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The complete process (from sample table to ICP-OES machine) takes at least 4 days in the very best scenario:

• Day 1 involves: sampling, polishing on the Diamond Wheel, cleaning (sonic bath), and drying samples overnight.
• Day 2: Crushing in the X-Press, grinding in the Shatterbox, a pre-ignition (for LOI) weight, and placing samples in the muffle furnace overnight.
• Day 3-4: Taking a post-ignition (for LOI) weight, giving ignited samples to the chemistry technician to add sample to the pre-weighed flux, and fusing the sample bead. The beads are then handed off back to the chemistry technicians to continue ICP analysis. 

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Note: LOI determines the amount of alteration of the sample, generally, scientists use this to determine the 'freshness' of the ingenious rock being analyzed.  Typically we use unignited powder in the bead preparation as that is what correlate to the certified values.  However it is not always the case. Please speak to the geochemists regarding their preference to ignited or unignited powders in the bead preparation. There are many standards (both unignited and ignited) available for the geochemists to include in their dataset.

Apparatus, Reagents, & Materials

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• Fisher Ashing muffle Furnace 
• Sample Bead Maker 

Dissolution/Dilution

• Wrist-action shaker 
• Acid baths 

• Maker

Reagents

• 0.172 mM LiBr wetting agent (0.15 mg ultrapure LiBr in 10 mL DI water)
• 400mg of drew sighed lithium metabolite flux (weighed on shore)
• 10% nitric acid (143 mL concentrated nitric acid/L of solution). Caution! always add acid to water.
• Isopropyl alcohol, laboratory grade
• Methanol, laboratory grade
• Acetone, laboratory grade
• DI water (18.2 M¿ laboratory water obtained from Chemistry Lab)

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• Beakers
• Glass cleaner
• Tweezers
• Teflon spatula
• X-Press aluminum die
• Core liner pieces and clear endcaps
• Delrin plugs
• 1-oz glass bottles
• Weighing paper, 6 x 6
• Kimwipes

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• Quartz crucibles
• Tongs
• Vials containing 400 mg lithium metaborate flux (preweighed on shore)
• Milligram calibration weighing set
• Weighing paper, 2 4 x 24
• Vials for excess ignited powder
• Agate mortar and pestle
• Pt-Ag crucibles

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• It may be desirable to hand-pick and separate alteration material such as vesicles and/or veins from whole-rock basalt
• Sometimes veins/alterations do not become apparent until after cleaning and drying.
• Speak to the petrologist about that method if alteration is visible

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Note: The diamond disc is attached to a magnetic disc which is then placed on the wheel plate. Diamond disks are located on the stud shelf in the ICP preparation area of the Thin Section Lab. Use the silver or purple (125 µm mesh) or purple (220 µm mesh) diamond disc.

Figure 1: Buehler Grinder Polisher. A. On/Off switch B. Power Indicator light C. Timer On/Off button D. Water On/Off switch E. Water flow control knob F. Disc speed control. G. Stop/Start. H. Emergency Stop.

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Loss on Ignition, or 'LOI', compares a mass measurement taken before and after a sample is subjected to extreme heat. Petrologists use LOI as an indication of degree of alteration. Low LOI values suggest relatively fresh, unaltered basalt; whereas high LOI numbers suggest alteration (clay, alteration minerals, etc.). LOI is determined by weighing a small amount of the sample (~5 g) before and after ignition. Samples typically lose weight as water is driven off, though an iron-rich, water-poor sample may gain weight. 5g of sample is suggested to reduce the %LOI error to around 1% or less. Advise the scientists if they want less ignited.

LOI is not required for all types of ICP Preparation. Check with the science party to determine if LOI is a desired measurement. If the science party does not want an LOI measurement move on to the section Making the Sample Bead.

Loss on Ignition

Determining a sample LOI comprises three procedures:

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Graphical Measurement Window: Shows a line graph of the live-time measurement weight and the running average weight.
Final Weight Panel: Displays the Final Weight after all measurement counts have been made.
Statistics Panel: Shows the average weight adjusting with time.
Counter Weight: Enter in the reference weight

