Standard organometallic

Oils can be injected directly or in a dilute form, e.g. diluted with xylene. Organometallic standards are recommended. 

Standardisation should be via organometallic standards, which are now available for a range of metals from B.D.H. and Hopkin Williams, as well as from specialised oil-standard organisations such as Conostan. 

The method may be used to determine Pb, Na, V, Ni and Zn in fuel and gas oils. It may also be applicable to olher elements. The sample is diluted with MIBK or xylene and comparison made to organometallic standards in the same solvent. For most elements the limits of detection will be in the range 1—5pgg . 

Use either commercially available oil base standards or organometallic standards prepared as described in Section III. Dilute these with the same solvent as used for the samples to prepare calibration standards. At least four standards including a blank should be prepared to cover an approximately linear range. This will vary from instrument to instrument but the following is a useful guide. 

The method is suitable for the determination of low levels of Ni and V (down to approximately 0.01 pgg-1) in fuel oils. Samples are diluted with xylene and comparison made with organometallic standards prepared in the same solvent. Electrothermal atomisation is used to achieve increased sensitivity. 

Standards for the analysis may be prepared from organometallic standards, analysed samples or the NBS (GM-5) Heavy Oil Standard. The most satisfactory results are likely to be obtained using the second or third options. The sensitivity available is critically dependent on the electrothermal device to be used. This and the size of aliquot chosen for injection into the atomiser (normally 5—100 pi) will determine the selection of the concentration ranges chosen for the standards. Refer to the manufacturers information on Ni and V sensitivity and linear range and prepare calibration standards accordingly. Always prepare a blank solution and at least three standards to cover the chosen range. 

The method is applicable to the determination of Ca, Ba, Mg and Zn in unused lubricating oils and may also be of use for the determination of other elements of interest. Limits of detection will normally be in the region of 0.005% w/w. The lubricating oil is diluted with white spirit and aspirated into the nitrous oxide—acetylene flame. Organometallic standards in white spirit are used for calibration. 

Using either commercially available metal in oil standards or organometallic standards, prepared as described in Section III, prepare calibration standards by dilution with white spirit. Standards for Ca, Ba and Mg must contain 1000/igKml-1 as ionisation suppressant. Choose a concentration range for each element which exhibits an approximately linear response. 

The method is applicable to the determination of Al, Ag, Cr, Cu, Fe, Ni, Si, Sn, Mg, Pb and Zn in used lubricating oils and may also be applicable to other elements of interest. Samples are diluted with MIBK and compared with organometallic standards in MIBK. Limits of detection will range from approximately 0.1/igml-1 for elements such as Zn and Cu, approximately 1 pgml-1 for elements such as Sn and Al and greater for Si. 

Acid digestion is recommended for the analysis of waste oils from of vehicles. A few jxL of the resulting aqueous leachates can then be pipetted onto Ag powder and the slurries dried and pressed into polyethylene slugs to produce pins that can eventually be submitted to GD-MS analysis for the assay of their Pb contents [658], Determinations can be performed by isotope dilution and concentrations as low as 3 pg/g Pb determined with a precision of better than 5%. GD-MS has also been used for the analysis of crude oils [659] and Cr, Cu, Fe. Mg, Na, Ni, Pb, Si, Sn and Ti can be determined in NIST SRMs, SPEX organometallic standard oils and refined oil composites. The method performs very well for limited amounts of sample, but the polyatomic interferences are a drawback. 

The stability of organometallic or inorganic compounds in a petroleum matrix is an important consideration in the sampling process. Stability studies on selected organometallic standards in petroleum... 

In the absence of a standard sample, spiked samples prepared by adding a known concentration of an organometallic standard to a petroleum matrix must be used. Because the form of most native metal species in petroleum is unknown and may be variable, the Trace Metals Project investigated the availability of organometallic materials to determine those best suited for the preparation of spiked samples and calibration standards in petroleum at the nanogram/gram level. 

Preparation of Standards. Even when organometallic standards are available, extreme care must be used to ensure satisfactory results. Most ... 

The elements were analyzed without the addition of chemical modifiers, using organometallic standards for the calibration. Gasoline sarqrles were analyzed directly, while jet and diesel fuel sarqrles were diluted 1+3 with n-heptane. 

Organometallic Standards—Multi-element standards, containing known concentrations (approximately 0.1 mass %) of each element, can be prepared from the individual metal concentrates. Refer to Practice D 4307 for a procedure for preparation of multicomponent liquid blends. When preparing multi-element standards, be certain that proper mixing is achieved. Commercially available multi-element blends (with known concentrations of each element at approximately 0.1 mass %) are also satisfactory. 

Some commercially available organometallic standards are prepared fix>m metal sulfonates and therefore contain sulfur. For sulfur determinations, a separate sulfur standard can be required. A sulfur standard can be prepared by blending NIST SRM 1622 with white oil. 

Petroleum additives can also be used as organometallic standards if their use does not adversely affect precision nor introduce significant bias. 

Check Standard—Prepare instrument check standards in the same manner as the working standards such that the concentrations of elements in the dieck standards are similar to the concentrations of elements in the test specimen solutions. It is advisable to prepare the check standi from alternative sources of certified organometallic standards. 

The precision of this test method was determined by statistical analysis of interlaboratory results. Fourteen participating laboratories analyzed twelve samples in duplicate. Most laboratories performed the analyses at three different levels of dilution, namely, 1 mass % sample in solvent, 2 mass % sample and S mass % sample. In this study, dilution solvents were limited to mixed xylenes, o-xylene, and kero-sine. The most common source of organometallic standards was metal sulfonates. Most laboratories used a peristaltic pump, and approximately half of the laboratories used... 

Organometallic Standards—Pre-prepared multi-element concentrates containing 100 mg/kg concentrations of each element are satisfactory. ... 

Check Standard— Jsini organometallic standards, mineral oil, and dilution solvent, prepare a check standard to contain analyte concentrations approximately the same as expected in the specimens. The concentration of oil in the check standard must be 10 % (m/m). 

Working Standard—Prepare an instrument calibration standard that contains 10 mg/kg each of vanadium, nickel, and iron. Combine the organometallic standard, dilution solvent and, if necessary, mineral oil so that the oil content of the calibration standi is 10 % (m/m). 

Working Standards—Prepare a blank (from mineral oil) and three additional working standards (from the organometallic standards) that cover the ranges of concentration specified in Table 2. 

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