Proportional Systematic Error Research Articles

Development and Single-Laboratory Validation of a Reversed-Phase Liquid Chromatography–Electrospray–Tandem Mass Spectrometry Method for Identification and Determination of Acrylamide in Foods

A rapid and accurate method using reversed-phase liquid chromatography-tandem mass spectrometry interfaced with electrospray was developed for determination of acrylamide in cooked food samples. A simplified sample treatment procedure using an extraction step with acidified water without cleanup was developed. A C18 column with an aqueous formic acid-methanol mixture as the mobile phase was used under isocratic conditions. The method was validated in-house for robustness, limits of detection (LOD) and quantitation (LOQ), linearity, recovery, and accuracy both on standard and baked-product and potato flour matrixes. Good results in the low ppb level were obtained for LOD (< 15 microg/kg) and LOQ (< 25 microg/kg) of acrylamide in samples. Excellent linearity (r2 = 0.999-1.000) was established over 2 orders of magnitude by performing statistical tests. The absence of both constant and proportional systematic errors demonstrated good method accuracy. Excellent results were obtained for intraday repeatability (RSD < 1.5%) and between-day precision (RSD < 5%). Extraction recoveries from food products were calculated in the 97 +/- 3-99 +/- 2% (n = 6) range with a labeled internal standard (13C3-acrylamide). The applicability of the method to determination of acrylamide in cooked food products was demonstrated.

Effect of different matrices on physiological amino acids analysis by liquid chromatography: evaluation and correction of the matrix effect

Free amino acids in plasma, muscle and liver tissues were determined using the Pico-Tag method which involves HPLC and pre-column derivatization. A study of the accuracy in the determination is carried out by means of external calibration, standard-added calibration, Youden calibration and analyte recovery. It is conclusively shown that the method is affected by a proportional systematic error due to matrix effects, but not by a constant one. A new function named matrix-corrected calibration is proposed to correct for proportional bias when free analyte matrices for matrix-matched addition is unavailable.

Rapid method for determination of chlormequat residues in tomato products by ion-exchange liquid chromatography/electrospray tandem mass spectrometry.

A rapid method has been devised for the direct determination of chlormequat in tomato samples. No clean-up is required, and analysis uses ion-exchange liquid chromatography/tandem mass spectrometry interfaced with electrospray ionization (LC/ESI-MS/MS). A cation-exchange column was used with an aqueous ammonium acetate/acetonitrile mixture as the mobile phase under isocratic conditions. The method was validated in terms of detection limits (LOD), quantitation limits (LOQ), linearity, recovery, precision and accuracy. Good results in the low micro g kg(-1) level were obtained for the LOD and LOQ of chlormequat in tomato samples. Comparison of solvent and matrix-matched calibration curves demonstrated the absence of significant matrix effects and the feasibility of using external calibration. Linearity was established over two orders of magnitude by performing homoscedasticity and Mandel fitting statistical tests. The absence of both constant and proportional systematic errors was verified by evaluating the recovery function, demonstrating good method accuracy. Excellent precision in terms of intra-day repeatability was calculated (RSD% <3.4). Extraction recoveries from tomato products were calculated, by using a labelled internal standard (d(4)-chlormequat), to be in the 93 +/- 5-99 +/- 7% range. The applicability of the method to the determination of chlormequat residues in tomato products was demonstrated.

Study of interference in the flame atomic absorption spectrometric determination of lithium by using factorial design

The severe interference of a number of metallic ions found in brines, marine sediments and sea water in the determination of lithium is demonstrated. Calcium, iron and sodium significantly depressed the absorption signal on lithium in an air/acetylene flame. Aluminium, magnesium and strontium up to 1500, 1000 and 200 μg/mL, respectively, showed no interference in the determination of lithium under the same conditions. Potassium produced some suppression of the lithium signal at levels in excess of 1500 μg/mL. Experimental data were examined using the factorial design method. Interference was demonstrated in two synthetic samples (models of “brine” and “marine sediments” ) and natural marine sediment. It was possible to eliminate all interferences using a higher temperature (nitrous oxide/acetylene flame). In addition, by using the standard addition method the interference disappeared, which confirmed the interference as a proportional systematic error.

Chemometric Protocol to Validate an Analytical Method in the Presence of Corrigible Constant and Proportional Systematic Errors

Abstract A statistical methodology to verify the trueness of an analytical method in the presence of corrigible systematic errors is presented. This protocol enables detection of constant and proportional components of error. By using the data set obtained in the Youden calibration with different sample test portions, the constant component of the error (Youden blank) can be determined. An analysis of covariance was applied to 3 calibration curves established with standard solutions and with standard additions to 2 different sample test portions. The slopes were compared, and the presence of any matrix-analyte interaction was detected. A method for removing the numerical components of systematic errors is proposed: a calculation procedure to obtain a correct analytical result and a statistical test to verify the correctness of analyte contents obtained from different calibrations. For demonstration purposes, the protocol was applied to spectrofluorometric determination of oxalates in spinach leaves.

