Determination of the acid value of instant noodles: interlaboratory study

An interlaboratory study was performed to evaluate the method for determining the acid value of instant noodles, based on the Japanese Agricultural Standard (JAS), with extraction of lipid using petroleum ether at a volume of 100 mL to the test portion of 25 g. Thirteen laboratories participated and analyzed 5 test samples as blind duplicates. Statistical treatment revealed that the repeatability (RSDr) of acid value was <6.5%, and the reproducibility (RSDR) of acid value was <9.6%. The HorRat values (RSDR/predicted RSDR) were 1.2-1.8, where the RSDR and the predicted RSDR were obtained in terms of free fatty acids in the noodles per unit weight, using the equation [acid value = percent free fatty acids (as oleic) x 1.99] and the extracted lipid contents. This method was shown to have acceptable precision by the present study.     

Ultramicrodetermination of nitrogen in organic compounds : VII. Determination of total nitrogen in dilute aqueous solution by sealed-tube method

The capillary immutability due to corrosion of glasses exposed to various solutions was studied. The analytical error of volume change caused by glass corrosion in a micro- and ultramicronitrometer was discussed. The present work has shown that the graduated tube of a decimicronitrometer made of borosilicate glass, which is used frequently in Dumas method, should be recalibrated after 1.5–2.3 months use. We therefore recommend the sealed tube method using an improved nitrometer for ultramicrodetermination of nitrogen in organic compounds.     

Determination of phytase activity in feed: interlaboratory study

An interlaboratory study was conducted to determine the performance characteristics of a new method for the determination of phytase activity in feed samples. The method is based on the principle that inorganic phosphate is released from the substrate phytate under defined assay conditions and has been validated for its suitability to measure the enzyme activity of various phytase products. Two different experimental designs of the study were applied, allowing for the estimation of the precision of the method under repeatability, intermediate precision and reproducibility conditions, respectively. The relative standard deviation for repeatability (RSDr) ranged from 2.2 to 10.6% and the RSD for reproducibility (RSDR) ranged from 5.4 to 15%. The suitability of the validated method for the intended purpose was demonstrated. The obtained performance profile of the method validated in this study was comparable to that of similar methods that were exclusively validated for one phytase product.     

Dissolution kinetics of fluorapatite in the hydrochloric acid solution

A thermochemical study of hydrochloric acid attack of synthetic fluorapatite was performed by a DRC. The calculated thermogenesis curves show one peak. The plot of the heat quantity as a function of the dissolved mass undergoes only one straight segment, and the thermogenesis curves present a single peak, suggesting the occurrence of a one-step dissolution process. The dissolution kinetics was examined according to the heterogeneous reaction models and showed that the dissolution is controlled by the product layer diffusion process with a reaction rate expressed by the following semiempirical equation; \(\left[ {1 + 2(1 - X) - 3(1 - X)^{{\frac{2}{3}}} } \right] = 3195 \times 10^{ - 2} C^{0.145} \left( {\frac{S}{L}} \right)^{ - 0.628} e^{{ - \frac{2600}{\text T}}} t\). The activation energy was determined as 21.6 ± 1.5 kJ mol^?1     

Determination of aflatoxin B1 in medical herbs: interlaboratory study

A method was developed for the determination of aflatoxin B1 in medical herbs (senna pods, botanical name Cassia angustifolia; devil's claw, botanical name Harpagophytum procumbens; and ginger roots, botanical name Zingiber officinale). The method, which was tested in a mini-collaborative study by 4 laboratories, is based on an immunoaffinity cleanup followed by reversed-phase high-performance liquid chromatography separation and fluorescence detection after post-column derivatization. It allows the quantitation of aflatoxin B1 at levels lower than 2 ng/g. A second extractant (acetone-water) was tested and compared to the proposed methanol-water extractant. Several post-column derivatization options (electrochemically generated bromine, photochemical reaction, and chemical bromination) as well as different integration modes (height versus area) were also investigated. No differences were found depending on the choice of derivatization system or the signal integration mode used. The method was tested for 3 different matrixes: senna pods, ginger root, and devil's claw. Performance characteristics were established from the results of the study and resulted in HorRat values ranging from 0.12 to 0.75 with mean recoveries from 78 to 91% for the extraction with methanol-water and HorRat values ranging from 0.10-1.03 with mean recoveries from 98 to 103% for the extraction with acetone-water. As a result, the method, with all tested variations, was found to be fit-for-purpose for the determination of aflatoxin B1 in medical herbs at levels of 1 microg/kg and above.     

