Calibration Substance Research Articles

Calibration of Dual-Channel Raman Spectrometer via Optical Frequency Comb.

The portable Raman spectrometer boasts portability, rapid analysis, and high flexibility. It stands as a crucial and powerful technical tool for analyzing the chemical composition of samples, whether biological or non-biological, across diverse fields. To improve the resolution of grating spectrometers and ensure a wide spectral range, many spectrometer systems have been designed with double-grating structures. However, the impact of external forces, such as installation deviations and inevitable collisions, may cause differences between the actual state of the internal spectrometer components and their theoretical values. Therefore, spectrometers must be calibrated to establish the relationship between the wavelength and the pixel positions. The characteristic peaks of commonly used calibration substances are primarily distributed in the 200-2000 cm-1 range. The distribution of characteristic peaks in other wavenumber ranges is sparse, especially for spectrometers with double-channel spectral structures and wide spectral ranges. This uneven distribution of spectral peaks generates significant errors in the polynomial fitting results used to calibrate spectrometers. Therefore, to satisfy the calibration requirements of a dual-channel portable Raman spectrometer with a wide spectral range, this study designed a calibration method based on an optical frequency comb, which generates dense and uniform comb-like spectral signals at equal intervals. The method was verified experimentally and compared to the traditional calibration method of using a mercury-argon lamp. The results showed that the error bandwidth of the calibration results of the proposed method was significantly smaller than that of the mercury-argon lamp method, thus demonstrating a substantial improvement in the calibration accuracy.

Ultra-Fast Polarity Switching, Non-Radioactive Drift Tube for the Miniaturization of Drift-Time Ion Mobility Spectrometer.

Drift-time ion mobility spectrometer (DT-IMS) is a promising technology for gas detection and analysis in the form of miniaturized instrument. Analytes may exist in the form of positively or negatively charged ions according to their chemical composition and ionization condition, and therefore require both polarity of electric field for the detection. In this work the polarity switching of a drift-time ion mobility spectrometer based on a direct current (DC) corona discharge ionization source was investigated, with novel solutions for both the control of ion shutter and the stabilization of aperture grid. The drift field is established by employing a switchable high voltage power supply and a serial of voltage regulator diode, with optocouplers to drive the ion shutter when the polarity is switched. The potential of aperture grid is stabilized during the polarity switching by the use of four diodes to avoid unnecessary charging cycle of the aperture grid capacitor. Based on the proposed techniques, the developed DT-IMS with 50 mm drift path is able to switch its polarity in 10 ms and acquire mobility spectrum after 10 ms of stabilization. Coupled with a thermal desorption sampler, limit of detection (LoD) of 0.1 ng was achieved for ketamine and TNT. Extra benefits include single calibration substance for both polarities and largely simplified pneumatic design, together with the reduction of second drift tube and its accessories. This work paved the way towards further miniaturization of DT-IMS without compromise of performance.

Содержание двойных связей в полиэтилене

The content of double bonds in high-pressure polyethylene of various brands obtained from Russian and foreign manufacturers was studied. The essence of the method was to build a calibration curve on an infrared Fourier spectrometer for standard substances with a previously known arrangement of the double bond, saturation of double bonds in the initial polyethylene using gaseous bromine, and subsequent assessment of the locations and number of double bonds in the studied brands of high pressure polyethylene. The calibration substances were trans-4-decene with a purity of 96%, 1-decene with a purity of 95%, and 2-methyl-1-heptene with a purity of 98%. To record infrared spectra, calibration substances were dissolved in carbon disulfide with a purity of 99.5%. The spectra of the calibration substances were recorded in the transmission mode. The recording of the spectra of the high-pressure polyethylene samples was carried out in the reflection mode. To calculate the molar adsorption coefficient of individual calibration substances, the areas of the peak absorption of individual substances were allocated. The Peak Separation NETZSCH software was used for this purpose. For all analyzed samples, both brominated and not brominated, the ratio of the areas of absorption peaks was calculated. For each sample of high-pressure polyethylene, the content of trans-vinylidene, vinyl, and vinylidene groups C=C per 1000 carbon atoms was determined. The total number of double bonds was calculated as the sum of all analyzed bonds contained in the polyethylene sample. The accuracy of the analysis method performed by a single laboratory on a single sample is ±10% of double bonds per 1000 carbon atoms. The technique allows one to evaluate such a characteristic of low density polyethylene as the content of double bonds. This characteristic is essential for the efficient development of crosslinkable polyethylene compounds.