Counts: The elapsed amount of measurements
Tare: Shows and applies the tare or 'zero' value.
Sample ID: Name the sample being measured.
Commands Panel: Executable commands
Weigh: Starts measurement
Tare: Determines the 'zero' weight. This value is applied to the final weight.
Halt: Stops a measurement before it has gone through all counts
History Panel: Shows statistics on all measurements taken. This file can be exported into an excel file by using the 'Export' button. Note: The 'Export CSV' file does not work.
Options Panel: Editable measurement parameters. We measure using the 'Counts' feature. 'Counts' is active when the dot is blue. Change the number of counts or measurements the balance takes here.
At the beginning of a series of measurements, tare the balances. To do this first make sure that the 'Counter Weight' field is set to '0' and then set the 'Count' value. The 'Count' is dependent of the sea state: 600 for calm waters and 1000 counts for rough waters. If seas are too rough than wait until the weather settles before continuing to measure.
A rule of thumb is that the measurement of a known reference mass shouldn't have a larger deviation than the accuracy desired. For example, our accuracy is +/- 0.05 grams; weigh a reference mass in the unknown balance that is close to the masses you are measuring (e.g., 25 grams) and perform the measurement with the appropriate counterbalance mass in the reference balance pan. You should get a final mass of 24.95—25.05 grams.
Once parameters are set, select the 'Tare' button. When the tare is complete the 'Final Weight' Section turns orange and the 'History' Section updates (Figure 31).

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Put in a reference weight into the "Reference' balance. With the tweezers, select the 20g weight and place it in the center of the 'Reference' balance (Figure 32). To have a more accurate measurement, the reference weight should be close to the expected 'Unknown' sample weight (roughly ~20g). Enter this reference weight into 'Counter Weight' in the Statistics panel.

Figure 32. Reference weights. A: Weights. B: Tweezers.

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Weigh out 5 grams of sample powder into the quartz crucible within +/- 0.05g (Figure 37). The total weight should be the crucible weight + 5 grams within +/- 0.05 grams. For example, a crucible weighs 14.32g, thus the total weight plus the sample will be between 19.27 – 19.37g. We use 5g because it is a good representation of the sample, to decrease the %LOI error to about 1%, and it fills the crucible  appropriatelyappropriately. You will find that you will loose some of the sample due to it sticking to the qtr quartz crucible when you are finished with the LOI.

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Samples are ignited in the Thermolyne Muffle furnace located in the Chemistry Laboratory. The entire ignition cycle takes approximately 20 hours to complete and cool down to ~200°C. After ignition, samples need to be taken out when they come down to ~ 50°C-200°C. If the samples sit for too long they will reabsorb moisture and the 'Post-Ignition Weight' will be inaccurate. Time this accordingly.

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Bring crucibles over to the Muffle Furnace (Figure 39). There is a wooden tray to assist with the transferor transfer of crucibles from one lab to the other. Turn the power switch on and the control panel will illuminate.

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When the furnace finishes it's cycle and cools down to ~50°–200°C, remove the crucibles with tongs or the padded gloves (if cool enough). Put samples onto a back into the wooden tray and store tray in the desiccator. Keep samples in the desiccator and remove one at a time while weighing. It is very important for the samples to not reabsorb moisture so begin weighing as soon as possible.

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Open the Excel File LOI_Spreadsheet in Local Disk > DATA >LOI > LOI_Spreadsheet.xlsx

The spreadsheet has three sheets:

• The first sheet is as follows:

• The second sheet is for repeats
• The third sheet is the format for uploading the data using the spreadsheet uploader (Figure 41)

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• Text ID: e.g., WDGE11258831 (Note: capital letter matters)
• Analysis: LOI
• Replicate: 1 (usually)
• crucible_number: Crucible ID (e.g., A, B, F...)
• crucible_preignition_mass: crucible mass only (small inner crucible) (component unit: grams)
• crucible_and_preignition_sample_mass: inner crucible with fresh sample before ignition (component unit: grams)
• crucible_and_postignition_sample_mass: inner crucible with ignited sample after ignition (component unit: grams)
• loi_percent: LOI in % (component unit: none; the value is already a percentage)
• reference_mass: sample mass (calculated difference) (component unit: grams)
• comment: specify temperature and time used for LOI (e.g., 950 deg C for 4 hours; used during Exp 391)

Figure 41. LOI Spreadsheet Upload Template 

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• An analytical procedural blank of Flux is prepared identically to the samples. The 0.4 g of flux (the pre-weighed flux) is fused with 10µL 0.172 mM of LiBr and dissolved. An additional 0.1 g of flux is NOT added to mimic the TDS of the 0.5 g mix of sample + flux because this would provide an inaccurate quantitation of the impurities introduced by the amount of flux used in preparation of the unknowns.

Making beads - protocol used during Exp 391

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• .

Weighing the Sample

Note: This process is typically done by the chemistry technicians.
Weighing the sample is a critical step. The sample weight should be as close to 100 mg as possible. Inaccuracies in the weight will show up in the analytical results. Print small labels for each sample and place on your small, clear capped vial. On the lid label a sticker with the core, section, and interval. Confirm with scientists what powder you will be using Fresh or Ignited.

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