Attachment_D_CARB_Gravimetric_Analysis_Requirements.pdf

State of California Bid Specifications

Attachment D

For CARB Primary Gas Standards Group III Gases

Gravimetric Analysis Requirements For CARB Primary Gas Standards

Scope

The purpose of this procedure is to define the requirements for the California Air Resources Board (CARB) primary gas standards. Gravimetric certification for CARB purposes is defined as adding a carefully measured weight of component as to an evacuated cylinder, followed by the addition of a carefully measured weight of balance gas.

The two (2) weights are converted by appropriate calculations into molar volumes and then given the appropriate gas concentration ratio in units of parts-per-million (ppm).

A sample example is as follows.

Example: Component Gas: 2000 ppm CO, Balance Gas: N2

1. Establish tare weight of cylinder (within + 0.05 grams).

2. Added weight of CO (component gas) = 13.573 g (within + 0.05 grams).

3. Added wt. of N2 (balance gas) = 6617.10 g.

4. Calculated molar quantities.

13.573 g-CO = 0.4846 moles for CO

28.01 g/mole

6617.10 g-N2 = 236.241 moles for N2

28.01 g/mole

Total Moles = 0.4846 + 236.241= 236.73 moles

5. Calculated Concentration (ppm) based on molar quantities.

0.4846 moles CO x 106 = 2051.2 ppm CO (mole/mole)

236.73 moles (Total)

Accuracy (± %)

100 x (twice total weighing error) = 100 x 2 x 0.05 = ± 0.74% (weight of component gas) 13.573

04/02/2018

State of California Bid Specifications

Attachment D

For CARB Primary Gas Standards Group III Gases

Gravimetric Analysis Requirements For CARB Primary Gas Standards

(continued)

Mixture Accuracy

The accuracy of the mixture shall be within ± 1% of the calculated value including all weighing tolerances.

Scale Capacity and Accuracy

The scale used to measure the gaseous components and the treated aluminum and steel cylinders shall be capable of weighing to within ± 0.05 grams, including all hysteresis and readability errors.

Accuracy of the scale must be traceable to the U.S. National Institute of Science and Technology (NIST). The date of the last certification must be included in the data submitted. In addition, the actual accuracy must be included with the analysis.

Balance Gases

The balance gas shall be as specified in Attachment A (Pricing Worksheet).

Component Gas

Component gas purity shall be stated in the analysis. In order to guarantee a ± 1% mixture accuracy, it will be necessary to use a diluted component gas in the preparation of gas mixtures below approximately 2000 ppm. If the component gas is a diluted mixture it must also have a traceable gravimetric analysis consistent with this procedure. The final delivered product shall be accompanied by a certificate of analysis of the contents.

Certification

All gravimetric mixtures to be analyzed against an existing gravimetric prior to certification. For zero air and zero nitrogen, the impurities must be verified against analytical standards traceable to NIST by weight and/or analysis. All primary standard gases mixtures must be traceable to NIST weights and/or NIST gas mixture reference materials.

Blend Tolerance

Primary gases shall meet the blend tolerances in Attachment C (Blend Tolerance Table). If they do not meet necessary criteria, they will be returned to the vendor.

04/02/2018