Peak Height Method Research Articles

The influence of heating rate on the TL response of glow peaks of beta-irradiated CaF2 : Dy (TLD-200)

In the current study, the influence of heating rates between 1 and 50 °C s−1 on the response of TL glow peaks of CaF2 : Dy (TLD-200) has been investigated using a computer glow curve deconvolution (CGCD) method before and after application of the thermal cleaning method at 90 and 170 °C. The trapping parameters of the main glow peaks were also obtained using the CGCD method as a function of heating rate. The results showed that the peak temperatures of all glow peaks increase with increasing heating rates. The peak height method showed that the peak value (Im) in the glow curve below 230 °C is approximately constant for low heating rates up to 10 °C s−1, but slightly increased after that by about 10% with increasing heating rate. The integrated total area of low temperature peaks below 230 °C is more stable. It remains constant for heating rates less than 25 °C s−1, then it slowly increases by about 10% with increasing heating rate up to 50 °C s−1. The increase in the total area of low temperature peaks is reduced after the application of the thermal cleaning method. The peak intensities and total area of high temperature peaks above 260 °C decrease continuously with increasing heating rate in the investigated region of heating rates.

The use of inverse gas chromatography and gravimetric vapour sorption to study transitions in amorphous lactose

The aim of this study was to measure the glass transition of amorphous lactose under well-controlled temperature and humidity, using inverse gas chromatography (IGC) and to relate these data to gravimetric vapour sorption experiments. Amorphous lactose (spray-dried) was exposed to a stepwise increment in the relative humidity (%RH) under isothermal conditions in an IGC. At the end of each conditioning step a decane injection was made, and the retention volumes were calculated using the maximum peak height ( V max) method. The pressure drop across the column was recorded using the pressure transducers. These measurements were performed at various temperatures from 25 to 40 °C. The extent of water sorption at identical humidity (%RH) and temperature conditions was determined gravimetrically using dynamic vapour sorption (DVS). At each T, it was possible to determine: (1) a transition at low RH relating to the onset of mobility; (2) changes in retention volume relating to the point, where T g = T; (3) changes in pressure drop, which were related to the sample collapse. The rate and extent of water sorption was seen to alter at T g and also at a collapse point. Combinations of temperature and critical %RH (%cRH required to lower the dry glass transition temperature to the experimental temperature) obtained from IGC were comparable to those obtained from DVS. It was shown that at each T, the sample spontaneously crystallised, when T g was 32 °C below T. Inverse gas chromatograph can be used in this novel way to reveal the series of transitions that occur in amorphous materials.

The Use of Inverse Phase Gas Chromatography to Study the Glass Transition Temperature of a Powder Surface

To measure the glass transition temperature (Tg) at the surface of a hydrophobic particle at different temperatures and humidities, on the hypothesis that the surface may be plasticized to a different extent to the bulk due to slow water sorption giving a concentration gradient of water through the particles. Amorphous indomethacin was exposed to a range of relative humidities (RH) and temperatures in an inverse gas chromatograph (IGC). The retention volumes of decane were calculated at all conditions using center of mass (Vcom) and peak height (Vmax) methods. The extent of water sorption was determined gravimetrically. The Vcom retention volumes were found to deviate from Vmax results at certain critical humidities at each temperature. This was taken as a novel method for determining the Tg of the sample surface at different experimental conditions. Extrapolating the critical RH to lower the Tg to experimental temperature to 0% RH yeilded a Tg similar to literature values. Water sorption data provided valuable information on changes in mobility of the amorphous form as a function of temperature and RH. It is possible to use IGC to determine the Tg of the surface of particles at defined conditions. This overcomes the problems of conventional methods of assessing Tg, relating to disruption of water sorption on heating. This helps in the understanding of the physical form of the surface of hydrophobic particles and how and when the surface will start to crystallize.

