Title: Petroleum Geochemistry Research Laboratory Total Organic and Method By: Thomas Oliver and Augusta Warden Date Published: 2020 Suggested Citation: Oliver, T., Warden, A., 2020, Petroleum Geochemistry Research Laboratory and Total Carbon Method: U.S. Geological Survey Web Page, https://doi.org/10.5066/P9X85HUF Keywords: TOC, Total organic carbon, total carbon, LECO, PGRL, Petroleum Geochemistry Research Laboratory, non-dispersive infrared cell, ND-IR Method Summary The Petroleum Geochemistry Research Laboratory (PGRL) performs analytical work in support of assessments and research on petroleum systems for the U.S. Geological Survey’s Energy Resources Program. In order to determine total organic carbon (TOC) and total carbon, the PGRL uses the ISO 10694:1995 standard with slight modifications. The PGRL method deviates from the ISO 10694:1995 standard in the following ways: 1) by not following the instructions listed for inorganic carbon removal, 2) the PGRL uses different standards than those listed as examples, 3) by not following the sample pretreatment procedures, and 4) the PGRL primarily analyzes rocks rather than soils.

Total carbon and TOC are determined by combusting ground geologic materials (for example shale or other rock types) to form CO2 which is detected by a non-dispersive infrared (ND-IR) cell. Scope and Application Total carbon is often the first analytical procedure performed in the PGRL to determine if there is any carbon present in a rock sample. Total carbon and TOC analyses are relatively quick processes requiring little preparation work making them ideal processes to use as screening tools. Total carbon provides a value for the combined amount of organic and inorganic carbon present in a sample. TOC is used as a measure of the organic richness of geologic materials and is an indicator of petroleum potential in geologic assessments of petroleum systems. A TOC measurement only indicates the potential richness, and does not indicate quality, thermal maturity, or other key factors necessary to fully assess a petroleum system. Interferences Incomplete removal of inorganic carbon is a potential interference for TOC analysis. This method does not address inorganic carbon removal as there are many techniques for this process. Safety Precautions This method does not attempt to address health and safety concerns. Adherence to appropriate health, safety, and regulatory practices are the responsibility of the end user. Sample Handling, Preservation, Storage, and Holding Times Samples are received in a variety of containers, though it is important that submitters use intact containers to avoid contaminating the sample. Glass containers are preferred to store samples after they are ground to approximately 60 mesh. Preservation, storage of samples, and holding times are not a concern for this method as rock is a geologically stable material. Apparatus

Example list

Compressed air, breathing air grade or higher Compressed oxygen, zero grade or higher Copper accelerant (LECO® Part Number 501-063 or equivalent) Iron chip accelerant (LECO® Part Number 501-077 or equivalent) Ceramic crucibles (LECO® PN 528-050 or equivalent) 1-gram stainless steel sample scoop Spatula Tongs Analytical balance capable of weighing to the nearest 0.1 mg LECO® Carbon Analyzer, Model C744 or equivalent Autosampler Computer LECO® Cornerstone Software Sample Preparation This method does not cover sample preparation as there are many ways to grind samples and to remove inorganic carbon. Total carbon and TOC analysis require samples to be ground to a flour-like consistency (roughly 60 mesh) prior to analysis. Care should be taken during sample preparation to minimize sample heterogeneity. TOC samples require removal of inorganic carbon prior to analysis. It is recommended that the technique used for inorganic carbon removal be documented and reported with TOC results. Reagents No reagents are used in this method Calibration A minimum of four calibration standards that ideally cover the range of samples to be analyzed are used to create a linear calibration curve for carbon and must meet a coefficient of determination (R2 value) of 0.999 to be acceptable. Carbon standards are available commercially from multiple sources, such as LECO® and ALPHA Resources. Sample Analysis