MEMBRANES MODIFIED BY NANOCOMPOSITES OF HYDRATED ZIRCONIUM DIOXIDE AND OXIDIZED GRAPHENE

Organo-inorganic membranes were obtained by impregnating ultrafiltration membranes with a composite modifier - zirconium (IV) hydroxide, containing oxidized graphene (0.5 wt.%). The modifier was precipitated in the active layer of the membrane, thus forming a "secondary active layer". The layer thickness calculated according to the Kozeny-Carman equation is 0.66-1.38 μm. A thinner layer is formed in the membrane with smaller pore size. The diffusion coefficients of Li+ and Na+ ions were found. The effect of the modifier on the retention ability relative to hardness ions (10-14%) and to protein compounds (95-98%) during filtration is determined. Mathematical modeling of the dependence of the permeate flux via time showed that the presence of ion exchanger particles in the polymer active layer prevents the accumulation of organic substances in the pores. Therefore, only the outer surface of the membrane is contaminated, and the precipitate can be easily removed mechanically. It was shown that insertion of a carbon component into pores of the membranes, in addition to the inorganic ion-exchangers, is advisable only in the case of a finely porous active layer. In particular, the performance of the initial polymer membrane (20 dm3/m3.h)) and the selectivity to the calibration substance with a molecular weight of 40 kDa (99%) serve as expediency criteria. In comparison with a membrane modified only with inorganic ion exchanger, selectivity is increased, the rate of filtration of protein solutions is higher, and resistance to contamination by organic substances is achieved. The results are discussed from the view of the hydrophobic-hydrophilic properties of oxidized graphene.

A novel approach to calibrating a photoacoustic absorption spectrometer using polydisperse absorbing aerosol

Abstract. A new technique for calibrating photoacoustic aerosol absorption spectrometers with multiple laser passes in the acoustic cavity (multi-pass PAS) has been developed utilizing polydisperse and highly absorbing aerosol. This is the first calibration technique for multi-pass PAS instruments that utilizes particles instead of reactive gases and does not require knowledge of the exact size or refractive index of the absorbing aerosol. In this new method, highly absorbing materials are aerosolized into a polydisperse distribution and measured simultaneously with a multi-pass PAS and a cavity-attenuated phase shift particulate matter single-scattering albedo (CAPS PMSSA, Aerodyne Inc.) instrument. The CAPS PMSSA measures the bulk absorption coefficient through the subtraction of the scattering coefficient from the extinction coefficient. While this approach can have significant errors in ambient aerosol, the accuracy and precision of the CAPS PMSSA are high when the measured aerosol has a low single-scattering albedo (SSA) and particles are less than 300 nm in size, in which case truncation errors are small. To confirm the precision and accuracy of the new calibration approach, a range of aerosol concentrations were sent to the multi-pass PAS and CAPS PMSSA instruments using three different absorbing substances: Aquadag, Regal Black, and Nigrosin. Six repetitions with each of the three substances produced stable calibrations, with the standard deviation of the calibration slopes being less than 2 % at 660 nm and less than 5 % at 405 nm for a given calibration substance. Calibrations were also consistent across the different calibration substances (standard deviation of 2 % at 660 nm and 10 % at 405 nm) except for Nigrosin at 405 nm. The accuracy of the calibration approach is dependent on the SSA of the calibration substance but is roughly 6 % for the calibration substances used here, which all have an SSA near 0.4 at 405 nm. This calibration technique is easily deployed in the field as it involves no toxic or reactive gases and it does not require generation of a monodisperse aerosol. Advantages to this particle-based calibration technique versus techniques based on ozone or nitrogen dioxide absorption include no reactive losses or impact from carrier gases and the broad absorption characteristics of the particles, which eliminate potentially significant errors in calibration that come with small errors in the peak wavelength of the laser light when utilizing gas-phase standards.

