Control Reference Material Research Articles

Peroxide Stability in Shortening: A Useful Reference Material

Vegetable shortening was studied to determine if its peroxide value was stable enough after storage for one year to be used as a quality control reference material. Shortening samples were deliberately oxidized to contain low, medium, and high levels of peroxide and were then stored at 4°C for one year. Peroxide value was measured approximately every 14 d during this year. A total of 27 different determinations was made at each of the three different peroxide levels. The results indicated minimum variability within each level of peroxide during the year, and suggested that shortening would serve well as a reference material for quality control in the fats and oils industry and in food and nutrition research.

Rheumatoid factors determined by fluorescence immunoassay: comparison with qualitative and quantitative methods.

Fluorescence immunoassay (FIA), a relatively new technique for measuring rheumatoid factors (RF), is automated, quantitative, and calibrated against the Centers for Disease Control reference material for RF. We studied the FIA method in relation to a panel of RF methods, both qualitative [latex (LA) and sheep cell agglutination (SSCA)], and quantitative [nephelometry and enzyme-linked immunoassay (ELISA)]. Regression analysis revealed a highly significant correlation between FIA and either LA (r = 0.90) or nephelometry (r = 0.87). The correlation between FIA and either SSCA (r = 0.62) or ELISA (r = 0.67) was less strong. FIA had the highest sensitivity (91%) of all these methods; the specificity was 86%. FIA provides an accurate, sensitive, and specific measure of RF, and is a good alternative for laboratories wanting to replace titer methods with automated laboratory analysis.

Bias and error in the determination of common macronutrients in foods: Interlaboratory trial

Chemical analyses of nutrient values in foods form the basis of much of the science and practice of nutrition and dietetics, but little is known about the atcuracy and precision of common macronutrient analyses. Therefore, an interlaboratory study was set up. One batch each of egg powder, full-fat milk powder, whole rye flour, whole wheat flour, biscuits, and French beans (snap beans, “haricots verts”) was thoroughly homogenized. Samples were sent to 19 leading food analysis laboratories in Europe and the U.S., and each performed analyses of macronutrients by its own routine methods. Most were government or semi-government laboratories and major contributors to national nutrient data banks. The results for dry matter content and ash agreed well between laboratories. For protein, the coefficient of variation between laboratories (CVbetween) ranged from 2.8% to 6.4 %. The reproducibility within laboratories was sometimes quite poor. The CVbetween for total fat ranged from 5.4 % to 54%. For “available” carbohydrates, the CVbetween ranged from 9% to 27%. The CVbetween for total dietary fiber ranged from 23% to 84%. Only part of the variability could be explained by the use of methods of different principle. It is concluded that leading laboratories produce widely different values for macronutrients in common foods. Quality control programs and reference materials of certified nutrient concentration are urgently needed. J Am Diet Assoc 88:556, 1988.

A comparison of serum electrolyte results by the flame III auto-analyser and a flame IV auto-analyser which utilises curve regeneration with a data acquisition system

Results obtained with a Technicon Flame Photometer Model IV Auto-Analyzer, which utilizes curve regeneration in conjunction with a mini-computer for the continuous-flow determination of serum electrolytes, is presented. The system, featuring optimal flow conditions, subjects sample peaks to a mathematical treatment to effectively remove exponential deformation. The evaluation, undertaken after 2 months of operation in the routine clinical laboratory, utilizes the Flame Photometer Model III as the "referee" procedure. The comparison includes a statistical analysis of quality control reference material, simultaneously determined patient data and an evaluation of repeated patient data. The system gave comparable results to those obtained for the Flame Photometer Model III and provides the additional benefits of increased sample throughput, decreased reagent comsumption and sample interaction and gives reductions in the clerical tasks associated with the retrieval of data from Auto-Analyzer systems.