Curing kinetic of the epoxy system badge n = 0/1,2 DCH by fourier transform infrared spectroscopy (FTIR)

The curing reaction of an epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n = 0) and 1,2-diaminocyclohexane (DCH) was studied by Fourier Trasform Infrared Spectroscopy (FTIR). From the infrared spectra using a peak-height method, that was based on the ratio of the height of the characteristic to reference absorbance peak, degree of conversion at different isothermal temperatures were calculated. From a kinetic study, the Horie et al. model was used; parameters such as rate constants and activation energies were determined. The results were compared to those obtained for same epoxy systems using scanning differential calorimetry (DSC). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3366–3372, 2001

A new method of determination of diffusion coefficients using capillary zone electrophoresis (peak-height method)

A new method of the determination of the diffusion coefficients,D, called “the peak-height method” has been developed. When the zone broadening of a species is solely caused by axial molecular diffusion, its diffusion coefficient can be calculated.

Determination of selenium at sub-μg/g-levels in biological materials by MIP-MS

Determination of Se in biological materials was attempted by microwave-induced plasma mass spectrometry (MIP-MS). (1) Serum samples were available after 10 times dilution with 0.5% nitric acid solution containing 0.1% Triton X-100. When oxygen gas was inserted into the plasma gas (nitrogen) in order to improve the combustion, the sensitivity was reduced to 45%. The detection limit of this method was 0.5 ng/mL. (2) Standard reference materials on commercial base were used to evaluate the accuracy of the Se determination by MIP-MS after microwave digestion. In samples like bovine liver and human hair with Se concentrations of more than 0.7 μg/g, the standard curve method after internal standard (IS) correction was acceptable. This procedure was unsuitable for samples with low Se concentrations such as milk powder (certified value of Se 0.11 μg/g), or plant leaf samples. (3) Instead of IS correction, the peak height of the spectrum was used for calculations from the matrix matched calibration curve. The results of all materials were close to the certified values, even at 25 ng/g. The detection limit of the MIP-MS with microwave digestion and IS correction was 0.05 ng/mL in standard solutions. The detection limit of the peak height method was 0.1 ng/mL and was estimated to be < 20 ng/g in plant materials.

Effects of resolution, peak ratio and sampling frequency in diode-array fluorescence detection in liquid chromatography

In this work, different methods of quantification that use both fluorescence spectral and retention time data were evaluated for accuracy and precision in diode-array fluorence detection in liquid chromatography. The methods evaluated include the peak height and peak area methods of quantification, an adaptive Kalman filter and the generalized rank annihilation method. All of these methods were used to estimate the concentration of a model led component in the presence of other partially resolved unmodelled components. The peak area and peak height methods of quantification gave the largest errors as the chromatographic resolution was decreased. The generalized rank annihilation method gave the most reliable results when the chromatographic resolution was greater than 0.3. However, this method was affected by retention time shifts between the calibration and unknown samples and the rate at which spectra were acquired.

Evaluation of a predictive curve-fitting method for processing data from flow systems: Part 1. Flow system with a mixing chamber

This paper describes the evaluation of a curve-fitting predictive approach to processing data from a flow system with a well-stirred mixing chamber. The method utilizes data from the leading edges of response peaks to predict the response that would be measured if sufficient sample were used to give a steady-state response. Advantages of the method under optimal conditions include a 10-fold reduction of dependency on sample volume relative to a peak-height method, a 20- to 65-fold reduction of dependency on flow-rate relative to a peak-area method, and extended linear ranges in situations involving nonideal detector response and situations involving slow reaction kinetics. Limitations include a requirement for larger sample volumes and degraded error coefficients for flow-rate relative to a peak-height method and chamber volume relative to a peak-area method. The new approach is judged to offer complementary features relative to peak-height and peak-area methods.

High-performance liquid chromatographic determination of acetone in blood and urine in the clinical diagnostic laboratory

A method for the determination of acetone in plasma or urine by high-performance liquid chromatography (HPLC) was developed. Plasma specimens are deproteinized with acetonitrile (1:1, v/v); 2,4-dinitrophenylhydrazine (DNPH) is added to the supernatant or to filtered urine samples, similarly treated with acetonitrile (2:1, v/v) to prevent crystallization of the synthesized phenylhydrazone. An aliquot (20 μl) of the reaction mixture was subjected to HPLC at ambient temperature using a reversed-phase Pecosphere 3 x 3 C 18 column with acetonitrile—water (45:55, v/v) as eluent at a flow-rate of 1 ml/min and detection at 365 nm. Hydroxyacetone and acetoacetate phenylhydrazone derivatives do not interfere. The identification of acetone by its retention time was confirmed by comparison with a laboratory-synthesized acetone DNPH derivative. The concentration of acetone, eluted within 3 min, was determined by the peak-height method. The detection limit was 0.034 mmol/l; the relative standard deviations were < 5% within run ( n  20) and < 10 % between run ( n  20).