Size Separation Techniques for the Characterisation of Cross-Linked Casein: A Review of Methods and Their Applications

Casein is the major protein fraction in milk, and its cross-linking has been a topic of scientific interest for many years. Enzymatic cross-linking has huge potential to modify relevant techno-functional properties of casein, whereas non-enzymatic cross-linking occurs naturally during the storage and processing of milk and dairy products. Two size separation techniques were applied for characterisation of these reactions: gel electrophoresis and size exclusion chromatography. This review summarises their separation principles and discusses the outcome of studies on cross-linked casein from the last ~20 years. Both methods, however, show limitations concerning separation range and are applied mainly under denaturing and reducing conditions. In contrast, field flow fractionation has a broad separation range and can be easily applied under native conditions. Although this method has become a powerful tool in polymer and nanoparticle analysis and was used in few studies on casein micelles, it has not yet been applied to investigate cross-linked casein. Finally, the principles and requirements for absolute molar mass determination are reviewed, which will be of increased interest in the future since suitable calibration substances for casein polymers are scarce.

Partial synthesis of ganglioside and lysoganglioside lipoforms as internal standards for MS quantification

Within recent years, ganglioside patterns have been increasingly analyzed by MS. However, internal standards for calibration are only available for gangliosides GM1, GM2, and GM3. For this reason, we prepared homologous internal standards bearing nonnatural fatty acids of the major mammalian brain gangliosides GM1, GD1a, GD1b, GT1b, and GQ1b, and of the tumor-associated gangliosides GM2 and GD2. The fatty acid moieties were incorporated after selective chemical or enzymatic deacylation of bovine brain gangliosides. For modification of the sphingoid bases, we developed a new synthetic method based on olefin cross metathesis. This method was used for the preparation of a lyso-GM1 and a lyso-GM2 standard. The total yield of this method was 8.7% for the synthesis of d17:1-lyso-GM1 from d20:1/18:0-GM1 in four steps. The title compounds are currently used as calibration substances for MS quantification and are also suitable for functional studies.

A newly identified calculation discrepancy of the Sunset semi-continuous carbon analyzer

Abstract. The Sunset semi-continuous carbon analyzer (SCCA) is an instrument widely used for carbonaceous aerosol measurement. Despite previous validation work, in this study we identified a new type of SCCA calculation discrepancy caused by the default multipoint baseline correction method. When exceeding a certain threshold carbon load, multipoint correction could cause significant total carbon (TC) underestimation. This calculation discrepancy was characterized for both sucrose and ambient samples, with two protocols based on IMPROVE (Interagency Monitoring of PROtected Visual Environments) (i.e., IMPshort and IMPlong) and one NIOSH (National Institute for Occupational Safety and Health)-like protocol (rtNIOSH). For ambient samples, the IMPshort, IMPlong and rtNIOSH protocol underestimated 22, 36 and 12% of TC, respectively, with the corresponding threshold being ~ 0, 20 and 25 μgC. For sucrose, however, such discrepancy was observed only with the IMPshort protocol, indicating the need of more refractory SCCA calibration substance. Although the calculation discrepancy could be largely reduced by the single-point baseline correction method, the instrumental blanks of single-point method were higher. The correction method proposed was to use multipoint-corrected data when below the determined threshold, and use single-point results when beyond that threshold. The effectiveness of this correction method was supported by correlation with optical data.

Simple Electrochemical Determination of Surface-Active Substances in Natural Waters

A simple electrochemical determination of surface-active substances by using time-dependent variation of the capacitive current in a.c. voltammetry at the HMDE is described. Surface-active substances were accumulated by stirring solution at the deposition potential of −0.6 V versus Ag/AgCl (sat. NaCl). The capacitive current was recorded for different deposition times in the range 0–120 s, wherefrom the linear calibration plot is constructed. The proposed method was verified for model surfactant TritonX-100 in the concentration range 0.02–0.25 mg/L and for humic acid in the concentration range 1.65–20 mg/L. The application of the method was demonstrated for freshwater samples of the Drava river, Danube river, and the wetland Kopački Rit, Croatia. The shape of theiac-Ecurves as well as the obtained concentrations of surface-active substances by using humic acid as the calibration substance are quite well describing the type and the nature of organic matter in the freshwater samples.

Determination of the enthalpy of fusion of Na3FeF6

AbstractThe areas of the fusion and crystallization peaks of Na3FeF6 and of four calibration substances (KCl, NaCl, Na2SO4, and K2SO4) were measured using the DSC mode of a high-temperature calorimeter. Using the measured quantities and known values of the enthalpy of fusion of the calibration substances, the enthalpy of fusion of Na3FeF6 was determined. Its value at the temperature of fusion 1224 K was 70 ± 4 kJ mol−1.