Repeatability and reproducibility of determination of the nitrogen content of fishmeal by the combustion (Dumas) method and comparison with the Kjeldahl method: interlaboratory study

Ten fishmeal samples (hidden duplicates of 4 meals plus 2 high-protein meals as a Youden pair), tryptophan, and nicotinic acid were analyzed by 18 laboratories using the Dumas method. Thirteen of the laboratories also analyzed the same 12 samples using their current Kjeldahl method. Recoveries (+/-SR) of tryptophan and nicotinic acid were 99.3+/-1.04 and 98.8+/-2.11% by Dumas and 97.1+/-3.03 and 74.6+/-26.76% by Kjeldahl. The Dumas method gave significantly greater values (P < 0.001) than the Kjeldahl method. For fishmeals, Kjeldahl N = 0.989 of Dumas N (P < 0.001). A similar proportionate difference (0.984 of Dumas N) was observed with tryptophan. Most laboratories failed to determine nicotinic acid correctly by Kjeldahl. For fishmeals, the relative standard deviations for repeatability and reproducibility were for Dumas 1.48 and 2.01% and Kjeldahl 1.62 and 2.37%, respectively. A single analysis conducted in 2 laboratories should not differ by more than 5.63% of the mean value when measured by Dumas or by more than 6.64% by Kjeldahl. It is concluded that with fishmeal, Dumas gives a more reliable measure of organic nitrogen than Kjeldahl, and, therefore, Dumas should be the method of choice.     

Determination of the moisture content of instant noodles: interlaboratory study

Determination of the moisture content of instant noodles, currently under discussion by the Codex Alimentarius Commission (CAC) requires 2 methods: one for fried noodles and the other for nonfried noodles. The method to determine the moisture content of fried noodles by drying at 105 degrees C for 2 h used in the Japanese Agricultural Standard (JAS) system of Japan can be applied to this purpose. In the present study, the JAS method for fried noodles was modified to be suitable for nonfried noodles by extending the drying time to 4 h. An interlaboratory study was conducted to evaluate interlaboratory performance statistics for these 2 methods. Ten participating laboratories each analyzed 5 test materials of fried and nonfried noodles as blind duplicates. After removal of outliers statistically, the repeatability (RSDr) and the reproducibility (RSD(R)) of these methods were 1.6-2.6 and 3.9-4.8% for fried noodles, and 0.3-1.5 and 1.3-2.9% for nonfried noodles, respectively.     

Determination of chlorite ion in dilute solution by pulse polarography

Chlorite is determined in the range 0–1.3 mg l^-1 by pulse polarography at pH 4.25–4.65. The detection limit is 0.05 mg l^-1.     

The solubility and isotopic fractionation of gases in dilute aqueous solution. I. Oxygen

