the need for fixation, stains, or an additional marker. Advances in instrumentation have made FTIR spectroscopic imaging the tool of choice for an increasing number of applications. The main applications are in the bioanalytical chemistry of cells and tissue, polymers, and recently as well as in homeland security. This report gives a short overview of current developments and recent applications. Figure FTIR image of a polymer blend reveals the chemical composition. Online Abstract Figure (365 KB).     

Polarization modulation Fourier transform infrared spectroscopy

Polarization modulation Fourier transform infrared spectroscopy can be measured by either double modulation FTIR or interferometric modulation FTIR techniques. The principles of both techniques are presented with examples of representative measurements. The relative advantages and disadvantages of each method are compared.     

傅里叶变换近红外光谱法快速检测人血清生化成分

应用傅里叶变换近红外光谱透射技术结合偏最小二乘法(PLS)建立了人血清中7种生化成分的定标模型,利用内部交叉验证和自动优化功能对定标模型进行了优化,确定了最优建模参数。模型对人血清中总胆固醇、甘油三酯、总蛋白、白蛋白、载脂蛋白B、低密度脂蛋白胆固醇、葡萄糖定标样品集的预测值与化学值的相关系数r分别为0.9011、0.9593、0.9249、0.761、0.8831、0.5191、0 9148,预测校正标准误差RMSECV分别为15mg/dL,21.6mg/dL,2 66g/L,3 96g/L,0.091g/L,16.2mg/dL,0.49mmol/L。