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Low-Angle Light Scattering Processing for SEC

Source: R/step_sec_lals.R
step_sec_lals.Rd

step_sec_lals() creates a specification of a recipe step that processes low-angle light scattering (LALS) signals for absolute molecular weight.

Usage

step_sec_lals(
  recipe,
  measures = NULL,
  concentration_col = NULL,
  angle = 7,
  laser_wavelength = 670,
  dn_dc = NULL,
  solvent_ri = 1.333,
  optical_constant = NULL,
  calibration_constant = NULL,
  output_mw = "mw_lals",
  min_signal = 0.01,
  role = NA,
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("sec_lals")
)

Arguments

recipe

A recipe object.

measures

Character vector of LALS measure columns. If NULL, the step searches for measure columns containing "lals".

concentration_col

Name of the concentration measure column (from step_sec_concentration() or similar).

angle

Detection angle in degrees (must be < 20 for LALS).

laser_wavelength

Laser wavelength in nm.

dn_dc

Refractive index increment (mL/g). Required unless optical_constant is provided.

solvent_ri

Solvent refractive index. Default is 1.333 (water).

optical_constant

Optional optical constant K; overrides dn/dc.

calibration_constant

LALS instrument calibration constant. If NULL, results are in relative units.

output_mw

Name for the molecular weight output column.

min_signal

Minimum signal threshold (as fraction of max) below which MW is set to NA.

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.

Details

LALS provides absolute MW using a low-angle detector (e.g., ~7 degrees). It assumes P(theta) ~ 1 for small particles and is most accurate when angular dependence is minimal.

When to use LALS vs MALS:

  • LALS: Preferred for smaller molecules (Rg < ~10 nm) or when multi-angle data is not available. Single-angle measurement is faster and simpler but cannot determine Rg.

  • MALS: Required for large molecules where angular dependence is significant. Provides both Mw and Rg from extrapolation to zero angle.

See also

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

Examples

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

rec <- recipe(~., data = sec_triple_detect) |>
  step_measure_input_long(ri_signal, location = vars(elution_time), col_name = "ri") |>
  step_measure_input_long(lals_signal, location = vars(elution_time), col_name = "lals") |>
  step_sec_concentration(detector = "ri", injection_mass = 0.2, flow_rate = 1.0) |>
  step_sec_lals(measures = "lals", concentration_col = "ri", dn_dc = 0.185) |>
  prep()
} # }