TY - JOUR T1 - A comparison of methods for the measurement of dissolved organic carbon in natural waters JF - Marine Chemistry Y1 - 1996 A1 - Peltzer, E. T. A1 - Fry, B. A1 - Doering, P. H. A1 - McKenna, J. H. A1 - Norrman, B. A1 - Zweifel, U. L. AB - A small suite of natural samples spanning a wide range of DOC concentrations and salinities were analyzed by three high-temperature combustion (HTC) techniques and persulfate oxidation, One of the HTC techniques, sealed-tube combustion (STC), served as a referee method, Using this method, it was possible to obtain absolute DOC concentrations for the natural samples free of any analytical blank offset, Prior to the comparison of samples, an exchange of carbon-free water and calibration standards showed that all methods were equally well calibrated, Linear correlation analysis was used to differentiate whether the differences observed between methods was due to variable oxidation yields or to an artifact of the instrument blank, Agreement among the various methods was quite good, but yields for all methods decreased compared to the STC technique at concentrations of > 400 mu M C. Persulfate results were found to be very similar to HTC results. Finally, carbon-free distilled water prepared by UV/H2O2 oxidation or Milli-Q systems had near-zero DOC concentrations and was adequate for blank correction of all the various techniques yielding DOC concentrations in excellent agreement with the referee method. VL - 54 IS - 1-2 N1 - Vj296Times Cited:50Cited References Count:49 JO - A comparison of methods for the measurement of dissolved organic carbon in natural waters ER - TY - JOUR T1 - Tic, Toc, Dic, Doc, Pic, Poc - Unique Aspects in the Preparation of Oceanographic Samples for C-14 Ams JF - Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms Y1 - 1994 A1 - McNichol, A. P. A1 - Osborne, E. A. A1 - Gagnon, A. R. A1 - Fry, B. A1 - Jones, G. A. AB - The radiocarbon content of discrete carbon pools (total (T), dissolved (D), and particulate (P) inorganic (I) and organic (O) carbon (C)) is a useful tracer of carbon cycling within the modem and past ocean. The isolation of different carbon pools in the ocean environment and conversion to CO2 presents unique analytical problems for the radiocarbon chemist. In general, isolation and preparation of inorganic carbon presents few problems; dissolved carbon is easily extracted by acidifying the sample and stripping with an inert gas. Carbon is also readily isolated from particulate carbonate samples; in this case, CO2 is prepared by hydrolysis of the substrate with phosphoric acid. The isolation and preparation of organic carbon presents a much greater problem. Dissolved organic carbon (DOC) must first be isolated from DIC and then oxidized in the presence of very high salt concentrations. We present results from a closed-tube combustion method in which the DIC-free seawater is evaporated to dryness, transferred to a clean combustion tube, and oxidized overnight at 550-degrees-C. Combustion of total organic carbon (TOC) in sediments with a high inorganic carbon content is also difficult. Removal of CaCO3 with acid leaves severely deliquescent salts which, if not thoroughly dried, cause combustion tubes to explode. Removal of the salts by rinsing can also remove significant amounts of organic matter. Finally, we present results from a local coastal region. VL - 92 IS - 1-4 N1 - Nv547Times Cited:82Cited References Count:9 JO - Tic, Toc, Dic, Doc, Pic, Poc - Unique Aspects in the Preparation of Oceanographic Samples for C-14 Ams ER -