Table of Contents

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Introduction

Inductively Coupled Plasma Optical Emission Spectroscopy, ICP-OES, is a method to perform elemental analysis on a sample in solution (ODP Technical Note 29). This manual covers hard rock sample preparation for ICP-OES analysis. Hard rock samples are prepared via the 'flux fusion' approach. This technique ensures complete dissolution of sample allowing a full elemental analysis. Solutions are stable which allows further analysis, and involves no HF making. It is a safe and ideal method for shipboard analyses (ODP Technical Note 29).

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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 correlates to the certified values.  However it is not always the case. Please speak to the geochemists regarding their preference of 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

Laboratory Apparatus

General Laboratory Equipment

• Compensated Dual Analytical Balance System (Mettler Toledo balances)
• Drying ovens at 110°C and 60°C
• Muffle furnace
• Sonicating bath

Hard Rock Processing

• Splitting room saw
• Buehler grinder/polisher with 70 µm grit diamond grinding wheel
• Sonicator (with small water bath)
• X-Press crusher 
• Spex Shatterbox with tungsten carbide (WC) grinding vessel 
• Spex Mixer Mill with tungsten carbide or alumina canisters 
• Retsch MM400 Mixer Mill

LOI/Bead-Making

• Fisher Ashing muffle Furnace 
• Sample Bead 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
• Deionized water (18.2 MΩ/cm² laboratory water obtained from Chemistry Lab)

Materials

Grinding Samples

• Beakers
• Glass cleaner
• Tweezers
• Teflon spatula
• X-Press aluminum die
• Core liner pieces
• Delrin plugs
• Sample vials or jars
• Weighing paper, 6 x 6
• Kimwipes

LOI/Sample Bead

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

Preparing Rock Samples

Rock samples are prepared for ICP analysis using the following procedures on each sample:

1. Cut to size (see Cutting Samples to Size below)
2. Polish (see Polishing Samples on Diamond Wheel below)
3. Clean (see Cleaning Samples below)
4. Dry (see Drying Samples below)
5. Crush (see Crushing Samples in the X-Press in XRD Sample Preparation Hard Rock )
6. Grind (see Grinding Samples in the Shatterbox in XRD Sample Preparation Hard Rock)

Cutting Samples to Size

To cut samples for the X-Press, use the splitting room rock saws (located in the Core Deck) following these guidelines:

• Cut samples to ~1–2 cm in length and width. Avoid cutting irregular pieces; ideal samples are cubes
• Avoid veins, infilled vugs, etc
• Remove as much contaminated material as possible
• Contact the petrologist(s) if cutting reveals unexpected features

Notes about altered samples:

• 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

Polishing Samples on Diamond Wheel

Polishing the samples remove contamination caused by drill bit, saw blade, or other unwanted material. Grind each surface (each outer side) on a high-speed, diamond disc.

Apparatus and Materials

• Buehler Grinder/Polisher
• Diamond grinding disc
• Sample Beaker

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Figure 3. Labeled beaker with polished rock inside. 

Cleaning Samples

To remove contamination (oil, skin, and residue from the diamond wheel) wash the polished samples in 70% isopropyl alcohol and DI water. From this point onward, wear gloves when handling samples to avoid reintroduction of contaminants.

Apparatus and Materials

• Sonicator with basket
• Beakers
• 70% Isopropyl Alcohol
• Tray(s)

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Repeat the rinse cycle until the water is clear. If the samples are soft and/or clay rich, they will not reach the "clear water" state. Continuing to sonicate will only dissolve the sample. If after 3–4 washings, the water still isn't clear, go to the next step. After the final rinse, decant as much water from the beaker as possible.

Drying Samples

This step requires at least 12 hours and therefore should be done towards the end of your shift. Turn oven on (Figure 5) and adjust the dial to about 110°C (this is marked on oven, or you will have to turn on oven a couple hours before and use the thermostat inside to get the temperature correct. It is important to not overheat the sample as it may affect some minerals. Temperatures less than 110°C is ok, but it may take longer than 12 hours for the sample to dry.

Apparatus and Materials

• ICP Oven
• Samples

Note: The ICP oven should be kept clean at all times, as samples are left open and are susceptible to contamination. The ICP oven should only be used for ICP samples. If the oven shows any sign of rusting, please notify the ALO as a new oven will need to be ordered.