A very precise and accurate new method is described for determination of the Henry coefficient k and the isotopic fractionation of gases dissolved in liquids. It yields fully corrected values for k at essentially infinite dilution. For oxygen the random error for k is less than 0.02%, which is an order of magnitude better than the best previous measurements on that or any other gas. Extensive tests and comparison with other work indicate that systematic errors probably are negligible and that the accuracy is determined by the precision of the measurements. In the virial correction factor (1+λP_t), where P_t is the total pressure of the vapor phase, the coefficient λ for oxygen empirically is a linear decreasing function of the temperature over the range 0–60°C. The simple three-term power series in 1/T proposed by Benson and Krause, $$\ln k = a_0 + a_1 /T + a_2 /T^2 $$ provides a much better form for the variation of k with temperature than any previous expression. With a₀=3.71814, a₁=5596.17, and a₂=?1049668, the precision of fit to it of 37 data points for oxygen from 0–60°C is 0.018% (one standard deviation). The three-term series in 1/T also yields the best fit for the most accurate data on equilibrium constants for other types of systems, which suggests that the function may have broader applications. The oxygen results support the idea that when the function is rewritten as $$\ln k = - (A_1 + A_2 ) + A_1 \left( {\frac{{T_1 }}{T}} \right) + A_2 \left( {\frac{{T_1 }}{T}} \right)^2 $$ it becomes a universal solubility equation in the sense that A₂ is common to all gases, with T₁ and A₁ characteristic of the specific gas. Accurate values are presented for the partial molal thermodynamic function changes for the solution of oxygen in water between the usual standard states for the liquid and vapor phases. These include the change in heat capacity, which varies inversely with the square of the absolute temperature and for which the random error is 0.15%. Analysis of the high-temperature data of Stephan et al., in combination with our values from 0–60°C, shows that for oxygen the fourterm series in 1/T, $$\ln k = - 4.1741 + 1.3104 \times 10^4 /T - 3.4170 \times 10^6 /T^2 + 2.4749 \times 10^8 /T^3 $$ where p=kx and p is the partial pressure in atmospheres of the gas, probably provides the best and easiest way presently available to calculate values for k in the range 100–288°C, but more precise measurements at elevated temperatures are needed. The new method permits direct mass spectrometric comparison of the isotopic ratio³⁴O₂/³²O₂ in the dissolved gas to that in the gas above the solution. The fractionation factor α=³²k/³⁴k varies from approximately 1.00085 (±0.00002) at 0°C to 1.00055 (±0.00002) at 60°C. Although the results provide the first quantitative determination of α vs. temperature for oxygen, it is not possible from these data to choose among several functions for the variation ofInα with temperature. If the isotopic fractionation is assumed to be due to a difference in the zero-point energy of the two species of oxygen molecules, the size of the solvent cage is calculated to be approximately 2.5 Å. The isotopic measurements indicate that substitution of a³⁴O₂ molecule for a³²O₂ molecule in solution involves a change in enthalpy with a relatively small change in entropy.     

Adsorption of benzotriazole on copper surfaces in a hydrochloric acid solution

The adsorption of benzotriazole (BTA) on commercial copper surfaces in hydrochloric (HCl) acid concentrations from 1 × 10^?3 to 5 × 10^?1 M was investigated using gravimetric measurements. BTA in bulk solution was tested in concentrations from 1 × 10^?5 to 1 × 10^?1 M at temperatures from 298 to 328 K. The adsorption mechanism is discussed using the objective function (OF) and in terms of applicability of the conventional isotherm models. The best fit was obtained using the Frumkin equation. The projected molecular area of BTA was calculated to elucidate inhibitor orientation in the adsorption process. Copyright © 2006 John Wiley & Sons, Ltd.     

Radiolytic degradation of 2,4-dichlorophenoxyacetic acid in dilute aqueous solution: pH dependence

The reactions of hydroxyl radical and hydrated electron intermediates of water radiolysis were studied in the radiolytic degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) at pH values of 4, 6 and 8. The hydrated electron reactions are also suggested to contribute to the aromatic ring decomposition in addition to the highly effective hydroxyl radical reactions. The experimental results suggest also some contribution from the O₂^−•/HO₂^• pair to the degradation. The degradation efficiency was found to be the highest at pH 8 and the lowest at pH 6.     

Determination of hydrochloric acid in organic solutions by gas chromatography

Summary A method is described for the determination of small quantities of hydrochloric acid in two chlorinated organic solvents (CHCl₃ and CCl₄). An excess of gaseous ethylene oxide is added to a liquid sample; the 2-chloroethanol formed is then analyzed by gas chromatography. The procedure is simpler and more sensitive in comparison with other conventional methods. It can be modified for other organic solvents.D.G.R.C.S.T. grant.     

