Modified Baker method

Another method used for nitrate determination on dried and milled herbage employs the nitrate selective electrode. One of the first published methods was that of Paul and Carlson (1968). Other anions, especially chloride, can interfere. These authors removed chloride with silver resin, but Barker ef al. (1971) omitted the resin because it tended to foul the electrode and cause excessive drift. Normally the Cl N03 ratio is so low as not to interfere, but saline precipitation from coastal plots could affect this. The method was further modified to allow storage of extracts for up to 64 h by adding a preservative of phenyl-mercuric acetate and dioxane, both very toxic (Baker and Smith, 1969). This paper mentions the need to change the electrode s membrane, filling solution and liquid ion exchanger every 2 months to minimize chloride interference. It is easy to overlook electrode maintenance between batches of nitrate analyses, and this can lead to errors and sluggish performance. 

Zinc was determined in filtered samples (0.45 xm pore size) by flame atomic absorption spectrometry after preconcentration. For the preconcentration, 8-hydroxyquinoline was added as a chelating agent to the acidified samples and subsequently buffered to pH 8. The hydroxyquinoline complexes were collected on C-18 columns (Baker) and eluted with 0.6 M HCl (modified after ref. 34). The preconcentration factor was 40. Blank values of this method were 2-3 nM Zn reproducibility was 1.5 nM. Recovery of Zn spikes added to lake water was 90-100%. 

Acknowledgment is gratefully made to Dr. Lillian E. Baker of the Rockefeller Institute for Medical Research for the use of her notes on this preparation. Hopkins original method, modified in several details, and made more precise, was found to give crystalline preparations more consistently than Soerensen 3 modification. 

Note that when a symplectic integration method is used, we have, from the discussion in Chap. 3, a perturbed energy function and, moreover, from Theorem 3.1, the error in energy H is OQf), nonetheless the perturbations are large for a large stepsize h. In the Shadow Hybrid Monte-Carlo (SHMC) method [2, 3, 188], the accept-reject test is based on the modified Hamiltonian Hh (see Chap. 3), derived from the Baker-Campbell-Hausdorff expansion. SHMC can improve efficiency by decreasing the rejection rate. 

Ratiaal functiaal ptimizatin. The rational functional optimization or RFO (Baneijee et al. 1985 Baker 1986, 1987) is another method that develops from the Newton-Raphson procedure. Essentially, Equation (47) is rearranged and modified into a rational functional ... 

Applying this method in the near field, i.e. close to the vessel surface, the calculated overpressures may results higher than the burst pressure, which is physically impossible. This inconvenience can be solved using a modified procedure for R<2 (Baker et al., 1983) this will introduce a di ontinuity in the overpressure values calculated aXR = 2. 

---