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Figure 6. Desiccators located in the X-ray lab

Crushing Samples in the X-Press

See XRD Sample Preparation Hard Rock 

Grinding Samples in the Shatterbox

See XRD Sample Preparation Hard Rock

Determining LOI

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:

• Pre-ignition weighing
• Igniting samples
• Post-ignition weighing

Advice on LOI Procedures (from Exp. 366 Methods, from Exp 393/Jeff Ryan)

Shipboard sample preparation and LOI determination procedures described in Murray (2000) and updated in recent IODP Proceedingsvolumes (e.g., Reagan et al. [2015] for Expedition 352) are appropriate for a range of sediment and rock compositions, but some care must be taken with unusual sample matrixes. As an example, attempting sample ignitions on carbonate-rich materials can lead to spurious results and issues with contamination if quartz crucibles are used for sample ignitions because carbonates will react with quartz upon heating to both devitrify and decompose the crucible. Alumina ceramic crucibles may be better for carbonates but risk contamination for Al and potentially other elements due to spallation over time. Putting carbonate rich samples or sediment in quartz crucibles ruins the crucibles and the LOI determination (consulted with Jeff Ryan on this, Exp 393). Consult with the scientists to be determine what crucible will be needed.

Maximum ignition temperatures of 1000°C and higher are appropriate for ultramafic and some mafic igneous materials but may result in sample sintering and/or sticking to some Si- or Ca-rich materials. Ignition temperatures of <850°C are inadequate to decompose carbonate minerals in sediment samples, even if samples are held at temperature for several hours. In general, igniting samples to at least 900°C as a maximum temperature is advisable to decompose all volatile-bearing phases and obtain reliable measures of LOI.

Pre-ignition Weighing

Apparatus and Materials

• Mettler Toledo Dual Balance
• Acid Washed Quartz or Alumina Ceramic Crucibles
• 4x4 Weigh Paper
• Reference Weights
• Thermolyne Muffle Furnace

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Place a large sheet of paper in front of the balances and place supplies here. For each sample you need weigh paper (Figure 28A), a scoopula (Figure 28C), and a crucible set (Figure 28B). Clean the scoopula with isopropyl alcohol in between each sample as it has direct contact with the sample powder.
Figure 28. Materials needed for weighing LOI. A: Clean paper or kim wipe. B: Crucible set. C: Scoopula. D: Samples

Setting up the Mettler Toledo Balances

Samples are weighed on the Mettler-Toledo Dual Balance. The Dual balance uses two weighing stations to compensate for shipboard motion: one a 'known' reference weight (Figure 29A) and the other an 'unknown' sample weight (Figure 29B). The balance takes a series of measurements and uses the average value as the final weight (for a more in-depth guide refer to the Balance User Guide on Cumulus). Each balance has a control panel plate, which constantly records weight. These plates communicate with the "Mettler Balances" program.

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

Weighing Crucibles

 The quartz crucibles have three sections: an outer (or large) crucible, an inner (or small) crucible, and a lid (Figure 33). If alumina ceramic crucibles are needed, as for carbonate rich samples or sediment samples, replace the inner quartz crucible with the ceramic crucible.

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Close the door and click 'Weigh'. Wait for the counts to finish and then record the 'Final Weight' in the spreadsheet under 'Crucible Wt'.

Weighing Sample

Weigh out 5 grams of sample powder into the 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 appropriately. You will find that you will loose some of the sample due to it sticking to the crucible when you are finished with the LOI.

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Figure 38. Complete crucible unit with sample, ready for ignition.

Igniting Samples

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.

Using the Muffle Furnace

Bring crucibles over to the Muffle Furnace (Figure 39). There is a wooden tray to assist with the 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 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.

Post-Ignition Weighing

Post-ignition measurements should be taken soon (within an hour) after removing crucibles from the furnace. Failure to do so will disrupt the LOI values. Reweigh the crucible plus the ignited sample to determine how much weight was gained or lost. Follow the same weighing procedure as in Pre-ignition Weighing.

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Note: By convention, weight lost during ignition is recorded as a positive LOI value; whereas weight gained is recorded as a negative LOI value. Report the results to 2 decimal places.

Uploading LOI Data To LIMS

Open the Excel File LOI_Spreadsheet in Local Disk > Documents > XRD > Sample and ICP Prep > LOI > LOI Spreadsheets > LOI_ExpXXX.xlsx

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• Text ID: e.g., WDGE11258831 (Note: capital letter matters)
• Analysis: LOI
• Replicate: 1 (usually) leave blank, unless true replication (not just reanalyzing) of a sample, then begin replicate numbering with '0', then '1', then '2'.
• 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)

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Copy and paste your spreadsheet into that uploader. Click the 'Edit' button and 'Validate Sheet'. This checks and highlights any errors that need to be fixed. When the spreadsheet comes up clean, click 'Lims' and 'Upload'. The sheet will turn green when the measurements are successfully uploaded. The data is now in LIMS under Chemistry > ICP-AES Solids >Expanded LOI.