Adenosine as corrosion inhibitor for mild steel in hydrochloric acid solution

Research on Chemical Intermediates - (2R,3R,4S,5R)-2-(6-amino-9H-purin-9-yl)-5-(hydroxymethyl)oxolane-3,4-diol (adenosine) is an identified component present in agarwood leaf extract. The corrosion...     

Chemiluminescence accompanying chitosane destruction in hydrochloric acid solution containing hydrogen peroxide

The chemiluminescence (CL) accompanies the destruction of chitosane (CTS) in the presence of H₂O₂. The CL kinetics has a complex character and can be described as a sum of two exponentials. The photoluminescence monitoring and IR spectra of the reaction mixture indicate the formation of carbonyl groups in the course of CTS destruction. The enhancement of the CL intensity by Fe²⁺ suggests the reaction of Fe²⁺ with hydroperoxides accumulated with CTS decomposition. The macroradicals ROO^· are assumed to be transformed through the cleavage of the glycoside bond via a six-membered cyclic intermediate to form the terminal peroxide radical and ketone.     

Viscoelastic study of the conformational transition of poly(methacrylic acid) in dilute aqueous solution

The dynamic viscosity of dilute aqueous solution of poly(methacrylic acid) (PMA) was measured over the frequency range 2–500 kHz for various degrees of ionization. The relaxation spectrum calculated from the viscosity exhibits a conformational relaxation spectrum in the short-time region and a rotational one in the long-time region. The former is fitted by the Zimm theory over the entire range of ionization, including the transition from a compact structure to an open one. The conformational relaxation time begins to increase at the midpoint of the transition region, but the rotational relaxation time increases very markedly in the initial stage of the transition. The present and previously reported experimental findings are interpreted in terms of the assumption that the compact structure is stabilized by short-range methyl–methyl bonding as well as “long-range” methyl–methyl bonding (bonding between methyl groups spatially close but remotely connected along the chain contour). In the initial stage of the transition, the latter primarily break up, resulting in expansion of overall chain dimensions, and subsequently the former are destroyed, resulting in the change in local chain conformation.     

Vibrational dynamics of carboxylic acid dimers in gas and dilute solution

Ultrafast mid-IR transient absorption spectroscopy has been used to study the vibrational dynamics of hydrogen-bonded cyclic dimers of trifluoroacetic acid and formic acid in both the gas and solution phases (0.05 M in CCl(4)). Ultrafast excitation of the broad O-H cyclic dimer band leads, in the gas phase, to large-scale structural changes of the dimer creating a species with a distinct free O-H stretching band on 20 ps and 200 ps timescales. These timescales are assigned to ring-opening and dissociation of the dimer, respectively. In the solution phase, no such structural rearrangement occurs and our results are consistent with previous studies. The gas phase dynamics are insensitive to both the specific excitation energy (over a span of 550 cm(-1)) and the chemical identity of the dimer.     

Corrosion inhibition performance of tannins for mild steel in hydrochloric acid solution

Research on Chemical Intermediates - The corrosion inhibition behavior of commercial hydrolysable tannin (tara tannin), condensed tannin (black wattle tannin) and complex tannin (bayberry tannin)...     

Synthesis of hydrochloric acid solution for total mercury determination in natural waters

Total mercury (Hg_T) determination requires the addition of concentrated hydrochloric acid solution (≥10 mol L⁻¹ HCl) in relatively high amounts to preserve the samples and to prepare reagent solutions. A method for the preparation of concentrated HCl with Hg_T concentration of lower than 5 ng L⁻¹ is described in this article. It is based on the well-known chemical reaction: 2 NH₄Cl + H₂SO₄ → (NH₄)₂SO₄ + 2 HCl. This method is validated thanks to the US Environmental Protection Agency method 1631 and standard reference materials BCR-579 (mercury in coastal seawater).