Weigh the powdered sample and record the weight (typical weight range is 70–150 mg); it is recommended to automate the recording of weights to reduce transcription errors. Samples for TOC analysis require removal of the inorganic carbon prior to analysis (this method does not cover the removal of inorganic carbon). Add accelerants to the sample crucible to assist in the combustion of the sample. Samples are introduced to the furnace either manually or through use of an autosampler. Samples are combusted in a continually flowing stream of oxygen. The oxygen stream moves the gases produced by combustion through a scrubber column (to remove moisture and inorganic halides), then over a platinized silica catalyst (to convert any carbon monoxide into ) and finally to a ND-IR detector. For each analytical run, a new calibration curve may be created, or an existing curve may be used. If using a previously generated curve, the curve is verified through analysis of daily operating standards (standards that have established values) that meet acceptance criteria. Shale standards ShMCO-1, ShBOQ-1, and ShWFD-1 are example PGRL daily operating standards available from the Geologic Reference Material Project of the USGS Geology, Geophysics and Geochemistry Science Center. Quality Assurance and Quality Control Daily operating standards are analyzed within each batch of samples. The PGRL daily operating standards have been validated through analysis against external standards. The range of values covered by the calibration curve can be extended by analysis of standards with higher or lower carbon concentrations that meet acceptance criteria. The PGRL either uses acceptance criteria from certificate values from external sources (typically acceptance criteria are three times the standard deviation) or acceptance criteria are determined through repeat analysis by PGRL analysts of standards over time. An average value and standard deviation are determined on the standards analyzed by the PGRL and initial typical acceptance criteria are plus or minus three times the standard deviation. Acceptance criteria are dynamic and are evaluated annually. At least one duplicate sample is typically analyzed within each batch of samples. Rock samples may be heterogeneous which is demonstrated in the range of relative percent difference (RPD) values obtained through duplicate analysis by the PGRL. Relative Percent Difference is calculated using the following equation: |푆 − 퐷| 푅푃퐷 = ∗ 100 0.5(푆 + 퐷)

Where: RPD = Relative Percent Difference S = Sample Result D = Duplicate Result

While most of the duplicate analyses have an RPD less than 3%, about 1% of the duplicates have a greater than 5% RPD due to suspected sample heterogeneity. Data Reduction, Calculations, and Reporting Data reduction is automatically performed by the instrument software and RPD is calculated by the Laboratory Information Management System. No other calculations are performed in this method. Reports include all total carbon or TOC results for all samples analyzed, a reference to the ISO 10694:1995 standard and any associated quality assurance data. Note that in cases where both total carbon and TOC results have been measured, the (TIC) can be calculated indirectly by difference using the following equation: TIC (%) = TC (%) – TOC (%) Where: TIC = total inorganic carbon TC = total carbon TOC = total organic carbon

Total inorganic carbon may also be expressed as a percent calcium carbonate using the following equation: CaCO3 (%) = (TC – TOC) * 8.33 (Bernard and others, 2004)

Method Performance Table 1 states the required repeatability requirements from the ISO 10694:1995 international standard. Table 2 demonstrates that the PGRL meets the repeatability criteria stated in the ISO 10694:1995 international standard.

Repeatability criteria for Carbon Content from the ISO 10694:1995 standard Range (g/kg*) Acceptable Variability greater than including 0 2.5 0.25 g/kg (absolute) 2.5 75 10 % (relative) > 75 7.5 g/kg (absolute)

Range (weight %**) Acceptable Variability 0 0.25 0.025 weight % (absolute) 0.25 7.5 10 % (relative) > 7.5 0.75 weight % (absolute) Table 1. Repeatability criteria from ISO 10694:1995 international standard. Note: ISO 10694:1995 international standard reports all data in grams per kilogram (g/kg) while the Petroleum Geochemistry Research Laboratory typically reports data in weight percent rather than in grams per kilogram. This table is a modification of Table 1 Repeatability found in the ISO 10694:1995 international standard. *grams per kilogram is abbreviated g/kg in the table ** percent is represented by the ‘%’ symbol in the table