Comparison of two dry chemistry analyzers and a wet chemistry analyzer using canine serum.

Canine serum was used to compare seven chemistry analytes on two tabletop clinical dry chemistry analyzers, Boehringer's Reflotron and Kodak's Ektachem. Results were compared to those obtained on a wet chemistry reference analyzer, Roche Diagnostic's Cobas Mira. Analytes measured were urea nitrogen (BUN), creatinine, glucose, aspartate aminotransferase (AST), alanine aminotransferase (ALT), cholesterol and bilirubin. Nine to 12 canine sera with values in the low, normal, and high range were evaluated. The correlations were acceptable for all comparisons with correlation coefficients greater than 0.98 for all analytes. Regression analysis resulted in significant differences for both tabletop analyzers when compared to the reference analyzer for cholesterol and bilirubin, and for glucose and AST on the Kodak Ektachem. Differences appeared to result from proportional systematic error occurring at high analyte concentrations.

Analytical bias due to calibrator matrix effects

Fresh serum specimens from 50 patients were analysed for all routine analytes using calibration with serum matrix calibrator as well as aqueous matrix calibrators. Despite good correlation, there is statistically significant bias between serum and aqueous matrix calibrations for most of the analytes. In addition, the bias in cases of glucose, cholesterol and triglycerides is more than the medically allowable error. A proportional systematic error was found pointing to a calibration disparity between the two types of calibrators. These findings suggest an analytical bias between serum and aqueous matrix calibrations that could result in a lack of commutability among various laboratories.

Horizontal strain and precision of EDM from repeated surveys of the Precise Geodetic Net of Japan

A simple statistical approach has been applied to the repeated electro-optical distance measurements (EDM) of 1,358 lines in the Tohoku district of Japan to obtain knowledge about the precision of EDM and the possible accumulation of strain. The average time interval between measurements is about seven or eight years. It is shown that the whole data of the difference between distance measurements repeated over a given lineδD are interpreted in terms of EDM errors comprising distance proportional systematic errors and standard errors expressed by the usual form\(\sqrt {\alpha ^2 + \beta ^2 D^2 } \). The rate of horizontal deformation must therefore be much smaller than the strain rates of about 0.7 ∼ 0.8 ppm over 7 to 8 years which have been hitherto expected.

Métodos instrumentales para la determinación de NaCl en las salmueras de aceitunas

Aplicability of flame photometric and ion selective (sodium or chloride) methods to determinate NaCI concentration in olive brines in comparison with the official one (Volhard), which uses AgNO 3 , is studied. According to the results using standard solutions or fermentative olive brines without previous lye treatment, no proportional systematic or constant systematic errors are detected and the percentaje of NaCl is evaluated by them with the same accuracy as by the reference. However, when the flame photometric or sodium ion-selective methods are used to determine this compound in Spanish olive brines, there is a deviation in comparison with the values obtained by the official one (Volhard) that is correlated with the combine acidity concentration of the solution. This fact is due to the presence of sodium organic salts, called combined acidity, that are formed during the lye treatment or cocido that these fruits are given before fermentation. Nevertheless, is does not represent any problem as there is a good correlation between such combined acidity and the magnitude of the deviation, that permit to calculate the corresponding correction factor. In addition these problems can be solved using the chloride selective ion method.

Analytical Remarks to Explain Some Discrepancies in the Determination of Dry Matter and Starch from Potato Tubers Density

Abstract1) Air adsorbed on potato tuber surface can result the accidental error, decreasing the true value of tuber density. Some deviations from normal temperature do not seem to change substantialy the tuber density.2) The dry matter determination should be precisely reexamined in a special series of experiments. The improper method can introduce a systematic error, increasing or decreasing the results.3) It is necessary to compare mostly used methods of starch determination in potato tubers and to estimate the possible systematic errors.4) The various slope of the regression line: dry mater/starch vs. potato density, can be resulted by different factors as follows: the variable intercellular spaces, the proportional systematic errors in analytical determination, the variable dry matter density, and increasing (or decreasing) value of non‐starch substances.5) The intercellular spaces can result either a constant or a proportional systematic errors in the tuber density determination. They can be eliminated by vacuum infiltration procedure, which should be, however, verified.6) The dry matter determination seems to be difficult analytical problem and it has not been definitely solved until now.7) The Maercker's constant has been until now an open question and its variability should be verified from analytical point of view.