Heat capacity functions of polystyrene in glassy and in liquid amorphous state and glass transition

The heat capacity or the specific heat is for any crystalline, partially amorphous or completely amorphous substance or material a significant thermodynamic property. The glass transition may be regarded as the melting point of amorphous substances and materials, a transition property of an outstanding technical importance. A crucial point is the fact that the presence of a glass transition is an unequivocal proof of an amorphous content of a material. Furthermore, the change of the specific heat at the glass transition temperature enables the quantitative determination of the amorphicity on a relative or absolute level of any substance or material. The absolute determination of the amorphicity affords a calibration with a reference corresponding to the material under investigation. The crystallinity for this reference substance must be known from the preparation and or by any independent analytical method. The literature data for the specific heat and the glass transition of polystyrene were collected and evaluated. Data were found for the specific heat in literature from 10 to 470 K. The data were unified for each of the reported temperature in a mean value and the corresponding standard deviation was determined. An excellent conformity was found in the glassy state of polystyrene with standard deviations lower than 0.7%. The standard deviations above the glass transition were considerably higher. All these literature data were transferred for each of the literature sets separately into linear specific heat functions in the vicinity of the glass transition. One set of our measurements performed with the DSC 204 and with polystyrene SRM 705a as sample material was additionally integrated in the mean of these functions for the glassy state and the liquid amorphous state respectively. The addition of our results gave practically no change of the mean coefficients and only a decrease of the standard deviations. In such a way, the data with the best statistical base for the specific heat of polystyrene are listed in this paper ( ‘Conclusions’). The glass transition as a transition in and out of a non-equilibrium state, the glassy state, is sensitive to all kind of influences such as thermal and mechanical treatments as well as to the selected experimental conditions. Therefore, certain standardized conditions procedures must be fulfilled to get reproducible data. The literature data for the glass transition temperature were also used to get a mean value. However, two values were omitted for the formation of the mean, because the authors reported values, which were too low on the base of impurities present. The mean value of the glass transition for polystyrene is according to the literature 369±2 K. A mean value of 370±2 K was extrapolated for an infinite molecular mass. The DSC and TMDSC measurements for the three thermodynamic properties reported in this paper, namely the specific heat, the glass transition temperature and the corresponding change of the specific heat gave results without significant differences compared with the literature values. Atactic polystyrene is a rather ideal polymer together with sapphire as calibration substance to elucidate and validate the DSC and TMDSC procedures for the determination of the specific heat and the glass transition.

Comparing antioxidative food additives and secondary plant products – use of different assays

Twelve food additives and six secondary plant products were analysed on their antioxidant activity by using three different test systems (Trolox equivalent antioxidant capacity, photochemiluminescence, ferric reducing antioxidant power). The results differed depending on the assay. All the food additives showed antioxidant activities comparable to the calibration substance Trolox. In contrast, the secondary plant products had an up to 16 times higher antioxidant potential. This might present a good reason for the food industry to use natural antioxidants instead of synthetic ones to get storage stability for processed food items – which, according to recent surveys, is in the interest of consumers.

Measurement of thermal conductivity by differential scanning calorimetry

A technique of measurement of thermal conductivity of solid materials by differential scanning calorimetry is presented. It concerns small samples having a diameter less than 8.0 mm, a height less than 2.0 mm and a low thermal conductivity. This method requires many samples with different heights which are heated in such a way that a calibration substance put on their top undergoes a first-order phase transition. The analysis of heat transfer of a such experiment predicts that the slope of the differential power during the transition is proportional to the factor 2 and inversely proportional to the sum of the thermal resistances. A measurement of the thermal conductivity of samples made of polytetrafluoroethylene powder, compressed at the density of 2.10±0.03 g cm −3, has been performed; the value obtained is 0.33±0.02 W m −1 K −1. Measurements of thermal conductivity of small metal hydride pellets are also presented. The precision of the measurements are on average 10%.

Vapour pressure of DSC calibration substances.

For a large number of DSC calibration substances the vapour pressure at room temperature or at transition temperature (whichever is the highest) is given. It is important to know the vapour pressure of substances, because a DSC measurement on a substance with a high vapour pressure requires encapsulation of the substance in a hermetically sealed crucible to prevent evaporation. Because the calibration procedure must be performed using the same type of sample pan as will be used during the actual measurements, the presented information allows one to decide which calibration substances and/or what type of sample pan should be used for calibration.

