v.378P

Hard Rock Preparation for ICP:
User Guide

Manual Information

In This User Guide

Introduction

Inductively Coupled Plasma Atomic Emission Spectroscopy, ICP-AES, 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-AES 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 a safe and ideal method (ODP Technical Note 29).
Rock samples are crushed to a fine, talc-like powder using multiple cleaning, crushing and grinding procedures. After grinding, loss on ignition (LOI) is determined. Ignited material is fused with flux powder forming a glass sample bead. Fused beads are then dissolved in 10% HNO_{3 .} This is further diluted and the resulting solution is processed by the ICP-AES machine.
The complete process (from sample table to ICP-AES machine) takes 3-4 days. Day 1 involves: polishing on the Diamond Wheel, cleaning, 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 furnace overnight. Day 3-4: Taking a post-ignition (for LOI) weight, and fusing the sample bead. The beads are handed off to the chemistry technicians to continue ICP analysis.

Apparatus, Reagents, & Materials

Laboratory Apparatus

General Laboratory Equipment

• Compensated Dual Analytical Balance System 
• Drying ovens at 110°C and 60°C

Rock Grinding

• 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 

LOI/Bead-Making

• Fisher Ashing Furnace 
• Sample Bead Maker 

Dissolution/Dilution

• Wrist-action shaker 
• Acid baths 

Reagents

• 0.0172 mM LiBr wetting agent (0.15 mg ultrapure LiBr in 10 mL DI water)
• 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)

Materials

Grinding Samples

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

LOI/Sample Bead

• Quartz crucibles
• Tongs
• Vials containing 400 mg lithium metaborate flux (preweighed on shore) (Figure 9)
• Milligram calibration weighing set
• Weighing paper, 2 x 2
• Acid-washed 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).
2. Polish (see Polishing Samples on Diamond Wheel).
3. Clean (see Cleaning Samples).
4. Dry (see Drying Samples).
5. Crush (see Crushing Samples in the X-Press).
6. Grind (see Grinding Samples in the Shatterbox).

Cutting Samples to Size

To cut samples for the X-Press, use the splitting room saw following these guidelines:

• Cut samples to ~1–2 cm in length and width. Avoid cutting irregular pieces; ideal samples are cubes. Cut the first samples small to get a feel for rock hardness.
• 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 vesicles and/or veins from whole-rock basalt.
• Speak to the petrologist about this method if alteration is visible.

Polishing Samples on Diamond Wheel

To remove contamination (drill bit, saw blade, or other unwanted material) and clean the samples, grind each surface on a high-speed, diamond disc.

Apparatus and Materials

• Buehler Grinder/Polisher
• Sample Beaker

...

Figure 2. 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
• Beakers
• 70% Isopropyl Alcohol
• Tray(s)

...

Repeat the rinse cycle until the water is clear. If the samples are soft and/or clay rich, they won't 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 involves an overnight portion and should be done towards the end of the shift.

Apparatus and Materials

• ICP Prep Oven
• Samples

Place the beakers into the ICP Oven at 110°C for 12 hours (Fig. 5). Turn on the power button and adjust the knob to 110°C, which is marked on the oven. A thermostat is located inside to double check temperature.

...

Figure 6. Desiccators located in the X-ray lab

Crushing Samples in the X-Press

The X-Press is a motorized hydraulic press that crushes samples into smaller pieces.
First clean the X-press with simple green and isopropyl alcohol. Clean the work area and materials with isopropyl alcohol for each sample.
Place a large KimWipe on your working surfaces for your clean materials. Next collect the following supplies that make up the 'crushing unit' of the X-press (Fig. 7). Materials are located in the drawer labeled 'X-PRESS SUPPLIES' in the X-Ray Prep Area.

...

After the sample has cracked remove the crushing unit. To remove the unit, loosen the 'pressure relief handle' and press down on the toggle switch. The pressure gauge should read zero and the metal platform will lower down. When the platform is level with the surface let go of the toggle of start unscrewing the jackscrew. Then open the door and remove the unit. The pieces can be poured into a labeled bottle that will eventually hold the finely ground powder. From here the pieces will then be put into the Shaterbox vessels.
If pieces are still too large then repeat the same setup and crush it again. Look out for and remove any pieces of the Derlin Discs that may have chipped off and gotten into the sample.

Grinding Samples in the Shatterbox

The shatterbox takes the crushed pieces from the X-Press and grinds them into a very fine powder. The Spex shatterbox is capable of grinding three standard size samples or one large sample. Our grinding vessels used are tungsten carbide.

Apparatus and Materials

• Shatterbox
• Tungsten Carbide Vessels: Vessel, Puck, and Lid
• Samples
• 1oz Sample Vials
• Sample Labels

...

The three pinned plate will hold three vessels while the one pinned plate will only hold one. If two samples need to be crushed select the three pinned plate. The large vessel will sit directly in shatterbox without an additional plate below it.