REPEATABILITY (in g/kg*) ShMCO-1 ShMCO-1 Total Carbon Total Organic Carbon Analysis Measured Relative percent Analysis Measured Relative percent Date Carbon (g/kg*) difference (RPD) Date Carbon (g/kg*) difference (RPD) (acceptance (acceptance criteria = criteria = ±10% **) ±10% **) Run 1 Run 2 Run 1 Run 2 04/19/19 31.09 31.21 -0.39 04/18/19 29.64 29.73 -0.30 04/30/19 31.20 31.62 -1.34 05/17/19 28.87 28.99 -0.41 06/10/19 33.34 33.08 0.78 06/12/19 32.10 31.47 1.98 06/13/19 34.25 32.74 4.51 06/24/19 31.58 31.88 -0.95 06/24/19 33.03 33.05 -0.06 06/26/19 31.58 31.81 -0.73 06/26/19 32.62 33.55 -2.81 07/08/19 32.67 32.13 1.67 07/08/19 34.32 35.01 -1.99 07/24/19 30.54 31.07 -1.72 07/10/19 32.54 31.23 4.11 08/06/19 31.08 31.76 -2.16 07/24/19 32.40 32.89 -1.50 09/17/19 29.60 29.42 0.61 08/06/19 29.55 30.90 -4.47 10/02/19 28.13 27.82 1.11 09/19/19 31.25 32.11 -2.71 01/14/20 28.14 28.42 -0.99 10/21/19 31.65 31.52 0.41 11/01/19 30.66 31.96 -4.15 02/24/20 29.97 30.47 -1.65

ShWFD-1 ShWFD-1 Total Carbon Total Organic Carbon Analysis Measured Absolute Error Analysis Measured Absolute Error Date Carbon (g/kg*) (acceptance Date Carbon (g/kg*) (acceptance criteria is ≤7.5 criteria is ≤7.5 g/kg *) g/kg *) Run 1 Run 2 Run 1 Run 2 04/05/19 84.76 85.18 0.42 04/18/19 78.64 78.68 0.04 04/18/19 81.69 84.02 2.33 05/17/19 79.42 77.00 2.42 04/19/19 82.83 82.43 0.40 05/29/19 77.80 77.36 0.44 04/30/19 81.70 79.94 1.76 05/30/19 75.32 75.68 0.36 05/17/19 83.78 79.84 3.94 05/31/19 77.29 75.33 1.96 05/29/19 82.53 82.92 0.39 06/03/19 77.66 76.31 1.35 05/30/19 82.77 82.89 0.12 06/11/19 78.06 78.94 0.88 06/10/19 82.24 81.97 0.27 06/25/19 80.61 74.70 5.91 06/12/19 84.73 84.43 0.30 06/26/19 79.77 75.22 4.55 06/25/19 82.76 83.55 0.79 06/27/19 75.68 79.41 3.73 06/27/19 81.05 82.00 0.95 07/09/19 81.21 80.99 0.22 07/09/19 83.77 83.68 0.09 07/10/19 76.55 78.22 1.67 07/10/19 85.00 83.20 1.80 07/23/19 75.81 77.85 2.04 07/24/19 81.48 81.22 0.26 07/25/19 79.42 76.27 3.15 07/25/19 85.16 83.82 1.34 08/05/19 77.72 80.68 2.96 08/05/19 84.54 84.42 0.12

Total Carbon Total Organic Carbon ShBOQ-1 ShBOQ-1 Analysis Measured Absolute Error Analysis Measured Relative percent Date Carbon (g/kg*) (acceptance Date Carbon (g/kg) difference (RPD) criteria is ≤7.5 (acceptance g/kg*) criteria = ±10%**) Run 1 Run 2 Run 1 Run 2 06/03/19 118.24 118.76 0.52 06/03/19 47.07 48.69 -3.38 06/27/19 116.32 117.56 1.24 06/12/19 51.05 48.89 4.32 07/11/19 118.96 118.81 0.15 06/27/19 49.25 49.48 -0.47 07/12/19 119.94 120.02 0.08 07/11/19 49.98 49.27 1.43 07/25/19 121.75 120.53 1.22 07/12/19 49.62 49.20 0.85 08/05/19 121.73 120.19 1.54 07/22/19 50.08 49.24 1.69 08/06/19 119.59 119.61 0.02 07/25/19 52.81 50.63 4.22 10/21/19 122.61 121.01 1.60 08/05/19 49.62 50.11 -0.98 10/22/19 115.84 118.92 3.08 08/06/19 48.48 49.75 -2.59 11/01/19 121.03 120.82 0.21 08/07/19 51.52 51.34 0.35 11/07/19 123.17 123.64 0.47 10/08/19 48.69 48.66 0.06 12/05/19 120.18 121.13 0.95 11/15/19 49.71 48.78 1.89 12/23/19 121.96 122.47 0.51 12/19/19 47.52 48.51 -2.06 01/02/20 119.26 117.54 1.72 12/20/19 50.33 50.32 0.02 01/21/20 116.69 118.62 1.93 12/31/19 49.79 48.78 2.05 01/21/20 117.04 118.26 1.22 01/22/20 119.55 116.48 3.07