A high-performance liquid chromatographic assay for the enantiomers of bevantolol in human plasma.

A method was developed and validated for the simultaneous analysis of (+)- and (-)-bevantolol in human plasma. The assay involves plasma protein precipitation, derivatization of racemic bevantolol to its diastereomeric thioureas with 2,3,4,5-tetra-o-acetyl-alpha-D-glucopyranosyl isothiocyanate, and solid-phase extraction of the diastereomers from 0.5 ml human plasma. Chromatographic separation was accomplished under isocratic conditions using a reversed-phase C-18 analytical column and mobile phase consisting of equal parts of 75 mM dibasic ammonium phosphate buffer (adjusted to pH 3.5 with phosphoric acid) and acetonitrile, with a detection wavelength of 220 nm. The absolute peak-height method was employed for quantitation. Retention times for the diastereomers of (+)- and (-)-bevantolol were 7.4 and 6.4 min, respectively. The method is suitable for the quantification of the enantiomers over a concentration range of 40 to 800 ng/ml per enantiomer.

Determination of Total Mercury in Human Hair Samples by Cold Vapor Atomic Absorption Spectrometry

A procedure for the determination of mercury in human hair by cold-vapor atomic absorption spectrometry with a new reaction vessel was developed and evaluated. To eliminate the so-called matrix effect, calibration was carried out in an isomedium under identical operating conditions. Under these conditions, the recovery percentage of mercury from human hair digest samples using the peak height method, was 102 +/- 2.2%. The method has been used for measuring the mercury level in hair of different groups of people living in the Nantes, France area.

Single-channel time-divided simultaneous multi-element atomic absorption spectrometry using an electrothermal atomiser

A single-channel time-divided atomic absorption spectrometric system is described that enables simultaneous multi-element data to be obtained using a multi-hollow cathode lamp, an electrothermal atomiser, one photomultiplier tube and a fast-response data acquisition system. No optical system (monochromator) is required. The emission intensity of the multi-hollow cathode lamp was higher than that of the conventional single-element hollow cathode lamps, especially for Cu and Fe. Precisions of ⩽5% were attained for both the peak-height and peak-area methods. The calibration graphs were linear in the ranges 20–200, 0.5–10 and 0.1–5 ng for Al, Cu and Fe, respectively. The proposed system is comparable to a conventional single-element electrothermal atomisation atomic absorption spectrometer with respect to precision and calibration ranges.

Determination of Carboxylesters by Indirect Photometric Ion Chromatography with an On-Line Enzyme Immobilized Column

Carboxylesters, carboxylic and inorganic anions were determined separately by photometric ion chromatography with an enzyme immobilized column. In the system, a carboxylesterase immobilized column (4.6 mm i.d.× 10 mm), which converted carboxylesters to carboxylic anions completely, was set between a sample injector and an analytical column. The other chromatographic conditions were as follows: an anion exchanger-type separation column (4.6 mm i.d.×250mm); phthalate-N-2-hydroxyethylpiperazine-N’-2-ethanesulfonic acid eluent (pH 6.5); an oven of temperature 40°C; a flow rate of 1.0ml/min; 280-nm UV detection; and an injection volume of 20 μl. Calibration curves for ethyl esters of acetate, propionate, butyrate and isovalerate were linear with the range 5×10-10mol to 1 × 100-7 mol according to the peak-height method; their detection limits were 10-10 mol levels. The present method was applied for the determination of carboxylesters in practical samples

Comparative Dosimetric Studies of Three LiF TL Phosphors

A comparative dosimetric study has been done on three low Z TL phosphors: LiF TLD-100, LiF (Mg,Cu) and LiF (Mg,Cu,P). The main TL (dosimetric) peak occurs at almost the same temperature (~205 oC) in all these phosphors. The relative TL sensitivities (peak height method) to 60Co gamma rays of LiF TLD-100, LiF (Mg,Cu) and LiF (Mg,Cu,P) were found to be 1, 3.3 and 25.4 respectively. Using our TLD reader system, the respective minimum measurable gamma ray doses were estimated to be 51, 34 and 4.6 µGy. The effect of different thermal treatments on the TL sensitivity was also studied.