Cleaning the Quartz or Alumina Ceramic Crucibles

1. Wash the crucibles with DI water and a small piece of a scouring pad (no soap).
2. Rinse several times with DI water.
3. Place crucibles in a 10% HNO₃ bath for 12 hr. If in urgent need, the quartz crucibles can be soaked a minimum of 2 hours, but extra flux blanks will need to be made and added to batches that use these crucibles.
4. Rinse the quartz crucibles 3 times with DI water after the acid bath. For the ceramic crucibles, rinse 3 times with DI and then soak them in a large beaker of DI water for 4-6 hours to dilute the acid absorbed by the crucibles.
5. Dry the either type of crucibles in the oven at a maximum temperature of 60°C. For the ceramic crucibles, heat them to 800°C in the muffle furnace for 2 hours and allow to cool to room temperature before removing.

Some crucibles will develop a thin white or red cloudy film, become spotted, or start flaking. If any of these things happen discard the crucible in the sharps container. When the crucible undergoes one of those changes the quartz has started to react at high temperatures, and could start contaminating the samples. 

Making the Sample Bead

• In a vial, mix 400 mg lithium metaborate flux (pre-weighed onshore) with either ignited or non-ignited powdered sample, check with the science party to determine which sample type should be used. Typically we use unignited powder as that is how our standard beads are prepared and what correlate to the certified values.  This step is typically completed by the chemistry technicians.
• Fuse both sample powder and flux into a glass bead (Figure 43). Dissolve the bead in nitric acid. This solution will be further diluted and analyzed by the ICP.

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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.

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.

1. Clean the countertop around the balance and the balance pans with isopropyl alcohol. Put sheets of white paper on all the working surfaces.
2. Arrange all supplies on the white paper: tweezers, scoopula, and a sheet of 6x6 weigh paper.
3. Ensure the following items are available and labeled for each sample.
   • 1 bottle of pre-weighed flux
   • 1 new, empty, acid-washed vial for the remaining ignited powder
4. Pre-label the bottles before weighing (one label each on the cap and the bottle).
5. Make two weigh boats. Cut a rectangular strip from your piece of weigh paper and fold up the two long sides. Put one on the 'Tare' Side and the other on the sample side. You will need to make a new boat for each sample. The tare boat will remain there for all of your samples.
6. Close the door of the balance and tare for 100 counts.
7. Remove a crucible of ignited powder (if using ignited powders) from the desiccator. If the powder has hardened from the furnace then transfer the sample from the crucible to a clean agate mortar and grind until it is a loose fine powder. If your sample is fine proceed to the next step. If using Fresh, use the vial of fresh powder that is provided by the XRay technician. Note if the fresh powder will be shared with XRF measurements. Once the 100mg is removed from the vial give back to the XRD technician for XRF analyses.
8. Keep your boat in the weigh pan and with your scoopula measure out 100 milligrams. Be careful not to spill your sample onto the pan. If you do, remove your sample boat and with a small brush wipe away the loose powder.
9. Close the door and weigh the sample, putting more sample on or off until you achieve a reproducible weight that is within ±0.00050 g of 0 (half a milligram).
10. When the sample weight is as close to 100 mg as you can get it (i.e., 0.0995–0.1005 g), open the labeled bottle with the pre-weighed flux and carefully pick up the paper with the sample powder on it and transfer all of the powder into the bottle containing the flux. Snap the paper a few times with a flick of your index finger to make sure everything goes in.
11. Homogenize the sample/flux mixture by holding the vial slightly off of vertical and rotating it. Tap it from time to time on the bench top as you rotate it to clear any powder from the sides of the vial. Avoid getting the sample/flux powder stuck around the cap.

Fusing the Sample into a Bead

The most critical aspect of bead-making is maintaining a constant sample to flux ratio. A ratio of 1:4 suffices in most situations. If samples are small (e.g., volcanic glasses), a sample mass <0.1 g may be used. However, the same ratio must be maintained between the samples and the calibration standards (otherwise the matrix will not match). For example, 0.05 g of sample requires 0.2 g flux.

Using the Beadmaker

Using the Bead Maker during rough seas is not advised, due to extra physical stress of the machine parts which could cause damage to the Bead Maker.

