Calculate Intrinsic Viscosity for SEC

step_sec_intrinsic_visc() creates a specification of a recipe step that calculates intrinsic viscosity ([eta]) from specific viscosity and concentration at each elution point.

Usage

step_sec_intrinsic_visc(
  recipe,
  specific_visc_col = NULL,
  concentration_col = NULL,
  output_col = "intrinsic_visc",
  min_concentration = 1e-06,
  units = c("dL/g", "mL/g"),
  role = NA,
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("sec_intrinsic_visc")
)

Arguments

recipe

A recipe object.

specific_visc_col

Name of the specific viscosity measure column (from step_sec_viscometer()).

concentration_col

Name of the concentration measure column.

output_col

Name for the intrinsic viscosity output column. Default is "intrinsic_visc".

min_concentration

Minimum concentration threshold below which intrinsic viscosity is set to NA. Default is 1e-6 mg/mL.

units

Output units for intrinsic viscosity. Default is "dL/g". Common alternatives are "mL/g" (multiply by 100).

role

Role for generated columns.

trained

Logical indicating if the step has been trained.

skip

Logical. Should the step be skipped when baking?

id

Unique step identifier.

Value

An updated recipe with the new step added, containing intrinsic viscosity at each elution point.

Details

Intrinsic viscosity is defined as the limit of reduced viscosity at infinite dilution:

$$[\eta] = \lim_{c \to 0} \frac{\eta_{sp}}{c}$$

In SEC, each elution slice has very low concentration, so the approximation [eta] = eta_sp / c is valid.

Applications of Intrinsic Viscosity:

• Universal Calibration: log([eta] * M) is linear with retention volume, allowing calibration transfer between polymer types

• Mark-Houwink Equation: [eta] = K * M^a, where K and a are polymer- and solvent-specific constants

• Branching Analysis: g' = [eta]_branched / [eta]_linear provides information about long-chain branching

• Polymer Conformation: The scaling exponent in [eta] vs M reveals chain conformation (coil, rod, sphere)

Typical Intrinsic Viscosity Values (dL/g):

• Polystyrene in THF (MW 100k): ~0.5

• PEG in water (MW 10k): ~0.2

• Proteins: 0.03-0.05 (globular), 0.2-1.0 (denatured)

See also

step_sec_viscometer() for specific viscosity calculation

Other sec-detectors: step_sec_concentration(), step_sec_dad(), step_sec_dls(), step_sec_lals(), step_sec_mals(), step_sec_rals(), step_sec_ri(), step_sec_uv(), step_sec_viscometer()

Examples

if (FALSE) { # \dontrun{
library(recipes)
library(measure)

# Calculate intrinsic viscosity
rec <- recipe(~., data = sec_visc_data) |>
  step_measure_input_long(dp_signal, location = vars(elution_time), col_name = "dp") |>
  step_measure_input_long(ri_signal, location = vars(elution_time), col_name = "ri") |>
  step_sec_baseline() |>
  step_sec_viscometer(dp_col = "dp") |>
  step_sec_ri(dn_dc = 0.185) |>
  step_sec_concentration(detector = "ri", injection_mass = 0.2, flow_rate = 1.0) |>
  step_sec_intrinsic_visc(
    specific_visc_col = "specific_visc",
    concentration_col = "ri"
  ) |>
  prep()
} # }