ASTM D5184 Standard Test Methods for Determination of Aluminum and Silicon in Fuel Oils by Ashing, Fusion, Inductively Coupled Plasma Atomic Emission Spectrometry, and Atomic Absorption Spectrometry
TEST METHOD A - INDUCTIVELY-COUPLED PLASMA ATOMIC EMISSION SPECTROMETRY
13. Preparation of ICP Instrument
13.1 Instrument - Consult the manufacturer's instructions for the operation ofthe instrument. Design differences between instruments, ICP excitation sources, and different selected analytical wavelengths for individual spectrometers make it impractical to specify the required manipulations in detail.
13.2 Peristaltic Pump - If using a peristaltic pump, inspect the pump tubing and replace it, if necessary, before starting each day. Verify the solution uptake rate and adjust it to the desired rate.
13.3 ICP Excitation Source - Ignite the ICP excitation source at least 30 min before performing an analysis. During this warm-up period, nebulize water.
NOTE 8 - Some manufacturers recommend even longer warmup periods to minimize the variability of the measurements.
13.4 Wavelength Profiling - Perform any wavelength profiling that may be called for in the normal operation of the instrument.
13.5 Operation Parameters - Assign the appropriate operating parameters to the instrument task file so that the desired elements can be determined. Parameters to be included are element, wavelength, background correction points (optional), interelement correction factors (optional), integration time and three consecutive integrations.
14. ICP Calibration
14.1 Perform a five point calibration consisting of the blank and calibration standards at the beginning of analysis of each batch of specimens. Use the check standard to determine if each element is in calibration. If the result obtained on the check standard is outside 5 % of the expected value for any element, make any adjustments to the instrument that may be necessary and repeat the calibration.
14.2 Alternatively, perform a two point calibration with the blank solution and most concentrated calibration standard. Use the check standard as described in 14.1.
15. Procedure
15.1 ICP Analysis:
15.1.1 Specimen Analysis - Analyze the specimen solutions (see Section 11) in the same manner as the calibration standards (that is, same integration time, background correction points, plasma conditions, etc.). Rinse the plasma torch between specimens by nebulizing water for 10 s. If the concentrations of aluminum or silicon in the specimen solution exceeds the calibration range, dilute the specimen solution with the blank solution to bring it within the range of the calibration standards.
15.2 Check Standard Analysis - Analyze the check standard after every fifth specimen. If the concentration of any element is outside 5 % of the nominal value, re-calibrate the instrument and re-analyze the sample solutions back to the previous acceptable check standard analysis.
15.3 Calculation and Report - See Section 18.
TEST METHOD B - FLAME ATOMIC ABSORPTION SPECTROMETRY
16. Preparation of AAS Instrument
16.1 Instrument - Consult the manufacturer's instructions for the operation of the atomic absorption instrument. Design differences between instruments make it impractical to specify the required manipulations here.
16.1.1 Proper operating procedures are required for safety as well as for reliability ofresults. An explosion can result from flame flash-back unless the correct burner head, gas flow rates and flame ignition/shutdown sequence are used.
16.2 Settings for Aluminum Analysis:
16.2.1 Fit the aluminum hollow cathode lamp, set the spectrometer to the specified wavelength (see Table 1) and adjust the wavelength control to get maximum output.
16.2.2 Using the correct burner for nitrous oxide/acetylene, and following the procedure specified in the manufacturer's operating instructions, ignite the nitrous oxide/acetylene flame. Aspirate an aluminum standard (for example, 25 mg/L) into the flame. Make adjustments to burner height, burner alignment, acetylene flow rate, and impact bead to give maximum absorbance (or minimum transmittance). Adjust the gain control to set the maximum within the recommended working region of the spectrometer.
16.3 Settings for Silicon Analysis:
16.3.1 Fit the silicon hollow cathode lamp, set the spectrometer to the specified wavelength (see Table 2) and adjust the wavelength control to get maximum output.
16.3.2 Follow a similar procedure to 16.2.2, aspirating a silicon standard (for example, 25 mg/L) into the flame.
17. Procedure
17.1 AA Calibration and Test Specimen Analysis:
17.1.1 The mode of calibration depends on the type of readout facility on the atomic absorption spectrometer.
17.2 Calibration must be carried out prior to analysis of each group of samples and after any change in instrumental conditions because variations occur in the instrument behavior. Readings may also vary over short times from such causes as build-up ofdeposits on the burner slot or in the nebulizer. Thus, a single standard must be aspirated from time to time during a series ofsamples to check whether the calibration has changed. The visual appearance of the flame is a useful check to detect changes of condition.
NOTE 9 - A check after every fifth specimen is recommended.
17.3 Spectrometers with Meter Readout:
17.3.1 Aspirate the calibration standards and blank solution sequentially into the flame and record the meter readings. Aspirate the blank between each specimen.
17.3.2 If the spectrometer output is linear in absorbance, plot a calibration curve of net absorbance (absorbance of a calibration standard minus the absorbance ofthe blank) against concentration. From this calibration curve, the concentration of aluminum or silicon in each specimen solution can be determined after similarly computing the net absorbance.
17.3.3 If the spectrometer output is proportional to transmission, the net absorbance is given by:
log(d0)/(d1)
where:
d0 = the meter reading due to the blank, and
d1 = is the meter reading given by the standard or specimen solution.
17.4 Spectrometers With Digital Readout and Built-in (Non-Microprocessor Controlled) Curvature Correction and Scale Expansion Facilities:
17.4.1 Follow the manufacturer's operating instructions. Aspirate the appropriate calibration standards and blank solution and set the digital readout to read directly in the required concentrations units carrying out a curvature correction program if necessary.
17.4.2 Read the concentration of each specimen solution and blank directly from the concentration readout given by the digital display from the spectrometer.
17.5 Spectrometers With Digital Readout and Microprocessor Controlled Calibration Facilities:
17.5.1 Follow the manufacturer's operating instructions, aspirating the appropriate calibration standards and blank solutions and using the recommended calibration program, to obtain a direct readout in concentration units.
17.5.2 The concentration of aluminum and silicon in each specimen solution can thus be directly obtained after aspiration.
17.6 Analyze the specimen solutions in the same manner as the calibration standards. If the aluminum or silicon concentrations in the specimen solutions exceed the calibration range, dilute the specimen solution with the blank solution to bring it into range of the calibration standards.
18. Calculation
18.1 Calculate the concentration in the sample according to the following equations:
aluminum, mg/kg = (100*C1*d)/M
silicon, mg/kg = (100*C2*d)/M
where:
M = mass of sample taken in g,
d = dilution ratio, if required, and
C1, C2 = concentrations of aluminum and silicon (respectively) in mg/L as determined from either the read out of the ICP instrument or the calibration curve or direct readout of the atomic absorption instrument.
19. Quality Control
19.1 Confirm the performance of the test procedure by analyzing a quality control (QC) sample (Section 15 for Test Method A or Section 16 for Test Method B).
19.1.1 When QC/Quality Assurance (QA) protocols are already established in the testing facility, these may be used to confirm the reliability of the test result.
19.1.2 When there is no QC/QA protocol established in the testing facility, Appendix X1 can be used as the QC/QA system.
19.1.3 Further guidance on QA/QC can be found in Practice D6792.