Chemical aspects of metrology in the chemical industry

A brief description is given about the role of metrology in the chemical industry both in production and analysis. Chemical aspects in metrology such as sample stability, homogeneity, cross-contamination, cross-interference not known to other measuring fields have to be taken into account. The measurement carried out to decide about the quality of a chemical product must be fit for purpose. The measurement index (MI) can be used as a readily available key figure for this task. The quotient of the standard deviation of the measurement and the overall standard deviation of the process defines the ability of a given method to monitor process changes for a specific test item. The definition, origin and quality of reference and working calibration substances used are explained. Comparability to the first lab sample and consideration of the customer's needs are of utmost importance in the chemical industry whereas traceability to SI units is normally restricted to the calibration of laboratory equipment.

Determination of the enthalpy of fusion of K3TiF6Cl

The enthalpy of fusion K 3 TiF 6 Cl at the melting temperature (964 K) has been determined by treatment of the data for K 3 TiF 6 Cl and calibration substances measured by a high-temperature calorimeter in the DSC mode with a scanning rate of 1 K min −1 . The obtained value was Δ fus H m (K 3 TiF 6 Cl) = (42 ± 3) kJ mol −1 .

Electrochemical measuring system for determination of surface-active substances in aqueous solutions

Diffusion controlled adsorption of surface active substances at the stationary mercury electrode causes a time dependency of the electric capacity of the interface electrode/electrolyte. This is the basis of the analytical method proposed. A computer controlled measuring system with a controlled growth mercury electrode is shown. Well-defined conditions for the measuring procedure are managed by electronic control of mercury drop size and a specific potential switch method. Results are given for pure, tap, natural and industrial waters and related to measurements using standard procedures (UV adsorption, methylene blue method). Using sodium dodecyl sulfate (SDS) as calibration substance, the limit of detection is 0.1 mg/1. Measurements in waste water of a tenside plant made with the electrochemical and the methylene blue methods gave a good agreement of the concentrations found. The advantages of the described electrochemical system are the high sensitivity, the simple use and the velocity of measurements. The disadvantages are lack of selectivity and the use of mercury as electrode material.

Calibration of gel-permeation columns in the high-molecular-mass range: fixed human thrombocytes for the estimation of interstitial volume and the haemocyanin of the Vineyard snail Helix pomatia as a molecular mass calibration substance

Human thrombocytes, fixed with formaldehyde, are shown to be a universal indicator of the interstitial volume m gel-permeation chromatography (size-exclusion chromatography) for gels of all molecular mass separation ranges. The fixed thrombocytes are simple to prepare and to handle. Furthermore, native or intramolecularly cross-linked haemocyanin of the Roman snail Helix pomatia is shown to be well suited as a molecular mass calibration substance. We propose 8.8 · 10 6 as its molecular mass for calibration. This haemocyanin can therefore be added to the list of globular protein molecular mass calibration substances in the range of very high molecular masses.

The temperature calibration of scanning calorimeters: Part 2. Calibration substances

The recommendation for temperature calibration consists of two parts. Part 1 (see section 2.3) presented a correct method for the calibration of scanning calorimeters (DSC) and of instruments for differential thermal analysis (DTA), irrespective of the instrument type. The present paper recommends calibration substances for the range 120-1350 K. Sections 2 and 3 indicate the documents to be taken into account and define the most important terms used. Section 4 consists of general requirements to be met by the calibration substances, a list of the substances and explanations with respect to their use. Basically, such materials have been selected as calibration substances which define fixed points of the International Temperature Scale of 1990 (ITS-go). Added to these are fixed point materials from the previously valid International Practical Temperature Scale of 1968 (IPTS-68, see References in Table 1). Moreover, two substances are recommended for temperature ranges for which no suitable fixed point material exists, and the respective uncertainty of measurement is stated.

Determination of the heat of fusion of bismuth with a heat-flux DSC

With a cylinder-type DSC the heat of fusion of bismuth (purity 99.995% and 99.9999%) was determined. The applied method of the quasi-direct comparison of the heat of fusion with heat generated electrically allows measurements to be performed with a small uncertainty because the calibration is not carried out here by the customary indirect calorimetric methods using calibration substances but with exactly known electric energy in close vicinity to the thermal effect investigated.