An Assessment on Reliability of Quantitative Calculation Method for Obtaining Volume Fractions of TextureComponents With the Reduced ODF

The reliability and the accuracy of a quantitative calculation method for obtaining volume fractions of texture components of cubic materials were verified for the reduced ODFs terminated at l max = 22 and at l max = 16. It is concluded that an integrated width of r = ±10° around selected ideal orientations may be used in quantitative analysis of texture components. It is also shown that the conventional peak height method, which does not consider volume fractions, can only roughly give informations about texture components.

A Stability-Indicating Simultaneous Analysis of Acetaminophen and Hydrocodone Bitartrate in Tablets Formulation by HPLC

Abstract A rapid, simple, stability indicating, reversed phase high-performance liquid chromotographic (HPLC) method is presented here for direct and simultaneous quantitation of Acetaminophen and Hydrocodone Bitartrate in tablets dosage form at a ratio of 100:1. This procedure not only separated the two active components but also separated known impurity and degradation product of acetaminophen, p-aminophenol and p-chloroacetanilide. The method described here also separates other opiates, codeine sulfate and hydromorphone. In this procedure a radial pak cartridge packed with chemically bonded octadecylsilane (C18, 4 micron) as a stationary phase and (16:84) acetonitrile with phosphate buffer (pH 3.3) as the mobile phase were utilized. Detection was made with a uv-spectrophotometer at 215 nm. Quantitation was performed by peak height and external standard method. The average recovery at 100% label claim and the relative standard deviation of the two respective components, acetaminophen and hydrocodone were: 99.03%, 1.29% and 98.78%, 0.3%.

メキシレチンの血中濃度の検討

As the therapeutically effective blood level of mexiletine (MX), a recently marketed antiarrhythmic agent, is narrow at 0.5-2.0μg/ ml, the side-effect occurrence rate increases when the blood level of the drug exceeds 2.0μg/ ml. Therefore, close monitoring of the blood level of the drug is required after administration of the drug.We developed a new method for this measurement using high-performance liquid chromatography (HPLC), which is more convenient than the previous method by gas chromatography. The general procedure is as follows: An internal standard (4-methylmexiletine) is added to the serum sample, followed by the addition of a sodium hydroxide solution, and the whole is mixed well, then injected into an extrelut (manufactured by Merck Co.). The mixture is extracted with diethyl ether, and the extract is evaporated to dryness, and dissolved in an elution solvent, then subjected to the HPLC analysis.The values obtained by the peak-height method showed a lineality at 0.2-5.0μg/ ml. The recovery rate from the serum, to which MX was added at 2.5μg/ ml, was 80.4-90.0%. Coefficient validity was 3.1%. Good chromatographic data was also obtained in measurement of serum levels in patients administered MX.

Dynamic Range Enhancement for Flameless Zeeman Atomic Absorption Spectroscopy

A method of extending the dynamic range in flameless ZAAS (Zeeman atomic absorption spectroscopy) was proposed. The calibration curve in this method was made as follows: Slice the absorbance-time profile at a height Awt, which is higher than (1/20)A0 and lower than (1/2)Ap0, where A0 is the peak height and Wt is the width resulted from this slicing procedure. The slicing was done so as to give a constant Wt for all the aliquot of the solutions. It was shown that the dynamic range can be extended more than 10 times compared to the usual peak height method.

Determination of Hydroxy-Testos-Terones by Isocratic, High-Performance Liquid Chromatography with an Internal Standard

Abstract A simple, isocratic, reverse-phase HPLC method to separate nine oxidative metabolites of testosterone is described. An internal standard, adrenosterone, was used to quantltate metabolites by the peak height method. An application of this method to the metabolism of testosterone by rat lung microsomes is presented.

Quantitative determination of ethylene glycol using head-space chromatography

A simple, easy to do, and precise method in the determination of ethylene glycol in biological material is presented. After oxidation of ethylene glycol with sodiummetaperjodate is the resulting formaldehyde with sodium-borhydride to methanol reduced. The stoechiometric amount of resulting methanol is determined by Head-Space-Gaschromatography. The determination is made with peakheight method.