Total Carbon 0.19 (standard purchased from a commercial distributor) ***

Analysis Measured Absolute Error Date Carbon (g/kg*) (acceptance criteria is ≤0.25 g/kg*)

Run 1 Run 2 02/08/19 2.12 1.95 0.17 03/22/19 1.85 1.85 0.00 04/02/19 2.00 2.04 0.04 04/03/19 1.74 1.80 0.06 04/18/19 1.91 1.96 0.05 04/19/19 1.89 1.94 0.05 05/29/19 2.07 1.99 0.08 05/30/19 1.92 2.03 0.11 06/11/19 2.07 1.88 0.19 06/13/19 1.70 1.67 0.03 06/25/19 1.96 2.00 0.04 06/26/19 1.60 1.72 0.12 06/27/19 1.89 1.94 0.05 06/28/19 1.86 1.90 0.04 07/08/19 1.94 1.96 0.02 07/23/19 1.78 1.76 0.02 07/24/19 1.73 1.82 0.09 07/25/19 1.93 2.02 0.09 08/02/19 1.79 1.79 0.00 08/05/19 1.91 2.10 0.19 08/07/19 2.04 2.08 0.04 08/08/19 1.72 1.73 0.01 08/19/19 1.83 1.60 0.23 08/23/19 2.12 2.07 0.05 09/05/19 2.01 1.96 0.05 09/30/19 1.79 1.70 0.09 10/01/19 1.93 1.89 0.04 10/17/19 2.08 2.12 0.04 10/18/19 1.80 1.86 0.06 12/06/19 2.15 2.17 0.02 12/17/19 2.11 2.17 0.06 12/18/19 2.15 2.07 0.08 01/02/20 1.85 1.70 0.15 01/07/20 1.91 1.71 0.20 01/08/20 2.04 2.02 0.02 01/10/20 2.12 2.17 0.05 01/22/20 2.06 2.13 0.07 02/18/20 1.81 1.81 0.00 02/24/20 1.95 2.00 0.05 02/27/20 1.78 1.83 0.05 02/28/20 1.97 2.05 0.08 03/02/20 1.63 1.63 0.00 03/11/20 2.09 2.11 0.02 03/24/20 1.89 2.12 0.23 03/25/20 1.74 1.76 0.02 03/30/20 1.86 1.79 0.07

Table 2 Analyses demonstrating that the PGRL meets the ISO 10694:1995 international standard repeatability criteria. Notes: *grams per kilogram is abbreviated g/kg in the table **percent is represented by the ‘%’ symbol in the table ***the 0.19 standard contains no total organic carbon, so total organic carbon measurements were not made.

Trademark Disclaimer The use of trade, product, or firm names in this method is for descriptive purposes only and does not imply endorsement by the U.S. Government. References Bernard, B.B., Bernard, H., Brooks, J.M., 2004, Determination of Total Carbon, Total Organic Carbon and Inorganic Carbon in Sediments, accessed April 15, 2020 at URL http:// www.tdi-bi.com/analytical_services/environmental/NOAA_methods/TOC.pdf. ISO 10694:1995 Soil quality – Determination of organic and total carbon after dry combustion (elementary analysis), ISO, Geneva.