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1. Lay a large Kim wipe and a piece of weigh paper down next to the Bead Maker. Unwrap a platinum crucible and place it on the weigh paper. Pour the powder mix into the crucible. The sample should evenly cover the bottom.
2. Pipette 10 µL of 0.172 mM LiBr wetting agent into the center of the sample powder.
3. Open the Bead Maker lid and place sample inside the sample holder. The short wide crucible will fit directly; whereas, the tall narrow crucible will need an additional ceramic ring (no longer have these?).
4. Close the lid. Double check both indicator lights are on. Press 'On' to start the program. The process will take 12 minutes and the sample is heated in three stages:
   • Stage 1:700°C for 2 min
   • Stage 2:1050°C for 5 min,
   • Stage 3: 1050°C in agitation for 5 min.
5. Be prepared to remove the crucible as soon as the timer reaches 0. The material hardens very quickly so be ready with safety glasses, gloves, and the platinum tipped tongs before the final stage has finished.
6. With the Pt-tipped tongs, lift out the crucible and swirl the contents around to get the entire sample into one bead. Wear eye protection! The bead is very hot and rapid cooling can cause it to shatter and fly out.
7. Place the crucible on its cooling rack. When seated properly the red light behind it will start flashing. When the beadmaker beeps it should be finished cooling.
8. Place a sheet of 6x6 weigh paper on the ceramic plate. Take crucible from the cooling rack and prepare to flip it upside down on the paper to extract the bead.gently tap the bottom of the crucible on the ceramic plate until the bead releases from the crucible.  If the bead is stuck, tap the base of the crucible at different angles on the ceramic plate gently.    Do not hit the rim of the crucible on the ceramic plate.  The platinum is malleable and can easily be damaged if too much force is used.
9. When the bead is loose in the crucible, tip the bead out of the crucible on to the weighing paper and then put With crucible in hand flip over and give it a firm whack on the weigh paper. The bead should pop off without much resistance. Put the bead back into the vial that contained the flux/sample mixture.  
10. If there are small pieces of bead left behind you can use your Teflon spatula to try pry it off. Do not use too much force. The platinum is malleable and will get scratched and damaged if put under too much force. If it still remains, make a note of the sample number and inform the chemistry technician. The residue (if any) should come off during the cleaning process.
11. Repeat process for all samples.
12. Hand off all beads to the chemistry technicians to continue on with the ICP analysis.

Cleaning Platinum Crucibles

1. Rinse crucibles with DI water.
2. If beads are stuck to the bottom, sonicate with DI water for 30 min or more.
3. Place crucibles in HNO3 10% bath for 12 hr. If you notice any signs of residue, leave in the acid bath for longer. If the crucibles are in urgent need, a minimum cleaning time in the HNO3 10% acid bath is 2 hrs, however, extra flux blanks should be made with these crucibles for analysis to ensure there isn't leftover contamination.
4. Clean a Tupperware container with isopropyl alcohol. Lay down sheets of paper towel and large Kimwipes.
5. Take crucibles out of the acid bath and rinse with DI water 3 times. Place crucible in the container. If the crucibles require polishing, see Polishing the Platinum Crucibles.
6. Cover all crucibles with a large Kimwipe and place in the drying oven in the Chemistry Laboratory. Leave overnight.
7. When dry remove crucibles and bring into the XRD laboratory. Wrap each crucible in a small Kimwipe and and place back in the safe. Lock the safe after all crucibles have been put back.

Polishing the Platinum Crucibles

It may be necessary to polish the crucibles to remove scratches. Do this no more than once per expedition because polishing thins the platinum and in time the crucible will crack. A polishing machine is located in the ICP prep area.

1. Wrap a silk cloth (like the cloth used to clean eyeglasses) around the polishing nozzle.
2. Apply a diamond paste (Grade 30, found in Thin Section Lab) to the front of the silk-covered nozzle and place the crucible over the nozzle.
3. Turn polisher on and polish the crucible bottom for ~30 s (the bottom will be shiny). Be careful because the crucible will get hot. Do not try to remove any deep scratches – the crucibles are not that thick. The least amount of polishing the better.
4. Clean the crucibles with isopropyl alcohol and put in 10% HNO3 bath for 12 hr.

Using the LOI Furnace to Make Sample Beads

If the bead maker breaks, use the LOI furnace to make beads.
Caution! Safety is a major issue with this procedure; use proper personal protection equipment and note where the nearest fire extinguisher is located.

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1. Place the sample crucible on a ceramic plate to cool. These crucibles are very hot and may burn anything near or under them. Take appropriate precautions.
2. Repeat this procedure until all samples are completed.

Credits

This document originated from Word document ICP_HR_Prep_UG_376.doc (see Archived Versions below for a pdf copy) that was written by H. Barnes & K. Bronk; later edited by N. Lawler & A. Armstrong. Credits for subsequent changes to this document are given in the page history.

LOI LIMS Component Table

Archived Versions

ICP Sample Prep User Guide: 29th September 2022

LMUG-ICPPreparation-230220-1915-158.pdf

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