Development and certification of the new SRM 695 trace elements in multi-nutrient fertilizer.

During the past seven years, several states within the US have enacted regulations that limit the amounts of selected non-nutritive elements in fertilizers. Internationally, several countries, including Japan, China, and Australia, and the European Union also limit the amount of selected elements in fertilizers. The elements of interest include As, Cd, Co, Cr, Cu, Hg, Mo, Ni, Pb, Se, and Zn. Fertilizer manufacturers and state regulatory authorities, faced with meeting and verifying these limits, need to develop analytical methods for determination of the elements of concern and to validate results obtained using these methods. Until now, there were no certified reference materials available with certified mass fraction values for all elements of interest in a blended, multi-nutrient fertilizer matrix. A new standard reference material (SRM) 695 trace elements in multi-nutrient fertilizer, has been developed to help meet these needs. SRM 695 has recently been issued with certified mass fraction values for seventeen elements, reference values for an additional five elements, and information values for two elements. The certificate of analysis includes an addendum listing percentage recovery for eight of these elements, determined using an acid-extraction inductively-coupled plasma optical-emission spectrometry (ICP-OES) method recently developed and tested by members of the Association of American Plant Food Control Officials.

Equivalency of protein determination in feed on Bran & Luebbe Traacs 800 autoanalyzer with AOAC semiautomated method: minicollaborative study.

A new generation of autoanalyzers was collaboratively studied for equivalency with instrumentation described in the AOAC method for crude protein in animal feeds. Twenty predigested samples were analyzed by 4 collaborators using standards that were provided. Means were comparable; the overall average difference was 0.07% protein. Analysis of variance indicated no evidence for an instrument difference. The method describing use of the Traacs 800 autoanalyzer as an alternative system has been adopted official first action.

Comparison of HgO and CuSO4/TiO2 as catalysts in manual Kjeldahl digestion for determination of crude protein in animal feed: collaborative study.

Because of environmental concerns about HgO, and because of lengthy digestion requirements for HgO and CuSO4, interest in alternative catalysts for the Kjeldahl determination of animal feeds remains high. A digestion system using a mixed CuSO4/TiO2 catalyst has been found to reduce digestion times to 40 min. A collaborative study was carried out to compare this system to the official AOAC HgO method, 7.015. Thirty-eight samples, consisting of blind duplicates of closely matched pairs and 2 standard materials, were analyzed once by each method. Results were received from 13 laboratories. Means and standard deviations of individual samples were comparable, with an overall difference of grand means of 0.005% protein. With only one exception, analyses of variance showed no significant method difference at the 95% confidence level. The CuSO4/TiO2 method has been approved interim official first action as an alternative method for determination of crude protein in animal feed.

CuSO4-TiO2 as Kjeldahl digestion catalyst in manual determination of crude protein in animal feeds.

The official AOAC manual Kjeldahl methods for determining crude protein in animal feeds have several disadvantages. For the HgO catalyst method, there are environmental concerns and a lengthy digestion. For the CuSO4 catalyst method, the digestion period is shorter, but still 90 min. A different catalyst combination, CuSO4-TiO2, makes 40 min digestion feasible. Comparison of these catalysts on a group of representative feeds resulted in a mean difference, Cu-Ti minus HgO, of 0.034% protein. Standard deviation of the differences was 0.36. A Student's t-test showed no significant difference. The method will be collaboratively studied.

Comparison of HgO and CuSO4 as digestion catalysts in manual Kjeldahl determination of crude protein in animal feeds: collaborative study.

The official AOAC manual Kjeldahl method for determining crude protein in animal feeds, 7.015, uses HgO as a catalyst in the digestion step. Because of environmental considerations, there is considerable interest in alternative catalysts. A collaborative study compares the official HgO-catalyzed method and an alternative using CuSO4. Fifty-four samples consisting of blind duplicates of closely matched pairs, representing a range of animal feed materials and 2 standard materials, were analyzed once by each method. Results were returned by 22 laboratories. Means and standard deviations between methods were comparable. The CuSO4-catalyzed method has been adopted official first action.

Possible role for cytotoxic oxygen metabolites in the pathogenesis of cardiac ischemic injury.

Parabiotically perfused, isolated cat hearts were subjected to global ischemia for 2 hours at 27 degrees C and were then reperfused for 2 hours. One group of hearts was simply perfused with hypothermic blood 5 minutes before ischemia and again before normothermic reperfusion. A second group received a crystalloid cardioplegic solution. A third group received cardioplegic solution supplemented with superoxide dismutase and catalase; at the start of reperfusion the anesthetized cats supplying blood to perfused hearts in this group received an i.v. infusion of these enzymes. Based on comparisons of postreperfusion ventricular pressure development, maximal ventricular dP/dt, rate-pressure products and coronary blood flow, we concluded that cardioplegic solution and enzyme treatment were superior to enzyme-free cardioplegia solution under otherwise similar experimental conditions. The results suggest that a component of "ischemic" cardiac damage may involve cytotoxicity from oxygen metabolites such as superoxide anion, hydrogen peroxide, or both, and that this component of damage can be reduced by enzyme supplements such as superoxide dismutase or catalase.

Superoxide dismutase plus catalase enhances the efficacy of hypothermic cardioplegia to protect the globally ischemic, reperfused heart.

Experiments were conducted in an attempt to improve upon the contractile and metabolic protection of globally ischemic and reperfused isolated hearts provided by hypothermic (27 degrees C) cardioplegia. Hypoxic substrate-free test solutions were perfused through isolated rabbit hearts for 5 minutes before and after an uninterrupted 2 hour period of global ischemia. Test solutions included a modified physiological saline solution (PSS) (not cardioplegic); a potassium- and magnesium-enriched cardioplegia solution; or a PSS or cardioplegic solution supplemented with superoxide dismutase (SOD) plus catalase (150,000 units/L each). Postreperfusion contractile and biochemical function was compared to preischemic function or that of nonischemic control hearts. On the basis of measurements of left ventricular pressure development, left ventricular compliance, spontaneous heart rate, coronary vascular resistance, and isolated mitochondrial oxidative phosphorylation, we concluded that supplementing hypothermic cardioplegia solution with enzymes gave protection which was significantly better than that obtained with the other interventions, with values of these indicators not significantly different from those of nonischemic perfused controls. The results indicate that SOD plus catalase significantly enhances the protection afforded by hypothermic cardioplegia. They also implicate cytotoxic oxygen radicals as important contributors to "ischemic" damage and suggest that this component of damage can be prevented effectively.