Loading the Shatterbox

Transfer the sample pieces into the grinding vessel. Pour sample pieces between the puck and the wall of the vessel (Fig. 21). There can't be any material on top of the puck or inside the sealing ring; otherwise the vessel will not seal properly and the sample can spill inside the Shatterbox. If any pieces are on top of the puck or ring, use gloves, tongs, or a KimWipe to move the sample into the vessel. Put on the lid and start assembling the shatterbox.

...

When the time is set press the 'Start' button (Fig. 28D). To temporarily pause the operation press the 'Pause/Stop' button once (Fig. 28E).To stop the machine press 'Pause/Stop' twice.
Normal Sounds: The shatterbox is extremely loud. The foam and strap surrounding the shatterbox helps keep it in place and minimize some of the noise.
Abnormal Sounds. If there are any metal on metal sounds shut off the shatterbox immediately. Something inside the shatterbox has probably come loose and will damage the inside of the container.
When the shatterbox cycle is done open the lid and remove the vessels, placing them on the counter. Open the grinding vessel and with clean tweezers take a bit of the powder and feel it against the inside of your wrist. The sample should feel like baby powder, if it does not, repeat the shatterbox cycle.

Transfer powder into Vial

Disassemble the vessel carefully wearing 'Powderless Nitrile' gloves. Clean off any powder on the lid or puck with clean gloves or a kim wipe. Carefully remove the puck from the vessel. Pour the sample onto a clean weighing paper. If any powder remains, use a clean plastic spatula, brush, or your finger to dislodge it.
Note: Never use metal to dislodge sample material, as any grooves or scratches in the vessels will increase the risk of contamination.

Cleaning the Grinding Vessels

Vessels must be cleaned in between samples and after all samples have been run for the day. Vessels should never be put away wet. This alters and tarnishes the vessel.
In Between Sample Runs

...

1. Take a scoop of quartz sand and put it in your vessel and run it as you would a sample for several minutes.
2. Remove the vessel and empty out the sand. Scrub the pieces with DI water and a scouring pad. Then spray with isopropyl alcohol and wipe down with Kim Wipe.
If your vessel is particularly dirty run a combination of quartz sand, a little hot water and detergent (Borax). This can be run for several minutes. A thick paste will form and you clean it with DI water and isopropyl as in the other cases.

Making the Sample Bead

Two processes are required to make a sample bead:

...

Figure 29. Fused glass bead. 

Weighing the Sample

Note: This process is typically done by the chemistry technicians.
Weighing the ignited 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.

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 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.
8. Keep your boat in the weigh pan and with your scoopula measure out 100 grams. 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

Collect platinum crucibles, platinum tipped tongs, 0.172 LiBr, and pipette tips from the safe above the Bead Maker (Figure 30). Get the 10-100ul pipette and teflon spatula from the drawer and clean with isopropyl alcohol. Have a tray of samples that need to be fused and an empty tray for finished beads.

 

...

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.
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 is done. 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 flashing stops the bead and crucible have finished cooling down.
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.
9. 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.
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.
4. Clean a Tupperware container with isopropyl alcohol. Lay down sheets of paper towel and a 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.

...

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.

Determining LOI

Loss on Igntion, 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.

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)

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. 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 Crucibles
• 4x4 Weigh Paper
• Reference Weights
• Thermolyne Muffle Furnace

...

 Place a large sheet of paper in front of the balances and place supplies here. For each sample you need weigh paper (Fig. 34A), a scoopula (Fig. 34C), and a quartz crucible set (Fig. 34B). Clean the scoopula with isopropyl alcohol in between each sample as it has direct contact with the sample powder.




Figure 34. 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 (Fig. 35A) and the other an 'unknown' sample weight (Fig. 35B). 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 record weight. These plates communicate with the "Mettler Balances" program.

...

Figure 38. 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 (Fig. 39).

...

Figure 42. Weighing an empty inner crucible.
 
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 quartz crucible within +/- 0.05g (Fig. 43). 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.

...

Figure 44. 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. 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 (Fig. 45). Turn the power switch on and the control panel will illuminate.

...

When the furnace finishes it's cycle and cools down to ~50°–200°C, remove the crucibles with tongs. Put samples onto a 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 immediately 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.

...

%LOI = 100 x (weight change during ignition)/ (fresh sample weight).
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 Upload Template' in Local Disk > DATA (Fig. 47). Put your LOI information into the spreadsheet following the example format. Fill in the Text ID, Analysis, Replicate, Crucible number, and all weights and units including the %LOI.

...

Figure. 48. Spreadsheet Uploader Icon.

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 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.
4. Rinse 3 times with DI water after the acid bath.
5. Dry the crucibles in the oven at a maximum temperature of 60°C.

...